Commercial Membrane Electrode Assembly Research Articles

(Invited) Research By Students That Were Inspired By Russ Kunz in High Temperature Pemfcs, DMFCs, Analysis for Polarization Loses and FC Durability

After retiring from United Technologies Corporation Dr. H. Russell Kunz, started a new career inspiring graduate, post-doctoral students and young researchers to innovate in fuel cell research at the University of Connecticut. These young researchers with the help of Russ published 47 peer reviewed publications, a book “Experimental Methods and Data Analyses for Polymer Electrolyte Fuel Cells (PEMFCs)” and produced three patents. This historical presentation will be presented with slides taken from Russ Kunz’s presentations from 1997 until 2014. From 1997 to 2004, research at UConn was focused on catalysts for methanol oxidation in phosphoric acid and direct methanol proton exchange membrane fuel cells (DMFCs), and development of selective CO oxidation catalysts for PEMFCs. From 2003 to 2014 membranes with barrier layers for DMFCs and high temperature membranes for PEMFCs were developed and studied. From 2004 to 2014, gas diffusion layers and catalyst structures were being developed along with high temperature membranes into innovative proton exchange membrane-electrode assemblies (MEAs) that provided excellent ionic conductivity and good performance in an under-saturated environment (120 oC, 1 atm., 35%RH and 70 oC, 1 atm., dry). To optimize the performance of these MEAs techniques for analysis of polarization curves to evaluate polarization loses were developed using air, oxygen, oxygen/helium experiments and AC impedance. Ionomen (a company founded by Russ Kunz, Len Bonville and Jim Fenton) together students from UConn demonstrated MEA performance that greatly exceeded that of commercial MEAs in a four-cell full-scale stack that provided 288 watts at a current of 120 A while providing 116 oC hot water. From 2006 on finding the degradation mechanisms for membrane and catalysts layers were explored along with the performance of MEAs with lower equivalent weight PFSA in the catalyst layers. From 2006 to 2013 Russ Kunz played a pivitol role in the leadership of the U.S. Department of Energy (DOE) High Temperature Membrane Working Group (HTMWG). The HTMWG investigated membrane performance at elevated temperature/low relative humidity conditions. For the final three years of the project, Russ and the team at the Florida Solar Energy Center worked with six teams to develop membrane electrode assembly (MEA) fabrication methods for their respective membranes.

Effects of the current density distribution on a single-cell DMFC by tuning the anode catalyst in layers of gradual loadings: Modelling and experimental approach

The performance of a single cell direct methanol fuel cell (DMFC) is optimized by evaluating the effect of the catalyst distribution in the membrane electrode assembly (MEA) via a 3D multi-physics, multi-component, two-phase, and not-isothermal model. The model is computed with Comsol® Multiphysics v4.4 platform, with a finite element analysis solver and simulation software. It consists of Maxwell-Stefan, Stokes-Brinckman, extended two-phase Darcy Law, modified Butler-Volmer and Tafel equations to simulate the performance of the DMFC, and to evaluate the electrochemical, fluid-dynamics and thermal phenomena. The use of a 3D model considering porous equation such as Stokes-Brinkman is helpful for understanding, describing the motions and hydrodynamic forces of interacting particles in Stokes flow, which is more realistic regarding catalyst description and validation. Moreover, the model can be used for evaluating intrinsic parameters of novel electrocatalysts. The model is validated against a set of experimental data, showing congruent and convergent data for a commercial 25cm2 MEA consisting of Nafion® 117 and electrodes (Pt/C at the cathode and Pt:Ru at the anode) at different temperatures and inlet methanol concentrations, confirming the accuracy of the model and the equations applied. The model is used to optimize the catalytic layer distribution to obtain a more uniform current density distribution along the anodic catalyst-membrane interface and a better cell performance. The optimized anodic catalytic distribution has been implemented in a 25cm2 in-house three-layer MEA and experimentally tested, included a short durability of 26h, showing better stability compared to a MEA with a classic homogenous catalyst loading distribution.

