Size-Dependent Multi-Electron Donation in Metal-Complex Quantum Dots Hybrid Catalyst for Photocatalytic Carbon Dioxide Reduction

The effective conversion of carbon dioxide (CO₂) into valuable chemical fuels relies significantly on the donation of multiple electrons. Its efficiency is closely linked to both the density and lifetime of excited charge carriers. In this study, a hybrid catalyst system comprising covalently bonded InP/ZnS quantum dots (QDs) and Re-complexes is showcased. The electronic band alignment between the QDs and the Re-complexes is revealed to dominate the multi-electron transfer process for photocatalytic conversion to methane (CH₄). Notably, the size of the QDs is found to be a determining parameter. Among the three QD sizes investigated, transient absorption spectroscopy studies unveil that rapid multi-electron transfer from the QDs to the Re-catalyst occurs in smaller QDs (2.3 nm) due to the substantial driving force. Consequently, the photocatalytic conversion of CO₂ to CH₄ is significantly enhanced with a turnover number of 6, corresponding to the overall apparent quantum yield of ≈1%. This research underscores the possibilities of engineering multi-electron transfer by manipulating the electronic band alignment within a catalytic system. This can serve as a guide for optimizing photocatalytic CO₂ reduction.