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.