The Promoting Role of Tungsten Oxides in the Anodic Oxidation of Methanol on Platinum-Based Catalysts

Carbon-supported Pt-WO3 catalysts formulated with different proportions of platinum and tungsten were synthesized by thermal decomposition of metal carbonyl precursors. The activity of the PtWO3/C catalysts towards the methanol electrooxidation reaction (MOR) was evaluated in half-cell configuration and as anode catalyst in a direct methanol fuel cell device (DMFC) with a homemade membrane electrode assembly (MEA). The presence of WO3 increases significantly the catalyst activity, expressed by higher oxidation currents at lower potential values than those obtained with Pt/C. DMFC power output is comparable to that obtained by using a commercial MEA containing twice of the Pt loading at the anode. Electron microscopy and X-ray diffraction analysis (XRD) revealed that monoclinic WO2.92 and hexagonal WO3 phases coexist in the PtWO3/C catalysts. In samples with equal Pt loadings, the Pt particle size increases and its active area decreased as tungsten is added to the catalyst formulation. As the tungsten loading is increased and carbon content is diminished, hexagonal WO3 appears as the predominant crystalline phase.

Proton Exchange Membrane Electrolyzer Systems Operating Dynamically at High Current Densities

The fluctuating behavior of renewable energy sources hinders the widespread integration of those in a reliable electricity grid. Presumably, the wide operation range and rapid response of proton exchange membrane (PEM) electrolyzers can stabilize the grid, yet the degradation effects are not fully understood. The results presented here show no negative effect of dynamic operation at current 0.8, 1.6, 2.5 and 3.3 A cm-2, on commercial membrane electrode assemblies (MEA) with two different catalyst loadings. Conversely, the reduction of the loading of precious metal in the MEA leads to a cell voltage increase by 100 mV at 3.3 A cm-2. In addition, stack temperature correction of industrial facilities is necessary for proper comparison of cell potential and analysis of degradation mechanisms.

Application of metal foams to high temperature PEM fuel cells

The performance of a high temperature proton exchange membrane fuel cell (HT-PEMFC) with metal foam as the flow field is investigated. The HT-PEMFC is assembled using commercial membrane electrode assembly, Advent TPS® HT PEM MEA. In addition to metal foam flow field, conventional graphite serpentine flow is also used to assemble a single cell using the same MEA for comparison. Effects of operating temperature, stoichiometry, gas preheating temperature, and humidification on cell performance are investigated. AC impedance analysis is also used to study the changes in various resistances and electrochemical mechanisms inside the cell.Results show that metal foam flow field, having high gas permeability, improves gas convection and diffusion, and increases the chance of reaction with the catalysts. The porous structure of metal foam can effectively reduce the contact resistance between the flow plate and carbon paper. The current density at 0.6 V of metal foam fuel cell is approximately 20% higher than conventional graphite serpentine flow channel fuel cell. Increasing the operating temperature, stoichiometry, or humidification, improves the cell performance. Initial 300 h operation test shows the cell is relatively stable.

Impact of Accelerated Stress Tests on High Temperature PEMFC Degradation

AbstractAccelerated stress tests (ASTs) have been used to provoke and investigate degradation mechanisms inside commercial high temperature proton exchange membrane electrode assemblies based on phosphoric acid doped polybenzimidazole (PBI). A novel load cycling test using high current densities of 0.6 and 1.0 A cm−2 has been developed and compared with a test utilizing lower current densities between 0.0 and 0.3 A cm−2. A high comparability is ensured by testing membrane electrode assemblies (MEAs) from the same supplier and batch under identical test conditions. Next to daily electrochemical characterization (polarization curves, electrochemical impedance spectroscopy, linear sweep and cyclic voltammetry), ex situ investigations including product water analysis by inductively coupled plasma mass spectrometry (ICP‐MS) and micro‐computed tomography (µ‐CT) as a powerful 3D imaging tool have been carried out. Clear demarcations of AST consequences for cell ageing have been identified. Especially, differences in platinum catalyst degradation and in loss of phosphoric acid as electrolyte over AST time have been revealed. Furthermore, influences of electrochemical characterization on MEA performance have been shown, which should be considered in future durability tests of fuel cells.

