Exchange Membrane Fuel Cell Performance Research Articles

La and Al co-doped CaMnO3 perovskite oxides: From interplay of surface properties to anion exchange membrane fuel cell performance

This work reports the first account of perovskite oxide and carbon composite oxygen reduction reaction (ORR) catalysts integrated into anion exchange membrane fuel cells (AEMFCs). Perovskite oxides with a theoretical stoichiometry of Ca0.9La0.1Al0.1Mn0.9O3-δ are synthesized by an aerogel method and calcined at various temperatures, resulting in a set of materials with varied surface chemistry and surface area. Material composition is evaluated by X-ray diffraction, energy dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy. The perovskite oxide calcined at 800 °C shows the importance of balance between surface area, purity of the perovskite phase, and surface composition, resulting in the highest ORR mass activity when evaluated in rotating disk electrodes. Integration of this catalyst into AEMFCs reveals that the best AEMFC performance is obtained when using composites with 30:70 perovskite oxide:carbon composition. Doubling the loading leads to an increase in the power density from 30 to 76 mW cm−2. The AEMFC prepared with a composite based on perovskite oxide and N-carbon achieves a power density of 44 mW cm−2, demonstrating an ∼50% increase when compared to the highest performing composite with undoped carbon at the same loading.

Investigation of catalytic vs reactant transport effect of catalyst layers on proton exchange membrane fuel cell performance

For proton exchange membrane fuel cells (PEMFC), the importance of catalytic (kinetic) effect is widely recognized with less attention being paid to mass transport (diffusion) effect. In this study, the importance of kinetic and diffusion effect on PEMFC performance is investigated experimentally by using different catalysts and catalyst layer (CL) fabrication methods of spraying and brush-painting, both of which are commonly used, simple and low-cost with volume-production capability. It is found that as a catalyst, 20% Pt/C has better kinetic characteristics than 60% Pt/C in terms of smaller Pt particle size, better Pt dispersion, less Pt agglomeration, and larger active surface area. For the same Pt loading, the porosity is almost identical for the CLs made of the two catalysts by the two fabrication methods, but the diffusion resistivity for the CLs made of 60% Pt/C is smaller than its counterpart for the CLs made of 20% Pt/C, due to difference in the effective diffusion coefficient and CL thickness. As a result, the performance of the PEMFC made of 60% Pt/C is better than the corresponding PEMFC made of 20% Pt/C. Similarly, for PEMFCs made of the same catalyst, the diffusion resistivity is smaller for CLs made by spraying compared with brush-painting method, leading to better performance for the PEMFC made by spraying method. These results highlight the importance of diffusion effect, hence the structure of the CLs, in determining the PEMFC performance.

Polyoxometalate decorated graphene oxide/sulfonated poly(arylene ether ketone) block copolymer composite membrane for proton exchange membrane fuel cell operating under low relative humidity

A phosphotungstic acid (PW) decorated graphene oxide (GO) is explored as a filler for sulfonated poly(arylene ether ketone) (SPAEK) block copolymer. The SPAEK/PW-mGO composite membrane shows higher proton conductivity than a pristine SPAEK membrane. At 80°C under 25% relative humidity (RH) condition, the fuel cell configured with the SPAEK/PW-mGO composite membrane shows improved fuel cell performance. A maximum power density of 772mWcm−2 is observed for the SPAEK/PW-mGO composite membrane, whereas the pristine SPAEK membrane exhibits a maximum power density of 10mWcm−2 operated under 25% RH at 80°C. Compared with the NRE-212 membrane, the SPAEK/PW-mGO composite membrane exhibits 4.8-times higher maximum power density. Furthermore, the maximum current density of the SPAEK/PW-mGO composite membrane (2271mAcm−2) is much higher than pristine SPAEK (39mAcm−2) and NRE-212 (734mAcm−2) membranes.

