Proceedings EFCF 2019€¦ · Fuel Cells, Electrolysers & H 2 Processing EFCF 2019 2 - 5 July, Lucerne/Switzerland PEFC Degradation & Testing, Acidic Membrane Materials, Chapter 05

www.EFCF.com/Lib

Proceedings

EFCF 2019 Low-Temperature

Fuel Cells, Electrolysers & H2 Processing

Chapter 05 - Sessions B02, B11, B15

B02: PEFC Degradation & Testing

B11: Acidic Membrane Materials B15: Diffusive Media for FC & Electrolysers

Edited by Prof. Hubert A. Gasteiger (Chair)

Prof. Aliaksandr Bandarenka (Chair)

Co-Edited by Olivier Bucheli Gabriela Geisser Fiona Moore Dr. Michael Spirig

Copyright © European Fuel Cell Forum AG

These proceedings must not be made available for sharing through any open electronic means.

ISBN 978-3-905592-24-5

http://www.efcf.com/Lib

Fuel Cells, Electrolysers & H2 Processing EFCF 2019 2 - 5 July, Lucerne/Switzerland

PEFC Degradation & Testing, Acidic Membrane Materials, Chapter 05 - Sessions B02, B11, B15 - 2/65 Diffusive Media for FC & Electrolysers

www.EFCF.com/Lib ISBN 978-3-905592-24-5

Chapter 05 - Sessions B02, B11, B15 B02: PEFC Degradation & Testing B11: Acidic Membrane Materials B15: Diffusive Media for FC & Electrolysers

Content Page B02, B11, B15 - ..

B0201 (Invited Talk) ........................................................................................................... 6 Multi-step Kinetic Model for Pt Dissolution

Kunal Karan (1), Barath Jayasankar (1,2) (1) Department of Chemical and Petroleum Engineering, University of Calgary 2500 University Dr NW, Calgary, Alberta, Canada (2) FCP Fuel cell powertrain GMBH, Chemnitz, Germany HRB 31357

B0203 (Published in EFCF Special Issue Series, www.EFCF.com/LIB) ...................... 11 CFD Simulation of Industrial PEM Fuel Cells with Local Degradation Effects

Clemens Fink (1), Sönke Gößling (2), Larisa Karpenko-Jereb (3) (1) AVL List GmbH, Hans-List-Platz 1, 8020 Graz, Austria (2) ZBT, Carl-Benz-Str 201, 47057 Duisburg, Germany (3) Graz University of Technology, Inffeldgasse 10/II, 8010 Graz, Austria

B0204 (Published in EFCF Special Issue Series, www.EFCF.com/LIB) ...................... 12 Sub-zero Start-up of Fuel Cell: Diagnostics, Modelling, and Strategies

Jianbo Zhang (1), Fusen Huang (1), Shangshang Wang (1), Lei Yao (2), Junning Wen (5), Jie Peng (2), Muriel Siegwart (3,4), Magali Cochet (3), Pierre Boillat (3,4), Zhili Chen (5), Takemi Chikahisa (6)

(1) School of Vehicle and Mobility, State Key Laboratory of Automotive Safety and Energy, Tsinghua University, Beijing 100084, China (2) Department of Engineering Mechanics, Tsinghua University, Beijing 100084, China (3) Electrochemistry Laboratory (LEC), Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland (4) Laboratory for Neutron Scattering and Imaging (LNS), Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland (5) Department of Mechanical Engineering and Aeronautics and Astronautics, School of Science and Technology, Tokai University, Hiratsuka 2591292, Japan (6) Division of Energy and Environmental Systems, Graduate School of Engineering, Hokkaido University, Sapporo, Hokkaido 0608628, Japan

B0205 (Published in EFCF Special Issue Series, www.EFCF.com/LIB) ...................... 13 Predictive model for performance and platinum degradation simulation of high temperature PEM fuel cells in transient operating conditions

Ambrož Kregar (1,2), Gregor Tavčar (1), Andraž Kravos (1), Tomaž Katrašnik (1) (1) UL, Faculty of Mechanical Engineering, Aškerčeva 6, SI-1000 Ljubljana, Slovenia (2) TU Graz, IPTC, Stremayrgasse 9 A-8010 Graz, Austria

B0206 (Abstract only, published elsewhere) ................................................................. 14 Carbon corrosion in PEMFC: linking startup/shutdown and accelerated stress tests

A. Bisello, E. Colombo, M. Coppola, A. Baricci, A. Casalegno Politecnico di Milano — Department of Energy, via Lambruschini 40, Milano 20156 Italy

B1101 (Published in EFCF Special Issue Series, www.EFCF.com/LIB) ...................... 15 PBI-type Polymers and Acidic Proton Conducting Ionic Liquids – Conductivity and Molecular Interactions

Jingjing Lin, Jürgen Giffin, Klaus Wippermann, Carsten Korte Forschungszentrum Jülich, Institut für Energie- und Klimaforschung (IEK-3)





B1102 ................................................................................................................................ 16 Heteropoly Acid Based Membranes for Excellent Durability and High Performance in Fuel Cell Applications

Andrew M. Herring, Andrew R. Motz, Mei-Chen Kuo Department of Chemical and Biological Engineering Colorado School of Mines, Golden, CO 80401, USA

B1103 (Abstract only, published elsewhere) ................................................................. 24 Chemical Stability Enhancement of Sulfonated Poly(arylene ether ketone) Fuel Cell Membrane by Fixation of Cerium Ion

Yongman Park, Dukjoon Kim School of chemical Engineering, Sungkyunkwan University, Suwon, Gyeonggi, 16419, Republic of Korea Tel.: +82-31-290-7250

B1104 (Abstract only, published elsewhere) ................................................................. 25 Atomistic MD study of Nafion in dispersions: Understanding the role of solvent in the ionomer aggregate structure, sulfonic group clustering and acid dissociation

Atefeh Tarokh, Kunal Karan, Sathish Ponnurangam Department of Chemical and Petroleum Engineering, University of Calgary 2500 University Dr NW, Calgary, Alberta, Canada

B1105 (Abstract only, published elsewhere) ................................................................. 26 Protic Organic Ionic Plastic Crystals as Novel Proton Conductors

Jiangshui Luo, Yingting Yi, Michael Wübbenhorst Department of Physics and Astronomy, KU Leuven Celestijnenlaan 200d - box 2416, 3001 Leuven, Belgium

B1106 ............................................................................................................................... 27 Anion Influence on the Properties of Acidic Protic Ionic Liquids

Hui Hou, Jürgen Giffin, Carsten Korte Forschungszentrum Jülich GmbH, IEK-3 Wilhelm-Johnen-Straße, 52428 Jülich, Germany

B1107 ............................................................................................................................... 33 Diagnosis of MEA Degradation for health management of Polymer Electrolyte Fuel Cells

Derek Low, Lisa Jackson, Sarah Dunnett Department of Aeronautical and Automotive Engineering Loughborough University Loughborough, United Kingdom

B1110 (Abstract only, published elsewhere) ................................................................. 44 Investigating Polymer Membrane Durability in Polymer Electrolyte Fuel Cells Operating at Intermediate Temperatures

Ahmed Ibrahim*, Ahmad El-kharouf Centre for Fuel Cell and Hydrogen Research, School of Chemical Engineering University of Birmingham, B15 2TT, UK

B1111 (Abstract only) ...................................................................................................... 45 In situ estimation of the effective membrane diffusion coefficient in a PEMFC

Kush Chadha, S. Martemianov, A. Thomas Institut Pprimé CNRS – Université de Poitiers – ISAE-ENSMA – UPR 3346 SP2MI – Téléport 2 11 Boulevard Marie Curie BP 30179 F86962 FUTUROSCOPE CHASSENEUIL Cedex EFCF 2019

B1112(Abstract only, published elsewhere) .................................................................. 46 Experimental and theoretical studies of transport properties of a protic ionic liquid

Jiangshui Luo, Yingting Yi, Michael Wübbenhorst Department of Physics and Astronomy, KU Leuven Celestijnenlaan 200d - box 2416, 3001 Leuven, Belgium





B1113 (Abstract only, published elsewhere) ................................................................. 47 Multi-block copolymers with highly sulfonated poly(arylene sulfone) block for Proton Exchange Membrane Fuel Cells

Sang-Woo Jo (1,2), Hee-Tak Kim (1), Young Taik Hong (2), Tae-Ho Kim (2) (1) Department of Chemical and Biomolecular Engineering, Korea Advanced Institute of Science and Technology (KAIST) 291 Daehak-ro, Yuseong-gu, 34141, Daejeon/Republic of Korea (2) Membrane Research Center, Korea Research Institute of Chemical Technology 141 Gajeong-ro, Yuseong-gu, 34114, Daejeon/Republic of Korea

B1114 ................................................................................................................................ 48 High-Temperature Polymer Electrolyte Fuel Cells based on Protic Ionic Liquid Electrolytes

Josef Sanarov, Jürgen Giffin, Carsten Korte Forschungszentrum Jülich GmbH Wilhelm-Johnen-Straße, DE-52428 Jülich