The application of power-generating fuel cell electrode materials and monitoring methods to breath alcohol sensors

A state-of-the-art fuel cell-based breath alcohol sensor (BrAS) testing station was developed and used to test electrocatalysts typically employed in power generating fuel cells for ethanol sensing. Sensor membrane-electrode assemblies (MEAs) were prepared with 20% Pt/C electrocatalysts and their sensitivity were compared to that of a commercial BrAS MEA that employs high loadings of Pt black. Using these Pt/C sensor MEAs, we were able to achieve raw sensitivity factors that approach that of the commercial sensor despite using 97% less Pt. The design of our test cell and station enabled in situ monitoring of MEA health through cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements in an operating sensor. MEAs prepared from Pt/C display a faster rate of sensor decay compared to the commercial sensor. CV and EIS measurements confirm that this loss is due to a combination of adsorbed intermediates on the anode surface as well dehydration of the catalyst layer. Sensitivity was completely restored by simple rehydration and potential cycling.

Effect of Operating Conditions on PAHs Emission from a Single H2-O2 PEM Fuel Cell

This study investigates the emissions of polycyclic aromatic hydrocarbons (PAHs) from a single hydrogen-oxygen proton exchange membrane (PEM) fuel cell (FC) under different flowrates, temperatures, sampling periods, and membrane-electrode assemblies (MEAs). The results show that Nap, PA, BeP, FL, Pyr, BbC, Ant, and Flu were dominant in anode and cathode emissions of the single PEMFC under different operating conditions. The emission concentrations of Total-PAHs and Total-BaP equivalent carcinogenic potency (BaP_(eq)) were lower from the anode than from the cathode emission. Moreover, the concentrations of molecular-weight (MW) classified PAHs were in the order low (L) MM- ＞ high (H) MW- ＞ middle (M) MW-PAHs. When the anode/cathode gas flowrates were greater or smaller than 52/35 sccm but at the same sampling volume, the emission concentrations of Total-PAHs and Total-BaPeq increased. The concentration of Total-PAHs decreased but the mass of Total-PAHs increased with the increase of sampling time. However, 64% and 82% of PAH mass were emitted within 12 and 24 h, respectively, based on 36 h sampling at anode/cathode gas flowrates = 52/35 sccm. The concentrations of Total-PAHs or Total-BaP_(eq) of anode or cathode emission were slightly higher at 90°C than at 65°C. The performances of commercial MEAs were in the order SGL ＜ E-TEK ＜ GORE. Nevertheless, the concentrations of anode or cathode emission Total-PAHs or Total-BaP_(eq) for the PEMFC using different MEAs followed the order GORE ＞ E-TEK2 ＞ E-TEK ＞ SGL, while the sums of anode and cathode Total-PAHs emission factors varied with the order SGL ＞ E-TEK ＞ E-TEK2 ＞ GORE (13.3 ± 0.55, 11.5 ± 0.21, 7.91 ± 0.47, and 3.17 ± 0.22 μg g^(-1)-MEA, respectively). When using the (lab-made) E-TEK2 as the MEA of PEMFC, the PAH profiles of anode and cathode emission gases were similar to those of some carbon materials.