Influence of various carbon nano-forms as supports for Pt catalyst on proton exchange membrane fuel cell performance

In this study, we discuss the influence of various carbon supports for Pt on proton exchange membrane (PEM) fuel cell performance. Here, Pt supported on various carbon nano-forms [Pt/carbon black (Pt/CB), Pt/single-walled carbon nanotubes (Pt/SWCNT), Pt/multi-walled carbon nanotubes (Pt/MWCNT) and Pt/graphene (Pt/G)] are synthesized by a facile, single step, microwave-assisted, modified chemical reduction route. Their physical, chemical and electrochemical characteristics pertaining to oxygen reduction reaction (ORR) catalytic activity and stability in PEM fuel cell are studied in detail by various techniques and compared. The study shows that the different carbon supports does not significantly affect the Pt particle size during synthesis, but leads to different amount of defective sites in the carbon framework which influence both the availability of active metal nano-catalysts and metal-support interaction. In-situ electrochemical investigations reveal that the different carbon supports influence both ORR catalytic activity and stability of the catalyst. This is further corroborated by the demonstration of varying polarization characteristics on PEM fuel cell performance by different carbon supported Pt catalysts. This study reveals MWCNT as the most suitable carbon support for Pt catalyst, exhibiting high activity and stability for ORR in PEM fuel cell.

Catalyst and Electrode Advances for High Performing PEM and AEM Fuel Cells

Recent advances in polymer electrolyte membrane fuel cells have brought the technology extremely close to finally fulfilling its promise as a high efficiency, sustainable energy source for transportation applications1,2. An overwhelming amount of work in this area has focused on the proton exchange membrane fuel cell (PEMFC), where high performance has been achieved. However, proton-based systems still suffer from very high materials cost of both the membrane and catalysts, and the need to drive costs down by reducing material loading generally leads to accelerated degradation of otherwise stable systems as well as increased sensitivity to water due to the reduced water capacity with thinning catalyst layer thickness. To overcome these limitations, our group has developed an air-assisted cylindrical liquid jets spraying system that allows for the precise control of the catalyst layer microstructure, leading to high-performance catalyst-coated membranes. The system design and influence of operating parameters on PEMFC performance will be shown. On the materials side, our team has produced Ni-rich PtNi alloys and Pt3Ni alloy nanocages that have shown very highly activity for the oxygen reduction reaction (ORR) and excellent stability at PEMFC cathode conditions. This poster will show the structure and chemistry of the Pt-Ni catalysts as well as their in-situ and ex-situ performance. The Pt-Ni nanocage PEMFCs have shown behavior that well exceeds the DOE targets for activity and comes very close to the DOE targets for durability. From both an activity and durability perspective, these Pt-Ni nanocage catalysts considerably outperform state-of-the-art commercial Pt/C catalysts. Another low-temperature alternative to the PEMFC that has been widely discussed in recent years is the anion exchange membrane fuel cell (AEMFC). The AEMFC has an effective pKa much higher than the PEMFC, and this basic environment has several possible advantages over the acid system, including a less corrosive environment for the catalyst and catalyst support, which opens up the periodic table with regards to possible materials to be employed. Also, it is well known that the kinetics for the ORR are more facile in alkaline media than acid media3, though the converse is true for the hydrogen oxidation reaction, which necessitates the study for advanced Pt catalysts such as PtRu4. Our recent work has shown that the internal water dynamics in the AEMFC is likely more complex than the PEMFC. In this poster, the influence of the membrane, ionomer and gas diffusion layer as well as the flow rate and dew points of the anode and cathode gases on anion exchange membrane fuel cell performance will be shown. After cell optimization, a peak power density of 1.2 W/cm2 has been reproducibly achieved with radiation-grafted ETFE membranes and ionomers.

Studies of sulfonated poly(phenylene)-block-poly(ethersulfone) for proton exchange membrane fuel cell

The polymers were prepared by nickel catalyzed carbon–carbon coupling reaction of 1,4-dichloro-2,5-dibenzoylbenzene (DCDBB) and sulfone oligomer. DCDBB was synthesized from oxidation reaction of 2,5-dichloro-p-xylene and followed by Friedel–Craft reaction with benzene. DCDBB monomer had good reactivity in polymerization by electron withdrawing group as benzophenone. Sulfone group of oligomer had improving flexibility and solubility. Post sulfonation was carried out to add sulfonic acid groups by using chlorosulfuric acid. These polymers were presumably stable against nucleophilic attack by hydrogen peroxide, hydroxide anion, and radical generated by proton exchange membrane fuel cell operation system. The number of sulfonic acid groups were controlled by varying the mole ratio of 1,4-dichloro-2,5-dibenzoylbenzene in synthesized polymer. A series of membranes were studied by 1H NMR spectroscopy, thermo-gravimetric analysis, ion exchange capacity, water uptake, and proton conductivity. Also surface morphologies were assessed by atomic force microscope (AFM).

