2, Los Alamos National Laboratory, Los Alamos, New Mexico, United States
3, Colorado School of Mines, Golden, Colorado, United States
In commercial electrolysis, the cost of electricity input drives the cost of hydrogen production. Electrolysis, therefore, is typically run at high catalyst loading and constant power input over long periods of time. Lowering water-splitting hydrogen production costs to a level comparable to steam methane reformation requires: coupling electrolysis with low-cost power input (wind, solar) to reduce feedstock costs; and minimizing capital cost at lower capacity.[1,2] Part of reducing capital cost includes reducing catalyst loading and while minimal durability loss is seen with thick catalyst layers, losses become more apparent with loading reductions.
Presented efforts include evaluating load-follow operation, start-stop operation, and contaminants, studying relevant mechanisms for loss in half-cell tests and how these losses are observed in single-cell tests. Electrolyzer durability was evaluated at low iridium-anode loading (0.1-0.5 mg cm-2) and with different power inputs (potentials, intermittency) to focus on systems aspects needed to significantly reduce hydrogen production costs. Within load-follow operation, iridium loss was driven by dissolution. Although higher potential accelerated single-cell loss, cycling (square/triangle wave) also increased the rate of performance decay since rapidly increasing input resulted in localized potential spikes within the catalyst layer. While start-stop operation accelerates loss through a variety of pathways (dry operation on membrane, pressure cycling on membrane and hydrogen crossover), these efforts focused on the effect of potential excursions on the catalyst. Simulated hard-stops were more detrimental to iridium durability than load-follow, likely due to surface and near-surface reduction increasing dissolution rates. The effect of contaminants was also evaluated based on likely metals added with water input. Contaminant effects in half-cell tests were observed but were relatively small and may have been due to the large amount of free electrolyte and desorption on iridium at high potential. Losses were more significant in single-cells and may have been exacerbated by contaminants blocking within the membrane and plating the cathode.
Several catalyst types have been tested, including metals (metal/hydroxide) and oxides with supports, high surface area, multicomponent, and alloys. These materials have been studied in half-cells for the activity improvement mechanism and in single-cells to evaluate potential advantages/disadvantages in electrolysis performance and durability. By including different catalyst types, we are looking to establish performance/durability guidelines and perspectives on how catalyst development and system controls factor into low temperature electrolysis at low loading and with intermittency. These tests have significant implications with a shift toward low-cost hydrogen production through electrolysis coupled with renewable power inputs.
 Alia, S. M., H2@Scale: Experimental Characterization of Durability of Advanced Electrolyzer Concepts in Dynamic Loading. Department of Energy, U. S., Ed. https://www.hydrogen.energy.gov/pdfs/review18/tv146_alia_2018_p.pdf, 2018.
 Denholm, P.; O’Connell, M.; Brinkman, G.; Jorgenson, J. Overgeneration from Solar Energy in California: A Field Guide to the Duck Chart; Vol. NREL/TP-6A20-65023; National Renewable Energy Laboratory: Golden, CO, 2015. Available at the following: http://www.nrel.gov/docs/fy16osti/65023.pdf.
 Alia, S. M.; Rasimick, B.; Ngo, C.; Neyerlin, K. C.; Kocha, S. S.; Pylypenko, S.; Xu, H.; Pivovar, B. S. J. Electrochem. Soc. 2016, 163, F3105−F3112.