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 C-2 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 mu mol 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.