B1116 (Abstract only, published elsewhere) ................................................................. 55 Activation energy landscape for Brønsted acid−base systems

Yingting Yi, Jiangshui Luo, Michael Wübbenhorst Department of Physics and Astronomy, KU Leuven Celestijnenlaan 200d - box 2416, 3001 Leuven, Belgium

B1501 (Published in EFCF Special Issue Series, www.EFCF.com/LIB) ...................... 56 Investigating the Influence of Structural Modification of MicroPorous Layer and Catalyst Layer on Performance and Water Management of PEM Fuel Cells through Neutron Tomography

A. Mohseninia(1), D. Kartouzian(1), P. Langner (1), M.Eppler(1), H. Markötter (2), J. Scholta (1),I. Manke (2)

(1) Zentrum für Sonnenenergie- und Wasserstoff-Forschung Baden-Württemberg (ZSW), Helmholtzstraße 8, 89081 Ulm, Germany (2) Helmholtz-Zentrum Berlin, Hahn-Meitner-Platz 1, 14109 Berlin, Germany

B1502 ............................................................................................................................... 57 Advances in PEM Fuel Cell Liquid Water Management

Preston Stolberg, Alexander Coverdill, Mehdi Mortazavi, Vedang Chauhan, Jingru Benner, Anthony D. Santamaria

Department of Mechanical Engineering Western New England University 1215 Wilbraham Rd, Springfield, MA 01119

B1503 (Abstract only, published elsewhere) ................................................................. 62 Mass transport of Water Vapor in a Polymer Electrolyte Fuel Cell with Evaporation Cooling

Magali Cochet (1), Victoria Manzi-Orezzoli (1), Dirk Scheuble (1), Pierre Boillat (1,2) (1) Electrochemistry Laboratory (LEC) (2) Laboratory for Neutron Scattering and Imaging (LNS) Paul Scherrer Institut, 5232 Villigen, Switzerland

B1504 (Abstract only) ...................................................................................................... 63 Next Generation Gas Diffusion Layers (GDLs) – A Design for Manufacture and Assembly (DFMA) Analysis

Whitney G. Colella (1), Jason Morgan (2) (1) Gaia Energy Research Institute LLC, Arlington, VA, 22203-1966, USA (2) AvCarb Material Solutions 2 Industrial Avenue, Lowell, MA, 01851, USA





B1505 (Abstract only, published elsewhere) ................................................................. 64 Correlation of porous transport layers properties and polymer electrolyte water electrolysis performance

Tobias Schuler (1), Thomas J. Schmidt (1,2), Felix N. Büchi (1) (1) Electrochemistry Laboratory, Paul Scherrer Institut CH-5232 Villigen-PSI, Switzerland (2) Laboratory of Physical Chemistry, ETH Zürich, CH-8093 Zürich, Switzerland

B1506 (Abstract only, published elsewhere) ................................................................. 65 Direct water pathways in PEFC GDLs for improved liquid water management

Christoph Csoklich (1), Thomas J. Schmidt (1,2), Felix N. Büchi (1) (1) Electrochemistry Laboratory, PSI, Forschungsstrasse 111, 5232 Villigen PSI, Switzerland (2) Laboratory of Physical Chemistry, ETH Zürich, 8093 Zürich, Switzerland





B0201 (Invited Talk)

Multi-step Kinetic Model for Pt Dissolution

Kunal Karan (1), Barath Jayasankar (1,2) (1) Department of Chemical and Petroleum Engineering, University of Calgary

2500 University Dr NW, Calgary, Alberta, Canada (2) FCP Fuel cell powertrain GMBH, Chemnitz, Germany HRB 31357

[email protected]

Abstract

Platinum and Pt-alloys remain the electro-catalyst with highest activity for oxygen reduction reaction in the cathodes of polymer electrolyte fuel cells (PEFCs). However, Pt-catalysts in PEFCs undergo a loss of electrochemically active surface (ECSA) as a result of cell potential changes experienced during operation. Performance degradation arising from Pt ECSA loss is a key limiting factor for PEFC durability. Understanding the mechanism of Pt ECSA loss could lead to better control/mitigation strategies that can arrest or minimize the loss. Platinum dissolution is the primary mechanism of ECSA loss during potential cycling between 0.6V and an upper potential of 1 V or higher. The mechanism of Pt dissolution occurring during these cycles has not been fully understood. The 2012 groundbreaking work of Karl Mayrhofer and colleagues using the electrochemical scanning flow (SCF) system coupled to ICP-MS system revealed many new information on Pt dissolution [1]. It showed that dissolution occurs both during anodic and cathodic scan, cathodic dissolution was greater than anodic dissolution, and cathodic dissolution rate increased with upper potential limit but anodic dissolution was minimally affected. In this work, we present an extension of our recently published unified model for O2 electrochemistry (oxide intermediates) comprising multi-step reaction scheme that captures cyclic voltammetry, logarithmic oxide growth and oxygen reduction reaction [2] to include the Pt dissolution reaction (see reaction scheme below). This model is able to simulate all key features of the SCF experiments. The validated model provides a deeper insight into the Pt dissolution mechanism.

http://www.efcf.com/Libmailto:[email protected]




Introduction Despite enormous research on non-precious metal group metal (non-PGM) catalysts, the electro-catalytic activity of Pt and Pt-alloys remain far superior than any of its contender. As a result, Pt and/or its alloys remain the only pragmatic catalyst solution for a functional PEFC stack. On the other hand, Pt catalysts in a polymer electrolyte fuel cells (PEFCs) undergo a loss of electrochemically active surface (ECSA) as a result of potential changes experienced during operation. Performance degradation arising from Pt ECSA loss is a key limiting factor for PEFC durability. Understanding the mechanism of Pt ECSA loss could lead to better control/mitigation strategies that can arrest or minimize the loss. Many different mechanisms for Pt surface area loss during operation has been proposed including Pt dissolution, Ostwald ripening, particle agglomeration, particle detachment from carbon support and corrosion of carbon support itself [3-5]. Platinum dissolution has been considered to be the key cause of Pt electrochemically active surface area (ECSA) loss. The mechanism of Pt dissolution/loss has been debated and summarized in review articles, most recently by Deborah Meyers and co-workers [6], which contains key references and discussion on the debate that had existed regarding Pt dissolution mechanism. Interesting observations have been made regarding the Pt dissolution phenomena. Under potentiostatic conditions, observable Pt dissolution is noted above 0.8 V and increases with an increase in potential [6]. Pt dissolution rates are accelerated upon potential cycling. The rate of dissolution depends on the shape of the potential scans, i.e. the scan rate, the potential range, and the dwell at the upper/lower potential [7]. Recently, in a novel flow cell experiment, Mayrhofer and co-workers demonstrated that Pt dissolution occurs both during anodic and cathodic scans of the potential cycle [1]. Interestingly, they observed the Pt dissolution rate to be significantly higher in the cathodic scan compared to that during the anodic scan. The models for Pt dissolution [8-10] capture many features of the Pt dissolution phenomena but none have discussed the transient behaviour of Pt dissolution during the cathodic and anodic scans observed [1]. In this work, we extended of our recently published unified model for O2 electrochemistry on Pt (oxide intermediates) comprising multi-step reaction scheme that captures cyclic voltammetry, logarithmic growth of oxide at high potential and oxygen reduction reaction [2] to include the Pt dissolution reaction. Our model considers Pt dissolution to occur via chemical dissolution of oxides species. With a single tuning parameter, the model was able to simulate all key features of the SCF experiments.

Key Points The details of the multi-step O2 electrochemistry model can be found in Ref [2]. The present work extends that model by including Pt dissolution, which is modelled via chemical dissolution of two oxide species, the place-exchange oxide (O-Pt) and hydroxide on such a place-exchanged site (O-Pt-OH):

O-Pt + 2H+ Pt2+ + H2O (1)

O-Pt-OH + 3H+ Pt2+ + H2O (2)





The kinetics follow a simple first-order dependency on the surface concentration of the two oxide species:

Rate of dissolution = kdiss O-Pt or kdiss O-Pt-OH (3) Here, three key results showing a direct comparison of recent data by Mayrhofer and colleagues (Topalov et al [1]) exemplifying of the trends observed in their experiments are shown. (a) Potential-dependent rate of platinum dissolution: Figure 1 below shows a comparison of the rate of platinum dissolution as function of upper potential. Each cycle comprised of a triangular wave from 0.1 V (vs RHE) to UPL. As can be noted fro the Figure 1, the model predictions are remarkably close to the experimental data. It must be noted that the rate constant for dissolution (kdiss) was tuned so as to match with a potential. The closeness of the experimental data and model prediction implies that the simple Pt dissolution model is able to capture the dissolution rate at 8 different potentials. This was a surprising result. However, our results imply that sub-surface oxides, which were modeled via an earlier kinetic model to simulate logarithmic sub-surface oxide growth on Pt, are the critical component for Platinum dissolution.

