Cathodized copper porphyrin metal–organic framework nanosheets for selective formate and acetate production from CO2 electroreduction

Abstract

An efficient and selective Cu catalyst for CO₂ electroreduction is highly desirable since current catalysts suffer from poor selectivity towards a series of products, such as alkenes, alcohols, and carboxylic acids. Here, we used copper(II) paddle wheel cluster-based porphyrinic metal–organic framework (MOF) nanosheets for electrocatalytic CO₂ reduction and compared them with CuO, Cu₂O, Cu, a porphyrin–Cu(II) complex and a CuO/complex composite. Among them, the cathodized Cu-MOF nanosheets exhibit significant activity for formate production with a faradaic efficiency (FE) of 68.4% at a potential of −1.55 V versus Ag/Ag⁺. Moreover, the C–C coupling product acetate is generated from the same catalyst together with formate at a wide voltage range of −1.40 V to −1.65 V with the total liquid product FE from 38.8% to 85.2%. High selectivity and activity are closely related to the cathodized restructuring of Cu-MOF nanosheets. With the combination of X-ray diffraction, X-ray photoelectron spectroscopy, high resolution transmission electron microscopy and Fourier transform infrared spectroscopy, we find that Cu(II) carboxylate nodes possibly change to CuO, Cu₂O and Cu₄O₃, which significantly catalyze CO₂ to formate and acetate with synergistic enhancement from the porphyrin–Cu(II) complex. This intriguing phenomenon provides a new opportunity for the rational design of high-performance Cu catalysts from pre-designed MOFs.