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Water management remains a significant challenge for the Proton Exchange Membrane Fuel Cell (PEMFC) with respect to performance, lifetime and operational flexibility. In recent years, microporous layers (MPL) have been widely used on the cathode side of the PEMFC in order to improve fuel cell performance and water management capabilities. Many modeling and experimental studies have with limited success attempted to analyze the underlying mechanisms that are responsible for the performance improvement due to the MPL. In this study, porous inserts along with various in-situ experimental techniques are used to investigate the MPLs. It was observed that the anode pressure drop increased when a cathode MPL was present, indicating water cross-over from the cathode towards the anode side. Further testing identified that the MPL improved cell performance due to the reduction of water saturation in the cathode catalyst layer, which resulted in enhanced oxygen diffusion. The influence of the MPL on the anode side was also studied with the aid of porous inserts and other techniques, and it was observed that the anode MPL improves cell voltage stability and reduces water accumulation in the anode catalyst layer. The present investigation provides further important information on the critical role of the MPL in the PEMFC. [ABSTRACT FROM AUTHOR]

Abstract: This study discusses the use of an additional layer in the cathode side of a proton exchange membrane fuel cell (PEMFC) for improved water management at dry conditions. The performance of fuel cells deteriorates significantly when low to no gas humidification is used. This study demonstrates that adding a non-porous material with perforations, such as stainless steel, between the cathode flow field plate and the gas diffusion layer (GDL) improves the water saturation in the cathode GDL and catalyst layer, increases the water content in the anode, and keeps the membrane hydrated. The slight voltage drop in the performance as a result of transport limitations is justifiable since the overall durability of the cell at these extreme conditions is enhanced. The results show that the perforated layer(s) enhances the operational life of the PEMFC under completely dry conditions. These extreme conditions (dry gases without humidification, 90 kPa, 75 °C) were used to accelerate the failure modes in the fuel cells. [Copyright &y& Elsevier]

Abstract: The electrochemical production of hydrogen (H2) from liquid methanol in acidic aqueous media was investigated in a proton exchange membrane (PEM) electrolyser, comprising a two-compartment glass cell with a membrane electrode assembly (MEA) composed of a Nafion® 117 membrane and gas diffusion electrodes (GDE). Methanol electrolysis was studied at concentrations ranging from 0 to 16M, where 0M corresponds to water electrolysis. The influence of catalysts (Pt and Pt–Ru), catalyst support (C or black), operating temperatures (23, 50 and 75°C) and operating modes (dry and wet cathode) were evaluated in the static mode. A theoretical thermodynamic analysis of the system was done as a function of temperature. The limiting current densities, kinetic parameters, including the Tafel slopes and current exchange density, and apparent activation energies were determined. [Copyright &y& Elsevier]

Abstract: Structure, activity, and stability of the Ru1−x Fe x Se y /C (x =0.0–0.46, y =0.4–1.9) catalysts, synthesized via hydrogen annealing of carbonyl precursors, are analyzed using X-ray diffraction, transmission electron microscopy, rotating (ring) disk electrode voltammetry, and cyclic voltammetry. Hydrogen annealing at 400°C enables nucleation of the pyrite phase, which strengthens the catalyst stability for oxygen reduction reaction (ORR) in the acidic electrolyte. Evaluation on the stable Ru1−x Fe x Se y /C catalysts indicates that the ORR activity increases with increasing iron content and Se content. Substitution of base metal Fe enhances the activity and reduces the material cost, but it also increases the H2O2 yield, which is measured less than 3.0% between 0.7 and 0.9V in contrast to 1.0% of the catalyst without iron. The high activity of Ru0.54Fe0.46Se1.9/C decays more rapidly than that of RuSe2.0/C in the stability test, probably because Fe and Se are preferentially leached in the potential cycling up to 1.2V. Still the two catalysts with pyrite structure exhibit much higher durability than the cluster-type catalyst of RuSecluster/C (Ru:Se=1:0.3) that was not annealed. [Copyright &y& Elsevier]

The formation, growth, and stability of oxygen bubbles inside the porous transport layer (PTL) pores of the anode of a polymer electrolyte membrane water electrolysis (PEMWE) cell was investigated by 1-dimensional mathematical modeling inside the PTL and into the flow channel. The effect of oxygen bubbles on the electrolysis overpotential has been evaluated, and the results were used to predict the effects of catalyst and PTL structures on the electrolysis cell performance. The results show how surface oxygen bubbles block active catalyst sites and decrease the electrochemically active surface area (ECSA). The effects of catalyst layer wettability, PTL wettability and pore size, and the operating conditions on the growth and detachment of bubbles from the catalyst surface were modeled. The model accounts for the growth and stability of three types of bubbles in a PEMWE cell: nucleation-driven, drag-driven, and buoyancy-driven bubbles. Nucleation-driven bubbles show the smallest overpotential: 28 mV at the reference operating conditions and PEMWE properties, compared to 35 mV for the drag-driven bubbles and 43 mV for the buoyancy-driven bubbles. Catalyst wettability is found to be the most influential material property concerning bubble overpotential for all three types of bubbles. PTL wettability and the cell pressure are the next most important factors in this regard. The modeling results can be used for improved PTL, catalyst layer, and flow field design for PEMWE cells. [ABSTRACT FROM AUTHOR]

