In-situ surface reconstruction of single-crystal (NiFe)₃Se₄ nano-pyramid arrays for efficient oxygen evolution

Transition metal-based selenides (TMSe) are considered as efficient pre-electrocatalysts towards oxygen evolution reaction (OER). However, the key factor in determining the surface reconstruction of TMSe under OER condition is not yet clear. Herein, we uncover that the crystallinity of TMSe will obviously impact the conversion degree from TMSe to transition metal oxyhydroxides (TMOOH) during OER. A novel single-crystal (NiFe)₃Se₄ nano-pyramid array grown on NiFe foam is fabricated by a facile one-step polyol process, which exhibits an excellent OER activity and stability, only requiring 170 mV to reach a current density of 10 mA cm^-2 and can sustain for more than 300 h. In situ Raman spectrum studies reveals that the single-crystal (NiFe)₃Se₄ is partially oxidized on its surface during OER, generating a dense heterostructure of (NiFe)OOH/(NiFe)₃Se₄. Benefiting from the in situ formed heterointerface, the adsorption of OER intermediates on Ni active sites calculated by density functional theory (DFT) analysis is optimized, leading to the reduced energy barrier, which accounts for the enhanced intrinsic activity. This work not only reports a novel single-crystal (NiFe)₃Se₄ nano-pyramid array electrocatalyst with high-efficient OER performance, but also gains a deep insight into the role of the crystallinity of TMSe on the surface reconstruction during OER.