Varied proton conductivity and photoreduction CO2 performance of isostructural heterometallic cluster based metal–organic frameworks

A family of isostructural heterometallic MOFs based on Fe2M clusters (MOF-Fe2M; M = Fe, Co and Ni, respectively) have been synthesized and serve as potential proton conductors and photocatalysts for CO2 photoreduction, exhibiting varied proton conductivities and photocatalytic performances. Among them, MOF-Fe3 exhibits the best proton conductive performance with a value of 3.39 × 10−2 S cm−1 at 70 °C and 98% RH. Furthermore, three proton conductive membranes based on MOF-Fe3 have been prepared, and the optimum membrane shows a high proton conductivity with σ = 5.46 × 10−3 S cm−1 at 60 °C and 98% RH. Additionally, all frameworks are employed as photocatalysts for converting CO2 into CO in the solid–gas mode without sacrificial agents and photosensitizers, where MOF-Fe2Ni exhibits the highest photocatalytic activity with a CO formation rate of 15.81 μmol g−1 h−1. It should be mentioned that MOF-Fe2M represent rare MOF based photocatalysts used for reducing CO2 in the solid–gas mode. Their great performances may be attributed to the following reasons: (i) appropriate structural features promote the formation of hydrogen bond networks and the adsorption of CO2; (ii) extensive Fe2M units can adsorb visible light and provide reaction active sites for CO2 photoreduction.