Phase Control of Cobalt Selenide: Unraveling the Relationship Between Phase Property and Hydrogen Evolution Catalysis

The development of phase engineering still confronts challenges including controlled synthesis of desired phase structures and unraveling of inner mechanism for phase-dependent applications. Herein, taking CoSe2 as a prototype, a facile wet-chemical method is developed to synthesize metastable orthorhombic phase CoSe2 (o-CoSe2). In the meantime, stable cubic phase CoSe2 (c-CoSe2) can be prepared by phase transition from o-CoSe2 using a general annealing approach. It is demonstrated that CoSe2 exhibits distinct phase-dependent hydrogen evolution performance in photo- and electrocatalysis. In electrocatalytic reaction, o-CoSe2 shows an overpotential of 300 mV better than c-CoSe2 (365 mV) at -10 mA cm(-2) in acid solution. Unlike electrocatalysis, as cocatalyst in photocatalytic hydrogen evolution, c-CoSe2/TiO2 exhibits a roughly 4.5-folds higher hydrogen evolution rate (12.001 mu mol h(-1)) than o-CoSe2/TiO2 (2.601 mu mol h(-1)). Combined with comprehensive theoretical and experimental analysis, it has been proposed that appropriate hydrogen adsorption ability of o-CoSe2 contributes to efficient electrocatalysis, whilst fast interfacial charge migration between TiO2 photo-harvester and c-CoSe2 cocatalyst is the dominating factor for photocatalysis. This article demonstrates the feasibility of improving catalytic activity of CoSe2 by phase engineering, and also, provides guidance into unmasking the relationship between phase structure and hydrogen evolution catalysis.

Automated summary

This study presents a facile wet-chemical method for synthesizing metastable orthorhombic phase CoSe2 (o-CoSe2) and stable cubic phase CoSe2 (c-CoSe2). The phase-dependent hydrogen evolution performance of CoSe2 in photo- and electrocatalysis is demonstrated. The results show that o-CoSe2 exhibits better electrocatalytic performance while c-CoSe2 shows higher photocatalytic hydrogen evolution rate. The study provides insights into the relationship between phase structure and hydrogen evolution catalysis.