Rational construction of uniform CoS/NiFe2O4 heterostructure as efficient bifunctional electrocatalysts for hydrogen evolution and oxygen evolution reactions

Enhanced oxygen evolution performance of iron-nickel oxide catalyst through dual-defect engineering

Transition metal oxides have been extensively investigated for oxygen evolution reaction (OER). While the introduction of oxygen vacancies (V_o) was found to be an effective way to enhance the electrical conductivity and the OER electrocatalytic activity of transition metal oxides, the oxygen vacancies are easily damaged during the long-term catalytic process, resulting in rapid decay of the electrocatalytic activity. Herein, we proposed the strategy of dual-defect engineering to enhance the catalytic activity and stability of NiFe₂O₄ by filling the oxygen vacancies of NiFe₂O₄ with phosphorus atoms. The filled P atoms could form coordination with iron and nickel ions to compensate the coordination number and optimize the local electronic structure, which not only enhances the electrical conductivity but also improves the intrinsic activity of the electrocatalyst. Meanwhile, the filling of P atoms could stabilize the V_o and thus improving the cycling stability of the material. The theoretical calculation further demonstrates that the improvement in conductivity and intermediate binding by P refilling remarkably contributes to enhancing the OER activity of NiFe₂O₄-V_o-P. Benefiting from the synergistic effect of filled P atoms and V_o, the derived NiFe₂O₄-V_o-P exhibits fascinating activity with ultra-low OER overpotentials of 234 and 306 mV at 10 and 200 mA cm^-2, together with the good durability for 120 h at relatively high current density of 100 mA cm^-2. This work sheds light on the design of high-performance transition metal oxide catalysts through defect regulation in the future.