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

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 pK_a and redox potentials (U_re) 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 U_re of two rate-determining steps are close, which is related to the closed E_onset 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.