Oxygen-Inserted Top-Surface Layers of Ni for Boosting Alkaline Hydrogen Oxidation Electrocatalysis.

Abstract

Precisely tailoring the electronic structures of electrocatalysts to achieve an optimum hydroxide binding energy (OHBE) is vital to the alkaline hydrogen oxidation reaction (HOR). As a promising alternative to the Pt-group metals, considerable efforts have been devoted to exploring highly efficient Ni-based catalysts for alkaline HOR. However, their performances still lack practical competitiveness. Herein, based on insights from the molecular orbital theory and the Hammer-Nørskov d-band model, we propose an ingenious surface oxygen insertion strategy to precisely tailor the electronic structures of Ni electrocatalysts, simultaneously increasing the degree of energy-level alignment between the adsorbed hydroxide (*OH) states and surface Ni d-band and decreasing the degree of anti-bonding filling, which leads to an optimal OHBE. Through the pyrolysis procedure mediated by a metal-organic framework at a low temperature under a reducing atmosphere, the obtained oxygen-inserted two atomic-layer Ni shell-modified Ni metal core nanoparticle (Ni@Oi-Ni) exhibits a remarkable alkaline HOR performance with a record mass activity of 85.63 mA mg-1, which is 40-fold higher than that of the freshly synthesized Ni catalyst. Combining CO stripping experiments with ab initio calculations, we further reveal a linear relationship between the OHBE and the content of inserted oxygen, which thus results in a volcano-type correlation between the OH binding strength and alkaline HOR activity. This work indicates that the oxygen insertion into the top-surface layers is an efficient strategy to regulate the coordination environment and electronic structure of Ni catalysts and identifies the dominate role of OH binding strength in alkaline HOR.