Advanced Biowaste‐Based Flexible Photocatalytic Fuel Cell ...chemeng.uwaterloo.ca/zchen/publications/documents/... · power generation. fPFCs consist of a photoelectrochemical cell

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Consequently, virtually all organic matter can be used as fuel in an fPFC, including resilient biowaste that are not easily con-verted to CO2 and H2O.[19–21] Second, a photoelectrochemical configuration allows these highly favorable redox reactions to simultaneously generate an electrical cur-rent.[17] Third, photocatalysts are inert materials that are not consumed during oxidation, do not create secondary forms of pollution, and are naturally self-regen-erating.[22,23] Therefore, photocatalysts are generally stable irrespective of their envi-ronment and do not need to be replaced.

These properties provide fPFCs with a distinct advantage over renewable power generation technologies such as enzymatic and microbial fuel cells.[24–28] Enzymatic fuel cells (EFCs) are a class of fuel cell that uses enzymes to oxidize fuel instead of electrocatalysts. Because of this, EFCs require specific operating parameters, including temperature, mediators, and buffer solu-tions in order to function properly. In addition, EFCs require relatively expensive enzymes that are chemically specific and cannot necessarily oxidize any organic material. For these rea-sons, fPFCs have the potential to provide a more comprehen-sive and resilient form of power generation.

We have developed for the first time an fPFC that can pro-vide green, wearable, energy conversion, and power genera-tion. The inherent flexibility of an fPFC allows for ad hoc and nonstandard solutions not accessible to the rigid configurations of conventional photocatalytic fuel cell (PFC) devices—there-fore greatly diversifying its potential application in real-world situations. These applications include: (i) wearable technolo-gies that generate power from biowaste; (ii) wearable or flexible technologies that can be used as sensors; and, (iii) flexible con-figurations for conventional wastewater remediation and water reservoirs.

The multifunctional performance of an fPFC is achieved through the oxidation of an organic fuel at the photoanode (Figure 1a). When a photon strikes the photocatalyst through the transparent current collector, an electron–hole pair is cre-ated. In an n-type semiconductor, the electron moves to the cur-rent collector and the external circuit. The hole in turn moves to the electrode surface and initiates an oxidation reaction with an adsorbed species, generating a free proton, H+ (Equation (1)). The proton diffuses to the cathode where it combines with O2 and incoming electrons to form H2O in a reduction reaction (Equation (2)). In the absence of oxygen, H2 gas can be formed in the reduction reaction instead (Equation (3)).[29,30] Therefore,

Advanced Biowaste-Based Flexible Photocatalytic Fuel Cell as a Green Wearable Power Generator

Gregory Lui, Gaopeng Jiang, Jared Lenos, Edric Lin, Michael Fowler, Aiping Yu, and Zhongwei Chen*

This study designs a wearable power generator from a flexible, photocata-lytic fuel cell (fPFC) using various biowaste sources (lactic acid, ethanol, methanol, urea, glycerol, and glucose) as fuel. The fPFC uses light irradiation and the decomposition of biowaste to generate electrical power under both flat and bending (r = 3 cm) conditions. When employed as a sweat band, the fPFC generates a maximum power 4.0 mW cm−2 g−1 from human sweat. The wearable fPFC is able to overcome many of the disadvantages of wearable microbial and enzymatic cells while providing comparable if not superior power density.

DOI: 10.1002/admt.201600191

G. Lui, G. Jiang, J. Lenos, E. Lin, Prof. M. Fowler, Prof. A. Yu, Prof. Z. ChenDepartment of Chemical EngineeringUniversity of Waterloo200 University Avenue WestWaterloo, ON N2L 3G1, CanadaE-mail: [email protected]

1. Introduction

Wearable technologies are a quickly expanding market addressing the demand for flexible and wearable electronics, including smart clothing, smart devices, activity trackers, and even medical devices.[1–4] The majority of progress in this field has been in the design of flexible battery,[5,6] supercapacitor,[7,8] and photovoltaic[9,10] devices, which can either store or convert energy in a wearable configuration. Several additional energy conversion methods have been used to harness energy directly from human body, including body heat,[11,12] mechanical move-ment,[13,14] and triboelectric charging.[15,16] However, little research has been performed on harnessing biowaste as a source of energy in a wearable power generation device.