Spatial proton exchange membrane fuel cell performance under bromomethane poisoning

The poisoning effects of 5 ppm CH3Br in the air on the spatial performance of a proton exchange membrane fuel cell (PEMFC) were studied using a segmented cell system. The presence of CH3Br caused performance loss from 0.650 to 0.335 V at 1 A cm−2 accompanied by local current density redistribution. The observed behavior was explained by possible bromomethane hydrolysis with the formation of Br−. Bromide and bromomethane negatively affected the oxygen reduction efficiency over a wide range of potentials because of their adsorption on Pt, which was confirmed by XPS. Moreover, the PEMFC exposure to CH3Br led to a decrease in the anode and cathode electrochemical surface area (∼52–57%) due to the growth of Pt particles through agglomeration and Ostwald ripening. The PEMFC did not restore its performance after stopping bromomethane introduction to the air stream. However, the H2/N2 purge of the anode/cathode and CV scans almost completely recovered the cell performance. The observed final loss of ∼50 mV was due to an increased activation overpotential. PEMFC exposure to CH3Br should be limited to concentrations much less than 5 ppm due to serious performance loss and lack of self-recovery.

Local potential evolutions during proton exchange membrane fuel cell operation with dead-ended anode – Part I: Impact of water diffusion and nitrogen crossover

Abstract Operating a PEMFC with a dead-ended anode may lead to local fuel-starvation because of water and possibly nitrogen accumulation in the anode compartment. In previous works, we used a segmented linear cell with reference electrodes to monitor simultaneously the local potentials and current densities during dead-ended anode operation. The results indicated that water transport as well as nitrogen crossover through the membrane were most probably the two key factors governing fuel starvation. In this first from a set of two papers, we evaluated with more details the contributions of nitrogen crossover and water transport to hydrogen starvation. To assess nitrogen contribution, the fuel cell cathode compartment was first supplied with pure oxygen instead of air. The results showed that in the absence of nitrogen (in the cathode side) the fuel starvation was much slower than with air, suggesting that nitrogen contribution cannot be neglected. On the other hand, the contribution of water flooding to hydrogen starvation was investigated by using different cooling temperature on the cathode and anode sides in order to drive water toward the colder plate. The results showed that with a colder anode side, fuel starvation was faster. In the opposite case of a hotter anode plate, water accumulation in the anode compartment was limited, nitrogen crossover through the membrane was the main reason for hydrogen starvation in this case. To fully assess the impact of the thermal configurations on membrane-electrode assembly (MEA) degradation, aging protocols with a dead-ended anode and a fixed closing time were also performed. The results showed that operation with a hotter anode could help to limit significantly cathode ElectroChemical Surface Area (ECSA) losses along the cell area and performance degradation induced by hydrogen starvation.

A systematic study on the use of short circuiting for the improvement of proton exchange membrane fuel cell performance

Proton exchange membrane fuel cells suffer from reversible performance loss during operation caused by the oxidation of the Pt catalyst which in turn reduces the electrochemically active surface area. Many fuel cell manufacturers recommend using short circuiting during the operation of the fuel cell to improve the performance of the cells over time. However, there is lack of understanding on how it improves the performance as well as on how to optimise the short circuiting strategy for different fuel cell systems. We present a simple procedure to develop an optimised short circuiting strategy by maximising the cumulative average power density gain and minimising the time required to recover the energy loss during short circuiting. We obtained average voltage improvement from 10 to 12% at different current densities for a commercial H-100 system and our short circuiting strategy showed ∼2% voltage improvement in comparison to a commercial strategy. We also demonstrated that the minimum short circuiting time is a function of double layer capacitance by the use of electrochemical impedance spectroscopy.

