Measurement of the Protonic and Electronic Conductivities of PEM Water Electrolyzer Electrodes

Abstract

Reducing anode catalyst layer proton-and electrontransport resistances in polymer electrolyte membrane water electrolyzers is critical to improving its performance and maximizing catalyst utilization at high current density. A hydrogen pump technique is adapted to measure the protonic conductivity of IrO x -based catalyst layers. The protonic resistance of the catalyst layer is obtained by subtracting the protonic resistance of an assembly of two NRE211 membranes hot-pressed together from an assembly of two NRE211 membranes with an IrO x intermediate layer. The through-plane and in-plane electronic conductivities were also measured using two-and four-probe methods, respectively. Using these techniques, the protonic and electronic conductivities of the IrO x catalyst layers with varying Nafion loading were measured. The results show that the limiting charge-transport phenomena in the IrO x catalyst layer can be either proton or electron transport, depending on the ionomer loading in the catalyst layer. These results are validated by numerical simulation, as well as by comparison to the high-frequency resistance of an electrolyzer with the same layer.

Nanoporous Iridium Nanosheets for Polymer Electrolyte Membrane Electrolysis

“…This results in a higher in‐plane and through‐plane resistivity compared to fuel cell catalyst layers employing carbon supported Pt. [ 13 ] Full realization of the importance of electronic conductivity, distinctly different from protonic conductivity, in influencing current distributions, reaction overpotentials, and overall PEMWE stack efficiency has only recently started to receive sufficient attention. [ 13–15 ] Efficiency losses are exacerbated as anode catalyst loading decreases and ionomer:catalyst ratios are shifted to improve protonic conductivity through the electrode.…”

“…[ 13 ] Full realization of the importance of electronic conductivity, distinctly different from protonic conductivity, in influencing current distributions, reaction overpotentials, and overall PEMWE stack efficiency has only recently started to receive sufficient attention. [ 13–15 ] Efficiency losses are exacerbated as anode catalyst loading decreases and ionomer:catalyst ratios are shifted to improve protonic conductivity through the electrode. [ 13–15 ] Current strategies to mitigate resistive losses in oxide‐based catalyst layers include: refining catalyst morphology to improve both utilization and inter‐particle contact and contact with the gas diffusion media, [ 6,15,16,21 ] inclusion of microporous layers to improve contact between the gas diffusion media and the catalyst layer, [ 5,15,17,18 ] addition of supporting materials to improve electrical contact and lower resistivity throughout the catalyst layer, [ 14,19,20 ] etc.…”

Insights into Interfacial and Bulk Transport Phenomena Affecting Proton Exchange Membrane Water Electrolyzer Performance at Ultra‐Low Iridium Loadings

“…[ 16 , 17 , 18 ] This narrative is at odds with recent work showing that i) oxygen transport through the titanium PTL may be a crucial limiting factor contributing to performance decline, [ 19 , 20 ] ii) high performance at ultra‐low loadings without MPLs is possible, [ 5 ] iii) catalyst layer ionic resistance dominates over electronic resistance when ionomer volume fraction is higher than 20%. [ 21 ]…”

Impact of Power Converter Current Ripple on the Degradation of PEM Electrolyzer Performances

“…The leading hypothesis is titanium passivation in the presence of oxygen at the anode side. This insulating layer on the titanium surface increases the contact resistance [42][43][44]; this measurement increase should be further investigated to test this phenomenon [39,45,46], which was not realized in this study.…”

“…These bubbles are supposed to be flushed out during changes in potential, resulting in the observed recovery. Periodically reducing or stopping the input current could be used as a specific dynamic operation to improve the performance and durability of a PEM [13,46].…”