A flexible photocatalytic fuel cell (fPFC) is one such concept that would be able to convert organic matter such as biowaste into electrical energy, effectively providing green, wearable power generation. fPFCs consist of a photoelectrochemical cell using a photoelectrode as the anode and an organic fuel source as the electrolyte.[17] The design of the fPFC in green power generation affords several significant properties. First, photocatalysis is a light-activated advanced oxidation pro-cess that is able to photogenerate highly oxidative hydroxyl radicals that nonselectively decomposed organic material.[18]

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PFCs are functionally related to conventional fuel cells, yet mechanistically distinct.[31,32] Relatively inexpensive photocata-lysts are used in place of precious[33–35] and nonprecious[36–38] metal electrocatalysts:

2R H 2h 2R 2H− + → ++ ′ + (1)

2H12

O 2e H O2 2+ + →+ − (2)

2H 2e H2+ →+ − (3)

In order to demonstrate flexibility, indium-tin-oxide-coated polyethylene terephthalate (PET) film (ITO/PET) was used as the photoanode current collector, Pt/C on carbon cloth was used as the cathode, and cellulose paper was used as the solid electrolyte membrane. The photoelectrochemical cell was sealed in a transparent plastic housing using a heat sealer. The configuration of the fPFC cell is illustrated in Figure 1b.

2. Results and Discussion

2.1. Flexible Photocatalytic Fuel Cell

The photoanode was prepared using commercial TiO2 nano-particles (P25). A slurry was made by mixing P25, ethanol, and titanium tetraisopropoxide and sonicating the mixture for 60 min. The slurry was then cast onto an ITO/PET film using a doctor blade to control the loading and thickness of the cata-lyst film. The TiO2 loading on the photoanode was found to be 0.92 mg cm−2.

Scanning electron microscopy (SEM) was used to charac-terize the topology of TiO2 photoanode (Figure S1, Supporting Information). The surface is uniform on a macroscopic level, while high magnification images reveal that the film consists of nanoparticles ≈20 nm in diameter. This is consistent with the size of nanoparticles used to make the electrode. A cross-sectional SEM image was also taken of the photoanode. The photocatalyst layer was found to be ≈19.1 µm thick, while the PET layer is roughly 100 µm thick. Energy-dispersive X-ray spectroscopy mapping was also used to confirm this configura-tion (Figure S2, Supporting Information). Lastly, X-ray diffrac-tion (XRD) was used to confirm that the nanocrystalline TiO2 consisted of both anatase and rutile phases characteristic of P25 (Figure S3, Supporting Information).[39]

In order to evaluate the potential ability of the fPFC to gen-erate power from biowaste, various organic fuels were tested. Electrolyte solutions were created using 1 m solutions of lactic acid, ethanol, methanol, glycerol, urea, and glucose in deion-ized water. No other components were added to the electrolyte. The photoelectrochemical properties of the fPFCs using var-ious fuels were tested using a 1 W 365 nm light-emitting diode (LED). The irradiance at the surface of the fPFC was found to be 217 mW cm−2 at a distance of 2.1 cm. The photocurrent response of the fPFC is shown in Figure 2a,b where the light source is turned on and off at intervals of 30 s. The response of the fPFC to light irradiation is almost instant, while the relaxation varies depending on the fuel used. Specifically, the relaxation of glucose and glycerol fuels exceeds that of the other fuels. This is likely due to the larger size of these molecules with more extensive degradation pathways. This increases the chance for current doubling which can prolong current genera-tion even after the light source has been removed.

The photocurrent response of the fuels generally exhibits an anodic or mixed (anodic–cathodic) current under light irra-diation. In fact, apart from ethanol, all other fuels exhibit ini-tial mixed current behavior. This is due to the sudden, initial generation of electron–hole pairs which push holes toward the photocatalyst surface and electrons toward the bulk. (Poten-tial reactions at the anode using the fuel tested in this work are given in Equations (S1)–(S6) in the Supporting Informa-tion.) After this initial photogeneration, electrons begin to recombine with the accumulated holes until an equilibrium is reached.[40–43] This equilibrium current depends on the rates of fuel oxidation (anodic) and recombination (cathodic). There-fore, the lack of observed mixed current behavior in the eth-anol fPFC suggests that the relative rate of ethanol oxidation is much greater than the rate recombination.[40] In terms of photo-current response, lactic acid fuel provides the highest current




Figure 1. a) Schematic outlining the basic operation of a PFC. b) Configu-ration and components of the fPFC.

