Tuning Hydrocarbon Selectivity in Electrochemical CO2 Reduction via Copper-Porphyrin Immobilization on Carbon Nanotubes

Abstract

Electrochemical CO2 conversion using renewable energy offers a promising pathway for producing value-added chemicals with zero emissions. In this study, copper porphyrin (Cu-TMCPP) molecules are immobilized on multi-wall carbon nanotubes (MWCNT) to form Cu-TMCPP/CNT, which serves as a tunable, heterogeneous electrocatalyst for electrocatalytic CO2 reduction (ECR). A systematic comparison of the synthesized catalyst with Cu-TMCPP stacked and physical mixture of Cu-TMCPP with MWCNT (Cu-TMCPP + CNT) showed that Cu-TMCPP/CNT catalyst not only suppressed hydrogen evolution reaction (HER) to a large extent but also improved selectivity towards hydrocarbon (total FE: 75.68%) mainly CH4 (FE: 37.3%) at potential of -1.08 V versus reversible hydrogen electrode (RHE) with a partial current density of 91.8 mA cm−2. The in-depth mechanistic analysis of in-situ and ex-situ X-ray adsorption spectroscopy (XAS) and electrochemical characterization illustrated the presence of ultrathin copper porphyrin blocks immobilized on CNT, presumably located at Helmholtz layer with high oxidation state and co-existence of Cu2+/Cu0 under reaction condition which are responsible for improved selectivity towards hydrocarbons. This research provides an insight into immobilization impact of molecular catalyst and the advantage of consequent high capacitance double layer for suppressing HER, enhancing electron transfer thereby improving heterogeneous electrocatalytic CO2 performance.