LAUSR

Spinel oxides (AB2O4) with unique crystal structure have been widely explored as promising alternative catalysts for efficient oxygen evolution reaction; however, developing novel methods to fabricate robust, cost-effective and high-performance spinel oxides based electrocatalysts is still a great challenge. Here, utilizing a complementary experimental and theoretical approach, pentavalent vanadium doping in the spinel oxides (i.e., Co3O4 and NiFe2O4) have been thoroughly investigated to engineer their surface structures for enhanced electrocatalytic oxygen evolution reaction. Specifically, when the optimal concentration of vanadium (ca. 7.7 at%) is incorporated into Co3O4, the required overpotential to reach a certain jGEOM and jECSA gets decreased dramatically for oxygen evolution reactions in alkaline media. Even after 30 hrs of chronopotentiometry, the required potential for V-doped Co3O4 is just increased by 16.3 mV, being much lower than that of the undoped one. It is observed that the penta-valent vanadium doping introduces lattice distortions and defects on the surface, which in turn exposes more active sites for reactions. DFT calculations further reveal the rate-determining step changing from the step of *O to *OOH to the step of *OH to *O, while the corresponding energy barriers decrease from 1.73 eV to 1.57 eV accordingly after high-valent V doping. Moreover, the oxygen intermediate probing method using methanol as a probing reagent also demonstrates a stronger OH* adsorption on V-doped Co3O4 surface. When vanadium doping is performed in the inverse spinel matrix of NiFe2O4, impressive performance enhancement in the oxygen evolution reaction is as well witnessed. All these results clearly illustrate that the V doping process can not only efficiently improve the electrochemical properties of spinel transition metal oxides but also provide new insights into the design of high-performance water oxidation electrocatalysts.