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

Coated Stainless Steel Bipolar Plates for Proton Exchange Membrane Electrolyzers

Given its rapid response to fluctuating currents and wide operation range, proton exchange membrane (PEM) water electrolysis is utmost suitable for generation of hydrogen from renewable power. However, it is still hindered by the high cost of the stack components compared to those used in the alkaline technology. In particular, the titanium bipolar plates (BPP) are an issue and the replacement of this metal by stainless steel is a challenge, due to the highly corrosive environment inside PEM electrolyzer stack. Herein, we coat stainless steel BPPs with 50–60 μm Ti and 1.5 μm Pt coatings by vacuum plasma spraying (VPS) and magnetron sputtering physical vapor deposition (PVD), respectively. The BPPs are evaluated at constant 1 A cm−2 for more than 1000 h. The thermally sprayed Ti coatings fully protect the stainless steel substrate during this period of time, and the Pt surface modification allows achieving a cell performance comparable to the baseline

Durable Membrane Electrode Assemblies for Proton Exchange Membrane Electrolyzer Systems Operating at High Current Densities

High efficiencies, wide operation range and rapid response time have motivated the recent interest in proton exchange membrane (PEM) electrolysis for hydrogen generation with surplus electricity. However, degradation at high current densities and the associated mechanism has not been thoroughly explored so far. In this work, membrane electrode assemblies (MEA) from different suppliers are aged in a commercial PEM electrolyzer (2.5 N m3 H2 h1 ), operating up to 4 A cm2 for more than 750 h. In all cases, the cell voltage (Ecell) decreases during the testing period. Interestingly, the cells with Ir-black anodes exhibit the highest performance with the lowest precious metal loading (1 mg cm-2). Electrochemical impedance spectroscopy (EIS) shows a progressive decrease in the specific exchange current, while the ohmic resistance decreases when doubling the nominal current density. This effect translates into an enhancement of cell efficiency at high current densities. However, Ir concurrently leaches out and diffuses into the membrane. No decrease in membrane thickness is observed at the end of the tests. High current densities do not lead to lowering the performance of the PEM electrolyzer over time, although MEA components degrade, in particular the anode

Low-Cost and Durable Bipolar Plates for Proton Exchange Membrane Electrolyzers

Cost reduction and high efficiency are the mayor challenges for sustainable H2 production via proton exchange membrane (PEM) electrolysis. Titanium-based components such as bipolar plates (BPP) have the largest contribution to the capital cost. This work proposes the use of stainless steel BPPs coated with Nb and Ti by magnetron sputtering physical vapor deposition (PVD) and vacuum plasma spraying (VPS), respectively. The physical properties of the coatings are thoroughly characterized by scanning electron, atomic force microscopies (SEM, AFM); and X-ray diffraction, photoelectron spectroscopies (XRD, XPS). The Ti coating (50 μm) protects the stainless steel substrate against corrosion, while a 50-fold thinner layer of Nb decreases the contact resistance by almost one order of magnitude. The Nb/Ti-coated stainless steel bipolar BPPs endure the harsh environment of the anode for more than 1000 h of operation under nominal conditions, showing a potential use in PEM electrolyzers for large-scale H2 production from renewables

PEM fuel cell cathode contamination in the presence of cobalt ion (Co2+)

