Coupling nonstoichiometric Cu2−xSe with stable Cu2Se berzelianite for efficient synergistic electrocatalytic hydrazine-assisted water splitting

Abstract

Electrochemical overall water splitting for sustainable hydrogen generation is severely hindered by anode water electrooxidation with sluggish kinetics. Thus, using the thermodynamically favorable hydrazine oxidation reaction (HzOR) to substitute the oxygen evolution reaction (OER) has attracted ever-growing attention. Herein, well-defined copper selenide nanoflakes, in situ grown on copper foam (termed Cu_xSe/CF), were synthesized by a one-step selenization strategy, which are composed of nonstoichiometric Cu_2−xSe with stable Cu₂Se berzelianite that show remarkable bifunctional activities for the hydrogen evolution reaction (HER) and HzOR electrocatalysis. Investigations into the mechanisms uncovered that the high copper deficiencies in the Cu_2−xSe phase make it both an excellent electron donor and acceptor, leading to faster electron transfers across the catalyst (electrode)–electrolyte interface, which greatly boosts the reaction kinetics of HER and HzOR processes. Meanwhile, the Cu₂Se berzelianite phase plays a pivotal role in the long-term electrocatalytic operation for the HER and HzOR. Encouraged by this synergistic advantage, the Cu_xSe/CF catalysts were further employed as good bifunctional catalysts for electrocatalytic hydrazine-assisted overall water splitting with a low cell voltage of 0.49 V at 25 mA cm⁻², as well as having good stability over 20 h, which indicates the broad potential for future industrialization of a sustainable hydrogen-based society.