Universal phase transformation of Ni–Se electrocatalysts induced by an electrochemical activation strategy for a significantly enhanced alkaline hydrogen evolution reaction

Abstract

The in situ reconstruction of electrocatalysts with the changes in the crystal structure and composition is a universal process, enabling the modulation of active sites for high catalytic performance. Therefore, tracking the evolution of nominal catalysts is of critical importance for the identification of the real active components and rational design of highly efficient electrocatalysts. Herein, a general electrochemical activation strategy is reported to induce the phase transformation from hexagonal Ni_0.85Se to hexagonal NiSe and rhombohedral Ni₃Se₂ and consequently a core–shell structure with NiSe with low crystallinity in the core and short-range ordered Ni₃Se₂ on the surface was generated due to Se leaching. The changes of the composition and structure were systematically tracked and more Se vacancies were formed during the activation process, enabling optimization of the electronic structure of the resulting electrocatalyst for an efficient alkaline hydrogen evolution reaction (HER). Promisingly, it was demonstrated that the phase transformation caused by the electrochemical activation strategy is universal regardless of the preparation method and the crystal structure with even higher Se content. This work provides constructive insight into the evolution of selenides during electrochemical measurements and will guide the rational design of efficient catalysts for various applications including water splitting for hydrogen production.