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(61.4 mA cm−2 g−1), followed by ethanol (56.7 mA cm−2 g−1), methanol (42.0 mA cm−2 g−1), glycerol (28.5 mA cm−2 g−1), urea (28.4 mA cm−2 g−1), and glucose (22.7 mA cm−2 g−1). The large current density of lactic acid is due to its acidity, which greatly increases the overall ionic conductivity of the electrolyte by pro-viding additional H+ ions. This improvement to the electrolyte is significant since no other components (besides water) are added to the electrolyte solution to improve its conductivity. Understandably, the simple alcohols provide high current densities due to their facile oxidation kinetics, while the more complex molecules (such as glucose and glycerol) have lower current densities due to slower kinetics and diffusion.[44,45] The long-term operational stability was demonstrated using 1 m lactic acid and is shown in Figure S4 (Supporting Information) where no additional fuel was added after initial injection. The fPFC was operated over a period of one hour with a relatively stable photocurrent density output. This result demonstrates the potential for power generation using an fPFC, provided that fuel is available for consumption.

Polarization curves of the fPFCs were also obtained (Figure 2c) and show a similar trend to the photocurrent response curves. The polarization curves show a distinct lack of activation polarization found in conventional fuel cells and appear to be dominated by concentration polarization. This is a common phenomenon in photocatalytic electrochemical cells is likely due to the excitation of charge carriers in photocata-lystic materials.[29,30,46–50] Because current is induced through the anode material as opposed to the external circuit, it is pos-sible that activation polarization is intrinsically overcome by the photogeneration of charge carriers in a catalyst with a sufficiently

large redox potential. All curves exhibit a similar open-circuit voltage (VOC) with values ranging from 0.90 to 1.03 V. The short-circuit current densities (JSC, the current density at 0 V) follow the same trend as the photocurrent densities, with lactic acid exhibiting the highest JSC value (76.8 mA cm−2 g−1) followed by ethanol (53.8 mA cm−2 g−1), methanol (51 mA cm−2 g−1), glycerol (33.9 mA cm−2 g−1), urea (33.8 mA cm−2 g−1), and glu-cose (25.0 mA cm−2 g−1). Power curves based on the same data (Figure 2d) show that the maximum power achievable for cells using lactic acid, ethanol, methanol, glycerol, urea, and glucose is 18.4, 14.5, 12.8, 9.7, 9.3, and 5.1 mW cm−2 g−1, respectively. These data are summarized in Table 1. Based on the maximum power output of the fPFC using each biofuel, calculated effi-ciency can be obtained and compared to similar technologies (Table S1, Supporting Information). Results showed that the theoretical first-law efficiencies of the biofuels were within the range of 40%–50%. When compared to competing technologies such as the microbial fuel cell, the fPFC provides comparable




Figure 2. Photocurrent responses of a) alcohols and b) organic matter found in human sweat, c) polarization curves, and d) corresponding power curves of the fPFC using different fuels.

Table 1. Photoelectrochemical results of fPFC using various fuels.

Fuel Iph [mA cm−2 g−1]

JSC [mA cm−2 g−1]

VOC [V]

Pmax [mW cm−2 g−1]

Lactic acid 61.4 76.8 0.990 18.4

Ethanol 56.7 53.8 0.899 14.5

Methanol 42.0 51.0 0.955 12.8

Glycerol 28.5 33.9 0.948 9.7

Urea 28.4 33.8 0.940 9.3

Glucose 22.7 25.0 1.033 5.1

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performance.[51] Similarly, when compared to fuel cells at appropriate operating voltages, the fPFC also provides compa-rable efficiencies.[52]

