Cold plasma synthesis of phosphorus-doped CoFe₂O₄ with oxygen vacancies for enhanced OER activity

Spinel-type metal oxides are promising electrocatalysts for the oxygen evolution reaction (OER) due to their unique electronic structure and low cost. Herein, we induced oxygen vacancies and doped phosphorus into CoFe₂O₄ using cold plasma. The abundant oxygen vacancies enhanced hydrophilicity and modified the electronic structure of CoFe₂O₄, while the phosphorus doping formed numerous new active centers. The doped P and formed FeP promoted the charge transfer and improved the conductivity of the catalyst. The phosphorus-doped CoFe₂O₄ exhibited exceptional OER activity with an overpotential of 180 mV at 10 mA cm^-2 and a Tafel slope of 65.8 mV dec^-1 in an alkaline electrolyte. DFT calculations confirmed that phosphorus doping can improve the charge distribution near the Fermi level and optimize the d-band center position.