Hydrogen production through water electrolysis using renewable electricity is a green route toward net-zero emission. However, the performance is limited by the sluggish oxygen evolution reaction (OER). To design and engineer electrocatalysts with higher and higher activity, the first step is to identify catalytic active sites and reaction mechanisms. In this presentation, I will delve into the active sites and reaction mechanics of OER Ni-based oxyhydroxides in alkaline media. I will show that under extremely oxidative conditions, the active phases are typically not as-prepared precursor phases, as an oxidative phase transition may occur. Under OER conditions, surfaces are likely not pristine but are in equilibrium with the electrolyte and electrode potential, i.e., they are covered by reaction intermediates. Thus, OER goes through Mars van Krevelen mechanics, rather than traditionally assumed Langmuir-hinshelwood mechanics. Also, active sites can be described by a synergistic dual-metal reaction center. This center is characterized by switching active sites during OER, and through simple surface Fe doping and the formation of dual Fe-Fe centers, they increase OER activity by over two orders of magnitude. This fundamental understanding not only elucidates the high OER activity of Ni (oxy)hydroxides with Fe-doping but also provides principles for developing OER catalysts with further improved performance. If time permits, I will also introduce our recent work in acidic water electrolysis.
