A New Class of Zn1 -x Fex -Oxyselenide and Zn1- x Fex -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 Zn1- x Fex -oxyselenide and Zn1- x Fex -LDH on Ni-foam is reported. The hydrothermally synthesized Zn1- x Fex -LDH/Ni-foam is successfully converted into Zn1- x Fex -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 Zn1- x Fex -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 Zn1- x Fex -oxyselenide/Ni-foam is decreased from 238 to 202 mV at 10 mA cm-2 after a stability test. Thus, the Zn1- x Fex -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 Zn1- x Fex -oxyselenide/Ni-foam is used as the anode and cathode in an electrolyzer for overall water splitting, Zn1- x Fex -oxyselenide/Ni-foam(+)ǁZn1- x Fex -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.