Investigating the Inductive Effect and Kinetics of Covalently Immobilized Molecular Catalysts for High-performance Electrochemical CO2 Reduction

Project: Research

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Description

Electrochemical CO2 reduction reaction (CO2RR) is a promising method to convert this greenhouse gas into value-added products. Among all the reported catalysts, molecular complexes with inexpensive metal centers have attracted tremendous attention due to their high selectivity towards CO production, which is an important starting molecule for manufacturing a wide range of chemical commodities. However, due to the poor conductivity of molecular catalysts and their severe agglomeration problem during electrode preparation, they often have sluggish CO2RR kinetics and low turnover frequency (TOF). The Principal Investigator has performed several mechanistic studies, which include the effect of catalysts agglomeration on CO2RR pathway, the influence of peripheral functional groups on the activity of cobalt tetraphenylporphyrin, and the impact of the electronic structure of conductive substrates on their catalytic activity. These mechanistic studies have allowed us to rationally design a covalently grafting strategy and achieve a current density of 25.1 mA/cm2 and a Faradaic efficiency of 98.3% at -0.6 V with a low loading of 60 µg/cm2. Despite all these encouraging breakthroughs, it remains inconclusive how the peripheral functionalities affect the CO2RR activity of molecular catalysts in a general context, and how the structure of the catalyst-electrode interface affects the kinetics of CO2RR. This proposal aims to demonstrate systematic steps to better understand some fundamental concepts in molecular catalysts for CO2RR. First, we will study the inductive effect of peripheral functionalities on the CO2RR activities. By correlating the CO2RR performances of tetraphenylporphyrin- and phthalocyanine-based catalysts, to the bond strengths of metal-COOH at the rate-determining step from Density Functional Theory calculation, a Volcano plot will be obtained to delineate the structure-activity relationship. Also, we will study the kinetics of electron transfer for covalently immobilized catalysts. By probing the TOFs and Tafel slopes of different covalent immobilization configurations, the electron transfer at the interface can be understood. Prompted by these mechanistic studies, we will build a flow cell with optimized electrode structure for a high-performance CO2RR. So far, our preliminary studies on the CO2RR performance of phthalocyanine derivatives have supported our hypothesis on the influence of functionalities. The successful implementation of this project will provide a comprehensive understanding of some intrinsic and extrinsic factors affecting CO2RR at a molecular level. We envision that the design principle of molecular catalysts concluded in this project and the demonstration of a flow cell electrolyzer will help the future development of catalysts for CO2 reduction with an industrial-relevance performance.

Detail(s)

Project number9048183
Grant typeECS
StatusActive
Effective start/end date1/10/20 → …