Figure 1. Platinum dissolution per cycle as a function of upper potential limit (UPL) during a triangular wave from 0.2 V to UPL at a scan rate of 10 mV/s.





(b) Pt dissolution during anodic and cathodic scan: One of the most interesting revelations of the SCF experiments of Mayrhofer and colleagues was to settle the question on when does Pt dissolution occur during potential cycling – anodic or cathodic scan? They showed that above 1.1 V of upper potential limit, the dissolution during cathodic scans far exceeds the dissolution during anodic scan. They also observed that the dissolved Pt amount during anodic scan was a weak function of upper potential limit but that during cathodic scan increased steadily with increasing upper potential. Again, our kinetic model captures these two trends surprisingly well as shown in Figure 2 below. The inset is the data from the experimental study of Topalov [1].

Figure 2. Platinum dissolution during a potential cycle. The upper potential limit in each subsequent triangular wave is increasing. The lower potential limit is 0.2 V and the scan rate is 10 mV/s. (c) Effect of scan rate on Pt dissolution: Another interesting result of the SCF experiments was the decrease in Pt dissolution per cycle upon increase in scan rate. However, when the same information is plotted on a per second basis, the Pt dissolution increases with increasing scan rate. Again, the simulation results from our model is able to capture these trends remarkably well as shown in Figure 3 below. The dissolution rate per cycle drops by more than a factor of two as the scan rate is increased from 10 mV/s to 50 mV/s.





Figure 3. Platinum dissolution per cycle as a function of upper potential limit (UPL) during a triangular wave from 0.2 V to UPL at a scan rate of 10 mV/s.

Summary - Conclusion A kinetic model for dissolution of Pt is introduced. The results shows that our simple chemical dissolution model can adequately describe several different experimental trends remarkably well. This lends credence to the dominant mechanism for Pt dissolution as: chemical dissolution coupled to sub-surface oxide coverage/concentration.

References [1] Topalov et al Angewandte Chemie Int. Ed., 51, 12613, (2012) [2] B. Jayasankar and K. Karan Electrochimica Acta, 273, 367 (2018) [3] Y. Shao-Horn et al Topics in Catalysis, 46, 285 (2007) [4] S. Cherevko et al., Nano Energy 29,275–298 (2016). [5] F. A. de Bruijn et al., Fuel Cells, 08, 1, 3–22 (2008). [6] D. Meyers et al, J Electrochem Soc (JES), 165, F3178 (2018) [7] A. Kneer et al JES 165, F805 (2018) [8] R. Darling and J. Myers, JES, 150, A1523 (2003) [9] S. Rinaldo et al, J Phys Chem C, 114,5773 (2010) [10] R. Ahluwalia et al JES 160, F447 (2013).





B0203 (Published in EFCF Special Issue Series, www.EFCF.com/LIB)

CFD Simulation of Industrial PEM Fuel Cells with Local Degradation Effects

Clemens Fink (1), Sönke Gößling (2), Larisa Karpenko-Jereb (3) (1) AVL List GmbH, Hans-List-Platz 1, 8020 Graz, Austria

(2) ZBT, Carl-Benz-Str 201, 47057 Duisburg, Germany (3) Graz University of Technology, Inffeldgasse 10/II, 8010 Graz, Austria

Tel.: +43-316-787-4618 Fax: +43-316-787-777 [email protected]

Abstract

The PEM fuel cell model of a commercial software package is presented in full detail. The basic model is extended by two chemical degradation effects: ionomer degradation and carbon corrosion with Pt oxidation. The ionomer degradation model describes the ionomer mass loss due to hydrogen peroxide formation and subsequent radical attack of the ionomer. The carbon corrosion model calculates the carbon mass loss caused by carbon oxidation and the active area reduction due to Pt oxidation. The degradation models are coupled with the agglomerate model of the catalyst layer. The model is validated against measurements on a 50 cm2 cell from ZBT. For these measurements, the cell is equipped with a segmented bipolar plate and a segmented measuring board which can be used to measure the current density distribution as well as the high frequency resistance of every segment. In order to test the predictability of the model at different operating conditions, measurements for stoichiometry and pressure variations are carried out. For the validation of the degradation model, calculated and measured current density distributions of the cell, aged by an accelerated stress test, are compared. Moreover, 3D results of the fresh and aged cell are analyzed in detail and the influence of operating conditions on fuel cell aging is pointed out.

Remark: The full paper is published in EFCF Special Issue Series (www.EFCF.com/LIB, SI EFCF 2019) in Journal "FUEL CELLS - From Fundamentals to Systems".

http://www.efcf.com/Libmailto:[email protected]://www.efcf.com/LIB





Sub-zero Start-up of Fuel Cell: Diagnostics, Modelling, and Strategies

Jianbo Zhang (1), Fusen Huang (1), Shangshang Wang (1), Lei Yao (2), Junning Wen (5), Jie Peng (2), Muriel Siegwart (3,4), Magali Cochet (3),

Pierre Boillat (3,4), Zhili Chen (5), Takemi Chikahisa (6) (1) School of Vehicle and Mobility, State Key Laboratory of Automotive Safety and Energy,

Tsinghua University, Beijing 100084, China (2) Department of Engineering Mechanics, Tsinghua University, Beijing 100084, China

(3) Electrochemistry Laboratory (LEC), Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland

(4) Laboratory for Neutron Scattering and Imaging (LNS), Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland

(5) Department of Mechanical Engineering and Aeronautics and Astronautics, School of Science and Technology, Tokai University, Hiratsuka 2591292, Japan

(6) Division of Energy and Environmental Systems, Graduate School of Engineering, Hokkaido University, Sapporo, Hokkaido 0608628, Japan

[email protected]

Abstract Cold start capability is the key bottleneck restricting large-scale commercialization of

fuel cell vehicles in cold regions. Fundamental understanding of freezing mechanism and utilization of super-cooled water is essential to further enhance the PEFCs sub-zero start-up capability. For this aim, this talk introduces our recent study on the sub-zero startup of PEFC, including the diagnostic and modeling of super-cooled water and ice, and the new strategies to start up the cell.

Advanced characterization tools, such as Cryo-SEM, neutron radiography, and electrochemical characterization methods, such as dynamic cyclic voltammetry (CV), dynamic electrochemical impedance spectroscopy (EIS), were employed in sub-zero start-up experiments to reveal the behavior of super-cooled water and the effects of ice formation on the sub-zero startup performance of fuel cell. The stability of super-cooled water and ice distribution are related to the cell size, operation conditions, and component properties. The ice does not cover the surface of the catalysts, but rather blocks the pores of cathode catalyst layer, resulting in the suffocation of oxygen supply to the reaction sites.

Based on these characterizations, a three-dimensional mathematical model was developed to simulate the transient start-up process. The stochastic freezing behavior of super-cooled water is considered, which is described by introducing the freezing probability function. Based on the model, two failure mechanisms, including anode dehydration and cathode pore blockage are systematically investigated with various initial membrane water content and startup current densities.

A single cell setup with adiabatic thermal boundary condition was proposed and tested to simulate the cell in the center of the stack. MPL was improved and the current control was designed to improve the cold start capability. Besides a novel technique using hydrogen pump method to start the cell from sub-zero temperature is proposed and verified. Remark: The full paper is published in EFCF Special Issue Series (www.EFCF.com/LIB,

SI EFCF 2019) in Journal "FUEL CELLS - From Fundamentals to Systems".

http://www.efcf.com/Libhttp://www.efcf.com/LIB





Predictive model for performance and platinum degradation simulation of high temperature PEM fuel

cells in transient operating conditions

Ambrož Kregar (1,2), Gregor Tavčar (1), Andraž Kravos (1), Tomaž Katrašnik (1) (1) UL, Faculty of Mechanical Engineering, Aškerčeva 6, SI-1000 Ljubljana, Slovenia

(2) TU Graz, IPTC, Stremayrgasse 9 A-8010 Graz, Austria Tel.: +386-1-4771-305 Fax: +386-1-2518-567

[email protected]

Abstract High temperature polymer electrolyte membrane fuel cells (HT-PEMFCs) are a promising and emerging clean energy conversion technology. Simultaneous reduction of production costs and prolongation of the service life are considered as significant challenges towards their wider market adoptions. To successfully tackle these challenges predictive virtual tools are applied during the development process of HT-PEMFC systems. In order to achieve significant progress in the addressed area, this contribution presents an innovative modelling framework based on: a) a mechanistically based spatially and temporally resolved HT-PEMFC performance model and b) a modular degradation modelling framework based on interacting partial degradation mechanisms (Figure 1). The core principle of the HT-PEMFC performance model is a computationally efficient approach combining 1D numerical and 2D analytic solution, denoted HAN. HAN modelling approach on one side allows for achieving high level of predictiveness in FC performance modelling, which is crucial for adequate virtual integration of FC in the plant model, and on the other side provides spatially and temporally resolved data of degradation stimuli. The later are crucial input parameters for the degradation modelling framework and are used by it as inputs to adequate causal chains of interacting partial degradation mechanisms. Presented results confirm credibility of the proposed modelling framework in modelling FC performance and Pt degradation as well as related carbon corrosion. Owing to its structured basis that covers the entire causal chain from FC operation and control over prediction of FC performance and degradation stimuli to prediction of degradation rates over longer time scales, the proposed innovative modelling framework enables more efficient exploration of the design space and higher fidelity model supported design of FC systems including their control functionalities.

