Highlights ORR-kinetics study on Pt and Ag by using thin-layer catalysts in a AEMFC at 80 °C. Ag shows a later onset potential for ORR and lower performance at high voltages. The Tafel slope of Pt is 75 mV dec−1 above 0.8 V, for Ag the slope is 160 mV dec−1. For Ag, a voltammetric anodic peak at 0.8 V, indicates formation of Ag2O. Ag performs better than Pt below 0.5 V, but its stability is affected above 0.8 V.

Side reactions leading to gas evolution are undesirable in batteries and result in reduced coulombic efficiency and shortened lifetime. Quantitative analysis of the gases that evolve is therefore important to improve understanding of the reactions occurring in the battery during cycling and could be used to optimize battery operation. However, the measurements are challenging because batteries are by their nature closed with limited gas space. Nickel metal hydride (NiMH) batteries are widely used due to their good rate capability, reliability, and environmental friendliness. The battery type has been extensively studied in terms of degradation and performance. However, very few studies have been conducted on the gas composition created during a work cycle. In this study, two methods for investigating the internal NiMH battery gas phase composition during different charge/discharge cycles using a mass spectrometer (MS) were developed. In the first method, the battery module was connected by a sampler system. In the second method, the battery was connected directly using a microcapillary, and the gas composition was continuously measured. In addition to the gas composition, the voltage, pressure, and temperature of the battery were recorded. The most abundant component in the measured gas phase was nitrogen, present in the cell from the assembly stage, followed by hydrogen. A clear rising trend of hydrogen pressure as depth of charge (DOC) increased was recorded, while oxygen levels were low except around the end of charge. The methods were found to be a reliable means of investigating NiMH gas composition without negatively affecting the battery and may be adapted to other battery chemistries. In this study, two methods for investigating the internal NiMH battery gas phase composition during different charge/discharge cycles using a mass spectrometer (MS) were developed.

Improved knowledge on Proton Exchange Membrane Fuel Cell (PEMFC) behaviour in the Intermediate Temperature (IT: 80-120 degrees C) is needed. Here, ionic conductivity and H2 permeability are analysed under H2/N2 using electrochemical impedance spectroscopy, linear sweep voltammetry for three catalyst-coated membranes (CCMs): Nafion HP (reinforced), Nafion 211 (non-reinforced) and a reinforced commercial membrane (RCM, membrane thickness 13 mu m). Multiple relative humidity (RH) levels and pressure configurations are analysed at IT. Results show that ionic conductivity and H2 permeability increase with temperature and RH. However, lower crossover is measured above 100 degrees C and wet conditions due to low H2 partial pressure. The highest crossover is measured with an overpressure on the H2 side which, especially for RCM, suggests possible convection. The membrane reinforcement might reduce the permeability and it decreases the conductivity. Mass spectrometry confirmed that sprayed CCMs suffer from higher crossover than pristine membranes, although the membrane thickness is unchanged.

Anion exchange membrane water electrolysis (AEMWE) is a promising and potentially low-cost technology for producing green hydrogen, but a novel manufacturing technique with rational design of the electrodes is essential to improve the performance and stability. In this work, we investigate the effect of electrode structure on activity and the stability of AEMWEs by fabricating membrane electrode assemblies (MEAs). For the first time, the decal transfer method with platinum-group-metal-free (PGM-free) catalyst was successfully used in AEMWEs. With this method, deposition of a compact catalyst layer (CL) on the membrane was achieved without damaging neither the CL nor the membrane. The MEAs were designed for AEMWE using 1 M KOH as the electrolyte and the ionomer content was optimized for both cathode and anode. In the anode, a low ionomer loading improved activity and ionic conductivity, however, a higher ionomer content was beneficial for the cathode. Furthermore, the type of ionomer on the anode side has shown to be the major reason of loss of performance over time. An ionomer with low (1.4–1.7 meq g−1) Ion Exchange Capacity (IEC) and Nafion™ ionomer greatly improved the stability.

Using stainless steel as material for bipolar plates (BPPs) in proton exchange membrane fuel cells (PEMFCs) carries a perceived risk of corrosion and subsequent metal ion contamination of the membrane electrode as-sembly (MEA). However, assessments in literature on this hazard to PEMFC systems have been based on ex-situ corrosion studies, where general assumptions made on the BPP environment might not be a correct simulation of real on-site conditions. In this contribution, uncoated BPPs from stainless steel grades 304 L, 316 L and 904 L were subjected to in-situ hybrid endurance/stress testing to simulate realistic conditions in operating fuel cell systems and re-evaluate the need of additional corrosion protection. A post analysis of the plates showed no signs of surface dissolution on any of the tested samples and the concentration of iron in the MEA averaged 7 to 10 ppm for uncoated samples and 7 to 11 ppm for coated and graphitic reference tests, displaying a negligible amount of trace metals compared to critical thresholds found in literature. Contact resistance values were stable for all samples and observable changes in cell performance and voltage degradation was confirmed to be un-related to the presence of uncoated bipolar plates. The combined effects of decoupling of bipolar plate surface potentials from electrode potentials and operational control of stable gas flow compositions to sustain stainless steel surface passivation, were identified as explanation for the experimentally observed corrosion resistance of uncoated stainless steel plates in PEMFCs.