This paper reports the effects of Co\ub2\u207a contamination on PEM fuel cell performance as a function of Co\ub2\u207a concentration and operating temperature. A significant drop in fuel cell voltage occurred when Co\ub2\u207a was injected into the cathode air stream, and Co\ub2\u207a contamination became more severe with decreasing temperature. To investigate in detail the mechanism of Co\ub2\u207a poisoning, AC impedance was monitored before and during Co\ub2\u207a injection, revealing that both charge transfer and mass transport related processes deteriorated significantly in the presence of Co\ub2\u207a, whereas membrane conductivity decreased to a lesser extent. Surface cyclic voltammetry and contact angle measurements further revealed changes in physical properties, such as active Pt surface area and hydrophilicity, furthering our understanding of the contamination process.Cet article signale les effets de la contamination par le Co2+ sur le rendement de piles MEP en fonction de la concentration et de la temp\ue9rature du Co2+. Une baisse importante de la tension d\u2019une pile \ue0 combustible s\u2019est produite lorsque du Co2+ a \ue9t\ue9 inject\ue9 dans le flux d\u2019air de la cathode et la contamination par le Co2+ s\u2019est aggrav\ue9e lorsqu\u2019on a abaiss\ue9 la temp\ue9rature. Afin d\u2019\ue9tudier en d\ue9tail le m\ue9canisme d\u2019empoisonnement au Co2+, on a suivi l\u2019imp\ue9dance c.a. avant et pendant l\u2019injection de Co2+, ce qui a r\ue9v\ue9l\ue9 que les m\ue9canismes li\ue9s au transfert des charges et au transport de masse se d\ue9t\ue9rioraient consid\ue9rablement en pr\ue9sence de Co2+, alors que la conductivit\ue9 de la membrane subissait une moindre diminution. Des mesures de voltamp\ue9rom\ue9trie cyclique de surface et des angles de contact ont en outre r\ue9v\ue9l\ue9 des modifications des propri\ue9t\ue9s physiques, comme la taille de la surface active du Pt et le caract\ue8re hydrophile, ce qui am\ue9liore notre connaissance du processus de contamination.Peer reviewed: YesNRC publication: Ye

Effect of Co2+ on oxygen reduction reaction catalyzed by Pt catalyst, and its implications for fuel cell contamination

The oxygen reduction reaction (ORR) catalyzed by Pt was studied in the presence of Co2+ using cyclic voltammetry (CV), rotating disk electrode (RDE), and rotating ring-disk electrode (RRDE) techniques in an effort to understand fuel cell cathode contamination caused by Co2+. Findings indicated that Co2+ could weakly adsorb on the Pt surface, resulting in a slight change in ORR exchange current densities. However, this weak adsorption had no significant effect on the nature of the ORR rate determining steps. The results from both RDE and RRDE indicated that the overall electron transfer number of the ORR in the presence of Co2+ was reduced, with ~9% more H2O2 being produced. We speculate that the weakly adsorbed Co2+ on Pt could react with the H2O2 intermediate and form a Co2+\u2013H2O2 intermediate, inhibiting the further reduction of H2O2 and thus resulting in more H2O2 production. The fuel cell performance drop observed in the presence of Co2+ could be attributed to the reduction in overall electron transfer number and the increase in H2O2 production. Higher production could intensify the attack by H2O2 and its radicals on membrane electrode assembly components, including the ionomer, carbon support, Pt particles, and membrane, leading to fuel cell degradation.Peer reviewed: YesNRC publication: Ye

Durability of PEM fuel cell cathode in the presence of Fe3+ and Al3+

The contamination effects of Fe\ub3\u207a and Al\ub3\u207a on the performance of polymer electrolyte membrane fuel cells were investigated by continuously injecting Fe\ub3\u207a or Al\ub3\u207a salt solution into the air stream of an operating fuel cell. Both metal ions individually caused significant cell performance degradation at a level of only 5ppmmol in air. In addition, elevated temperature accelerated fuel cell performance degradation in the presence of Fe\ub3\u207a. Moreover, the presence of Fe\ub3\u207a in an operating fuel cell resulted in the cell\u2019s sudden death, due to the formation of membrane pinholes that may have been promoted by the enhanced production of peroxy radicals catalyzed by Fe species. Half-cell tests in liquid electrolyte revealed that the presence of Al\ub3\u207a in the electrolyte changed the kinetics and mechanisms of the oxygen reduction reaction by reducing the kinetic current densities and the electron transfer number.Peer reviewed: YesNRC publication: Ye