Figure 1: A schematic diagram of the intertwined degradation mechanisms.

Remark: The full paper is published in EFCF Special Issue Series (www.EFCF.com/LIB,

SI EFCF 2019) in Journal "FUEL CELLS - From Fundamentals to Systems".





B0206 (Abstract only, published elsewhere)

Carbon corrosion in PEMFC: linking startup/shutdown and accelerated stress tests

A. Bisello, E. Colombo, M. Coppola, A. Baricci, A. Casalegno Politecnico di Milano — Department of Energy, via Lambruschini 40, Milano 20156 Italy

Tel.: +39-02-2399-3840 [email protected]

Abstract

Fuel Cell (FC) technology is broadly accepted as a long-term solution for the replacement of internal combustion engines, however for automotive application many requirements must be observed, including specific needs such as tolerance to numerous start-up/shutdown (SUSD). Carbon corrosion in the electrodes of MEAs (membrane-electrode assembly) is known as a major cause for voltage degradation during SUSD cycles, when a slow H2/air front flow in the anode opposite an air-filled cathode leads to reverse-current mechanism which increases cathode potential as high as 1.5 V. This work aims at increasing the understanding of degradation process that occurs during SUSD. Firstly, aging tests on single cell, active area 25 cm2, were conducted using custom setup that combine a segmented cell and local reference electrodes, to investigate the link between performance decay and local operating conditions during SUSD (to taking into account different user profiles). The results at different operating parameters, showed the predominant effect of temperature on degradation rate, exhibiting the same trend for kinetic and mass transport loss between SUSD and AST at 80°C (Figure 1 left). Conversely, at 40°C performance loss was mitigated but, on the other hand, the measurements with RHE indicated an increase of maximum potential (Figure 1 right). To elucidate the complex contributions of carbon corrosion, double layer and platinum oxidation during SUSD, a modelling activity were introduced. Finally, we showed that transient physical model, which considers simultaneously faradaic and capacitive currents, gives a consistent fit with experimental data collected during SUSD at different operating conditions.

Remark: Only the abstract is available, because the authors chose to publish elsewhere.

Please see Presentations on www.EFCF.com/LIB or contact the authors directly.






PBI-type Polymers and Acidic Proton Conducting Ionic Liquids – Conductivity and Molecular Interactions

Jingjing Lin, Jürgen Giffin, Klaus Wippermann, Carsten Korte Forschungszentrum Jülich, Institut für Energie- und Klimaforschung (IEK-3)

Wilhelm-Johnen-Straße, 52425 Jülich Tel.: +49 2461 61-9804 Fax: +49 2461 61-6695

[email protected]

Abstract

The operation of low temperature polymer electrolyte fuel cells (LT-PEFC) at elevated tem-peratures of above 100°C would allow a much simpler system setup: i) no feed gas humidi-fication, ii) a more efficient cooling system (easier water and heat management), iii) the possibility of recovering high-grade waste heat, and iv) a higher tolerance against feed gas impurities. Currently, (high temperature) HT-PEFC, based on phosphoric acid doped poly-benzimidazole (PBI) membranes, cannot compete with the performance characteristics of NAFION-based LT-PEFCs. The presence of H3PO4 causes a slow cathodic oxygen reduc-tion reaction kinetics (ORR). Thus, there is a necessity for new non-aqueous proton con-ducting electrolytes operational for the temperature range between 100–120 °C.

Proton conducting ionic liquids (PIL) with acidic cations are promising candidates for the use as non-aqueous electrolytes at operation temperatures above 100 °C. In this contribution, an experimental study on the interaction of PBI based proton exchange membrane (PEM) with a betaine-type highly acidic PILs is presented. 2-Sulfoethylmethylammonum triflate exhibits a ~3 times higher ORR current densities on Pt compared to H3PO4 [1]. There is a (slow) uptake of the electrolyte by PBI due to a swelling process, up a weight increase of 135%. The doping process was monitored by Raman spectroscopy, proving the protonation of base imidazole groups on PBI chains. TGA measurements show stable coulombic interaction between triflate group and PBI, which is provided by protonation.

NMR analysis has been applied to elucidate the molecular interactions between PBI, PIL and residual water, which is present during fuel cell operation. The total conductivity depends highly on the H2O concentration. The acidic betaine-type PIL is able to protonate H2O. Thus, proton conduction may take place by a vehicle transport via PIL cations or H3O+ but also by cooperative mechanism involving both species. Proton exchange, respectively an interaction between the polar groups and water can be observed in the spectra, indicating a network of H-bonds in doped PBI.

Compared to the neat PIL, the proton conduction in the doped PBI membrane is restricted due to the constraining network of the polymer chains. To optimise the conductivity but also the uptake of the PIL into the polymer, the use of solution casting methods has been studied for these materials.

Remark: The full paper is published in EFCF Special Issue Series (www.EFCF.com/LIB, SI EFCF 2019) in Journal "FUEL CELLS - From Fundamentals to Systems"..

http://www.efcf.com/Libhttp://www.efcf.com/LIB




B1102

Heteropoly Acid Based Membranes for Excellent Durability and High Performance in Fuel Cell

Applications

Andrew M. Herring, Andrew R. Motz, Mei-Chen Kuo Department of Chemical and Biological Engineering Colorado School of Mines, Golden, CO 80401, USA

Tel.: +1-303-273-3730 Fax: +1-303-384-2081 [email protected]

Abstract

Heteropoly acids (HPAs), a subclass of the polyoxometalates, are a class of proton conducting radical activating or decomposing molecules. Several types of HPAs have demonstrated the ability to improve membrane chemical stability through polymer blends, but they still suffer from migration and only result in marginal gains. A method of covalent bonding HPAs to carbon in the catalyst layer has also shown some improvements in chemical stability, but chemical degradation mitigation within the membrane is needed. Our group has developed two membrane platforms with HPAs covalently attached and immobilized within a polymer membrane, serving as the proton conducting acid. More recently, the outstanding chemical stability of one of these platforms has been demonstrated, however, the stability demonstrated in this study was criticized for using rather thick, 80 µm membranes in sub-scale fuel cells. In a recent study a 50 cm2 fuel cell was fabricated using a thin, 25 µm membrane with covalently attached silicotungstic acid, which was subjected to an accelerated stress test for chemical degradation and displayed an OCV decay rate of 520 µV h-1. To the authors knowledge, this is the first reported fuel cell of a larger practical area containing a hybrid HPA film and represents a significant step towards demonstrating this technology on a commercially relevant scale. The resulting data was analyzed to show the loss in OCV is mainly due to an electrical short and not increased reactant gas crossover. This study further analyzes the chemical stability observed in these membranes and proposes a mechanism for radical decomposition. A reaction mechanism is proposed utilizing reactions found in literature as well as density functional theory (DFT) calculations. The main conclusion from this work is that covalently attached HPAs could be more efficient radical scavengers with less susceptibility to migration, accumulation, and leaching when compared to the use of Ce(III) cations. We have recently realized a method for cleaning these membrane materials, removing many of the impurities formed during synthesis and have also begun to cross-link these material to eliminate swelling and achieve a dimensionally stable films. These much-improved materials show even higher performance in fuel cells and could potentially solve many of the issues associated with the PFSA materials.





Introduction Electrochemical energy conversion devices have great potential to replace the internal combustion engine and transform the electrical grid; this can be accomplished with batteries, fuel cells, or flow batteries. One main advantage that fuel cells have over batteries when it comes to the automotive sector is the rapid rate of refueling hydrogen is similar to petroleum refueling. While the field has greatly progressed in the last decade, some room for improvement still exists. The DOE has developed technical targets for membranes for transportation applications. At the core of this is the development of a membrane with an ASR of 0.02 Ωcm2 at 80 °C and at the maximum operating temperature of the envisioned fuel cell stack at low partial pressures of water (pH2O 25 kPa at 80°C, 40 kPa at 120°C). Cross over of 2 mA cm-2 for hydrogen and oxygen and a minimum electrical resistance of 1,000 Ω cm2 need to be achieved. In addition, the film should survive 20,000 cycles of the DOE wet/dry mechanical test and >500 hours of the chemical crossover OCV test.