In order to determine the potential of the PFC as a flex-ible device, the performance of the fPFC was obtained under bending. A comparison was made between the flat and bending (radius of curvature = 3 cm) performance of an fPFC using glycerol fuel (Figure 3). Optical images in Figure 3a convey the functionality of a glycerol fPFC by generating an open-circuit voltage of 958 mV under irradiation in a bending configura-tion. This value is functionally identical to that under flat con-ditions (Figure 2c). The photocurrent response (Figure 3b) of the device under bending (26.2 mA cm−2 g−1) is marginally lower than in a flat configuration (28.5 mA cm−2 g−1). It can be seen that bending the fPFC introduces a small amount of noise during irradiation. This noise is due to the introduction of non-uniform contact between the electrodes and the cellulose mem-brane under bending. These irregularities cause fluctuations in the overall current as points of contact are lost or gained under bending. The polarization curve of the fPFC under bending is in agreement with the average of the photocurrent response results (Figure 3c). Under bending, the fPFC has a short-circuit current density of 25 mA cm−2 g−1 and a maximum power den-sity of 6.6 mW cm−2 g−1.

Lastly, electrochemical impedance spectroscopy (EIS) was used to further investigate the electronic properties of the fPFC under light irradiation and bending (Figure 3d). In the absence of light irradiation, the cells exhibit fairly linear (corresponding to Warburg impedance, ZW) behavior with a minimal charge transfer component. For this reason, the EIS data were mod-eled using a simple Randles circuit that includes a Warburg diffusion element (Figure S4a, Supporting Information). It is

apparent that under bending the angle of the Warburg diffu-sion region increases (with respect to the x-axis). This increased angle corresponds to a smaller impedance when projected onto the real axis, and a decrease in the overall ionic resistance of the system.[53] Under both flat and bending conditions, the series resistance (RS) is 315.3 and 316.4 Ω, respectively.

Once the device is exposed to light irradiation, the EIS curves undergo change. First, it appears that charge-transfer elements are introduced to the system (Figure S4b, Supporting Information). This is indicated by the introduction of two charge-transfer semicircles. The first semicircle (Rct1) can be assigned to the charge-transfer resistance between TiO2 par-ticles on the photoanode, while the second semicircle (Rct2) can be assigned to the TiO2–electrolyte charge-transfer resist-ance.[54] This is explained by the fact that light irradiation introduces photogenerated electron–hole pairs which undergo charge-transfer and redox reactions with the fuel present in the electrolyte. Without light irradiation, there is no charge carrier generation and therefore no activated charge transfer. A drop also occurs in RS (from 315.3 to 257.2 Ω), indicating an increase in conductivity of the overall system. Under bending, the series resistance decreases even further due to the improved contact between the components at the point of bending. In addition, Rct1 and Rct2 decrease from 26.5 and 200.9 Ω to 0.175 and 13.5 Ω, respectively. This reduced resist-ance indicates an overall improvement in charge transfer in the photoanode under bending. All tabulated data can be found in Table S2 (Supporting Information). Similar phenomenon is observed with the other fuels tested in this study (Figure S5, Supporting Information). These results demonstrate that var-ious types of organic waste can in fact be used as fuel to gen-erate power in a flexible PFC.




Figure 3. a) Optical images showing open circuit voltage of fPFC with and without light irradiation. b) Photocurrent response, c) polarization and power curves, and d) EIS plots of fPFC under flat and bending (radius of curvature = 3 cm) conditions. Inset: high-frequency region of the EIS curves.

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2.2. fPFC Has a Sweatband Power Generator

