K. Sundmacher: Electrochemical Energy Conversion using Fuel Cell Systems NTNU, 29 June 2007 1 Electrochemical Energy Conversion using Fuel Cell Systems

NTNU, 29 June 2007 K. Sundmacher: Electrochemical Energy Conversion using Fuel Cell Systems 1

Electrochemical Energy Conversion using Fuel Cell Systems

Kai Sundmacher1,2

1 Max-Planck-Institute for Dynamics of Complex Technical Systems, Magdeburg2 Otto von Guericke University Magdeburg, Process Systems Engineering


Research Institutes at Magdeburg/Germany

Otto von Guericke University Magdeburg (11.000 students)

Max Planck Institute for Dynamics of ComplexTechnical Systems 1998 started 4 departments ~ 200 employees

Fraunhofer Institute forFactory Operation and Automation

Experimental Factory

EnvironmentalResearch Center

(UFZ)


World Energy Demand

• Strongly increasing energy demand, particularly in Asia

• Dependence of many countries on limited fossile resources

economic impact:increasing costs for energy „harvesting“ and transport political impact:fair distribution of resources

• Emissions local: air polution

global: climate change

Ref.: IEA (International Energy Agency) World Energy Outlook 2002 – Forecast of world energy consumption until 2020.


Solution Strategies

Classical Energy Carriers Renewable Resources

Need for higher efficienciesGeneration

Distribution

Consumption

Dispersed power systems:+ lower losses+ combined cycles+ higher net stability- net operation difficult

• Sun• Wind• Water Flow• Geothermal• Biomass

Balancing Availability and Demand in Time and Space

Intelligent energy storage and transport


Solution Strategies



Distribution

Consumption


• Sun• Wind• Water Flow• Earth heat• Biomass



…how can Fuel Cellscontribute?


Solution Strategies: The Role of Fuel Cells



Distribution

Consumption





More efficient production of

electrical energy!





Distribution

Consumption





Direct conversion of primary energy at

the site of consumption!





Distribution

Consumption





Fuel Cells ideally suited for

combined cycles!





Distribution

Consumption





Fuel cells are key component in future hydrogen economy!


Working Principle of H2-O2 Fuel Cell (PEMFC)

PEM

PorousAnode

PorousCathode

Electrolyte

Hydrogen

Polymer Electrolyte Membrane Air

Bipolar Plate

Gas Diffusion Layer

Catalyst Layer


Fuel Cell Stack

Ucell = 0,5 - 0.9 V

Stacking N cells in series leads to higher voltages.

Larger cross sectional area A leads to higher currents:

+

- +

-

-

-

-+

+

+UStack = N · Ucell

Stack by ZSW, GermanyElectrical Power: 1 kW

ca. 350 mm

100 mm

100 mm

Stack

Single Cell

A IStack = Icell = A · icell,av


Outline

Introduction

Solid Oxide Fuel Cell: SOFC

Molten Carbonate Fuel Cell: MCFC

Proton Exchange Membrane Fuel Cell: PEMFC

Enzymatic Fuel Cell

Summary

1000 °C

600 °C

80 °C

37 °C


Working Principle of MCFC

T = 580 - 650 °C

Anode

CO32-

Cathode½O2+CO2+2e-CO3

2-

(CH4)(H2)(CO)CO2

H2O

O2

CO2

ExchaustAir

Electrolyte

e-

CH4

H2O

Ucell

H2 + CO32- H2O + CO2 +2e-

CO + CO32- 2CO2+2e-

O2

N2

(Air)

CatalyticCombustion

CH4 + H2O CO + 3H2

CO + H2O CO2 + H2

(N2)(H2O)

Internal Reforming Anode:Ni-10% Cr3 – 6 m Pores60 % Porosity1 mm Thickness

Cathode:NiO7 – 15 m Pores

Electrolyte Matrix:-LiAlO2/-Al2O3

0,5 mm Thickness

Electrolyte:62% Li2CO3

38% K2CO3


250 kW MCFC Fuel Cell Plant “HotModule”

HotModule System being installed atthe University Hospital in Magdeburg• Molten Carbonate Fuel Cell: MCFC• 342 Cells, 250 kW Electrical Power• ca. 48% Electrical Efficiency• Feed Gas: Natural Gas• Size (L x W x H): 7,3 m x 2,5 m x 3,2 m• Mass 15 t

Developed by: MTU CFC Solutions, Germany

N2 / O2

ExhaustAir

StainlessSteal Vessel

Electrical.Heater

CatalyticCom-bustion

Feed Gas CH4 / H2O

CO2 / O2

Fresh AirN2 / O2

MixingChamber

GasDistributor

FC Stack

Fan

4 / H2O

CO2 / O2


System Features:• 3-dimensional cell stack• Cross-flow operation• External recycles

