Water Vapor-Enhanced Selective Production of Methane During Photothermal CO₂ Reduction: Mechanistic Insights Into Boron-Doped Nickel Catalysts

The development of efficient CO₂ reduction technologies is crucial for mitigating climate change and advancing sustainable energy systems. In this study, the photothermal catalytic reduction of CO₂ to methane (CH₄) using boron-doped Ni as a catalyst, focuses on enhancing product selectivity through reaction parameter optimization. Notably, addition of water vapor substantially improves both CH₄ yield (195.85 mmol g·h⁻¹) and selectivity (80.21%), representing a significant advancement over traditional approaches. Through integrated experimental characterization and density functional theory (DFT) calculations, the underlying mechanism involving competitive adsorption dynamics is elucidated between CO₂ and H₂O molecules on the boron-doped Ni surface, along with their parallel dissociation pathways. DFT calculations also confirm that boron doping upshifts the Ni d-band center, strengthening CO adsorption for subsequent hydrogenation. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) measurements indicated that the reverse water-gas shift (RWGS) reaction on boron-doped Ni proceeded primarily via a dissociation pathway. Furthermore, the introduction of H₂O enables alternative CO₂ reduction mechanisms through the carboxylate and bicarbonate pathways. This study demonstrates the significant potential of boron-doped Ni catalysts for enhanced CO₂ methanation and provides valuable mechanistic insights into how reaction parameters influence the photothermal CO₂ reduction process.