Understanding the Oxygen Evolution Reaction on a Two‐Dimensional NiO2 Catalyst

Abstract Solar water splitting is a promising technology to store energy in chemicals but the technology suffers from a lack of efficient catalysts. Nickel oxyhydroxide (NiOOH) is an outstanding catalyst for the oxygen evolution reaction (OER). NiOOH is composed of partially hydrogenated nickel oxide (NiO 2 ) two‐dimensional (2D) sheets that are stacked together. Owing to recent advancements in fabrication it is possible to isolate a single layer of the material. Such 2D catalytic systems are extremely promising, especially due to the wider exposed surface. However their reactivity is not completely understood, and density functional theory (DFT) is an appropriate tool to address that issue. In the current paper we use DFT to model several OER mechanisms. We show that the catalytic activity of these 2D materials is not limited to the defect sites and to the edges, as usually assumed, but rather many reaction centers are available on the NiO 2 surface itself. In addition, we will provide evidence for the inhibiting effect of hydrogen ad‐atoms on such layers, thus supporting the necessity of operating in highly basic conditions. The new insights that we are providing here on NiO 2 reactivity, and the detailed understanding of the surface mechanisms regarding OER processes, will be key for further developments of 2D tailored catalysts. Indeed, as a main outcome of our work, NiO 2 sheets are found to be significantly more reactive than bulk NiOOH itself.