In order to investigate stability of oxygen reduction reaction (ORR) on a Pt3Y thin film under relevant fuel cell conditions, we performed an accelerated stress test (AST) consisting of 3600 potential cycles between 0.4 and 1.4 V at 1 V s−1 in a single proton exchange membrane fuel cell (PEMFC). The ORR activities were evaluated via polarization curves before and after the AST. Electrochemical active surface area (ECSA) was obtained by CO-stripping voltammetry whereas the morphological changes were monitored by means of scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Variations in surface composition and electronic structures were evaluated by energy-dispersive X-ray spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS). After AST, the polarization curves show loss of ORR activity in all voltages for both Pt and Pt3Y. Except at very high voltages (E > 0.85 VRHE), the ORR activity of Pt3Y after AST is very close to that of Pt before AST. This correlates well with the results from the deconvolution of Pt-4f XPS spectra where the binding energy of metallic Pt in Pt3Y is comparable to pure Pt (71.22 eV). SEM and TEM images demonstrate that the morphologies of the aged Pt3Y and as-sputtered Pt are similar, whereas EDX results confirm a steady bulk composition of Pt3Y thin films throughout the entire electrochemical test. By correlating all these results, we conclude that the loss of ORR activity for Pt3Y is due to an increase in the thickness of the Pt overlayer which induces a relaxation of the Pt overlayer decreasing the compressive strain effect. For pure Pt, the loss of ORR activity is associated with a growth of the Pt domains associated with Ostwald ripening process.

The integration of proton exchange membrane fuel cells (PEMFCs) in heavy-duty vehicles would be facilitated if operating temperatures above 100 degrees C were possible. In this work, the effect of temperature in the intermediate range of 80-120 degrees C is investigated for a commercial membrane electrode assembly (MEA) through polarization curves and electrochemical impedance spectroscopy. The importance of oxygen partial pressure on voltage is systematically studied by decoupling it from humidity and temperature. The results show that adequate oper-ation at intermediate temperature is achievable if the oxygen partial pressure is sufficient. Although the cathode kinetics is faster with rising temperatures, the voltage gain is counteracted by the decreasing equilibrium po-tential. At intermediate temperature, the water transport is enhanced, levelling out the relative humidity dif-ference between anode and cathode. However, ionic conductivity in the polymer can become limiting at high currents, due to a smaller relative humidity increase at these temperatures. To conclude, a higher operating temperature does not inherently cause a decrease in obtained current density. Rather, the difficulty to simul-taneously have sufficient oxygen partial pressure and high relative humidity causes limitations within the cathode that to some extent can be solved by pressurizing the cell.

The bipolar plate (BPP) is a component with vast cost-reduction potential in proton exchange membrane fuel cells (PEMFCs). Apart from mechanical and heat transfer requirements, the most desired BPP properties are high corrosion and low electrical contact resistance. In this study we confirm that due to ionic decoupling between BPPs and electrodes, the surface potentials of the BPPs remain stable even at varying operation loads. These mild potentials, in combination with low metal-ion leeching due to passive-transpassive-passive dissolution in stainless steels, suggest that low-cost carbon-coated stainless steel can readily be used as a BPP in PEMFCs. To prove this, single-fuel cell tests were carried out under realistic driving conditions, including electrochemical analysis, in-situ contact-resistance measurements, and post-mortem investigation of the membrane electrode assembly (MEA) by inductively coupled plasma trace-metal analysis, combined with electron microscopy and Auger spectroscopy of the BPPs. The results show that due to the ionic decoupling, conditions at the BPP surfaces are much less corrosive than previously thought. Furthermore, carbon-coated stainless-steel BPPs prove to be unaffected by global hydrogen starvation, which causes severe MEA degradation independent of the presence or absence of BPPs.

Alloying platinum is an approach to increase the oxygen reduction reaction (ORR) activity and at the same time reduce the amount of precious platinum catalyst in proton exchange membrane fuel cells (PEMFC). In this work the cathode activity of thin films of rare earth metals (REM) alloys, Pt 3 Y, Pt 5 Gd and Pt 5 Tb, produced by sputter deposition onto gas diffusion layers, are evaluated in a fuel cell by means of polarization curves in O 2 /H 2 , and cyclic- and CO-stripping voltammetry in N 2 /5% H 2 . Prior to evaluation, the model electrodes were acid-treated to obtain a Pt skin covering the PtREM alloy bulk, as was revealed by energy-dispersive X-ray spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS). The core shell alloys of Pt 3 Y and Pt 5 Gd catalysts show a specific activity enhancement at 0.9 V of 2.5 times compared to pure Pt. The slightly lower enhancement factor of 2.0 for Pt 5 Tb is concluded to be due to leaching of the REM, that resulted in a thicker, and subsequently less strained, Pt overlayer. The high activity, combined with the minor changes in surface composition, achieved in the fuel cell environment shows that PtREM core shell catalysts are promising for the cathode reaction in PEMFC.

Trace-metal contamination poses a threat to performance and stability of proton exchange membrane fuel cells (PEMFCs). In this study the source of origin and degree of metal dissolution from carbon-coated 316L bipolar plates (BPPs) are evaluated after a long-term PEMFC test run under conditions resembling a real-life automotive application. Despite intact carbon-coating, metal dissolution occurs from uncoated oxycarbide stains on the plates? surface. Which correlates with post-mortem detection of chromium, iron and nickel in the membrane electrode assembly. The rate of cell voltage decrease throughout the high current operations is found to be twice as high in the presence of metal ions. Metal dissolution can be correlated with transients in cell voltage during dynamic current load cycling as a result of temporary global fuel starvation. The observed difference in metal dissolution on the anode and cathode BPP indicates weak galvanic coupling between the bipolar plate(s) and the electrode layer(s). ? 2020 The Authors. Published by Elsevier Ltd on behalf of Hydrogen Energy Publications LLC. This is an open access article under the CC BY license (http://creativecommons.org/ licenses/by/4.0/).