Electrochemical Reduction of CO2 Using a Metal-Free Polymer Catalyst: Synergy of Pyrrole and Quinone Interfacial Sites

Abstract The electrocatalytic reduction of CO2 to value-added chemicals leads to a combined solution to address carbon dioxide emission and the demand for sustainable energy storage. Although metal catalysts have dominated and defined a benchmark in the field of electrochemical CO2 reduction (CO2RR), recent research has shifted toward the use of metal-free carbon-based catalysts. The catalytic role of metal-free polymers has remained unexplored, and they are primarily used as interfacial modifiers and electrolytes for CO2RR. The present study bridges a gap in this direction wherein a redox-active, benzoquinone-pyrrole copolymer (BQ-Py) is proposed as a durable, metal-free catalyst for CO2RR. The polymer catalyzes the reduction of CO2 to CO, HCOOH, and H2 over a potential range of –1.4 to –1.8 V vs RHE. Using operando ATR-IR spectroscopy, Raman spectroscopy, and DFT calculations, the reaction pathway to formic acid is confirmed via the formation of the *HCOO intermediate on the C atom adjacent to pyrrolic N. This study highlights the crucial role of various pyrrolic N-environments in the catalyst on product formation and its distribution through different mechanistic pathways during CO2 reduction. It further demonstrates the catalytic competency of pyrrolic-N toward electrochemical CO2 reduction. Preliminary studies reveal the possibility of integrating the polymer catalyst into rechargeable Zn-CO2 batteries.