Local potential evolutions during proton exchange membrane fuel cell operation with dead-ended anode – Part II: Aging mitigation strategies based on water management and nitrogen crossover

Abstract Proton exchange membrane (PEM) fuel cells operate with dead-ended anode in order to reduce system cost and complexity when compared with hydrogen re-circulation systems. In the first part of this work, we showed that localized fuel starvation events may occur, because of water and nitrogen accumulation in the anode side, which could be particularly damaging to the cell performance. To prevent these degradations, the anode compartment must be purged which may lead to an overall system efficiency decrease because of significant hydrogen waste. In the second part, we present several purge strategies in order to minimize both hydrogen waste and membrane-electrode assembly degradations during dead-ended anode operation. A linear segmented cell with reference electrodes was used to monitor simultaneously the current density distribution along the gas channel and the time evolution of local anode and cathode potentials. To asses MEA damages, Platinum ElectroChemical Surface Area (ECSA) and cell performance were periodically measured. The results showed that dead-end mode operation with an anode plate maintained at a temperature 5 °C hotter than the cathode plate limits water accumulation in the anode side, reducing significantly purge frequency (and thus hydrogen losses) as well as MEA damages. As nitrogen contribution to hydrogen starvation is predominant in this thermal configuration, we also tested a microleakage solution to discharge continuously most the nitrogen accumulating in the anode side while ensuring low hydrogen losses and minimum ECSA losses provided the right microleakage flow rate is chosen.

CO2-Oxy underground coal gasification integrated proton exchange membrane fuel cell operating in a chemical looping mode of reforming

O2/CO2 based underground coal gasification (UCG) is a promising clean coal technology for the exploitation of deep underground coal resources with a minimal difficulty of the operation. However, the generated syngas of the underground is enriched with carbon monoxide and it should be converted into a clean gas on the above ground for the end use. In the present study, a clean mode of power generation is proposed using the CO enriched UCG syngas. Firstly, the UCG gas is reformed into pure hydrogen using chemical looping reforming (CLR) method. Secondly, the pure hydrogen obtained from CLR process is used suitably to generate electric power in a proton exchange membrane fuel cell (PEMFC) system. Hence, carbon energy is converted into hydrogen energy through the CLR technique and this clean gas is efficiently transformed into electrical energy using the PEMFC system. A net efficiency for converting CO enriched gas into H2 through conventional system using water gas shifting reactors is evaluated and compared with the CLR system. An energy analysis of O2/CO2 based UCG integrated with CLR-PEMFC shows 43.6% net efficiency with carbon capture and storage (CCS).

Performance Benefits of Multiwall Carbon Nanotubes in the Polymer Electrolyte Membrane Fuel Cell Gas Diffusion Layer

In a polymer electrolyte membrane (PEM) fuel cell, the effective removal of product liquid water is necessary for achieving high power output. Liquid water produced at the cathode catalyst layer (CL) accumulates in the pores of the gas diffusion layer (GDL) and impedes oxygen diffusion from gas channels to the catalytic reaction sites. To reduce liquid water build up in the GDL, dual-layer GDLs comprised of a carbon fiber macro-porous substrate and a micro-porous layer (MPL) are typically used. The MPL covers the large surface pores of the substrate yielding a smooth interfacial contact region between the CL and the GDL. This smooth interface results in superior thermal and electrical conductivities as well as reduced water accumulation in the region between the CL and GDL. The MPL is typically a mixture of carbon black particles and hydrophobic agents. The structural properties of the MPL, such as surface crack size and porosity distribution, are dependent on its composition. An MPL containing 20-40 wt. % of hydrophobic agent was shown to facilitate product water removal at high current density operation1. Recently, it was found that the addition of carbon nanotubes (CNT) led to the strong adhesion between carbon black particles and the reduction of ohmic and mass transport losses 2-4. In this work, the physical properties of the SGL 25 series GDLs (SGL Group) were characterized by various imaging methods. Three types of commercially available GDLs were studied: SGL 25BC, 25BI and 25BN. SGL 25BC is the standard MPL with 23 wt.% PTFE, while SGL 25BI contains a reduced PTFE content of 10 wt.%. In SGL 25BN, CNTs are added to the standard MPL (i.e. 23 wt.% PTFE with CNT). Scanning electron microscopy (SEM) images of each GDL are shown in Figure 1. High intensity X-rays generated at the BMIT-BM beamline of the Canadian Light Source were utilized to image the fuel cell in operando, and the liquid water distribution in the resulting radiographs was identified with in-house post-processing algorithms. Images were obtained with a pixel resolution of 6.5 µm at a frame rate of 0.33 frames per second. In this work, the performance of these materials will be discussed, in particular, within the context of their varying microstructure. Reference 1. Qi Z, Kaufman A. Improvement of water management by a microporous sublayer for PEM fuel cells. J Power Sources. 2002;109(1):38-46. 2. Lin S, Chang M. Effect of microporous layer composed of carbon nanotube and acetylene black on polymer electrolyte membrane fuel cell performance. Int J Hydrogen Energy. 2015;40(24):7879-7885. 3. Fan C, Chang M. Improving proton exchange membrane fuel cell performance with carbon nanotubes as the material of cathode microporous layer. Int J Energy Res. 2016;40(2):181-188. 4. Schweiss R, Steeb M, Wilde PM, Schubert T. Enhancement of proton exchange membrane fuel cell performance by doping microporous layers of gas diffusion layers with multiwall carbon nanotubes. J Power Sources. 2012;220:79-83. Figure 1