Membrane Electrode Assemblies for Water Electrolysis using WO3‐Supported IrxRu1‐xO2 Catalysts

AbstractA hydrogen economy is one of the most promising concepts for the future energy infrastructure. The conversion of sunlight into hydrogen (H2) using directly coupled photovoltaics (PV) and a proton exchange membrane (PEM) water electrolysis cell could compliment the required hydrogen production by using excess renewable electricity. It has many advantages such as producing pure hydrogen at high photon‐to‐chemical energy efficiency and simple technical operation, but it suffers from the high cost of the catalyst. Here we show single‐cell tests using commercial membranes and an in‐house synthesized WO3‐supported IrxRu1‐xO2 anode catalyst. The catalyst was synthesized by Adam’s Fusion protocol and loaded onto the support using an annealing procedure. Membrane electrode assemblies (MEAs) were prepared using an airbrush spraying technique. The electrolysis activity was greatly increased by adding tungsten carbide (WC) to the support, leading to a higher current density than commercial MEAs; however it also showed very fast degradation, losing most of the activity in minutes. The biggest issue in terms of stability seems to be on the cathode side of the cell.

Radiation-Grafted Polymer Electrolyte Membranes for Water Electrolysis Cells: Evaluation of Key Membrane Properties.

Radiation-grafted membranes can be considered an alternative to perfluorosulfonic acid (PFSA) membranes, such as Nafion, in a solid polymer electrolyte electrolyzer. Styrene, acrylonitrile, and 1,3-diisopropenylbenzene monomers are cografted into preirradiated 50 μm ethylene tetrafluoroethylene (ETFE) base film, followed by sulfonation to introduce proton exchange sites to the obtained grafted films. The incorporation of grafts throughout the thickness is demonstrated by scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM/EDX) analysis of the membrane cross-sections. The membranes are analyzed in terms of grafting kinetics, ion-exchange capacity (IEC), and water uptake. The key properties of radiation-grafted membranes and Nafion, such as gas crossover, area resistance, and mechanical properties, are evaluated and compared. The plot of hydrogen crossover versus area resistance of the membranes results in a property map that indicates the target areas for membrane development for electrolyzer applications. Tensile tests are performed to assess the mechanical properties of the membranes. Finally, these three properties are combined to establish a figure of merit, which indicates that radiation-grafted membranes obtained in the present study are promising candidates with properties superior to those of Nafion membranes. A water electrolysis cell test is performed as proof of principle, including a comparison to a commercial membrane electrode assembly (MEA).

Cross-Linked Phosphoric Acid Doped PBI Membranes and Their Performance on Operation As Automotive Range Extender

One of the promising application areas for high temperature proton exchange membrane technology is as a range extender in a battery electric vehicle. Unlike low temperature PEM fuel cells dependent on perfluorosulfonic acid type membranes, HT-PEM fuel cells need no humidification, the conductivity of the membrane having much lower dependence on degree of hydration, and their use therefore eliminates water management issues. The operation conditions of a fuel cell for range extender application differ from those when the PEMFC stack is used for the power train. Thus the stack is subjected less to transients and operates in semi-continuous mode, but with stop/start events corresponding to the normal start up and shut down of vehicle operation. HT-PEM membranes are based upon polybenzimidazole (PBI) polymers that are doped with (generally) phosphoric acid. This acid "doping" may be achieved by immersion of a polymer membrane in acid, or by methods involving the preparation of the PBI polymer in polyphosphoric acid followed by membrane casting and a controlled hydrolysis step, or the dissolution of PBI in a polyphosphoric acid/phosphoric acid followed by membrane casting, in a thermoreversible sol-gel transition. The last two approaches lead to very high acid contents, easily exceeding 20 molecules H3PO4/PBI repeat unit, and the resulting membrane is soft with poor mechanical properties. Polymer cross-linking is a recognized means for improving membrane strength. To date, in the case of PBI, acid doping has been carried out on the cross-linked membrane, resulting in low phosphoric acid uptake. We have developed an approach that allows the covalent cross-linking of PBI by introduction of a molecular cross-linking species at the polymer dissolution stage, following by membrane casting and thermal curing to give the cross-linked membrane. Since this approach provides mechanical stabilization to an acid-swollen membrane containing a high content of acid, it is a means leading to highly proton conducting membranes of satisfactory mechanical properties. A range of synthesis parameters including the amount of cross-linking, temperature for thermal curing etc., have been examined and, most recently, we have provided experimental evidence for cross-linking with the help of X-ray photoelectron and nuclear magnetic resonance spectroscopies. Membrane electrode assemblies (MEAs) have been developed using the novel cross-linked acid doped PBI membranes, and fuel cell test protocols relevant to range extender application, based upon load cycling at 160 °C, have been applied. The results demonstrate that the novel MEAs comprising cross-linked PBI have lower voltage decay on load cycling than is observed using commercial MEAs, reaching >1000 h operation without the voltage dipping below the end-of-life criterion. The research leading to these results has received funding from the European Community’s Seventh Framework Programme for the Fuel Cells and Hydrogen Joint Undertaking under grant agreement ARTEMIS no. 303482.