1. Scientific Approach We have developed completely new ionomer systems based on incorporation of inorganic super acids into polymer systems [1, 2], which have high proton conductivity under conditions of low humidity, higher temperature operation, high oxidative stability, and little swelling when wet. The technical concept is to use functionalized inorganic super acids that utilize little water for high proton conductivity, as the protogenic group covalently attached to a polymer backbone optimized for all other functions of the membrane. Many composite inorganic/polymer films have been fabricated, but unless the particles have dimensions on the nano-scale there is no advantage as the improvement to film properties occurs at the particle polymer interface. The limit of this approach is to use molecules with high acidity as the highly activating functionalities, but to do this we must immobilize them, control the morphology of the proton conducting channel, and fabricate an amorphous material. In previous work, we demonstrated both composite membranes and true inorganic/polymer hybrid materials with very high proton conductivity, but the inorganic super acid in the membrane was not immobilized and the inorganic/polymer hybrid material transformed into undesirable crystalline phases at low RH. These materials are not yet fuel cell ready. In this project, we will overcome all of these disadvantages with an innovative approach to amorphous materials to produce high proton conductivity and all other properties desired of a PEM. The HPA silicotungstic acid (HSiW) is able to conduct at high temperatures with minimal hydration, making it an ideal acidic moiety. This study discusses the synthesis of a new material based on HSiW moieties covalently attached to a functionalized perfluorinated elastomer. The use of HSiW results in a film with a low area specific resistance (ASR) at elevated temperatures and superior performance to Nafion® under standard operating conditions. The material easily passes the DOE mechanical test due to the perfluorinated backbone and the chemical test due to the ability of the HPA to destroy oxygenated radicals [3].





2. Experiments/Calculations/Simulations Materials: Diethyl (4-hydroxyphenyl)phosphonate (DHPP) was purchased from Synquest (catalog number 6677-1-07) and a polyvinylidene-co-hexafluoropropylene (PVDF-HFP) fluoroelastomer (FC-2178) was supplied by 3M. Hydrochloric acid (HCl) (37%, ACS reagent grade) was purchased from Pharmco-Aaper. Sodium hydride (NaH) (60% dispersion in oil) and bromotrimethylsilane (TMSBr) (97%) were purchased from Sigma-Aldrich. All other reagents were purchased from Sigma-Aldrich with >99% purity and were used as received. Preparation of PolyPPE: FC-2178 (31.78 g) was washed with methanol, dried at 40°C under vacuum for two days, then dissolved in 150 mL anhydrous dimethylformamide (DMF). In a separate flask, 20.0 g DHPP was added to 100 mL anhydrous DMF and allowed to dissolve at room temperature, followed by cooling to 0°C. Once cooled, NaH was added slowly to the DHPP solution, under a N2(g) flow, producing H2(g) bubbles. After 2 h, bubble formation subsided and the FC-2178 solution was slowly added over a period of 30 minutes. The combined solution was then heated to 50°C and allowed to react for 24 h, darkening with time, before precipitation in 1M HCl. The precipitate is then isolated, washed with water, and dried under vacuum for 48 h, producing phenol phosphonic ester functionalized FC-2178 (PolyPPE). Preparation of PolyPPA: The PolyPPE was then dissolved in 450 mL acetonitrile overnight at room temperature. The following day, 32 mL bromotrimethylsilane (TMSBr) was added under a N2 environment. The reaction was heated to 45°C and allowed to react overnight, producing a cloudy mixture. The reaction solution was filtered and the filtrate was dissolved in 600 mL MeOH with 20 mL concentrated HCl, quenching the reaction. The reaction solution was dried resulting in the phenol phosphonic acid functionalized FC-2178 (PolyPPA). The PolyPPA was subsequently washed with water, dried, and stored at room temperature, yield = 38.5g (77%). Preparation of PolyHPA: 4.50 g PolyPPA was added to 180 mL n,n- dimethylacetamide (DMAc) and allowed to dissolve overnight at 80°C. Next, 10.50 g -K8SiW11O39•13(H2O) (HSiW), synthesized according to the protocol previously reported,(4) was slowly added. The mixture was cloudy, but rapid stirring with a magnetic stir bar ensured no precipitate formed on the bottom. Next, 12 M HCl (1.356 mL) was added dropwise, turning the solution into a transparent amber. The reaction took place over 70 h at 80 °C, then the solution was filtered with a paper filter followed by a filtration using a medium porosity glass frit Büchner Funnel to remove potassium chloride crystals. The volume was then reduced to ca. 60 mL using a rotary evaporator. This solution was then cast on Kapton® using a doctor blade to control thickness and dried at room temperature over night (16 h). When dried, the films ranged from 20-80 µm. Next, thermal annealing under pressure (5 min, 26.7 kN, 160°C) was used to finish the attachment reaction and make the film more uniform. The resulting film was then soaked in 1 M H2SO4 to ion-exchange (3x) followed by rinsing in DI water (3x). Each rinse was more than 1 h. Potentiostatic Electrochemical Impedance Spectroscopy (PEIS). PEIS experiments were performed in a TestEquity environmental chamber to accurately control the temperature and relative humidity. The membranes were placed across four platinum electrodes in cells designed after Bekktek FC-BT-115 conductivity cells and the PEIS measurements were performed using a BioLogic VMP3 potentiostat. Data were fit using a Randles circuit and the results were used to calculate an in-plane conductivity. Small Angle X-ray Scattering (SAXS). The SAXS data was collected on beamline 12-ID-B at the Advanced Photon Source, Argonne National Lab in a custom built environmental chamber, using 13.3 keV radiation. The chamber, described in detail elsewhere [5], is able to control temperature and humidity and the conditions are outlined below. A Pilatus 3M detector was used.





Fuel Cell Testing: The Nafion standard membrane electrode assembly (MEA) was fabricated using a catalyst coated membrane (CCM), N211, with catalyst supplied by Tanaka Holdings Co. Ltd. The anode catalyst layer consisted of TEC10EA30E, 30% Pt/C, 0.055 mg cm-2 and a cathode catalyst layer consisted of TEC10E50EHT, 50% Pt/C, 0.35 mg cm-2 and had an active area of 2x5 cm2. The PolyHPA MEAs were fabricated using commercial gas diffusion electrodes (GDE)s for both the anode and cathode (((Johnson Matthey Pt/C electrocatalyst, PFSA ionomer, 0.35 Pt mg cm-2). The PolyHPA-70 (70 wt% theoretical HSiW loading) MEA had an active area of 2x5 cm2 and the PolyHPA-75 (75 wt% theoretical HSiW loading) MEA was 5 cm2. The 10 cm2 fuel cells were run using flow rates, 4 L min-1 at the anode and 8 L min-1 at the cathode while the 5 cm2 fuel cell was run using flow rates of 2 L min-1 at the anode and 4 L min-1 at the cathode.

3. Results A four-step synthesis, reported elsewhere [6], was used to covalently attach HSiW to FC-2178, where hexafluoropropylene accounts for ca. 20 mol% of the polymer [7]. To avoid the over dehydrofluorination, the reagent was changed to NaH, as the hydride is a stronger base than K2CO3, but still a weak nucleophile. This change allows for attachment of DHPP at much lower temperatures, Scheme 1. The polymer was processed into films at 160°C for 5 min to enhance crosslinking and avoid thermal decomposition.

Scheme 1: Full synthetic reaction scheme for the synthesis of PolyHPA (final product) from

FC-2178 and DHPP

Two peaks appear in the SAXS, one at 0.097 and the other at 0.6 Å-1 corresponding to d-spacing values of 6.5 and 1.0 nm (Figure 1). The 1.0 nm feature is likely the spacing between two adjacent HSiW molecules and the 6.5 nm feature is likely the spacing between HSiW rich and deficient domains. Interestingly with this system of HSiW and PolyPPA, this same SAXS pattern predominates whenever the material is processed. This strongly implies that a thermodynamic minimum is achieved with clusters of HSiW separated by a characteristic length of ca. 6.5 nm. Examination of the high q peak shows a shift to lower q, or larger d-spacing that is highly dependent on RH. This is indicative of water moving towards the surface of the HSiW moieties and pushing them further apart.

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The proton conductivity, seen in Figure 2, is >0.1 S cm-1 at all of the temperatures measured (50-90 °C and 95 %RH) and exhibits two different regimes of transport that

intersect near 60 °C, the T of the hydrophilic sidechains. The values at 80 °C and 95 %RH are remarkably high, 0.228 and 0.298 S cm-1 for the PolyHPA-70 and PolyHPA-75, respectively. This high conductivity is achieved due the super acidic, and thus highly mobile, nature of the protons of silicotungstic acid.

Figure 1: SAXS at 80 °C in air at various humidities and in liquid water

Figure 2: In-plane conductivity of PolyHPA-70 at 95 %RH and various temperatures with

trend lines to guide the eye.