0.8 m

1.2

m

2.5 m ; 342 Cells

MCFC Fuel Cell “HotModule”

Catalytic Com-

bustion

Anode Feed

Cathode Feed

Anode Effluent

Exhaust Air Cathode Gas Recycle

CathodeEffluent

Fresh AirSupply


2D Model of MCFC Fuel Cell “HotModule”

Enthalpy and Mass Balances of Gas Phases

,,

,,

,,0

Enthalpy Balance in Solid Phase

,,2

2

ssss

Charge Balances at Electrolyte

,, saii

cell

A

IdAi

Conductive heat transport,parabolic PDE

Convective mass transport,hyperbolic PDE

Convective energy transport,hyperbolic PDE

Total mass balance,ODE in space

Local charge balance,ODE in time

Galvanostatic condition,Integral equation

Number

17 PDE, 4 ODE, 1 IE

2x7=14 PDE

2x1=2 PDE

2x1=2 ODE

1 PDE

2x1= 2 ODE

1 IE

K. Chudej, P. Heidebrecht, V. Petzet, S. Scherdel, K. Schittkowski, H.J. Pesch, K. Sundmacher, ZAMM 85 (2005) 132-140.


Steady State MCFC Simulation ResultsAverage Current Density: 125 mA/cm²; S/C = 2.5; Fuel Utilization: 70%

P. Heidebrecht, K. Sundmacher, Journal of the Electrochemical Society 152, 2005, A2217-2228.

Current Density

Hydrogen at Anode

Temperature at Cathode

AnodeFeed

CathodeFeed

CH4 / H

2O O

2 / CO

2


Dynamic Response to Load Change

0.85Icell

0.7

step=0.1

=500

P. Heidebrecht, K. Sundmacher, Journal of the Electrochemical Society 152, 2005, A2217-2228.

DoubleLayerCharging

Mass Transfer toElectrodes

Heat Transportin SolidParts

Time, - step

Cel

l Vol

tage

, U

cell


Model-based Observer

Measurable: cell voltage, gas exit temperatures, gas exit compositions

Desirable for process control and monitoring: Information on internal temperatures and gas compositions very difficult to measure!

Solution:

Observer / State Estimator

?



RealProcess

Inputs u

MCFC Sensoreny

States x

Sensor Modelsxx

!

)x(hy y

Outputs y

?

MCFC ModelObserver

Observer Correction

yyk

)(x)(x

+

-

messt

,x,xf

x

z

t


• Experimental results: Estimation Experimental Data

Experimental Information for Filter Correction

Good Filter Convergence

Experimental Information for Filter Validation

Good Precision of State Estimation



Outline

Introduction




Enzymatic Fuel Cell

Summary

1000 °C

600 °C

80 °C

37 °C


SOFC: Candidate for Steady State Power Plants

SOFC: Solid Oxide Fuel CellElectrolyte: Solid Oxide Ceramics (YSZ)Effectiveness: 55 – 65 %Temperature: 800 - 1000 °CFuture Use: Power plants for kW - GW range

AnodeSolid OxideCathode

Fuel Gas

AirSource: Siemens-Westinghouse, www.powergeneration.siemens.com/en/fuelcells

Gas Feed

Electrical Switches

Electrolyte

Anode

Cathode

CathodeContactors

DC/AC Converter

USV


Temperature Effects in Electrical Conductors

Metallic Conductor • Charge transport by electrons• Electrical conductivity decreases at

increasing temperature• If local temperature increases:

local current density decreases local heat production decreases

(Ohmic losses) self-stabilizing effect

Oxygen Ion Conductor (Fuel Cell)• Charge transport by ions• Electrical conductivity increases at

increasing temperature • If local temperature increases:

local current density increases local heat production increases (Ohmic losses + reaction heat) de-stabilizing effect

+

-current density

-

+current density

Mangold, M., Krasnyk, K., Sundmacher, K., Chemical Engineering Science 59 (2004) 4869 - 4877


Simple 1D Model for SOFC

Model asumptions: 1D approach (gradients only in y-direction) Heat transport via heat conduction (Fourier’s law) Concentration polarization neglected Infinitely high electrical conductivity of electrodes Arrhenius-type temperature dependence of electrical conductivity



SOFC: Dimensionsless Model Equations

• Energy balance:

12

2

BiiUiB cell

• Boundary conditions: ),(Bi,

02

0

),(Bi,

12

1

1

exp1

)1(exp1

exp/

///

///CA

eqCACAeq

CAeqCACACA Ki

• Electrochemical kinetics at anode and cathode:

• Ohm’s law for ion transport in electrolyte:

totCAEE expi

1

• Overall charge balance for electrodes: 1

0

diI tot Arrhenius term


SOFC: Phase Portrait at Ucell = const.