The fPFC was fabricated into a sweatband in order to evaluate its ability to generate power from human sweat. Artificial sweat solution was created using median concentrations of major constituents outlined by Harvey et al., specifically: 0.031 m NaCl, 0.014 m lactic acid, 0.01 m urea, and 1.7 × 10−4 m glu-cose.[55] Using a 1 W 365 nm LED, the photoelectrochemical performance of an fPFC in a flat configuration using this arti-ficial sweat as fuel is shown in Figure 4a,b. Despite the low concentrations of organic material (lactic acid, urea, and glu-cose), the initial photocurrent response of the artificial sweat fPFC shows comparable values to those found in Figure 2. The photocurrent appears to decrease immediately after the initial current spike when light irradiation is provided. This is explained by the lower concentrations of fuel and subsequent low mass transfer of reactants to the anode surface. The polari-zation and power curves of the artificial sweat fPFC (Figure 4b) show that the device has an open circuit voltage of 0.9 V, a short circuit density of 17.3 mA cm−2 g−1, and a maximum power density of 4.0 mW cm−2 g−1. When compared to current enzy-matic biofuel cells using artificial sweat as fuel, the fPFC can provide higher or comparable power densities.[25–27] This per-formance is also accomplished without the use of buffer solu-tions, electrochemical mediators, or expensive and sensitive enzymes. Working from these baseline results, the fPFC was evaluated as a sweatband by combining four cells in series (Figure 4c). Using artificial sweat as the fuel, the sweatband was illuminated by the LED at a distance of 6 in. and the power output was measured across a 2.7 kΩ resistor. As shown in Figure 4d, under light irradiation, the flexible sweatband has

a steady output of 0.35 mA at 0.94 V (0.33 mW with a specific power density of 1.6 mW cm−2 g−1). These results demonstrate the potential application of fPFCs in generating electrical power from fuels such as human sweat.

Lastly, in order to explore additional applications, the fPFC was used to generate power from the decomposition of meth-ylene blue (MB) dye under solar simulated light (Figure S6, Supporting Information). The fPFC is able to draw power from the photodegradation of MB over the course of 5 h, showing distinct decoloration of the waste water compared to the identical experiment without using the fPFC. Methylene blue is often used as an electrochemical mediator in microbial fuel cells with concentrations up to 1 × 10−3 m.[56,57] However, when used for the purpose of decomposition, the fPFC can provide larger power densities from the degradation of MB (Figure S7, Supporting Information).[58] The fPFC also provides comparable energy output to microbial cells in the decomposi-tion of other dyes.[59,60] A comparison of power generation per-formance using sweat and organic dye fuels can be found in Table S3 (Supporting Information).

3. Conclusion

In summary, a fPFC was fabricated that demonstrates the fea-sibility of a light-powered, biowaste-based wearable power gen-erator. This fPFC was shown to produce power using various biowaste fuels (lactic acid, ethanol, methanol, urea, glycerol, and glucose) and even under bending conditions (r = 3 cm). The photoelectrochemical performance of these cells was determined and analyzed using photocurrent measurements,




Figure 4. a) Photocurrent response and b) polarization and power curves of fPFC using artificial sweat as fuel. c) Diagram of fPFC-based sweat band with four fPFCs in series. d) Optical images of fPFC-based sweat band in operation, generating 0.94 V and 0.35 mA (0.328 mW) across a 2.7 kΩ resistor. Inset: a top-view of the sweat band.

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polarization curves, and EIS. These measurements shed light on the operation and intrinsic differences between light/dark and flat/bending regimes of an fPFC. Potential applications for the fPFC were explored by using the flexible device as a wear-able power generation device using human sweat as a fuel source. The fPFC was also employed as a flexible device for in the degradation of organic waste in water. Even in flexible configurations, fPFCs are able to outperform or match the per-formance of microbial and enzymatic biofuel cells in literature. At the same time, the fPFC can perform nonselective oxidation of organic species and is self-regenerating. These results dem-onstrate the potential application of fPFCs in various energy production and wastewater remediation technologies as a renewable, green technology.

4. Experimental SectionPhotoanode Fabrication: The flexible photoanode was fabricated

by creating a slurry containing 0.95 mL ethanol, 0.05 mL titanium tetraisopropoxide, and 100 mg P25 (Degussa, 21 nm particles). The slurry was sonicated for 10 min and then cast onto an ITO-coated PET sheet (Sigma Aldrich, 60 Ω cm−2). A doctor blade was used in order to control the thickness of the film. The prepared anode was then heat treated at 150 °C for 1 h using a ramp rate of 10 °C min−1.

Flexible Photocatalytic Fuel Cell Assembly: The fPFC was assembled using the prepared photoanode and Pt/C on carbon cloth (FuelCellEtc) as the flexible cathode. Cellulose paper was used as the solid electrolyte membrane and separator. The combined electrodes were then pressed between two sheets of plastic sheets and sealed using a heat sealer.

