Molecular stabilization of sub-nanometer Cu clusters for selective CO2 electro-methanation

Abstract

Electrochemical CO 2 methanation powered by renewable electricity provides a promising approach to utilizing CO 2 in the form of a high-energy-density, clean fuel. Cu nanoclusters have been predicted by theoretical calculations to improve methane selectivity. Direct electrochemical reduction of Cu-based metal-organic frameworks (MOFs) results in large-size Cu nanoparticles which favor multi-carbon products. Herein, we report an electrochemical oxidation-reduction method to prepare Cu clusters from MOFs. This derived Cu clusters exhibit a faradaic efficiency of 51.2% for CH 4 with a partial current density >150 mA cm -2 . High-resolution microscopy, in-situ X-ray absorption spectroscopy, in-situ Raman spectroscopy, and a collective of ex-situ spectroscopies indicate that the distinctive CH 4 selectivity is due to the sub-nanometer size of the derived materials as well as stabilization of the clusters by residual ligands of the pristine MOF. This work offers a new insight into steering product selectivity of Cu by an electrochemical processing method.