Fuel cells were fabricated using commercial GDEs, which resulted in good performance, see below. Figure 3a shows the cross-over data for a fuel cell in the DOE mechanical AST, and it can be clearly seen that the material passes. While this is an achievement, films with mechanical supported are often able to easily pass this AST and this problem is considered solved by many in the community. The challenge that motivated this research was making a film that was highly chemically stable. To test the hypothetical chemical stability of this material, a chemical AST was performed at 90 °C, 30 %RH, under an H2-O2 environment at OCV. Under these conditions, standard polymer electrolyte membranes degrade rapidly, this is due to radical generation and subsequent attack of the polymer film. It has been previously demonstrated that the decay is much more rapid under an O2 environment, as used here, as opposed to air, the standard DOE protocol [8]. Under O2 during this test Pt has been shown to dissolve and precipitate as a Pt band in the membrane, this phenomenon





is also seen in real fuel cells that are cycled through OCV. The accelerated degradation, in the AST using O2, has been attributed to decomposition of the PFSA polymer near the Pt band, which is more prevalent in O2 environments [9]. Below in Figure 3 b is the OCV vs. time for two different batches of PolyHPA-70 (80 µm) and a Nafion® 211 control. This remarkably low OCV decay (100 µV hr-1), without OCV recovery, and under very harsh conditions represents the lowest rate reported to date in the literature [10].

Figure 3: (a) LSV for PolyHPA-70 (80 µm) after wet/dry cycling and beginning of life and

end of life crossover targets (b) OCV hold test at 90 °C/ 30 %RH under H2-O2 flow and no current. Two different batches of PolyHPA-70 (80 µm) easily pass the test while N211 film for comparison (bottom trace). The typical target is 500 h while retaining a voltage above

0.8 V which is marked (x). The PolyHPA-70 fuel cell was evaluated under low humidity operation at 80 °C, see Figure 4. A drop in voltage and an increase in HFR is seen, as expected as the RH is dropped. At low current densities the HFR starts out near 1000 mΩ cm2, but drops to 141 mΩ cm2 at 2 A cm-2. This HFR drop can be attributed to increase in water generation from increasing current densities. Looking at the HFR values at low current density, an order of magnitude increase occurs when the humidity is reduced from 100 to 50 %RH, indicative of poor transport under low RH. Finally, a full scale 50 cm2 MEA using a 30 µm PolyHPA-70 film was prepared and tested at NREL [11] . The goal of this test was to ensure the chemical stability was sufficient even with thinner films where H2 crossover is higher and chemical stability is lowered. This was the first MEA of this size and the performance was worse than the smaller fuel cells with films of similar thickness and membrane composition. This is mainly attributed to a high

interface resistance between the PolyHPA-70 membrane and the Nafion GDEs. See the polarization data in Figure 5 compared to the data in Figure 4. The HFR at 80 °C and saturated gasses (ca. 200 mΩ cm2) is much higher than would be expected with a PolyHPA-70 membrane that is 30 µm thick. This is attributed to the need to optimize the fuel cell design for this new material and should not affect the chemical stability. After the preliminary data collection in a H2-O2 environment, a standard OCV hold in H2-air at 90°C and 30 %RH was performed with hydrogen crossover measurements at 20-72 h intervals. After 500 h, the OCV had dropped to 0.72 V.





Figure 4: PolyHPA-75 voltage (a) and HFR (b) at different humidities vs. current at 80°C.

Figure 5: I-V data for the 50 cm2 fuel cell fabricated using a 30 µm PolyHPA-70 film.

Figure 6: Crossover from LSV for different types of crossover.

The slope used to calculate the electrical shortage was much higher later in the test and resulted in negative values for the artificial, H2 crossover only current. While the H2 crossover





values are not reliable, what is clear is the electric short current increases with OCV hold test time and can be attributed to the drop in OCV, not an issue with H2 crossover, Figure 6. The membranes are not mechanically supported and likely suffer from thinning under high compression. Mechanical support must be investigated in the future to stop membrane thinning and electrical shorting.

References [1] J. L. Horan, A. Lingutla, H. Ren, M. C. Kuo, S. Sachdeva, Y. Yang, S. Seifert, L. F.

Greenlee, M. A. Yandrasits, S. J. Hamrock, M. H. Frey and A. M. Herring, Journal of Physical Chemistry C, 118, 135 (2014).

[2] A. M. Herring, Journal of Macromolecular Science, Part C: Polymer Reviews, 46, 245 (2006).

[3] A. R. Motz, M.-C. Kuo, J. L. Horan, R. Yadav, S. Seifert, T. P. Pandey, S. Galioto, Y. Yang, N. V. Dale, S. J. Hamrock and A. M. Herring, Energy & Environmental Science, 11, 1499 (2018).

[4] D. C. Duncan, R. C. Chambers, E. Hecht and C. L. Hill, Journal of the American Chemical Society, 117, 681 (1995).

[5] Y. Liu, J. L. Horan, G. J. Schlichting, B. R. Caire, M. W. Liberatore, S. J. Hamrock, G. M. Haugen, M. A. Yandrasits, S. n. Seifert and A. M. Herring, Macromolecules, 45, 7495 (2012).

[6] A. R. Motz, M.-C. Kuo and A. M. Herring, ECS Transactions, 80, 565 (2017). [7] A. Taguet, B. Ameduri and B. Boutevin, Fuel Cells, 6, 331 (2006). [8] A. Ohma, S. Suga, S. Yamamoto and K. Shinohara, Journal of The Electrochemical

Society, 154, B757 (2007). [9] A. Ohma, S. Yamamoto and K. Shinohara, Journal of Power Sources, 182, 39 (2008). [10] R. Yadav, G. DiLeo, N. Dale and K. Adjemian, ECS Transactions, 53, 187 (2013). [11] A. R. Motz, M.-C. Kuo, G. Bender, B. S. Pivovar and A. M. Herring, Journal of The

Electrochemical Society, 165, F1264 (2018).






Chemical Stability Enhancement of Sulfonated Poly(arylene ether ketone) Fuel Cell Membrane by

Fixation of Cerium Ion

Yongman Park, Dukjoon Kim School of chemical Engineering, Sungkyunkwan University, Suwon,

Gyeonggi, 16419, Republic of Korea Tel.: +82-31-290-7250 Fax: +82-31-290-7272

[email protected]

Abstract

OH radicals are the major cause for the degradation of polymer electrolyte membrane in polymer electrolyte membrane fuel cell (PEMFC) or direct methanol fuel cell (DMFC) operation. As cerium ion (Ce3+) is well known as an effective OH radical quencher, it is introduced into membrane to convert the OH radicals into water for long term anti-oxidation stability of polymer electrolyte in this study. Additionally, aminoethyl-15-crown-5 is grafted on the sulfonated poly (arylene ether ketone) (SPAEK) to prevent the migration of cerium ions from the membrane, as aminoethyl-15-crown-5 possibly forms a coordination complex with cerium ions. The chemical and physical structure of the aminoethyl-15-crown-5 grafted SPAEK are examined using 1H NMR, EDX, and SAXS. The physical properties such as proton conductivity, water uptake, and mechanical strength of the aminoethyl-15-crown-5 grafted SPAEK membrane are investigated and compared with those of the aminoethyl-15-crown-5 blended and cerium blended ones. While the grafting of aminoethyl-15-crown-5 does not significantly affect the thermal and mechanical and water uptake behaviors of membranes, it results in a significant improvement of anti- degradation effect compared with other blend systems via Fenton׳s test. The proton conductivity decreases with addition of cerium but its effect is lessened by introduction of aminoethyl-15-crown-5. Dual sulfonation of PAEK at the pendant site leads to enhancement of proton conductivity.








Atomistic MD study of Nafion in dispersions: Understanding the role of solvent in the ionomer

aggregate structure, sulfonic group clustering and acid dissociation

Atefeh Tarokh, Kunal Karan, Sathish Ponnurangam Department of Chemical and Petroleum Engineering, University of Calgary

2500 University Dr NW, Calgary, Alberta, Canada Tel.: +1-403-220-5754, +1-403-210-7342

[email protected], [email protected]

Abstract

Nafion belongs to the perfluorinated sulfonic acid (PFSA) class of ionomers and serves its primary functionality of proton conduction in the membrane and the catalyst layers (CLs) of polymer electrolyte fuel cells (PEFCs). Its solvent-dependent structural characteristics in dispersions and thereby in the colloidal catalyst ink (comprising Pt/C catalyst and ionomer in a solvent/media) has been speculated to play an influential role in the structure, property and performance of CLs made thereof [1-5].

We use fully atomistic Molecular Dynamics (MD) simulations to investigate the dispersion of the Nafion ionomer in hydrogen-bonding solvents with varying polarity (water, ethanol, IPA and glycerol). Two distinct aggregation behavior is observed. In water, the sulfonic acid is dissociated and aggregation of backbone attributed to hydrophobic effect. In organic solvents, the sulfonic group and the counter ions are not dissociated and ionomers aggregate via the clustering of the ion-pairs. Network of clusters of sulfonic groups forming the so-called hydrophilic ionic domains are crucial for long-range proton transport in membranes and ionomer thin films. Observed differences in finer-scale structure of Nafion (and other ionomers) in different solvents may help us understand what factors affect the transport properties of the ionomers in the PEFC CLs.

