Strategy for improving the activity and selectivity of CO2 electroreduction on flexible carbon materials for carbon neutral

Abstract

Selective electrochemical reduction of CO2 is of interest in relieving the accumulation of CO2 in the atmosphere and the global energy crisis. This study investigates active sites and reaction mechanisms for CO2 electroreduction over metal N-doped flexible carbon materials using Phthalocyanine (Pc) and Iron Phthalocyanine (FePc) molecules as model catalysts. Both the FePc molecule and Pc molecule show catalytic activity for CO production and H2 evolution based on experimental results and DFT calculations. The presence of Fe atom results in a significantly higher activity for CO production and a little lower activity for H2 evolution. Calculated pKa and redox potentials (Ure) are introduced for the multi-step proton-coupled electron transfer (PCET) steps of two competitive reactions. Specifically, a comparison between them is conducted to explain the competition between CO2 electroreduction and H2 evolution reaction with the support of energy diagram. The rate-determining steps for CO2 reduction and H2 evolution are also investigated. Both the CO and H2 formation on Pc molecule depend on electron transfer process. Besides, the Ure of two rate-determining steps are close, which is related to the closed Eonset for CO and H2 formation in the experiment. This study demonstrates that the mechanism for CO2 reduction from DFT calculation is in agreement with the experimental results. The technological approach and reaction mechanism can be applied to other types of CO2 electroreduction on carbon materials. Thus, this work provides a guidance in the rational design of the green catalyst and the implementation of carbon neutral.