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[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]

Cobalt phosphide (CoP) is a promising electrocatalyst due to its abundance and excellent stability in alkaline solution. However, its poor conductivity and intrinsic catalytic activity limit its potential in electrochemical water splitting. To address this, a heterogeneous atom doping strategy has been proposed to synthesize magnesium-doped cobalt phosphide nanoneedle arrays, or Mg-doped CoP. Our theoretical calculations show that transition metal Mg atoms doping into the CoP lattice can enhance the electronic structure and modulate the free energy of reacting species, resulting in a significant improvement in the intrinsic catalytic activities for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) process. The electrochemical tests reveal that the optimal 10% Mg-doped CoP nanoneedle arrays exhibit outstanding HER and OER electrocatalytic activities with overpotential values of 85 and 236 mV at 10 mA/cm2, respectively, outperforming previously reported CoP-based catalysts. This study not only presents a strategy to enhance the catalytic activity of CoP-based materials, but also offers a reference for achieving efficient electrochemical hydrogen production by hydrolysis. [Display omitted] • The charge compensation effect optimizes not only the electronic structure but also the free energy of H∗ and HOO∗ species. • The low-valent Mg2+ ions replace part of the Co3+ sites in the CoP lattice. • The creation of phosphorus vacancies in adjacent sites to maintain electroneutrality. [ABSTRACT FROM AUTHOR]