Catalyst development for low temperature water electrolysis has been pursued in the electrochemistry community. Booming research and development in this area are due in part to near-commercialization of fuel cell vehicles and potential adoption of renewable electricity for water electrolysis. Two types of reactions, oxygen evolution reaction (OER) and hydrogen evolution reactions (HER) have been widely studied. Studies on the OER prevail in both acidic and basic media, while the HER studies are predominant in basic media. The increasing research interests have been reflected in this recurring symposium. At Giner Inc., we have developed a variety of highly active and durable catalysts (e.g, Ir nanotubes, Ir supported on titanium oxide, cobalt oxide on nanocarbon) for both proton and anion exchange membrane electrolysis.

This work aims to provide insightful guidance on the catalyst development from an industrial point of view. Compared to fuel cells, the catalyst cost in a water electrolyzer is less significant due to prohibitive cost of feedstock (electricity). Therefore, when regular (expensive) electricity is used for water electrolysis, the catalyst studies should be centered on the intrinsic activity improvement to lower the over-potential so as to increase the energy efficiency. On the other hand, when the renewable (low-price) electricity becomes available, the catalyst studies should be focused on the mass activity to lower the platinum-group metal (PGM) loading. Provided that the global supply of industry standard OER catalyst Ir is very limited, the development of non-PGM catalysts for both proton and anion exchange membrane electrolysis is very meaningful.

The second consideration is the catalyst performance in a real electrolyzer cell. The vast majority of research work is on the rotating disk electrodes (RDE) using liquid electrolyte. However, the RDE data may not be necessarily reproduced in real electrodes that use ionomer as an ion conductor. The interaction of the catalyst with other components (e.g., membrane, ionomer and gas diffusion media) determines electrode morphology and structure thus tremendously impacting the electrode performance.

The last consideration is the long-term durability of the catalysts, which is equal and even more important than the initial performance, from an industrial point of view. However, unlike the well-established durability benchmarks for fuel cells, the catalyst durability of water electrolyzer has not been thoroughly studied. Therefore, accelerated stress tests (AST) need to be implemented to evaluate the long-term durability of the catalysts.

Acknowledgement: The financial support is from the Department of Energy under the Contract Grant DE-SC0007471.