Synthesis and Study of Structurally Ordered FePt Nanoparticles As Highly Active and Durable Catalysts for Oxygen Reduction Reaction

Finding a highly active and durable nanocatalyst under routinely used proton exchange membrane fuel cell operating conditions (60 - 80 oC) is urgent for the commercialization of fuel cells. Many nanocatalysts have been reported to have much improved oxygen reduction reaction (ORR) activity compared to the commercially used Pt/C catalyst. However, few of them can meet the durability requirement. In this report, monodisperse face-centered-tetragonal (fct) (L10) FePt nanoparticles with size of ~ 9 nm were synthesized from dumbbell-like face-centered-cubic (fcc)-FePt-Fe3O4 nanoparticles. The durability of C-fct-FePt nanoparticles as ORR catalysts at 60 oC was studied and it was found that these nanoparticles served as a highly active and durable ORR catalyst. Its mass activity was found to be about 5.4 times that of commercial Pt/C. Also, no obvious loss in ORR activity was observed after 10,000 cycles. A perchloric acid-treatment and subsequent annealing treatment were found to improve the durability of fct-FePt nanoparticles at 60 oC. The highly ordered L10 structure, with alternating layers of Fe and Pt atoms, as well as the Pt skin formed after the acid-treatment, were hypthesized to be the main reason for the durability enhancement. Our work demonstrates a reliable approach to structurally ordered FePt nanoparticles as a promising candidate for practical use in fuel cells.

In situ investigation of proton exchange membrane fuel cell performance with novel segmented cell design and a two-phase flow model

A novel segmented fuel cell device based on the multi-layered printed circuit board (PCB) flow field plates is designed to study the localized fuel cell performance with various operation conditions. With embedded sensors, distributions of current density, relative humidity (RH) and temperature for both anode and cathode are measured simultaneously along the direction of straight parallel flow channels. Meanwhile, a stationary two-phase flow fuel cell model is developed to study the internal reaction parameter distributions and the results are compared with the in situ experimental measurements. In the co-flow operation mode of hydrogen and air, current density and reactants' RH distributions are sensitive to the stoichiometry of air but the effect from hydrogen is minor. Water transfer behavior, local reactants' RH status, temperature gradients and their impacts on current distributions are analyzed based on the in situ measurements and the coupled model analysis. The segmented cell device discussed in this paper, as well as the experimental and modeling results can be employed to optimize stack design and operating parameters with “visible” internal distributions of water, RH and temperature inside membrane electrode assembly (MEA). Further investigation on fuel cell performance and lifetime with different reactant flow directions is also suggested.