Performance investigation of Passive Direct Methanol Fuel Cell in different structural configurations

Abstract The aim of the present work is to systematically investigate the performance of a Passive Direct Methanol Fuel Cell (PDMFC) with different structural configurations. The PDMFCs are an attractive option for powering advanced electronic devices in the future due to the high power densities, easy fuel storage, low operating temperature, low noise level and simple design. The cell is completely passive, without external pumps and auxiliary devices; it takes oxygen from the surrounding air and the methanol solution is stored in a built-in tank in contact with the active area. We used a commercial hot-pressed Membrane Electrode Assembly with an active surface of 5 cm 2 composed of a Nafion 117 membrane and two Gas Diffusion Layers with catalyst loadings of 4 mg/cm 2 Pt–Ru on the anode side and 4 mg/cm 2 PtBlack on the cathode side. The supporting external case was manufactured in polymethylmethacrylate; the electrodes consist of two stainless steel SS316 plates and the gaskets are made of PTFE and silicone. The performance of the cell with three different assembly configurations and two different current collector geometry was investigated changing methanol molar concentration (ranging between 1 M and 4 M).

Characterisation tools development for PEM electrolysers

Electrochemical impedance spectroscopy (EIS), current interrupt (CI) and current mapping (CM) were investigated as in-situ characterisation tools for PEM electrolysers. A 25 cm2 cell with titanium anode and carbon cathode plates were utilised in this study. A commercial MEA consisting of 1 mg IrO2/cm2 on the anode and 0.3 mg Pt/cm2 on the cathode was used. The electrocatalyst was deposited on Nafion® membranes. The electrochemical losses in a PEM electrolyser namely: activation, ohmic and mass transfer losses were identified using EIS and CI and both the advantages and disadvantages of the methods were discussed. The current distribution over the membrane electrode assembly (MEA) at different current densities was measured using the current mapping method. It is also shown that under the given experimental conditions the current density decreases along the serpentine flow field.

Pulse Current Electrodeposition of Nanocatalysts Using Different Waveforms for Use in PEMFCs

An electrochemical method based on pulse current electrodeposition (PCE) utilizing different waveforms was developed and used for fabricating membrane-electrode assemblies (MEAs) with low catalyst loading for use in proton exchange membrane (PEM) fuel cells. It was found that both peak deposition current density and duty cycle control the nucleation rate and the growth of platinum crystallites. Based on the combination of parameters used in this study, the optimum conditions for PCE were found to be a peak deposition current density of 400 mA cm-2, a duty cycle of 4%, and a pulse generated and delivered in the microsecond range utilizing a ramp-down waveform. MEAs prepared by PCE using the ramp-down waveform show performance comparable with commercial MEAs that employ several times the loading of platinum catalyst.

