Unveiling the reconstructed active phase of Ni3Se2 model for water splitting

Abstract

Nickel-based (Ni-based) compounds have been regarded as one of the most potential electrocatalysts for water splitting due to their tunable d-band electronic structures. However, the local structures of Ni-based electrocatalysts would change in situ during the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), which makes it difficult to identify and design active structures. In this study, we studied metallic Ni₃Se₂ films as model catalysts to figure out the structural change rules during HER and OER processes. According to the operando X-ray absorption fine structure (XAFS) spectroscopy and other experimental results, during the HER process, the active Ni sites at the surface tended to adsorb hydroxyl to form local Ni–OH environments and trigger further water dissociation with the assistance of Se sites as hydroxyl acceptors; during the OER process, the valence states of Ni increased with the increase in potential, proving that high-valence Ni centers in NiOOH activated species are beneficial in boosting OER catalytic activity.