Graphene-doped electrospun nanofiber membrane electrodes and proton exchange membrane fuel cell performance

Abstract A rational electrode structure can allow proton exchange membrane (PEM) fuel cells own high performance with a low noble metal loading and an optimal transport pathway for reaction species. In this study, we develop a graphene doped polyacrylonitile (PAN)/polyvinylident fluoride (PVDF) (GPP) electrospun nanofiber electrode with improved electrical conductivity and high porosity, which could enhance the triple reaction boundary and promote gas and water transport throughout the porous electrode. Thus the increased electrochemical active surface area (ECSA) of Pt catalysts and fuel cell performance can be expected. As results, the ECSA of hot-pressed electrospun electrodes with 2 wt% graphene oxide (GO) is up to 84.3 m 2 /g, which is greatly larger than that of the conventional electrode (59.5 m 2 /g). Significantly, the GPP nanofiber electrospun electrode with Pt loading of 0.2 mg/cm 2 exhibits higher fuel cell voltage output and stability than the conventional electrode.

Investigation of self-humidified and dead-ended anode proton exchange membrane fuel cell performance using electrochemical impedance spectroscopy

Self-humidified dead-ended anode proton exchange membrane fuel cell is increasingly being used in some special applications due to its need for simpler and lower cost subsystems. However, the performance of such a fuel cell is more affected by the operational parameters and conditions than the traditional proton exchange membrane fuel cells. Therefore, realizing the most effective parameters and determining their optimum values are essential. In the present study, electrochemical impedance spectroscopy is used to examine the effect of working conditions on the performance of a self-humidified dead-ended anode fuel cell. Working temperature, air stoichiometry, and purge interval are selected to assess their effects on the fuel cell performance. The results show that the performance enhances by increasing the working temperature up to 50 °C, but further increase of the temperature causes an intense reduction in the performance due to a combination of severe membrane drying and build-up of nitrogen in the anode side. The impedance spectra are greatly influenced by the air stoichiometry since increasing the air stoichiometry may lead to severe membrane drying in one hand and increasing mass transport resistance due to accumulation of N2 in the anode side, on the other hand. While the impedance spectra are less affected by the purge interval at its low values, large values of the purge interval lead to significant mass transport issues. Wasted electrical energy and wasted energy due to hydrogen purging are calculated and compared at different purge intervals.

The Impact of Dynamic Anode Hydrogen Starvation on Proton Exchange Membrane Fuel Cell Performance

Due to high efficiency and environmentally friendly benefits, proton exchange membrane fuel cell (PEMFC) vehicles have widely received attention by automotive manufacturers. With many years of research and development, fuel cell technologies have gradually grown to a point of market introduction. However, cost and robustness are two major challenges that need to be overcome to enable commercial viability of fuel cells in automotive applications. Simplifying the controls hardware, algorithms and software through robust cell designs can reduce the cost and overall complexity of the system. There are a few operating stages1 within a fuel cell system such as start/stop2, anode/cathode starvation, and local anode starvation3 that need careful consideration in developing the controls systems. GM has developed a series of screening protocols to assess how these events impact the electrode performance. Anode dynamic hydrogen starvation can happen when the requested load is higher than the amount of hydrogen being fed to a single or a few cells in the stack. In this work, we have performed a detailed study to simulate these dynamic starvation events in a single cell and investigate the effects of such events on PEM fuel cell performance. Single cells built with 53-cm2 catalyst coated diffusion media (CCDM) membrane electrode assemblies (MEAs) equipped with a high-speed mass spectrometer (HSMS) on the anode side were employed for investigating the cell performance with gas evolution before, during, and after a short dynamic anode hydrogen starvation. Two levels of anode loadings (0.5X and 1X) were screened for their robustness against the undesired anode hydrogen starvation events. Figure 1 shows cell voltage and gas evolution profiles during anode hydrogen starvation from 0.2 A/cm2 up to 0.6 A/cm2 within 90 seconds at 80 °C. At 0.2 A/cm2, the cell voltage was ~0.8V and the gas composition was N2 and unreacted H2. As the current density went up to 0.6 A/cm2, the H2 flow rate is insufficient for the current demanded, and the cell voltage quickly dropped to ~-0.8- -1.0V, which initiated oxygen evolution reaction (OER) followed by carbon oxidation reaction (COR) as the cell voltage kept decreasing. The current density was switched back to 0.2 A/cm2 when the cell voltage hit to -1.5 V. to prevent excessive / uncontrolled damage to the cell in a single event. Three events are shown in Figure 1 to observe the changes of OER and COR on the anode electrode. The peak areas of O2 and CO2 from gas evolution indicate that the OER deactivated while the COR was sustained to meet the current demand. Twelve events at two levels of anode loading were conducted in this test for evaluating the robustness of the anode and cathode electrodes. In this presentation, we will discuss the test protocol to evaluate the robustness of anode electrode against anode hydrogen starvation. The results show that the anode was damaged with increased starvation events depending on starvation duration time, current demand, electrode loadings, and anode electrode materials. Results indicate that a combination of anode electrode material development and engineering design is the best approach to addressing anode hydrogen starvation. Acknowledgement The authors would like to thank Dr. Manish Sinha for his helpful discussion on anode hydrogen starvation in a PEM fuel cell system.

