On the Acid Stability of PGM-Free OER Catalyst for H2 Production in PEMWE

Abstract

Low temperature proton exchange membrane water electrolyzer (PEMWE) represents a critical technology for green hydrogen production. It offers the advantages of significantly higher current density and higher H2 purity, rendering it a preferred technology when high energy efficiency and low footprint are essential.Working in the oxidative and acidic environment under high polarization voltage, however, adds substantial demand to the electrode catalyst and the support. This is particularly the case at anode where the oxygen evolution reaction (OER) takes place. At present, the platinum group metal (PGM) materials such as Ir black or Ir oxide are catalysts of choice. Their high cost and limited reserve, however, adds a significant cost to PEM electrolyzer, which contributes to the overall expense of hydrogen production next only to the cost of electricity. Replacing Ir with earth-abundant transition metal oxides could help to reduce the electrolyzer system cost.Argonne National Laboratory has recently designed and prepared a new family of PGM-free OER catalyst for PEM electrolyzer. The new catalysts have high porosity and unique nanoarchitecture, and have demonstrated very promising activity and durability in both rotating disk electrode (RDE) and in operating PEMWE.The most challenging aspect of PGM-free OER catalyst is its stability in the acidic media. To this end, we conducted extensive structural characterizations as well as computational modeling. Particularly, in situ X-ray absorption spectroscopy combined with high resolution imaging revealed insightful information on the electronic and surface structural changes during the electrochemical reaction. Computational Pourbaix diagram also elucidated the catalyst stability under the acidic OER operating condition. Acknowledgement: This work is supported by U. S. Department of Energy, Hydrogen and Fuel Cell Technologies Office through Office of Energy Efficiency and Renewable Energy and by Office of Science, U.S. Department of Energy under Contract DE-AC02-06CH11357.