Cu supported on polymeric carbon nitride for selective CO2 reduction into CH4: a combined kinetics and thermodynamics investigation

Abstract

Metal-based cocatalysts have been widely applied in the photocatalytic CO₂ reduction reaction (CO₂RR) and the integration of cocatalysts/semiconductors is expected to enhance the selectivity of the catalytic reaction. Nevertheless, the type and yield of products manifest a large discrepancy even for the same cocatalyst/semiconductor photocatalytic system, which requires a comprehensive study into the reaction mechanism and product distribution in detail. Here we provide kinetics evidence that selective CO₂ reduction into CH₄ is realized on Cu loaded carbon nitride (Cu/CN), in comparison with that on Au species (Au/CN) which yield both CO and CH₃OH. Besides, it is revealed that the adsorption/desorption thermodynamic behavior of CH₃OH is a crucial factor to determine the product distribution. By the establishment of binary electron transfer channels at the interface between adsorbed CH₃OH and the Cu/CN surface, intensified activation of CH₃OH is accomplished, resulting in the over-all reduction of CO₂ into methane. Owing to the combined kinetics and thermodynamics investigation at the atomic level, this work may provide pioneering design schemes of precisely tailored cocatalyst/semiconductor photocatalytic systems for the selective CO₂RR.