Surface Intermediate Stabilization and Proposed Multicarbon Formation Pathways in Photocatalytic CO2 Conversion over a Bismuth-Based Chalcohalide

Bismuth-based chalcohalides offer tunable electronic structures for photocatalytic CO2 conversion, yet directing carbon intermediates toward multicarbon products remains challenging because of unfavorable surface accumulation and C–C coupling. Here, ternary bismuth tellurium iodide (BiTeI) is investigated for photocatalytic CO2 conversion, producing CO, CH4, and a range of C2–C4 hydrocarbons. The C2+/CH4 molar ratio reached approximately 0.85, while the carbon-based selectivity toward C2+ hydrocarbons was approximately 17.15% among the detected gaseous carbon-containing products, including CO. In-situ Raman spectroscopy revealed spectral features tentatively assigned to *CO, H*CO, H*COH, and possible C–C coupled intermediates, providing insights into the evolution of surface carbon-containing species. Complementary DFT calculations using a representative BiTeI surface model suggest possible thermodynamic stabilization of selected carbon-containing intermediates through interactions with surface Bi and Te sites. Together, the spectroscopic observations and theoretical calculations provide a plausible mechanistic hypothesis involving *CO adsorption, hydrogenation, and possible C–C coupling. However, the identities of the proposed intermediates and the detailed reaction sequence remain to be independently verified.