In situ growth of Co_0.85Se nanoflakes on Co foam as bifunctional electrocatalysts for water splitting

Transition metal selenides supported on three-dimensional metal foams have received increasing attention as noble metal-free electrocatalysts for water splitting. Herein, we for the first time present a facile one-pot hydrothermal approach for in situ growth of vertically aligned and interconnected Co_0.85Se nanoflakes on cobalt foam (denoted as Co_0.85Se@Co foam). The as-prepared Co_0.85Se@Co foam demonstrates excellent electrocatalytic activity for hydrogen evolution reaction in alkaline electrolyte, demanding a low overpotential of 100 mV to achieve the current density of 10 mA cm⁻², a Tafel slope of 165 mV dec⁻¹, and good durability. It also displays good catalytic performance toward oxygen evolution reaction with an overpotential of 360 mV at the current density of 50 mA cm⁻², and a Tafel slope of 81.6 mV dec⁻¹. The good electrocatalytic performance of Co_0.85Se@Co foam is largely attributed to the direct growth of active Co_0.85Se nanoflakes on Co foam with sufficient active sites, the seamless integration of Co_0.85Se nanoflakes and three-dimensionally porous Co foam substrate for efficient electrons and ions transport.