Characterization: A field-emission scanning electron microscope (Zeiss ULTRA Plus) was used to determine the microstructure and cross-sectional composition of the photoanode. XRD (Bruker AXS D8 Advance) was used to confirm the crystal phase of the photoanode material.

Photoelectrochemical characterization was performed using an electrochemical work station (Princeton Applied Research VersaSTAT MC) and a 1 W 365 nm LED (Digikey). Photocurrent measurements were performed without any applied bias or current. Polarization curves were determined using galvanodynamic measurements (100 µA s−1). Nyquist plots were obtained using EIS. A frequency ranging from 1 Hz to 1 MHz was applied, using an alternating signal of 100 mV. EIS data were modeled using the ZSimpWin data analysis software.

In order to show the potential application in flexible, wearable technologies, the performance of the fPFC was determined artificial sweat as a fuel. The fPFC was fabricated into a sweat band where the absorption of sweat under light irradiation would generate power. The artificial sweat solution is based on median concentrations of major constituents outlined by Harvey et al., specifically: 0.031 m NaCl, 0.014 m lactic acid, 0.01 m urea, and 1.7 × 10−4 m glucose.[55] The power output of the sweatband is measured across a 2.7 kΩ resistor, and the voltage and current are measured using digital multimeters (Agilent 34411A and 34401A).

In order to show potential application in wastewater treatment, the photocatalytic performance of the fPFC was determined through the photodegradation of methylene blue under solar simulated light (ABET Technologies LS 10500, 100 mW cm−2). The fPFC was placed inside a beaker (r = 3 cm) containing 10 × 10−6 m MB under stirring. The solution was allowed to stir in the dark for 60 min in order for the fPFC to reach adsorption–desorption equilibrium. The fPFC was then irradiated with solar simulated light for 5 h, with samples taken every hour. A UV–vis spectrophotometer (Fischer Scientific, GENESYS 10S) was used to measure the absorbance of the solution over time.

Supporting InformationSupporting Information is available from the Wiley Online Library or from the author.

AcknowledgementsThis work was supported by the Natural Sciences and Engineering Research Council of Canada (NSERC).

Received: August 24, 2016Revised: November 21, 2016

Published online: December 21, 2016

[1] A. Nathan, A. Ahnood, M. T. Cole, L. Sungsik, Y. Suzuki, P. Hiralal, F. Bonaccorso, T. Hasan, L. Garcia-Gancedo, A. Dyadyusha, S. Haque, P. Andrew, S. Hofmann, J. Moultrie, C. Daping, A. J. Flewitt, A. C. Ferrari, M. J. Kelly, J. Robertson, G. Amaratunga, W. I. Milne, Proc. IEEE 2012, 100, 1486.

[2] X. M. Tao, Wearable Electronics and Photonics, Woodhead Pub-lishing, Cambridge, England, 2005.

[3] W. Zeng, L. Shu, Q. Li, S. Chen, F. Wang, X.-M. Tao, Adv. Mater. 2014, 26, 5310.

[4] M. Stoppa, A. Chiolerio, Sensors 2014, 14, 11957.[5] X. Pu, L. Li, H. Song, C. Du, Z. Zhao, C. Jiang, G. Cao, W. Hu,

Z. L. Wang, Adv. Mater. 2015, 27, 2472.[6] Y.-H. Lee, J.-S. Kim, J. Noh, I. Lee, H. J. Kim, S. Choi, J. Seo, S. Jeon,

T.-S. Kim, J.-Y. Lee, J. W. Choi, Nano Lett. 2013, 13, 5753.[7] Y. Meng, Y. Zhao, C. Hu, H. Cheng, Y. Hu, Z. Zhang, G. Shi, L. Qu,

Adv. Mater. 2013, 25, 2326.[8] K. Jost, D. Stenger, C. R. Perez, J. K. McDonough, K. Lian,

Y. Gogotsi, G. Dion, Energy Environ. Sci. 2013, 6, 2698.[9] S. Pan, Z. Yang, P. Chen, J. Deng, H. Li, H. Peng, Angew. Chem.,

