Manipulating\nd‑Electronic States via Transition\nMetal Doping in MnO<sub>2</sub> to Boost Direct Seawater Electrolysis

With the increasing scarcity of fresh water, seawater\nelectrolysis\nholds great potential for hydrogen production. However, the slow kinetics\nof anodic oxygen evolution reaction (OER) limits the Faraday efficiency,\nand the high concentration of chloride ions in seawater leads to the\ncompetitive reaction that produces highly corrosive byproducts such\nas chlorine or hypochlorite. MnO<sub>2</sub> has demonstrated exceptional\nstability under acidic conditions, remarkably outperforming state-of-the-art\nOER noble metal catalyst, RuO<sub>2</sub>. Conversely, the OER activity\nof MnO<sub>2</sub> is far inferior to that of RuO<sub>2</sub>. In\nthis study, we have designed 13 transition metal-doped γ-MnO<sub>2</sub> catalysts (TM-MnO<sub>2</sub>) and screened 6 potential catalysts\nfor direct seawater electrolysis with high activity and selectivity\nbased on density functional theory. We thoroughly investigated the\norigin of activity and the effect of pH on selectivity. Our work demonstrates\nthat the dispersed TM in γ-MnO<sub>2</sub> enhances the high\ncovalency of the TM–O bond, thereby triggering the lattice\noxygen mechanism (LOM) instead of the traditional adsorbate evolution\nmechanism (AEM). Notably, there is a volcano-type relationship between\nintegrated crystal orbital Hamilton population (ICOHP) of the TM–O\nbond and the TM d-band center (ε<sub>d</sub>), unveiling that\nthe doping strategy can manipulate the covalency of the TM–O\nbond through tuning the TM ε<sub>d</sub>, thereby regulating\nthe activity. Moreover, we determine the stability of the catalysts\nat a range of potential <i>U</i> and pH values through constructing\nthe Pourbaix diagrams. Finally, we validate that γ-MnO<sub>2</sub> doped with Mo exhibits superior OER performance with an overpotential\nof 0.27 V and high selectivity in suppressing the chloride oxidation\nreaction (ClOR). This study provides theoretical insights into the\ndesign and development of advanced OER catalysts, which can simultaneously\nsuppress ClOR for direct seawater electrolysis.