Iridium and Iridium Oxide Performance in Electrolysis and Resolving Half- and Single-Cell Test Differences
Authors: Alia Shaun M , Ha Mai-Anh , Anderson Grace C. , Ngo Chilan , Pylypenko Svitlana , Larsen Ross E. 
Published: February 2020

In commercial electrolysis today, the cost of electricity input drives the cost of hydrogen production. Electrochemical water splitting, therefore, typically uses high catalyst loading and constant power input at high capacity. Catalyst development under these operating conditions, for cost reduction or durability improvement, are less immediate a focus. To reach hydrogen production targets, however, electrolyzers will need to be coupled directly with low-cost power sources to reduce feedstock costs. At that point, catalyst loading reductions are needed to reduce capital cost and catalyst efforts to evaluate material performance and durability become critical.[1-3]
We will present efforts comparing half- and single-cells and evaluating to what extent rotating disk electrodes can be used to project membrane electrode assembly performance and durability. In rotating disk electrodes, coating technique and test parameters have a clear influence on baseline activity and the observed properties of materials. Under specific conditions, changes to these variables can shift the activity of standard catalysts by orders of magnitude. Similarly, how membrane electrode assemblies are coated, including spray temperature, ink composition, and ionomer content, has an impact on their initial performance and long-term operation. Although kinetic activities in half- and single-cell tests do not match, half-cell testing appears to be a reasonable indicator of cell performance provided that robust baselines are used. Performances between the two techniques were correlated for a variety of material types, including supported catalysts, alloys, and multicomponent materials with consistent activity trends observed.
In certain cases, however, particularly for different surface types (metals, hydroxides, oxides) a disconnect was found between rotating disk electrodes and membrane electrode assemblies. Testing methodologies were explored to resolve these discrepancies and single-cell conditioning was found to incorporate aspects of half-cell durability testing. Modeling has been used to address performance differences between these surfaces, including: how surface and near-surface oxidation influences activity; and how that activity changes over time. By evaluating different catalysts and test parameters, we are looking to establish performance and durability guidelines for catalyst development efforts, and to share our perspective on how catalyst development and system controls factor into electrolysis at low loading and with intermittent operation. These tests have significant implications as electrolysis shifts toward low-cost hydrogen production coupled with renewable power inputs.
[1] 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.
[2] 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.
[3] 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.