Construction of an Indium-based Coordination Polymer with Redox Non-Innocent Ligand for High-Efficient Electrochemical CO2 Reduction

Developing high-activity and long-term stable electrocatalysts for electrochemical CO2 reduction reaction (eCO2RR) to valuable products is still a challenge. An in-depth understanding of reaction mechanisms and the structure-function relationship is required for the development of an advanced catalytic eCO2RR system. Herein, a coordination polymer of indium(III) and benzenehexathiol (BHT) was developed as an electrocatalyst (In-BHT) for eCO2RR to HCOO-, which displayed an outstanding catalytic performance over the entire pH range. However, experimental results revealed significantly different catalytic pathways in the acid and neutral/alkaline solutions, which are attributed to the influence of redox non-innocent ligands on the rate-determining step (RDS). In the acid solution, the RDS is the formation of *OCOH intermediate through the proton transfer that originates from H2O in the solution, leading to relatively sluggish kinetics. But in the neutral or alkaline solution, the thiolate groups could be protonated during the catalytic process, and such proton can attack on carbon of absorbed CO2 via an intramolecular proton transfer, promoting the formation of *OCHO intermediate, resulting in faster kinetics. Our findings revealed the pivotal roles of the redox non-innocent ligands of metal active sites for eCO2RR, providing a new idea for designing highly efficient electrocatalysts.