Amorphous NH2-MIL-68 as an efficient electro- and photo-catalyst for CO2 conversion reactions

To produce metal-organic framework (MOF) catalysts with both high activity and durability is interesting but challenging. We report an amorphous MOF (NH2-MIL-68), which combines the advantages of (1) a large number of open metal sites, (2) the basic building blocks and connectivity of crystalline NH2-MIL-68, and (3) hierarchically meso- and microporous structure. It exhibits high performances in electrocatalytic reduction of CO2 and photochemical cycloaddition of CO2 under mild conditions. For the former reaction, the maximum Faradaic efficiency for product formic acid (FEHCOOH) reaches 93.3% with a current density of 34.2 mA·cm−2 at −2.05 V vs. Ag/Ag+ catalyzed by amorphous NH2-MIL-68, while the crystalline NH2-MIL-68 shows FEHCOOH of 67.7% with considerable productions of CO and H2 at the same experimental conditions. For the photochemical cycloaddition of CO2 with styrene oxide, the yield by amorphous NH2-MIL-68 can reach 94.1% at 12 h, which is higher than the reported value under similar conditions. The structure—efficiency relationship of the catalyst for the two reactions was investigated. This work opens up new possibility for designing high-performance MOF and MOF-based catalysts.