Deciphering electrochemical interactions in metal-polymer catalysts for CO2 reduction

Polymers play a critical role in catalyst design to stabilize metal nanoparticles on the cathode for electrochemical carbon dioxide reduction reaction (CO2RR). However, electrochemical interactions between the metal and polymer complex remain unclear due to the lack of quantitative analysis of catalytic process variations tailored by such structure modifications on the cathode surface. In this study, we investigate the effects of polymer physical binding on cathode surface polarity, intermediate adsorption, and the barriers of CO2RR. We examine the resultant selectivity, taking into account mass transport and charge transfer. Especially, we select polytetrafluoroethylene (PTFE) as the model polymer to minimize ion flux interference, since the structure of PTFE, with the absence of ionic groups for ion transport, exhibits unmatched physiochemical performance. By utilizing PTFE, we ensure the integrity of our observations, enabling a precise analysis of the effects of polymer physical binding on the performance and selectivity of CO2RR. In addition, a comprehensive multiscale simulation-experiment tandem analysis is conducted for the PTFE-Cu complex to identify the mass and charge transfer processes. Our analysis offers a mechanistic foundation for different CO2RR pathways through both dynamic processes and molecular mechanisms. Our study reveals an unusual shift of surface reaction mechanism induced by direct mass transport alternation and indirect charge transfer from the redistribution of H+/CO2 adsorption on the cathode surface. Specifically, our modeling results demonstrate a significant enhancement in the binding energy of CO2 (from -0.31 eV to -0.38 eV) and critical intermediates involved in CH4 generation (from -1.56 eV to -1.63 eV) upon the addition of PTFE. Our experimental findings validate these results by revealing a 29.9% reduction in surface charge when 10% PTFE is introduced, in comparison to pristine Cu. This binding energy increment and surface charge reduction reinforces the CO2 reduction process, modifies the CO2RR pathway, and ultimately enhances the average CH4 production by 10%. It is worth noting that despite a 32.26% increase in ohmic resistance, the benefits of PTFE addition persist and lower the energy barrier from 1.14 eV to 0.68 eV during CO protonation. Our findings unveil a novel approach for polymer binding in metal design, leading to simpler and more effective materials compared to the intricate polymer encapsulation for CO2RR.

Automated summary

In this study, the effects of polymer physical binding on the performance and selectivity of CO2RR were investigated. The addition of polytetrafluoroethylene (PTFE) was found to enhance the CO2 reduction process, modify the CO2RR pathway, and ultimately increase the average CH4 production by 10%. Despite an increase in ohmic resistance, the addition of PTFE lowered the energy barrier for CO protonation.