context: Inspired by the remarkably active Mn4CaO5 clusters for water oxidation, Mn3O4 with high-concentration and stable Mn3+ has, therefore, been extensively researched as an efficient electrocatalyst for OER. In the spinel structure Mn2+Mn23+O4, Mn existed as Mn2+ and Mn3+; here, Mn3+ occupied the octahedral site and Mn2+ ion occupied the tetrahedral site. The coexistence of Mn2+ and Mn3+ offers excellent OER activity. Therefore, numerous studies have focused on exploring high-quality Mn3O4 catalysts for efficient electrocatalytic OER. Further, earlier studies have also demonstrated that Mn3O4 electrocatalysts are highly active toward OER in neutral and alkaline media. For example, Nam's group reported the fabrication of 4 and 8 nm Mn3O4 nanoparticles (Fig. 13a and b). Owing to the enlarged surface area and improved electrical conductivity, the as-obtained Mn3O4 nanoparticles showed apparently higher OER activity in comparison with other Mn oxides (Fig. 13c). Remarkably, the optimized 8 nm Mn3O4 nanoparticles that were loaded on the surface of NFs exhibited outstanding OER activity with overpotential of only 395 mV at 10 mA cm−2 under neutral conditions, which was much superior to those of Fe-, Co-, and Ni-based oxides. As demonstrated by Maruthapandian et al., Mn3O4 catalysts also showed excellent electrocatalytic performance for OER in basic solutions (Fig. 13d and e). In particular, they demonstrated the synthesis of Ni-doped Mn3O4 catalysts, which showed significantly enhanced OER electrocatalytic activity in 1 M KOH solution with overpotential of 283 mV at 10 mA cm−2 (Fig. 13f). Further, a mechanistic study revealed that the largely improved OER performance could be ascribed to the enhanced adsorption/desorption of hydroxide and oxygen atoms, boosting the formation of metal oxyhydroxide/hydroperoxo. Moreover, the efficient electron charge between the electrolyte and Mn3O4 and enlarged electrochemical surface active sites facilitated the promotion of electrocatalytic OER performance.