Detecting proton exchange membrane fuel cell hydrogen leak using electrochemical impedance spectroscopy method

When a proton exchange membrane (PEM) fuel cell runs short of hydrogen, it suffers from a reverse potential fault that, when driven by neighboring cells, can lead to anode catalyst degradation and holes in the membrane due to local heat generation. As a result, hydrogen leaks through the electrically-shorted membrane-electrode assembly (MEA) without being reacted, and a reduction in fuel cell voltage is noticed. Such voltage reduction can be detected by using electrochemical impedance spectroscopy (EIS). To fully understand the reverse potential fault, the effect of hydrogen crossover leakage in a commercial MEA is measured by EIS at different differential pressures between the anode and cathode. Then the signatures of these leaky cells were compared with the signatures of a no-leaky cells at different oxygen concentrations with the same current densities. The eventual intent of this early stage work is to develop an on-board diagnostics system that can be used to detect and possibly prevent cell reversal failures, and to permit understanding the status of crossover or transfer leaks versus time in operation.

일차계 모델을 이용한 고분자전해질 연료전지 스택의 CO Poisoning 및 Air Bleeding 효과 분석

상업용 막전극접합체를 사용하여 제작한 고분자전해질 연료전지의 CO poisoning 및 air bleeding 효과가 스택의 셀전압 성능에 미치는 영향을 분석하였다. 실험을 통해 확보한 동적 응답 데이터에 일차 미분방정식으로 표현되는 일차계 모델을 적용하여 정상상태 이득과 시간상수를 계산하는 방법으로 스택 셀전압의 응답 특성을 정량화하였다. 연료전지 개질기로부터 공급되는 개질 가스에 포함된 CO 농도가 1 ppm 증가할 때마다 셀전압은 1.3~1.6 mV 저하되고, CO 농도의 변화폭이 클수록 정상상태에 도달하기까지 걸리는 시간이 점점 짧아지는 것으로 분석되었다. CO poisoning에 의해 저하된 스택 성능을 회복시키기 위해 air bleeding을 수행할 경우, 주입하는 공기의 농도를 증가시킬수록 셀전압 상승폭(정상상태 이득)이 커지고 회복시간(시간상수)은 짧아지나, 1% 수준의 air bleeding만으로도 CO poisoning이 일어나기 전 셀전압의 87%~96%를 1~30 min 이내에 회복시킬 수 있는 것으로 분석되었다. We analyze the effects of CO poisoning and air bleeding on the performance of a PEM (polymer electrolyte membrane) fuel cell stack fabricated using commercial MEA (membrane electrode assembly). Dynamic response data from the experiments on the performance of a stack are identified by obtaining steady-state gains and time-constants of the first-order system model expressed as a first-order differential equation. It is found that the cell voltage of the stack decreases by 1.3-1.6 mV as the CO concentration rises by 1 ppm. The time elapsed to reach a new steady state after a change in the CO concentration is shortened as the magnitude of the change in the CO concentration increases. In general, the steady-state gain becomes bigger and the time-constant gets smaller with increasing the air concentration (air-bleeding level) in the reformate gas to restore the cell voltage. However, it is possible to recover 87%-96% of the original cell voltages, which are measured with free of CO, within 1-30 min by introducing the bleed air as much as 1% of the reformate gas into the stack.

Pulse electrodeposition of platinum catalyst using different pulse current waveforms

The effects of waveform and other associated parameters on the pulse current electrodeposition of platinum electrocatalysts for use in polymer electrolyte membrane fuel cells were investigated. Using microsecond pulses with ramp-down waveforms yielded well dispersed, high surface area nanoparticles of 2–3nm diameter, which, when incorporated into fuel cell membrane-electrode assemblies (MEAs), resulted in fuel cell performance comparable with commercial MEAs that employed ten times as much platinum loading.