Int. Ed. 2014, 53, 6110.[10] B. J. Kim, D. H. Kim, Y.-Y. Lee, H.-W. Shin, G. S. Han, J. S. Hong,

K. Mahmood, T. K. Ahn, Y.-C. Joo, K. S. Hong, N.-G. Park, S. Lee, H. S. Jung, Energy Environ. Sci. 2015, 8, 916.

[11] V. Leonov, IEEE Sens. J. 2013, 13, 2284.[12] S. J. Kim, J. H. We, B. J. Cho, Energy Environ. Sci. 2014, 7, 1959.[13] Y.-K. Fuh, J.-C. Ye, P.-C. Chen, H.-C. Ho, Z.-M. Huang, ACS Appl.

Mater. Interfaces 2015, 7, 16923.[14] M. Zhang, T. Gao, J. Wang, J. Liao, Y. Qiu, Q. Yang, H. Xue, Z. Shi,

Y. Zhao, Z. Xiong, L. Chen, Nano Energy 2015, 13, 298.[15] S. Wang, L. Lin, Z. L. Wang, Nano Lett. 2012, 12, 6339.[16] W. Seung, M. K. Gupta, K. Y. Lee, K.-S. Shin, J.-H. Lee, T. Y. Kim,

S. Kim, J. Lin, J. H. Kim, S.-W. Kim, ACS Nano 2015, 9, 3501.[17] P. Lianos, J. Hazard. Mater. 2011, 185, 575.[18] O. Carp, C. L. Huisman, A. Reller, Prog. Solid State Chem. 2004, 32,

33.[19] A. Sonune, R. Ghate, Desalination 2004, 167, 55.[20] A. Marco, S. Esplugas, G. Saum, Water Sci. Technol. 1997, 35,

321.[21] M. Henze, P. Harremoes, J. la Cour Jansen, E. Arvin, Wastewater

Treatment: Biological and Chemical Processes, Springer Science & Business Media, Germany, 2001.

[22] S. H. Lin, C. L. Lai, Water Res. 2000, 34, 763.[23] M. I. Litter, in Environmental Photochemistry Part II, (Eds: P. Boule,

D. W. Bahnemann, P. K. J. Robertson), Springer, Berlin 2005, Ch. 325.

[24] H. Lee, T. K. Choi, Y. B. Lee, H. R. Cho, R. Ghaffari, L. Wang, H. J. Choi, T. D. Chung, N. Lu, T. Hyeon, S. H. Choi, D.-H. Kim, Nat Nano 2016, 11, 566.

full p

aper





[25] M. Falk, D. Pankratov, L. Lindh, T. Arnebrant, S. Shleev, Fuel Cells 2014, 14, 1050.

[26] W. Jia, X. Wang, S. Imani, A. J. Bandodkar, J. Ramirez, P. P. Mercier, J. Wang, J. Mater. Chem. A 2014, 2, 18184.

[27] W. Jia, G. Valdés-Ramírez, A. J. Bandodkar, J. R. Windmiller, J. Wang, Angew. Chem., Int. Ed. 2013, 52, 7233.

[28] B. E. Logan, Microbial Fuel Cells, Wiley, New Jersey, USA, 2008.[29] D. Wang, Y. Li, G. Li Puma, C. Wang, P. Wang, W. Zhang, Q. Wang,

Appl. Catal., B 2015, 168-169, 25.[30] B. Seger, G. Q. Lu, L. Z. Wang, J. Mater. Chem. 2012, 22, 10709.[31] Z. Chen, D. Higgins, A. Yu, L. Zhang, J. Zhang, Energy Environ. Sci.

2011, 4, 3167.[32] D. Higgins, P. Zamani, A. Yu, Z. Chen, Energy Environ. Sci. 2016, 9,

357.[33] T. Wu, H. M. Zhou, B. Y. Xia, P. Xiao, Y. Yan, M. S. Xie, X. Wang,

ChemCatChem 2014, 6, 1538.[34] R. Wang, D. C. Higgins, M. A. Hoque, D. Lee, F. Hassan, Z. Chen,

Sci. Rep.-Uk 2013, 3, 2431.[35] S. H. Ryan, H. Drew, C. Zhongwei, Nanotechnology 2010, 21,

165705.[36] W. Li, J. Wu, D. C. Higgins, J.-Y. Choi, Z. Chen, ACS Catal. 2012, 2, 2761.[37] D. C. Higgins, J.-Y. Choi, J. Wu, A. Lopez, Z. Chen, J. Mater. Chem.

