Manganese doping motivated cobalt site and unique hexagonal morphology to boost electrochemical water electrolysis.

[Display omitted] • By optimizing the internal electronic structure and exposing more active sites. • The synergistic effect of heterogeneous atoms and oxygen defects. • The unique hexagonal morphology is more favorable to the exposure of active sites. • The highly active and stable bifunctional cobalt oxide-based catalysts. Undesirable conductivity and insufficient electrocatalytic activity are the current bottlenecks of cobalt tetroxide from achieving efficient water electrolysis. Herein, by optimizing the internal electronic structure and the controlled design of the morphology, we design a unique hexagonal Mn-Co 3 O 4 -200 nanostructure that exhibits superior water electrolysis performance with low overpotentials and excellent long-term durability under strongly alkaline conditions, outperforming many other previously reported cobalt oxide-based compounds. Theoretical combined with characterization analysis indicates that introduced Mn atoms induce an increase in the high spin-orbital occupancy of Co2+ to optimize free energy of the OOH*→O 2 step, which excites the catalytic activity of the Co sites, resulting in a substantial increase in the catalytic activity of the Mn-Co 3 O 4. Furthermore, we briefly summarize the catalytic activity variation pattern of several catalysts with different microscopy morphologies and innovatively propose a more intuitive means to evaluate their exposed active areas. Compared with other morphologies, the special hexagonal morphology with abundant pores and large effectively exposed catalytic surface area can promote the exposure rate of active centers, mass transfer of electrolytes and diffusion of hydrogen and oxygen in the electrocatalytic process, thus accelerating the rate of electrocatalytic reactions. [ABSTRACT FROM AUTHOR]