Amorphous Ni-Fe-Se hollow nanospheres electrodeposited on nickel foam as a highly active and bifunctional catalyst for alkaline water splitting.

Developing earth-abundant highly efficient catalysts for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is indispensable for the widespread implementation of electrochemical water splitting to store renewable energy. Herein, amorphous bimetallic selenide (Ni-Fe-Se) hollow nanospheres electrodeposited on nickel foam (Ni-Fe-Se/NF) are developed as a bifunctional catalyst for the HER and OER. The HER and OER bifunctional activity of Ni-Fe-Se/NF outperforms those of monometallic Ni-Se/NF and Fe-Se/NF owing to the synergy of Ni and Fe in Ni-Fe-Se/NF. Moreover, the amorphous hollow spherical morphology of Ni-Fe-Se/NF increases the active site density and facilitates the mass transfer of electrolytes and H/O products. Ni-Fe-Se/NF drives a current density of 10 mA cm with an overpotential of ∼85 mV for the HER and 100 mA cm with an overpotential of ∼222 mV for the OER. As the HER and OER bifunctional catalyst, Ni-Fe-Se/NF can split alkaline water with total voltages of ∼1.52 V and ∼1.66 V at 10 mA cm and 100 mA cm, respectively, and remain stable over 50 hours of operation in 1 M KOH.