Solutions for a fuel cell of infinite length:

Periodic solutions along space coordinate possible!


left boundary:

),0(20

Bi

right boundary:

),0(20

Bi

SOFC: Phase Portrait at Ucell = const.

Solutions for a fuel cell of finite length:


SOFC: Current Instabilities at Icell = const.


E1 E

2>E1

E3>E

2


Outline

Introduction




Enzymatic Fuel Cell

Summary

1000 °C

600 °C

80 °C

37 °C


PEMFC: Use in Mobile Applications

PEMFC: Polymer Electrolyte Membrane Fuel Cell

Electrolyte: Polymeric Membrane as Ion Conductor

Efficiency: 30 - 50%

Temperature: 20 - 100 °C (Goal: 180 °C)

Use: Cars, portable devices, battery substitute

H+

O2

e-

AnodePEM Cathode

H2

H2O

Source: Adam Opel AG Opel HydroGen 3 (2001) H2-operation, 150 km/h, 400 km distance

Problem: Membrane Water Management


PEMFC: Multiple Steady Operating States

PEM Fuel Cell:

inOHOHsat

OHOHREM papa ,2222

)(

car

aa

OHL

OHOH

PROD

)(

)()(

2

2

2

Water production curve:

Water removal line:

H2 + ½ O2 H2O

Water activity in membrane, aH2O

Map of Operating Modi

Hanke, Mangold, KS, Fuel Cells 5 (2005) 133Hanke-Rauschenbach, Mangold, KS, JPS (2006) in prep.

Hydrogen Feed Flow

Gas Humidity


PEMFC: Nonlinear Operating Dynamics

R. Hanke-Rauschenbach, M. Mangold, K. Sundmacher, JPS (2006) in prep.

R. Hanke-Rauschenbach, M. Mangold, K. Sundmacher, AIChE Meeting, San Francisco, 12-17 Nov. 2006.

Current Voltage Curve

Humidityreduction

Response behaviour at load variations


Outline

Introduction




Enzymatic Fuel Cell

Summary

1000 °C

600 °C

80 °C

37 °C


Enzymatic Fuel Cells: Possible Biomedical Applications

Hearing Devices

Neuro-Stimulators

ICD/CHF Devices LVAD Artificial Hearts

Pacemakers

Drug PumpsInsulin Pumps

Incontinence Devices

Bone Growth Stimulators Goal: Implantable fuel cell in the mW to W range


Redox Processes in Biology

OH

OH

OH

CH2OH

OH COOH

H2OO

OH

OH

CH2OH

OH

O

O2

FADH2FAD

O

OH

OH

CH2OH

OH

OH

H2O2

-D-glucose -gluconolactone gluconic acid

+2e-

+2H+

-2e-

-2H+

Oxidation

Reduction

FAD =

Flavin Adenin Dinucleotid

is a redox cofactor

of the enzyme

Glucose Oxidase

Glucose Oxidase, GOX

FAD


Enzymatic Fuel Cell: Working Principle

Ano

de

Cat

hode

H+

e- e-

glucose

gluconic acid

O2

H2O

enzymes

redox center

e-

Anode: C6H12O6

Cathode: ½ O2 + 2e- + 2H+

C6H10O6 + 2e- + 2H+ Oxidation E = - 0.5 V

H2O Reduction E = 0.7 V

Overall: C6H12O6 + ½ O2 C6H10O6 + H2O ΔE = 1.2 V

Voltage

Immobilisation

Electron transfer

ANODE

Current ~ Enzymes per Area


Immobilisation of Glucose Oxidase at Gold Electrode

SNH2

SNH2

S NH2

PQQS NH PQQ

H2N FAD

S NH PQQ NH FAD

apo-GOX

S NH PQQ NH FAD

e-

e-

glucose

gluconic acid

EDC, NHS EDC, NHS

Au

PQQ = Mediator: redox-active component for electron transfer between enzyme and electrode

N

O

O

HN

COOH

HOOC

HOOC


Enzyme Electrode: Proof of Principle with Glucose

S NH PQQ NH FAD

apo-GOX

S NH PQQ NH FAD

e-

e-

gluconic acid

glucose

Th

erm

od

yna

mic

po

ten

tia

l

On

set

po

ten

tia

l

Overpotential


Summary: Important Trends in Fuel Cell Engineering

High temperature fuel cells: Molten Carbonate fuel cells (HotModule) are very close to the market Efficient co-production of electricity and heat Internal direct reforming (DIR) is most attractive process variant

Low temperature fuel cells: PEMFC: Problem of water management in membranes Development of water-free membranes for mobile applications

Enzymatic fuel cells: Biomedical applications: interdisciplinary collaboration between

chemical engineering, electrochemistry and organic chemistry necessary

Documents

K. Sundmacher: Electrochemical Energy Conversion using Fuel Cell Systems NTNU, 29 June 2007 1 Electrochemical Energy Conversion using Fuel Cell Systems