A New Class of Zn_{1 -x}Fe_x–Oxyselenide and Zn_{1- x}Fe_x–LDH Nanostructured Material with Remarkable Bifunctional Oxygen and Hydrogen Evolution Electrocatalytic Activities for Overall Water Splitting

The scalable and cost-effective H₂ fuel production via electrolysis demands an efficient earth-abundant oxygen and hydrogen evolution reaction (OER, and HER, respectively) catalysts. In this work, for the first time, the synthesis of a sheet-like Zn_{1- x}Fe_x–oxyselenide and Zn_{1- x}Fe_x–LDH on Ni-foam is reported. The hydrothermally synthesized Zn_{1- x}Fe_x–LDH/Ni-foam is successfully converted into Zn_{1- x}Fe_x–oxyselenide/Ni-foam through an ethylene glycol-assisted solvothermal method. The anionic regulation of electrocatalysts modulates the electronic properties, and thereby augments the electrocatalytic activities. The as-prepared Zn_{1- x}Fe_x–LDH/Ni-foam shows very low OER and HER overpotentials of 263 mV at a current density of 20 mA cm⁻² and 221 mV at 10 mA cm⁻², respectively. Interestingly, this OER overpotential is decreased to 256 mV after selenization and the HER overpotential of Zn_{1- x}Fe_x–oxyselenide/Ni-foam is decreased from 238 to 202 mV at 10 mA cm⁻² after a stability test. Thus, the Zn_{1- x}Fe_x–oxyselenide/Ni–foam shows superior bifunctional catalytic activities and excellent durability at a very high current density of 50 mA cm⁻². More importantly, when the Zn_{1- x}Fe_x–oxyselenide/Ni-foam is used as the anode and cathode in an electrolyzer for overall water splitting, Zn_{1- x}Fe_x–oxyselenide/Ni-foam(+)ǁZn_{1- x}Fe_x–oxyselenide/Ni-foam(-) shows an appealing potential of 1.62 V at 10 mA cm⁻². The anionic doping/substitution methodology is new and serves as an effective strategy to develop highly efficient bifunctional electrocatalysts.