Synergistic effect of Co and Fe bimetallic oxides/hydroxides composite structure as a bifunctional electrocatalyst for enhancing overall water splitting performance

Designing a bifunctional electrocatalyst with low overpotential and rapid charge reaction kinetics is of great significance to solve the energy crisis and environmental pollution in society today. In this work, the "flower-sphere" CoFe-LDH/CoFe2O4 composite structure bifunctional electrocatalyst with high efficiency and stability was successfully prepared on porous Ni foam by a two-step hydrothermal method. The as-prepared composite structure array electrocatalyst demonstrates superior catalytic activities of HER and OER, because of the unique "flower-sphere" structure composed of nanosheets and the synergistic effect of bimetallic oxides/hydroxides. CoFe-LDH/CoFe2O4/NF electrode can drive a current density of 10 mA/cm2 with low overpotential of 106 mV and 162 mV for HER and OER, respectively. What's more, it also only needs overpotential of 341 mV and 400 mV for HER and OER to deliver a large current density of 100 mA/cm2, respectively. In the overall water splitting with CoFe-LDH/CoFe2O4/NF electrode as cathode and anode, a current density of 10 mA/cm2 was achieved at a bias voltage of only 1.55 V. This work may provide an optimal design idea for the application of CoFe bimetallic heterojunction electrocatalysts in actual electrolytic water.