Nanoporous nickel with rich adsorbed oxygen for efficient alkaline hydrogen evolution electrocatalysis

Abstract

Sluggish water dissociation kinetics severely limits the rate of alkaline electrocatalytic hydrogen evolution reaction (HER). Therefore, finding highly active electrocatalysts and clarifying the mechanism of water dissociation are challenging but important. In this study, we report an integrated nanoporous nickel (np-Ni) catalyst with high alkaline HER performance and the origin of the corresponding enhanced catalytic activity. In 1 mol L−1 KOH solution, this np-Ni electrode shows an HER overpotential of 20 mV at 10 mA cm−2, along with fast water dissociation kinetics. The excellent performance is not only attributed to the large surface area provided by the three-dimensional interconnected conductive network but also from the enhanced intrinsic activity induced by the unique surface properties. Further studies reveal that the types of oxygen species that naturally form on the Ni surface play a key role in water dissociation. Remarkably, when the lattice oxygen almost disappears, the Ni surface terminates with adsorbed oxygen (Oads), exhibiting the fastest water dissociation kinetics. Density functional theory calculation suggests that when Oads acts as the surface termination of Ni metal, the orientation and configuration of polar water molecules are strongly affected by Oads. Finally, the H—OH bond of interfacial water molecules is effectively activated in a manner similar to hydrogen bonding. This work not only identifies a high-performance and low-cost electrocatalyst but also provides new insights into the chemical processes underlying water dissociation, thus benefiting the rational design of electrocatalysts.