2012, 22, 3727.[38] F. Jaouen, E. Proietti, M. Lefevre, R. Chenitz, J.-P. Dodelet, G. Wu,

H. T. Chung, C. M. Johnston, P. Zelenay, Energy Environ. Sci. 2011, 4, 114.

[39] Z. Zhang, C.-C. Wang, R. Zakaria, J. Y. Ying, J. Phys. Chem. B 1998, 102, 10871.

[40] L. M. Peter, Chem. Rev. 1990, 90, 753.[41] K.-S. Ahn, Y. Yan, S.-H. Lee, T. Deutsch, J. Turner, C. E. Tracy,

C. L. Perkins, M. Al-Jassim, J. Electrochem. Soc. 2007, 154, B956.[42] H. Chen, G. Liu, L. Wang, Sci. Rep.-Uk 2015, 5, 10852.[43] K. Szacilowski, W. Macyk, G. Stochel, J. Mater. Chem. 2006, 16,

4603.

[44] B. Wang, H. Zhang, X.-Y. Lu, J. Xuan, M. K. H. Leung, Chem. Eng. J. 2014, 253, 174.

[45] L. Li, S. Xue, R. Chen, Q. Liao, X. Zhu, Z. Wang, X. He, H. Feng, X. Cheng, Electrochim. Acta 2015, 182, 280.

[46] K. Li, H. Zhang, T. Tang, Y. Xu, D. Ying, Y. Wang, J. Jia, Water Res. 2014, 62, 1.

[47] K. Iyatani, Y. Horiuchi, M. Moriyasu, S. Fukumoto, S.-H. Cho, M. Takeuchi, M. Matsuoka, M. Anpo, J. Mater. Chem. 2012, 22, 10460.

[48] K. Li, Y. Xu, Y. He, C. Yang, Y. Wang, J. Jia, Environ. Sci. Technol. 2013, 47, 3490.

[49] B. Seger, T. Pedersen, A. B. Laursen, P. C. Vesborg, O. Hansen, I. Chorkendorff, J. Am. Chem. Soc. 2013, 135, 1057.

[50] Z. Wu, G. Zhao, Y. Zhang, J. Liu, Y.-n. Zhang, H. Shi, J. Mater. Chem. A 2015, 3, 3416.

[51] X. Xie, M. Ye, P.-C. Hsu, N. Liu, C. S. Criddle, Y. Cui, Proc. Natl. Acad. Sci. 2013, 110, 15925.

[52] J. Larminie, A. Dicks, in Fuel Cell Systems Explained, Wiley, England, 2013, 25.

[53] H. Xu, Y. Song, H. R. Kunz, J. M. Fenton, presented at Proton Con-ducting Membrane Fuel Cells IV: Proc. Int. Symp. Electrochemical Society, Honolulu, USA, October, 2006.

[54] M. Kaneko, S. Suzuki, H. Ueno, J. Nemoto, Y. Fujii, Electrochim. Acta 2010, 55, 3068.

[55] C. J. Harvey, R. F. LeBouf, A. B. Stefaniak, Toxicol. In Vitro 2010, 24, 1790.

[56] Y. Hubenova, M. Mitov, Bioelectrochemistry 2010, 78, 57.[57] F. Davis, S. P. J. Higson, Biosens. Bioelectron. 2007, 22, 1224.[58] T. H. Han, M. M. Khan, S. Kalathil, J. Lee, M. H. Cho, Ind. Eng.

Chem. Res. 2013, 52, 8174.[59] E. Fernando, T. Keshavarz, G. Kyazze, Bioresour. Technol. 2014, 156,

155.[60] Z. Li, X. Zhang, J. Lin, S. Han, L. Lei, Bioresour. Technol. 2010, 101,

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