Sea urchin-like cobalt selenide/N-doped carbon dots as efficient bifunctional electrocatalysts for water electrolysis

Designing high-efficient, durable and low-cost bifunctional electrocatalysts is of great significance to realize green hydrogen production by electrolytic water splitting. Herein, 3D sea urchin-like CoSe2 arrays modified with nitrogen doped carbon dots grown on Ni foam (CoSe2/NCDs/NF) was successfully constructed via an easy hydrothermal reaction combined with anion exchange process. The designed CoSe2/NCDs/NF catalyst exhibits enhanced catalytic activity and stability for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in different electrolyte, with reduced overpotential of 268 mV to afford 70 mA cm-2 for OER and low overpotentials of 94/102 mV in acid/alkaline solution at 10 mA cm-2 for HER, respectively. Impressively, when assembling a two-electrode alkaline electrolyzer with CoSe2/NCDs/NF simultaneously acts as the anode and cathode, the cell voltage of only 1.61 V is obtained to drive 30 mA cm-2, with robust stability(for at least 70 h). The excellent catalytic activity is attributed that the 3D sea urchin-like structure significantly augments exposure of active sites and facilitates mass/charge transport; the synergy effect of NCDs and CoSe2 effectively promotes electron transfer, optimizes electronic environment, and adjusts the adsorption/desorption free energy of the intermediates; and in situ growth of materials and introduction of carbon materials ensures structural stability and enhances the electrical conductivity. This work provides a feasible guidance for the rational design of transition metal selenide catalysts with outstanding performance.