Microenvironment engineering for improved electrochemical reduction of CO₂

Copper-based catalysts are highly active for electrochemical reduction of CO₂ (CO₂R) to several desirable hydrocarbon products, such as methane (CH₄), formic acid (HCOOH), ethylene (C₂H₄), and ethanol (C₂H₅OH). CO₂R is dually beneficial, as it allows for the conversion of excess atmospheric CO₂ into useful chemicals. However, using copper-based catalysts for CO₂R depends intimately on the microenvironment of the catalyst–electrolyte interface. Where the catalyst increases the rate of the chemical reaction, and the electrolyte is a substance (e.g., water) used for conducting an electrical current.

The microenvironment consists of several factors, such as the applied electrode potential, electrolyte composition, catalyst morphology, and the local pH near the interface. Ultimately, the various effects of the microenvironment on the chemical pathways for CO₂R exhibit a complex interdependence that has traditionally been challenging to disentangle in experiments. Among the many possible pathways, adsorbed carbon monoxide (CO) has been proposed as the key and common intermediate state for many desired products. That is, during the reduction process, CO₂ is commonly transformed into CO, before being turned into a specific chemical product. Thus, understanding the extent of CO coverage (represented as a percentage, where 100% is full coverage) at the surface of the catalyst and how it affects the microenvironment may provide important insights for improved electrocatalytic performance.

To this end, a team of LLNL materials scientists used computer modeling to quantify the complex interdependence between electrode potential, CO coverage, and the interfacial field strength during CO₂R. While previous studies assume fixed CO coverage, this new research indicates that CO coverage strongly influences the field strength and, therefore, the reaction’s electrochemical potential. These insights provide a basis for microenvironment engineering through surface additives, catalyst design, and electrolyte composition—which could, in turn, increase the production of multicarbon products.

[H. Yu, S.E. Weitzner, J.B. Varley, B.C. Wood, and S.A. Akhade, Surface Engineering of Copper Catalyst through CO* Adsorbate, J. Phys. Chem. C (2023), DOI: 10.1021/acs.jpcc.2c06456.]

–Physical and Life Sciences Communications Team