Atmosphere-driven oriental regulation of Ru valence for boosting alkaline water electrolysis

Modulating the electronic characteristics of nanomaterials has been key to advancing sustainable energy technologies. In this study, we controlled the Ru electronic properties of NiRuOx by varying the calcination atmospheres (Air and Argon), resulting in two distinct electrocatalysts: NiRuOx-O2 with Ru4+ species and NiRuOx-Ar with Ru0 species as the main component. We established the relationship between the valence of Ru and its HER and OER catalytic activity as NiRuOx for example. Specifically, NiRuOx-Ar with metallic Ru demonstrates better alkaline HER activity with a smaller overpotential (94 mV) at 100 mA cm- 2 than NiRuOx-O2 with Ru4+ due to the reduced Ru0 superiority towards H*. Conversely, NiRuOx-O2 shows superior alkaline OER performance with only 275 mV overpotential at 100 mA cm- 2 compared with that of NiRuOx-Ar (383 mV) due to Ru4+ receiving electrons from Ni species and reduced Ru-O covalence. The NiRuOx-O2//NiRuOx-Ar electrolyzer in 1 M KOH achieves 10 mA cm- 2 at 1.475 V with 100 h durability, surpassing the RuO2//Pt/C cell (1.516 V). Revealing the correlation between Ru valence and activity offers important insights for the rational design of Ru-based catalysts for HER and OER.