The sources of hydrogen affect the productivity and selectivity of CO2 photoreduction on SiC

Abstract Photocatalysis of CO2 into CH4 and O2 on marigold-like SiC@MoS2 has recently been reported with high product yield of 323 and 621 μL·g−1·h−1, respectively, where protons produced from MoS2 were directly used as hydrogen source for CO2 reduction on the SiC surfaces (JACS, 2018, 140, 14595). However, the yields are only 98.1 and 26.9 μL·g−1·h−1 for CH4 and CO, respectively, if the hydrogen source is from the hydroxylated SiC (ChemComm, 2019, 55, 1572). To unravel the productivity and selectivity of the reaction, we first provide that the limiting potential of CO2 to CH4 on SiC(1 1 1) surface is ∼0.7 V lower than that of hydroxylated SiC(1 1 1) surface. Due to the ΔGdes (1.68 eV) of CO is close to the ΔGmax (1.33 eV) of the hydroxylated SiC(1 1 1) surface, a small amount of CO are produced. Furthermore, we found the reverse water-gas shift (RWGS) mechanism has much lower limiting potential than those proposed in the experiments.