Metallic NiPS3@NiOOH Core–Shell Heterostructures as Highly Efficient and Stable Electrocatalyst for the Oxygen Evolution Reaction

Abstract

We report metallic NiPS 3 @NiOOH core–shell heterostructures as an efficient and durable electrocatalyst for the oxygen evolution reaction, exhibiting a low onset potential of 1.48 V (vs RHE) and stable performance for over 160 h. The atomically thin NiPS 3 nanosheets are obtained by exfoliation of bulk NiPS 3 in the presence of an ionic surfactant. The OER mechanism was studied by a combination of SECM, in situ Raman spectroscopy, SEM, and XPS measurements, which enabled direct observation of the formation of a NiPS 3 @NiOOH core–shell heterostructure at the electrode interface. Hence, the active form of the catalyst is represented as NiPS 3 @NiOOH core–shell structure. Moreover, DFT calculations indicate an intrinsic metallic character of the NiPS 3 nanosheets with densities of states (DOS) similar to the bulk material. The high OER activity of the NiPS 3 nanosheets is attributed to a high density of accessible active metallic-edge and defect sites due to structural disorder, a unique NiPS 3 @NiOOH core–shell heterostructure, where the presence of P and S modulates the surface electronic structure of Ni in NiPS 3, thus providing excellent conductive pathway for efficient electron-transport to the NiOOH shell. These findings suggest that good size control during liquid exfoliation may be advantageously used for the formation of electrically conductive NiPS 3 @NiOOH core–shell electrode materials for the electrochemical water oxidation.