Highly selective conversion of CO₂ to C₂H₆ on graphene modified chlorophyll Cu through multi-electron process for artificial photosynthesis

Artificial photosynthesis is a promising strategy for converting carbon dioxide into hydrocarbon fuels through solar energy as it is clean, economical and environmentally friendly. Herein, we developed a selective and stable photocatalyst for CO₂ photocatalytic reduction into C₂H₆ through a multi-electron transfer pathway without the external sacrificial regents. The core component of this composite catalyst was extracted from a silkworm excrement and modified to make chlorophyll Cu (Chl-Cu), which contained a porphyrin structure as an antenna for light absorption and a Cu cation as an active centre. We found that C₂ hydrocarbons such as C₂H₂, C₂H₄, and C₂H₆ tended to generate on chlorophyll-a/graphene. After substituting Mg²⁺ with Cu²⁺ cations in the centre of the porphyrin and modifying with graphene, only C₂H₆ was detected in the 18 hours reaction. This photocatalyst presented an outstanding activity and selectivity for the photocatalytic CO₂ reduction (CO₂RR) with a C₂H₆ yield rate at 68.23 μmol m^-2 h^-1 under visible light irradiation and an apparent quantum efficiency of 1.26% at 420 nm. In this system, the porphyrin rings were excited to produce electron-hole pairs by light. The photo-induced holes oxidized water to produce oxygen while graphene worked as an adsorption centre and electron acceptor for the CO₂ reduction.