A facile Mo doping strategy for high-entropy spinel oxide towards efficient oxygen evolution reaction

Hydrogen production via water electrolysis is limited by the high energy barrier of the oxygen evolution reaction (OER). As an emerging oxide material, high-entropy oxides (HEOs) are regarded as promising OER electrocatalysts owing to the multielement synergistic effect. Herein, a facile approach is proposed to synthesize Mo-doped high-entropy spinel oxide Mo-(FeCoNiCrMn) 3 O 4 nanoparticles (Mo-HEO). Interestingly, only low-content Mo doping into HEO can reduce the crystallite size, prevent particle agglomeration, and modulate the electron structure. Consequently, the electrocatalyst of 6% Mo-HEO exhibits superior OER performance with overpotentials of only 280 and 324 mV at 10 and 100 mA cm −2 . In situ Raman spectroscopy confirms the transformation of surface spinel sites to metal oxyhydroxide, highlighting the Mo-driven surface reconstruction. Furthermore, Mo doping as a versatile strategy has been successfully extended to other spinel oxides with significant activity improvements, offering a great potential in the development of spinel-typed HEO electrocatalysts.