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 photocatalytic 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 μmol·g−1·h−1, an excellent CH4 production rate of 21.32 μmol‧g−1‧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.