In-situ interfacial engineering of Co(OH)2/Fe7Se8 nanosheets to boost electrocatalytic water splitting

[Display omitted] •Two-dimensional Co(OH)2/Fe7Se8 nanosheets heterostructure is prepared.•Rich interfaces are constructed via self-transformation and in-situ selective selenization.•The nanointerface interaction of Co(OH)2/Fe7Se8 regulates the electronic structure of Co atoms.•The optimized d-band center and lower hydrogen adsorption energy favor for enhanced OER and HER.•Co(OH)2/Fe7Se8 nanosheets exhibits water splitting activity with the overpotential of 1.62 V. Rational design of bi-functional catalysts with desirable activity and stability remains a challenge for overall water splitting. Herein, two-dimensional Co(OH)2/Fe7Se8 nanosheets are prepared via self-transformation and in-situ selective selenization to construct rich heterogeneous interfaces. The in-situ interfaces induced by Fe7Se8 assist to regulate electronic structure of Co(OH)2/Fe7Se8 heterostructure. The incorporation of Fe species along with selective selenization offer strong interfacial coupling effect between Co(OH)2 and Fe7Se8. The in-situ formed interfaces contribute to optimized d-band center, lower energy barrier of intermediates and higher desorption capability of intermediates. Hence, the Co(OH)2/Fe7Se8 nanosheets exhibit superb electrocatalytic activity for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), requiring overpotentials of 183 and 278 mV at 10 mA cm−2 in 1.0 M KOH solution, respectively. In addition, the Co(OH)2/Fe7Se8 electrode requires only 1.62 V at 10 mA cm−2 in a two-electrode assembled electrolyzer, suggesting the promising application as overall water splitting electrocatalysts.