Insight into Photocatalytic CO2 reduction on TiO2-supported Cu nanorod: A DFT study on reaction mechanism and selectivity

Abstract

Photoreduction of CO2 into hydrocarbons is a potential strategy for reducing atmospheric CO2 and effectively utilizing carbon resources. Cu-deposited TiO2 photocatalysts stand out in this area due to their good photocatalytic activity and potential methanol selectivity. However, the underlying mechanism and factors controlling product selectivity remain less understood. Using the first-principles calculations, this study systematically investigates the possible reaction network for CO2 photocatalytic reduction on TiO2 supported Cu-nanorod (nr-Cu/TiO2), driven by the surface-bound *H species generated via a Volmer-like process (H+ + e− + * → *H). Our results reveal that the initial hydrogenation of CO2 on nr-Cu/TiO2 is energetically more favorable via the formate (HCOO) pathway than the carboxyl (COOH) route. Notably, HCOO requires further hydrogenation for effective C-O bond cleavage, with H2COOH identified as the key intermediate. Both CO (CO2 → HCOO → H2COOH → H2CO → CO) and CH3OH (CO2 → HCOO → H2COOH → H2CO → CH3OH) production share the H2CO intermediate, with CO formation proceeding via an unexpected "forth-back” mechanism. Energy profiles suggest that CH3OH formation is more favorable than CO. Additionally, excess photogenerated electrons were found to enhance CO2 activation and C-O bond cleavage to some extent but have minimal impact on other reaction steps. This study provides atomic-level insights into the CO2 photoreduction mechanism, offering potential guidance for improving product selectivity.