Degradation mechanism study of PTFE/Nafion membrane in MEA utilizing an accelerated degradation technique

Nafion membranes are widely used for commercial membrane electrode assemblies (MEAs) in proton exchange fuel cells (PEMFCs). The polytetrafluoroethylene (PTFE)/Nafion (PN) composite membrane has the advantages of being low in cost, high in mechanical strength, and does not swell excessively. This study focuses on the properties of PTFE/Nafion membranes and PTFE/Nafion MEAs by comparing the durability and performance of the PN MEAs to commercial Nafion 211 MEAs. In an accelerated degradation test (ADT), the characterization of PTFE/Nafion and Nafion MEAs were analyzed using in-situ electrochemical methods such as polarization curves, AC impedance, cyclic voltammetry (CV), and linear sweep voltammetry (LSV). The results demonstrate an increase in the internal resistance on the PTFE/Nafion MEA only. The three mechanisms behind this unique result were proposed to be: (a) Separation of the catalyst layer from the membrane due to creep deformation; (b) Separation of the outer Nafion layer film from the core PTFE/Nafion membrane due to creep deformation; (c) Degradation of the Nafion plane (or Nafion dissolution) from the PTFE surface.The scanning electron microscope (SEM) images indicate that only the PTFE/Nafion MEA curved after the ADT. Mechanism (a) was therefore the most possible phenomenon for the increase in internal resistance of the PN MEA.

Dissolution and Migration of Platinum in PEMFCs Investigated for Start/Stop Cycling and High Potential Degradation

AbstractDissolution and migration of platinum due to start/stop degradation and increased cathode potentials were studied for commercial membrane electrode assemblies (MEA). The chosen conditions closely mimic real situations in automotive operation. In start/stop tests, we observed a strongly enhanced platinum dissolution due to the dynamic interplay of repeated cell start‐up and consecutive normal fuel cell operation, which is related to platinum oxidation (start‐up) and reduction (normal operation) cycles. Consequently, the performed test protocols distinguish between dynamic and static load profiles. Electrochemical investigations before and after degradation monitor the loss in cell performance. Since electron microscopy offers the unique possibility to unravel and distinguish degradation due to carbon corrosion and agglomeration or platinum dissolution, a focus was set on this method. For the start/stop MEA pronounced platinum dissolution accompanied by the formation of large platinum precipitations in the membrane was found. Carbon corrosion was also observed, but did not lead to a significantly reduced porosity and loss in platinum dispersion. In contrast, the MEA which was exposed to high constant potentials exhibited severe damage to the 3D cathode structure due to carbon corrosion. However, no pronounced platinum dissolution was observed and only few Pt precipitations were found in the membrane itself.

Preparation and characterization of membrane electrode assembly (MEA) for PEMFC

Fuel cell is a system that converts chemical energy to electrical energy from an oxidation–reduction reaction of hydrogen and oxygen. In this study, Pt/C catalyst, solvent, and a binder agent were mixed to prepare catalyst ink. First, we applied carbon black ink to the carbon paper to supply hydrophobic and hydrophilic structure on its surface, which is called as microporous layer (MPL). Then catalyst ink was deposited on the treated carbon paper to form gas diffusion layers (GDLs) for anode and cathode side of the fuel cell. At this position, catalyst layer surfaces and carbon paper were analyzed by using scanning electron microscopy (SEM) and it was seen by energy dispersive spectroscopy (EDS) analysis that the catalysts were spread uniformly on a carbon paper. A membrane is fixed between GDLs and hot-pressed at 120°C, 75 kg cm− 2 to compose membrane electrode assembly (MEA). In a fuel cell test unit, MEA has internal resistance, which was evaluated by applying current interrupt method and current–voltage curve was drawn by load application. As a result of the test, I-V curves were formed and compared with characteristic curve of commercial MEA. It was seen that the shapes of the curves are similar. Maximum power values are 100, 275, and 390 mW for homemade MEA without MPL, with MPL, and commercial MEA, respectively. MEA without MPL was susceptible to flooding, especially at high-currrent values. MPL is helpful to increase the porosity of the diffusion layer and this effect can improve the oxygen transfer rate and lead to a higher performance. Compared with commercial MEA, homemade MEA did not reach high-current and -power values due to lots of parameters which affects the fuel cell performance as catalyst activity, conditions of MEA preparation, and disorder of measurement conditions, etc. Copyright © 2010 John Wiley & Sons, Ltd.