Pure water



Non-polar






Protic Organic Ionic Plastic Crystals as Novel Proton Conductors

Jiangshui Luo, Yingting Yi, Michael Wübbenhorst Department of Physics and Astronomy, KU Leuven

Celestijnenlaan 200d - box 2416, 3001 Leuven, Belgium [email protected]

Abstract

High temperature polymer electrolyte membrane fuel cells (PEMFCs) operating between 100 °C and 200 °C are desirable because they offer significant benefits, such as improved electrode kinetics, simpler water and heat management, and better tolerance to fuel impurities, leading to higher overall system efficiencies [1]. However, state-of-the-art high temperature PEMFCs suffer from leakage problems associated with liquid electrolytes, such as H3PO4 and protic ionic liquids. Recently, organic ionic plastic crystals (OIPCs) [2−6], which are unique electrolyte materials due to their superior properties such as intrinsic ionic conductivity, non-flammability, negligible vapor pressure, plasticity (mechanical flexibility), high thermal stability, and wide electrochemical window, are promising ionic conductors for electrochemical devices. While the OIPCs used as electrolytes for PEMFCs should be proton-conducting, they are often doped plastic crystals, which employ acids, protic ionic liquids or bases as the dopants for doping the matrix of certain neat plastic crystals. In order to obviate the use of dopants that may be incompatible with the host matrix of plastic crystals, we have developed some highly proton-conductive pure plastic crystals which are protic OIPCs (abbreviated as “POIPCs”) [3−6] and in essence are solid protic organic salts formed by proton transfer from a Brønsted acid to a Brønsted base. In this talk, we will present our recent work on some pure POIPCs with wide plastic crystalline phases as novel, fast solid-state proton conductors for the realization of all-solid-state high temperature PEMFCs [3−6]. The physicochemical properties of POIPCs, including thermal, mechanical, structural, morphological, thermodynamic, crystallographical, spectral and ion-conducting properties, as well as proton conducting mechanisms, isotope effects and fuel cell performances, are studied comprehensively in both fundamental and device-oriented aspects.

References [1] Q. Li, J. O. Jensen, R. F. Savinell, N. J. Bjerrum, Prog. Polymer Sci., 34 (2009) 449-477. [2] D. R. MacFarlane, M. Forsyth, Adv. Mater., 13 (2001) 957-966. [3] J. Luo, Ph.D. Thesis, KU Leuven, 2012. [4] J. Luo, O. Conrad, I. F. J. Vankelecom, J. Mater. Chem. A, 1 (2013) 2238-2247. [5] J. Luo, A. H. Jensen, N. R. Brooks, et al., Energy. Environ. Sci., 8 (2015) 1276-1291. [6] X. Chen, H. Tang, T. Putzeys, J. Sniekers, M. Wübbenhorst, K. Binnemans, J. Fransaer, D. E. De Vos, Q. Li, J. Luo, J. Mater. Chem. A, 4 (2016) 12241-12252.

Remark: Only the abstract is available, because the authors chose to publish elsewhere. Please see Presentations on www.EFCF.com/LIB or contact the authors directly.





B1106

Anion Influence on the Properties of Acidic Protic Ionic Liquids

Hui Hou, Jürgen Giffin, Carsten Korte Forschungszentrum Jülich GmbH, IEK-3

Wilhelm-Johnen-Straße, 52428 Jülich, Germany Tel.: +49-2461-61-85360 Fax: +49-2461-61-6695

[email protected]

Abstract

To run polymer electrolyte fuel cells (PEFCs) at an operating temperature above 100 °C, there is a growing need for new proton conducting membrane electrolytes that can be used when water activity is low. This would allow for a system setup without feed gas humidification and a more efficient cooling system. Nafion® membranes as used for low temperature PEFCs (LT-PEFCs) suffer from drying effects which will result in very low proton conductivity. H3PO4 doped PBI membrane, as used in high temperature PEFCs (HT-PEFCs), will result in a low power density because of low O2 solubility, as well as a specific adsorption of H3PO4 species on the platinum redox catalyst. Proton conducting ionic liquids (PILs) based on sulfonic acid derivatives may be used as alternative liquid electrolytes because they exhibit sufficient proton conductivity, electrochemical and thermal stability over a wide temperature range and specifically faster ORR kinetics compared to H3PO4 [1]. It was shown in a previous work by Wippermann et al. that the ORR limiting current density of the 2-sulfoethylammonium triflate with a strong acidic cation is significantly higher compared to H3PO4 in a high potential range [2]. However, the conductivity is about one order of magnitude lower. In this study, we investigate strong acidic PILs based on a 2-sulfoethylmethylammonium cation combined with various anions such as HSO4-, mesylate, tosylate, benzenesulfonate and triflate. Acidity influence of the anion on the ORR kinetics (oxygen diffusion coefficient and oxygen solubility), thermal and electrochemical stability as well as conductivity, was measured at different temperatures for the neat PILs as well as for various amounts of water. The measured values are compared to phosphoric acid and correlated to the anion properties to find an optimum. Literature: [1] Mitsushima, Shigenori, et al. Electrochimica Acta 55 (22), 6639-6644 (2010). [2] Wippermann, Klaus, et al. Journal of The Electrochemical Society 163.2, F25-F37 (2016).

http://www.efcf.com/Libmailto:h.hou@fz-juelich.




Introduction State-of-the-art low temperature polymer membrane fuel cells (PEFC) based on Nafion® membranes, are still facing with drying problem when increasing the operation temperature beyond 80 °C. A complex feed gas humidification and a water recirculation system are necessary. Thus, high temperature PEFCs (HT-PEFC) were widely investigated. HT-PEFC based on phosphoric acid (H3PO4) doped polybenzimidazole membranes (PBI), allow operation of up to 160 °C – 180 °C. There are many advantages for the application of HT-PEFC: (i) no water management system, (ii) tolerance against feed gas impurities like CO, (iii) the high grade waste heat can be used in the system[1]. However, H3PO4 species have a poisoning effect on the Pt redox catalyst and a low solubility of O2 in H3PO4 result in a sluggish ORR (oxygen reduction reaction) kinetics[2]. In this experimental study the basic electrochemical properties of protic conducting ionic liquids (PIL) are investigated, providing their use as alternative electrolytes for fuel cell applications. The requirements for a suitable PIL are as follows: (i) thermal stability up to at least 120 °C, (ii) electrochemical stability, (iii) sufficient conductivity (10-1 - 10-2 S/cm), (iv) fast ORR kinetics, (v) possibility to upscale for production scale. A major drawback of H3PO4 is the adsorption of phosphate species onto the Pt surface[3]. While compared with H3PO4, sulfonic acid and trifluoromethanesulfonic acid have less poisoning effect to a Pt redox catalyst[4,5]. Thus, the anion of the PIL is varied from HSO4-, mesylate, tosylate, benzenesulfonate to triflate and the measured performances of the PILs are compared with H3PO4.

1. Scientific Approach The PILs are synthesized by a neutralization reaction of a strong acid HA and an (organic) base B. The reaction scheme is shown as follows:

HA + B ⇌ BH+ + A− [1]

In this study, N-methyltaurine is used as common base B. The cation BH+ is referred as [2-Sema]. The acid HA is altered between sulfuric acid, methanesulfonic acid, p-toluenesulfonic acid, benzenesulfonic acid and trifluoromethanesulfonic acid. The anions A- are referred as [HSA]-, [MSA]-, [TSA]-, [BSA]- and [TfO]-, respectively. The structure of the PIL [2-Sema][TfO], is shown as follows:

Figure 1 Structure of the protic ionic liquid [2-Sema][TfO]

In the experiments section, the synthesis processes of PILs ([2-Sema][HSA], [2-Sema][MSA], [2-Sema][TSA], [2-Sema][BSA] and [2-Sema][TfO]) are illustrated. The physical and electrochemical properties of these PILs, such as the thermal stability, ionic conductivity, oxygen reduction reaction kinetics, oxygen diffusion coefficient and oxygen concentration (solubility), are investigated.





2. Experiments/Calculations/Simulations Synthesis of the PILs [2-Sema][TfO]: N-methyltaurine (reagent, Biosynth) was dried at 120 °C overnight and cooled to room temperature under a nitrogen atmosphere. Trifluoromethanesulfonic acid (reagent grade, 98 %, Sigma Aldrich) was added to a stoichiometric (1:1) amount of N-methyltaurine. The mixture was stirred at 90 °C for 1 hour. Considering its strong hygroscopicity, [2-Sema][TfO] has to be stored under nitrogen atmosphere. [2-Sema][HSA]: same procedure as [2-Sema][TfO]. [2-Sema][MSA]: same procedure as [2-Sema][TfO]. [2-Sema][TSA]: Since p-toluenesulfonic acid is a solid at room temperature, it was heated up to its melting point. The melted acid was added to a stoichiometric (1:1) amount of N-methyltaurine. From this point, the same synthesis procedure was adopted. [2-Sema][BSA]: same procedure as [2-Sema][TSA]. Characterization of water contents in PILs The water contents of neat PILs were measured by using Karl Fischer titration (852 KF Titrando, Metrohm). Since the PILs exhibit high viscosities, they were diluted with water-free acetic acid. The mixtures were homogenized for 30 min before starting the measurements. Thermal analysis Thermal stabilities of PILs were examined with a Perkin Elmer STA 6000 device. All PILs samples were measured under nitrogen atmosphere. ORR kinetics The ORR kinetics of the PILs were measured in a three-electrode testing cell under ambient pressure in the temperature range between 80 °C – 120 °C. The homemade Pt working electrode with a diameter of 250 μm was used. The roughness factor of the Pt surface was determined to 1.3. A palladium-hydrogen electrode (Pd-H electrode) was used as a reference electrode. The Pd-H reference electrode was prepared according to the literature[6-8]. The testing cell with a volume of about 3 ml – 4 ml was in-house-designed. A schematic drawing of testing cell is shown in Fig. 2. A Pt crucible (99.9 % purity, m&k GmbH) was used both as the measurement vessel and as the counter electrode. The measurement setup is described in detail by Wippermann et al.[8].





