High entropy spinel oxide (Ni0.2Co0.2Zn0.2Cu0.2Mg0.2)Fe2O4 nanofibers for efficient oxygen evolution reaction

Developing efficient oxygen evolution reaction (OER) catalysts was urgent for producing clean hydrogen energy. High-entropy oxides (HEOs) have become a focus of interest, were widely used for OER. HEOs would provide multiple degrees of freedom, allowing modification of the composition and atomic arrangement to fine-tune the electronic structure or active sites to optimize catalytic activity in OER. However, achieving multi-ion crystallization in HEOs while maintaining porous or nanostructured morphology still remained a challenge. In this work, (Ni0.2Co0.2Zn0.2Cu0.2Mg0.2)Fe2O4 nanofibers were prepared by the electrospinning method. (Ni0.2Co0.2Zn0.2Cu0.2Mg0.2)Fe2O4 exhibited enhanced OER activity (η10 =286 mV, Tafel slope =136 mV dec-1) and strong catalytic stability compared with single, binary, ternary, and quaternary oxides. The oxygen vacancies generated during the OER were confirmed by EPR experiments. XPS, TEM and In situ Raman spectroscopy confirmed the self-reconstruction of (Ni0.2Co0.2Zn0.2Cu0.2Mg0.2)Fe2O4 during the OER. DFT calculations revealed that the high entropy structure would promote the shift of the D-band center towards the Fermi level and reduce the ΔGmax, which were consistent with the catalytic performance results. This research demonstrated the significant importance of high-entropy concept to boost the performance of high entropy materials for electrochemical application.