Significant Enhancement of Photothermal‐Assisted Broad‐Spectrum CH ₄ Photosynthesis from CO ₂ and H ₂ O Through Heterojunction and Cocatalyst Engineering on Metallic TiN

Abstract Metallic materials are promising photocatalysts due to their high carrier concentrations, exceptional photothermal properties, and wide light absorption spectra. However, their practical applications in CO 2 methanation are hindered by severe charge recombination and unfavorable redox sites, which limit the ability to manipulate C 1 intermediate binding strengths and generate ample electrons and protons for successive hydrogenation and deoxygenation. Herein, it is demonstrated that the CO 2 ‐to‐CH 4 conversion efficiency of metallic TiN can be dramatically improved through heterojunction formation with Fe 2 O 3 substrate and coating with Ni x Cu 1−x (OH) 2 bifunctional cocatalysts. Mechanistic studies reveal that Ohmic contact between TiN and Fe 2 O 3 facilitates barrier‐free transfer of electrons and holes to their respective Ni x Cu 1−x (OH) 2 overlayers for CO 2 reduction and H 2 O oxidation. The Ni x Cu 1−x (OH) 2 wrapping raises photothermal utilization of TiN, accelerating charge separation and activation of CO 2 and H 2 O. Additionally, Ni─Cu synergy reduces energy barriers for both redox reactions and promotes successive *CO protonation over desorption. Consequently, the optimal catalyst achieves a CH 4 yield of 260.3 µmol g cat −1 h −1 , 329.5 times higher than pristine TiN, outperforming all reported metallic photocatalysts, with an apparent quantum efficiency of 2.0% at 808 nm—the highest among reported infrared‐responsive photocatalysts. This work delivers a feasible strategy to advance the efficiencies of metallic photocatalysts.