Figure 2 Schematic drawing of testing cell[8]

Before starting the electrochemical measurements, the PILs samples were saturated with O2 for 2 h with a gas flow rate to 20 ml/min. The O2 flow rate was reduced to 10 ml/min during the measurements to avoid disturbances. The temperature was monitored in-situ by a thermocouple sensor. All electrochemical measurements were performed by using the electrochemical workstation (Zahner Elektrik GmbH). Conductivity measurements The total conductivities of PILs were measured in the temperature range of 80 °C - 120 °C by using the two-electrode testing cell as described above, see Fig. 2. The Pt electrode was used as working electrode and the Pt crucible as counter electrode. The cell constant was determined using 0.1 M KCl solution. The cell constant of 0.42 cm-1 was found to be constant in the volume range between 3.7 ml and 5 ml.

3. Results ORR kinetics The ORR polarization curves in H3PO4, [2-Sema][TfO], [2-Sema][HSA] and [2-Sema][BSA] with a water content 23 mol% at 100 °C are depicted in Fig. 3. In the potential range between 0.8 V and 0.2 V, significantly different current densities are observed and thus cell different performances can be measured. At a cell potential of 0.7 V, the current density of [2-Sema][TfO] is 5 times larger compared with H3PO4 and 26 times larger compared with [2-Sema][BSA] as well as [2-Sema][HSA]. In the potential range between 0.7 V and 0.9 V, which is relevant for fuel cell application, [2-Sema][TfO] shows a better performance compared with the other PILs and H3PO4. The comparison of the limiting current densities is as follows:

jlim([2-Sema][TfO])/ jlim([2-Sema][BSA] ≈ 1.4,

jlim([2-Sema][TfO])/ jlim(H3PO4) ≈ 4,

jlim([2-Sema][TfO])/ jlim([2-Sema][HSA] ≈ 7.





Figure 3 Polarization curves of ORR in PILs and H3PO4

Mass transport characteristics

The oxygen concentrations cO2s and the (Fick’s) oxygen diffusion coefficients DO2s in the PILs chosen for investigation are determined by chronoamperometry. Potential steps were applied to the cell by switching from OCV to a potential in the region of the limiting current and then back to OCV. The measured current as a function of elapsed time was recorded. The dynamic I vs.t curves were fitted with the Shoup-Szabo equation to determine the oxygen diffusion coefficient and oxygen concentration[9] (Fig. 4). The oxygen diffusion coefficients in the PILs are about 1 magnitude smaller compared with H3PO4. However, the oxygen concentrations (solubilities) in the PILs are 1 - 2 magnitude higher compared with H3PO4. The highest solubilities in the measured temperature range can be found in the case of [2-Sema][TfO].

Figure 4 Oxygen diffusion coefficients in H3PO4 and PILs (left), oxygen concentrations in

H3PO4 and PILs (right), water contents in PILs and H3PO4: 23 mol%





4. Conclusions The highest ORR limiting current at 100 °C can be found for [2-Sema][TfO]. It outperforms H3PO4 by a factor of 5. The ORR performance depends on the redox kinetics on the electrode surface, which can be interfered by strong adsorption of anionic species, but it also depends on the matter transport to the electrode. [2-Sema][TfO] exhibits a worse oxygen diffusion coefficient compared to phosphoric acid, but the oxygen solubility seems to overcompensate this lack.

When comparing [2-Sema][TfO], [2-Sema][HSA] in respect to H3PO4, the least influence on the ORR kinetics is found in the case of [2-Sema][TfO] with the least nucleophilic anion (from the super acid TfOH). Despite the fact that the oxygen diffusion coefficients of both PILs are comparable and the oxygen solubility of [2-Sema][HSA] is still higher compared with H3PO4, [2-Sema][HSA] with a HSO4− anion performs worse compared with H3PO4.

References [1] Yasuda, Tomohiro, and Masayoshi Watanabe. MRS bulletin 38.7 (2013): 560-566. [2] Hsueh, K‐L., et al. Journal of the Electrochemical Society 131.4 (1984): 823-828. [3] Hsueh, K. L., E. R. Gonzalez, and S. Srinivasan. Electrochimica Acta 28.5 (1983): 691

697. [4] Scharifker, Benjamin Ruben, Piotr Zelenay, and JO'M. Bockris. Journal of the

Electrochemical Society 134.11 (1987): 2714-2725. [5] Zelenay, P., et al. Journal of the Electrochemical Society 133.11 (1986): 2262-2267. [6] Fleischmann, M., and J. N. Hiddleston. Journal of Physics E: Scientific Instruments 1.6

(1968): 667. [7] Vasile, M. J., and C. G. Enke. Journal of the Electrochemical Society 112.8 (1965):

865-870. [8] K.Wippermann, J.Wackerl, W. Lehnert, B. Huber and C. Korte, J. Electrochem. Soc.

163-2 (2016) F25-F37. [9] Shoup, David, and Attila Szabo. Journal of Electroanalytical Chemistry and Interfacial

Electrochemistry 140.2 (1982): 237-245. [10] Hsueh, K. L., E. R. Gonzalez, and S. Srinivasan. Electrochimica Acta 28.5 (1983): 691-

697.





B1107

Diagnosis of MEA Degradation for health management of Polymer Electrolyte Fuel Cells

Derek Low, Lisa Jackson, Sarah Dunnett Department of Aeronautical and Automotive Engineering

Loughborough University Loughborough, United Kingdom

Tel.: +44 (0)1509 227309 [email protected]

Abstract

Diagnostics and health management are fundamental components in a strategy to improve durability and lifetime of polymer electrolyte fuel cells. Fuel cells require a range of operating conditions to be well managed for achieving performance or durability objectives. So far, water management issues and single parameter diagnostics for individual degradation modes have been the focus of research in the literature. However, there has been minimal research on the application of fuzzy inference systems for online, multiple parameter diagnosis of fuel cells. This research presents an advanced fuzzy inference system for diagnostics and health management of a membrane electrode assembly (MEA) for polymer electrolyte fuel cells. The fuzzy inference system facilitates simplified connections of the complex relationships between numerous operating conditions and subsequent degradation modes. The approach utilises the most important operating parameters for diagnosis of high priority degradation modes using multiple health sensors. The developed fuzzy inference system classifies the fuel cell input data into simple linguistic categories for example ‘cell voltage is very high’ or ‘stack temperature is low’ through a fuzzification process. Based on a set of antecedent-consequent (if-then) rules, an inference calculation is performed without necessity for complex mathematical models. This enables a fast diagnosis with fuel cell parameters classified on a scale of inclusion to the linguistic categories. The linguistic classification of a degradation mode is converted back into a numerical value through a defuzzification process. The output data can be used to inform the user on the fuel cell state of health. The investigation has focused on the diagnosis of MEA degradation as it has been identified as having critical impact on fuel cell performance and lifetime. A single cell with a 25cm2 active area was used for testing under numerous moderate to extreme operating conditions known to cause membrane and electro-catalyst degradation. A database of if-then rules was initially developed based on knowledge in the literature and refined with experimental testing. Results so far have supported validation of the fuzzy inference system membership functions and the rule base for diagnosing the consequential degradation modes based on fuel cell operating conditions. This diagnostic and health management approach facilitates proactive decision making for mitigation strategies to be employed according to performance or lifetime targets and can increase fuel cell availability and lifetime therefore improving the overall value of the system.





Introduction Polymer electrolyte fuel cells (PEFC’s) are a promising technology that can produce electricity efficiently with zero carbon emissions. Therefore, the development of fuel cell technology plays an important part in the decarbonisation of industry and progression towards a low carbon sustainable society. The reliability and durability of PEFC’s is still a remaining technological challenge as industry lifetime targets for automotive and stationary applications of 5,000hrs and 40,000hrs respectively are yet to be achieved [1][2]. Achieving these targets are crucial in order to compete with conventional technologie

Documents

Proceedings EFCF 2019€¦ · Fuel Cells, Electrolysers & H 2 Processing EFCF 2019 2 - 5 July, Lucerne/Switzerland PEFC Degradation & Testing, Acidic Membrane Materials, Chapter 05