Molecular engineering including the design of ligand structure and the selection of support and loading methods was used for constructing the CuPc system for electrocatalytic CO₂ reduction to hydrocarbons, it is found that the polypyrrole-coated CuPc promoted the reduction of CO₂ to methane and the modified groups influenced the selectivity of methane.

Abstract

Efficient electrochemical CO₂ reduction reaction (ECO₂RR) to multi-electron reductive products remains a great challenge. Herein, molecular engineering of copper phthalocyanines (CuPc) was explored by modifying electron-withdrawing groups (EWGs) (cyano, sulfonate anion) and electron-donating groups (EDGs) (methoxy, amino) to CuPc, then supporting onto carbon paper or carbon cloth by means of droplet coating, loading with carbon nanotubes and coating in polypyrrole (PPy). The results showed that the PPy-coated CuPc effectively catalysed ECO₂RR to CH₄. Interestingly, experimental results and DFT calculations indicated EWGs markedly improved the selectivity of methane for the reason that the introduction of EWGs reduces electron density of catalytic active center, resulting in a positive move to initial reduction potential. Otherwise, the modification of EDGs significantly reduces the selectivity towards methane. This electronic effect and heterogenization of CuPc are facile and effective molecular engineering, benefitting the preparation of electrocatalysts for further reduction of CO₂.