Phase Transition in Cobalt Selenide with a Greatly Improved Electrocatalytic Activity in Hydrogen Evolution Reactions
Jianpeng Sun, Lifang Jiao, Zizhen Li, Xiude Hu, Hongcun Bai, Xiangchao Meng
Abstract
Surface properties such as electronic structures and valence state determine the electrocatalytic activity in hydrogen evolution reactions (HERs). Herein, we prepared a novel orthorhombic CoSe2-NC (o-CoSe2-NC) electrocatalyst from hexagonal CoSe-NC (h-CoSe-NC) via a phase-transition method. As-prepared o-CoSe2-NC exhibited excellent HER activity with 147 mV at 10 mA cm–2 and a high stability (24 h). Density functional theory results revealed that the active sites for h-CoSe-NC in electrocatalytic hydrogen evolutions were the anion Se sites (ΔGH* = 0.34 eV). After the phase transition, Co sites (ΔGH* = 0.20 eV) in o-CoSe2-NC became more active than Se sites. Moreover, the d-band central of Co in o-CoSe2-NC was closer to the Fermi level than that of h-CoSe-NC after the phase transition. Also, o-CoSe2-NC exhibited a metallic behavior with excellent electrical conductivity. This work not only prepared cost-effective cobalt selenide-based electrocatalysts but also highlighted the significance of the crystal phase in electrocatalytic hydrogen evolutions.