A semi-empirical non-isothermal model incorporating coupled momentum, heat and mass transport phenomena for predicting the performance of a proton exchange membrane (PEM) water electrolysis cell operating without flow channels is presented. Model input parameters such as electro-kinetics properties and mean pore size of the porous transport layer (PTL) were determined by rotating disc electrode and capillary flow porometry, respectively. This is the first report of a semi-empirical fully coupled model which allows one to quantify and investigate the effect of the gas phase and bubble coverage on PEM cell performance up to very high current densities of about 5 A/cm 2 . The mass transport effects are discussed in terms of the operating conditions, design parameters and the microstructure of the PTL. The results show that, the operating temperature and pressure, and the inlet water flowrate and thickness of the PTL are the critical parameters for mitigating mass transport limitation at high current densities. The model presented here can serve as a tool for further development and scale-up effort in the area of PEM water electrolysis, and provide insight during the design stage. [ABSTRACT FROM AUTHOR]

Abstract: A colloidal silica incorporated porous anodic aluminum oxide (AAO) was utilized as a dual-template to prepare mesoporous carbon nanofibers (MCNFs). Such a strategy is simple because it takes advantage of commercially available materials (i.e., colloidal silica and AAO) and the templates can be removed in one step. The as-prepared MCNF shows a hierarchical nanostructure consisting of open macroporous channel connected with large mesopores and micropores. As a result of the large surface area and unique hierarchical nanoarchitecture which facilitates fast mass and electron transport, the MCNF reveals a discharge capacity of 679 mA h g−1 at 25 mA g−1. This value is significantly greater than that (i.e., 394 mA h g−1) observed for an ordered mesoporous carbon (OMC) with a similar specific surface area. Furthermore, at 3000 mA g−1, the MCNF demonstrates a discharge capacity of 585 mA h g−1, which is about twice that (i.e., 256 mA h g−1) of the OMC. [Copyright &y& Elsevier]

Abstract: Anode water removal (AWR) is studied as a diagnostic tool to assess cathode gas diffusion layer (GDL) flooding in PEM fuel cells. This method uses a dry hydrogen stream to remove product water from the cathode, showing ideal fuel cell performance in the absence of GDL mass transfer limitations related to water. When cathode GDL flooding is limiting, the cell voltage increases as the hydrogen stoichiometry is increased. Several cathode GDLs were studied to determine the effect of microporous layer (MPL) and PTFE coating. The largest voltage gains occur with the use of cathode GDLs without an MPL since these GDLs are prone to higher liquid water saturation. Multiple GDLs are studied on the cathode side to exacerbate GDL flooding conditions to further confirm the mechanism of the AWR process. Increased temperature and lower cathode RH allow for greater overall water removal so the voltage improvement occurs faster, though this leads to quicker membrane dehydration. [Copyright &y& Elsevier]

Abstract: Various anode-supported solid oxide fuel cells (SOFC), based on 10 mol% Dy-doped La2Mo2O9 (LDM) electrolyte, are prepared analytically and operated under single chamber conditions to explore the connections between electrode and power performance. The cathode of tested SOFCs is compositionally graded with three composites of samarium strontium cobaltite and Gd-doped ceria (GDC) to relax the thermal stress, because of sizable thermal expansion differences above 400 °C. We focus the research attention on varying the anode pore structure and composition to promote the power performance in methane/air mixture at 700 °C. For the one-layer support of GDC+NiO+LDM anode, addition of 10 wt% graphite minimizes its mass transport resistance through creating 8–5 μm long and ∼1 μm wide slit-shaped pores. The graphite pore former raises the peak power value by 80 mW cm−2. Adopting a more porous and active outer layer, the double-layer support further enhances the cell power. The peak power was first raised by 48 mW cm−2, using an outer layer that was prepared with 63 wt% NiO. Dosing 3% Pd on this outer layer uplifts another 59 mW cm−2. In this study, with an improved anode, the peak power value reaches 437 mW cm−2. [Copyright &y& Elsevier]

Abstract: Nitrogen-doped (N-doped) carbon, denoted as Fe–UF–CNx, is synthesized through nitridation of an iron-doped gel precursor on the Vulcan support. It exhibits a legitimate activity on catalyzing oxygen reduction reaction (ORR). Its polarization curve, measured with a rotating disk electrode in O2-saturated H2SO4, indicates Fe–UF–CNx has a widely distributed ORR activity and a high onset potential 0.859 V. The widely distributed activity originates from its complex nitrogen sites on the graphitic sheet, evidenced by the broad N1s spectrum of Fe–UF–CNx, which is featured with twin peaks of nearly equal intensity for pyridinic and pyrrolic nitrogens. The high onset potential suggests, despite an overall mediocre activity, the Fe–UF–CNx activity involves a small fraction of very active sites. When properly joining with the RuSe2 pyrite nanoparticles, the high potential active sites of Fe–UF–CNx uplift the ORR activity to the level of carbon-supported Pt catalyst. The platinum–level activity is manifested by a small half-wave potential difference 0.03–0.04 V between the joint catalyst of RuSe2–Fe–UF–CNx and the commercially available Pt/C catalyst. Additional merits of RuSe2–Fe–UF–CNx, such as high stability, methanol tolerance, low peroxide yield, are also measured and discussed. [Copyright &y& Elsevier]

Abstract: One of the predominant failure modes of polymer electrolyte membrane (PEM) fuel cells is the degradation of the PEM, especially when the fuel cell is used for transportation applications. Numerous studies have been carried out regarding this issue but many aspects of the degradation are not yet understood. This paper reviews the available literature regarding membrane degradation, and attempts to classify the degradation modes into three categories: mechanical, thermal and chemical/electrochemical. The factors that contribute to each mode are discussed, along with detailed mechanisms for some degradations. Some possible mitigation strategies are also explored. [Copyright &y& Elsevier]