Hydroxy-Group-Functionalized Single Crystal of Copper(II)-Porphyrin Complex for Electroreduction CO2 to CH4

Purposefully developing crystalline materials at molecular level to improve the selectivity of electroreduction CO2 to CH4 is still rarely studied. Herein, a single crystal of copper(II) complex with hydroxy groups was designed and synthesized, namely 5,10,15,20-tetrakis(3,4-dihydroxyphenyl)porphyrin copper(II) (Cu-PorOH), which could serve as a highly efficient heterogeneous electrocatalyst for electroreduction of CO2 toward CH4. In 0.5 m KHCO3, Cu-PorOH gave a high faradaic efficiency of 51.3 % for CH4 and drove a partial current density of 23.2 mA cm(-2) at -1.5 V versus the reversible hydrogen electrode in H-cell. The high performance was greatly promoted by the hydroxy groups in Cu-PorOH, which could not only form stable three-dimensional frameworks through hydrogen-bonding interactions but also stabilize the intermediate species by hydrogen bonds, as supported by density functional theory calculations. This work provides an effective avenue in exploring crystalline catalysts for CO2 reduction at molecular level.