There is a need to decrease our dependence on fossil fuels for producing energy and chemicals, and there is a great interest in using sunlight to drive fuel-forming reactions to produce solar fuels. Solar fuels are important future energy carriers and provide a way to store solar energy, and this makes for a theme that is continuing to move up the global research agenda. Alternatively, with solar and wind power creating increasingly large amounts of electricity, an important question is how can we take advantage of the expanding increase of renewable electricity for catalysis? By applying a voltage in electrocatalysis, we can harness the flow of electrons to form and break chemical bonds, with the remaining challenge to carry out this catalysis with high selectivity and energy efficiency utilizing sustainable electrocatalyst materials.

Renewable H₂ technologies could provide alternatives to fossil fuels, and this could be enabled by H₂ production from water electrolysis and generation of electricity using H₂ fuel cells. However, lack of highly active, stable, earth-abundant electrocatalysts for carrying out the hydrogen evolution reaction (HER) in water electrolyzers and the hydrogen oxidation reaction (HOR) in fuel cells, is a major technical challenge for developing economical polymer electrolyte membrane (PEM)-based electrolyzers and fuel cells. Carrying out these reactions in strongly acidic conditions is desirable because of the advantages of using proton exchange membranes, including compact system design, lack of liquid electrolyte, high current density and energy efficiency, and high gas purity. Recently, we have found a material that demonstrates excellent HER and HOR activities in acids using non-platinum group metal (PGM) catalysts [1]. Processing hafnium oxide with an atmospheric nitrogen plasma forms an acid-insoluble hafnium oxynitride material. We propose that under electrochemical environments this material is transformed into an active oxynitride hydroxide that demonstrates unprecedented high catalytic activity and stability for both HER and HOR in strong acidic media for earth-abundant materials. The zero onset potentials and high current densities demonstrate that this material is a promising alternative to Pt. This opens up new opportunities to develop technologically and economically viable PEM-fuel cells, regenerative fuel cells, and electrolyzers. Furthermore, these results have broad implications for using nitrogen incorporation (e.g. by nitrogen plasma treatment) to activate other non-conductive compounds and films to form new active electrocatalysts.

1. X. Yang, F. Zhao, R.S. Selinsky, Z. Chen, Y.-W. Yeh, N. Yao, C.G. Tully, and B.E. Koel, Nature Communications, 10, 1543−1−8 (2019).