Mn Doping-Induced Charge-Carrier Redistribution in Co₃O₄ for Enhanced CO₂ Photoreduction Toward CH₄ with H₂O

Photocatalytic CO₂ reduction to CH₄ with H₂O is hindered by rapid charge recombination and sluggish multielectron/proton-coupled hydrogenation kinetics. Herein, we show that Mn doping induces charge-carrier redistribution within Co₃O₄, thereby enhancing CO₂ photoreduction to CH₄ under sacrificial-agent-free conditions. The optimized Mn5-Co₃O₄ achieves CH₄ and CO production rates of 16.9 and 9.8 μmol g^-1 h^-1, respectively, with its CH₄ production rate reaching 10.6 times that of pristine Co₃O₄. Mechanistic investigations indicate that Mn doping modulates carrier dynamics and surface-intermediate hydrogenation. Photoelectrochemical and photoluminescence measurements demonstrate that Mn incorporation promotes charge-carrier separation, with Mn5-Co₃O₄ exhibiting the most favorable separation efficiency, as reflected in an extended average photoluminescence lifetime of 23.17 ns compared with 9.95 ns for pristine Co₃O₄. In situ irradiated X-ray photoelectron spectroscopy shows shifts of the Mn and Co signals toward lower and higher binding energies, respectively, indicating electron enrichment at Mn sites and hole accumulation at Co sites. In situ Fourier-transform infrared spectroscopy further reveals enhanced bands tentatively assigned to *COOH, *CHO, and *CH₃O intermediates, supporting their progressive hydrogenation toward CH₄. These findings provide a mechanistic framework for coordinating charge redistribution with surface hydrogenation during multielectron/proton-coupled CO₂ conversion with H₂O.