Electronic-supply Crystal Facet Guiding Enhancement of Interfacial Charge Transfer in Homologous Covalent Heterojunction NiO/Ni-BDC for Efficient Photocatalytic CO2 Reduction

Heterojunction engineering has been an effective strategy to improve separation of charge carriers and photo-catalytic activity of semiconductor photocatalysts. Where and how to build effective interface connections for facilitating interface charge migration has always been the key to the construction of high-performance heterojunction. Here, a series of covalently linked homologous heterojunction photocatalysts NiO(1 1 1)/Ni-BDC (Ni-BDC = Ni3(BDC)2(OH)2(H2O)4; H2BDC = terephthalic acid) were fabricated by H2BDC in-situ etching octahedral NiO(1 1 1) and fully characterized, which were used for photocatalytic reduction of CO2 (pCO2RR) into CH4 and CO. The NiO(1 1 1)/Ni-BDC-3 with a proper component proportion and etching degree exhibited an optimal pCO2RR performance with an electron consumption rate (Rele) of 222.68 mu mol & sdot;g- 1 & sdot;h-1, an excellent CH4 pro-duction rate of 21.32 mu mol center dot g- 1 center dot h-1 and a 76.6% CH4 selectivity, being far superior to most oxide/inorganic semiconductor and oxide/MOF heterojunctions. Comprehensive investigations with extensive photoelectric characterizations, control experiments and DFT calculations based on the homologous NiO(1 0 0)/Ni-BDC and non-homologous NiO(1 0 0)-Ni-BDC heterojunctions demonstrated that the excellent photocatalytic activity and methane selectivity of NiO(1 1 1)/Ni-BDC-3 could be attributed to two points: i) The homologous coordination etching forms a full range of interfacial covalent connections to promote tight MOF-semiconductor integration, yielding a large number of atomic-level electron transfer channels to accelerate the interfacial charge transfer; ii) the alternating polar Ni-O-Ni layer arrangement in NiO(1 1 1) crystal facet induces high-throughput electron supply and the enhanced surface charge density effectively promotes the 8-electron reduction process of methane production. Additionally, the durability of NiO(1 1 1)/Ni-BDC-3 and the possible charge-transfer mechanisms were also systematically investigated.