Anode Catalyst Durability in Low Temperature Electrolysis and the Impact of Hydrogen Crossover

Abstract

Anode Catalyst Durability in Low Temperature Electrolysis and the Impact of Hydrogen CrossoverShaun Alia,1 Kimberly S. Reeves,2 Haoran Yu,2 Elliot Padgett,1 Deborah Myers,3 David Cullen2 1 Chemical and Material Sciences Center, National Renewable Energy Laboratory, Golden, Colorado 2 Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 3 Chemical Sciences and Engineering Division, Argonne National Laboratory, Lemont, IllinoisHydrogen has unique advantages as an energy carrier, with a high energy density and abilities for long term storage and conversion between electricity and chemical bonds. Although hydrogen currently has a significant role in transportation and agriculture, its use in energy consumption overall has been limited, particularly in the case of electrochemical water splitting. With decreasing electricity prices, electrolysis cost reductions can be achieved and allow for an opportunity for greater use.(1) While load-following renewable power sources can reduce feedstock cost, further cost reductions can be achieved by reducing the platinum group metal (PGM) content.(2) Efforts are needed to understand and mitigate electrolyzer degradation, particularly when accounting for lower PGM loadings and intermittent operation.Previous efforts have developed anode catalyst-specific accelerated stress tests for intermittent operation that focused on catalyst layer changes and interfacial loss with standard material sets. (3) Under cycled testing between open circuit and operating potentials, performance losses primarily appeared through kinetics and were accompanied by anode catalyst dissolution, migration, and interfacial tearing. Performance losses were further aggravated by a reduced anode catalyst loading or a thinner catalyst layer, an increase in cycling frequency, and an increase in cell potential.In this study, the impact of hydrogen crossover on anode catalyst durability during device shutdown was evaluated and found to significantly increase performance loss through catalyst reduction and higher dissolution kinetics when operation resumed. Large drops in kinetics accounted for the majority of cell performance changes and corresponded to increased anode catalyst migration and aggregation within the catalyst layer. Compared to intermittent operation, however, ohmic losses disproportionately grew and higher rates of interfacial tearing were found ex-situ, particularly when simulated shutdowns incorporated brief periods of water deprivation and drying. While various anode catalyst types were evaluated for their potential in materials mitigation, high loss rates were found in all cases. Sub-stoichiometric oxides may be a driver for performance losses due to increase subsurface metal dissolution once near-surface oxides are reduced. Understanding catalyst layer degradation and the impact of shutdowns is critical to developing catalyst- and device-level accelerated stress tests and forming operational mitigation strategies.[4][1] B. Pivovar, N. Rustagi and S. Satyapal, The Electrochemical Society Interface, 27, 47 (2018).[2] K. Ayers, N. Danilovic, R. Ouimet, M. Carmo, B. Pivovar and M. Bornstein, Annual Review of Chemical and Biomolecular Engineering, 10, 219 (2019).[3] S. M. Alia, S. Stariha and R. L. Borup, J. Electrochem. Soc., 166, F1164 (2019).[4] Electron microscopy was performed at the Center for Nanophase Materials Sciences, which is a DOE Office of Science User Facility.