Synthesis of transport layers with controlled anisotropy and application thereof to study proton exchange membrane fuel cell performance

We report on a novel method for the synthesis of fibre-based proton exchange membrane (PEM) fuel cell porous transport layers (PTLs) with controllable fibre alignment. We also report the first application of such layers as diagnostics tools to probe the effect of within-plane PTL anisotropy upon PEM fuel cell performance. These structures are realized via adaptation of electrospinning technology. Electrospun layers with progressive anisotropy magnitude are produced and evaluated. This novel approach is distinguished from the state-of-the-art because an equivalent study using commercially available materials is impossible due to lack of structurally similar substrates with different anisotropies. The anisotropy is visualized via scanning electron microscopy, and quantified using electrical resistivity. The capacity is demonstrated to achieve fibre alignment, and the associated impact on transport properties. A framework is presented for assessing the in-situ performance, whereby transport layer orientation versus bipolar plate flow-field geometry is manipulated. While an effect upon the commercial baseline cannot be discerned, electrospun transport layers with greater anisotropy magnitude suggest greater sensitivity to orientation; where greater performance is obtained with fibres cross-aligned to flow-field channels. Our approach of electrospun transport enables deterministic structures by which fuel cell performance can be explained and optimized.

Analysis of mechanism of Nafion® conductivity change due to hot pressing treatment

In previous work, the authors observed that multiple hot-pressing cycles of Nafion 212 prior to Proton Exchange Membrane Fuel Cell (PEMFC) operation was found to result in significant performance gains. In order to further explore this effect, Nafion 212 samples were subjected to various thermal treatments and then to various analytical techniques in order to probe whether changes to the membrane contributed to these performance gains in a substantial way. Electrochemical Impedance Spectroscopy (EIS) measurement sought to validate that the treatment caused a proton conductivity change. Thermogravimetric Analysis (TGA) and Fourier Transform Infrared Spectroscopy (FTIR) measurements were implemented to determine whether chemical changes in the membrane occurred. Results suggest that the hot pressing treatment causes a significant effect in the electrical properties of Nafion 212, however the physical change that occurs in the polymer is not chemical in nature. Further analysis attempts to support the idea that the change in proton conductivity is due to water channel reconfiguration in the membrane, activated by elevated temperature and compressive stress at the glass transition temperature of the Nafion 212.

Impact of Ionomer Content on Proton Exchange Membrane Fuel Cell Performance

AbstractThe effect of Nafion ionomer content on performance of a proton exchange membrane (PEM) fuel cell operated with home‐made anodic and cathodic electrodes fabricated from a novel metal organic framework (MOF) derived Pt‐based electrocatalyst was investigated via numerical simulation and experimental measurement. First, the parameter sensitivity analysis was performed to identify the most influential parameters of the model. Then, these parameters were calibrated for different fuel cell designs investigated in the current study by employing the corresponding experimental data. Afterwards, the calibrated model was used to examine the impact of Nafion content in the catalyst layer of home‐made electrodes. Finally, the qualitative trend predicted by this model was experimentally surveyed by varying the Nafion content between 10–50 wt.% in the catalyst layer of home‐made electrodes. At the anode side, the performance of home‐made electrode in a PEM fuel cell demonstrated small dependency on Nafion content. For the cathodic home‐made electrode, Nafion content was found to affect the PEM fuel cell performance more strongly. Although the model could correctly capture the impact of Nafion content on calculated polarization curves, the model predicted optimum values significantly deviate from the experimental results. This was related to the several simplifications made during model development.