Efficient hybrid solar-to-alcohol system via synergistic catalysis between well-defined Cu-N4 sites and its sulfide (CuS)

In order to selectively produce liquid hydrocarbon fuels by photoelectroreduction of carbon dioxide (CO2) with titania (TiO2) photoanode, copper sulfide (CuS) nanoparticles (NPs) anchored on Cu-porphyrin (CuPor)-based metal-organic framework nanosheets (NSs) were used as cathode catalysts to efficiently convert CO2 to hybrid alcohol products, in particular, ethanol. Crystal size of CuS increased from 24.6 to 48.1 nm with partial decomposition of CuPor, when sulfuration-time increased from 2 to 6 h. Fractal dimension of CuS/CuPor catalyst surface first surface first increased from 1.12 to 1.31 with the increase in sulfuration-time to 4 h because of generated CuS NPs, and then decreased to 1.26 at 6 h. Formation of the heterojunction between CuS NPs with crystal surface (1 1 0) and CuPor NSs with crystal surface (0 0 4) contributed to synergistic catalytic effect on efficient reduction of CO2. The total carbon atom conversion rate in CO2 photoelectroreduction over stable CuS/CuPor-4 h cathode catalyst reached 5174 nmol h(-1) cm(-2) with a high selectivity of 74.4% for ethanol product. Density functional theory calculations indicated that CuS exhibited high catalytic activity by strengthening binding energy to adsorb CO* in S atoms (1.5 eV), and then CO* was gradually converted to alcohol on the surface of CuPor NSs. The remarkable performance in CO2 electroreduction over cathode catalysts was attributed to synergistic catalysis between the structure of Cu-N4 in 2D macroporous CuPor NSs and its sulfide CuS NPs with high binding energy toward CO* intermediate.