Journal Article

The presence and role of the intermediary CO reservoir in heterogeneous electroreduction of CO2

Li, Yifan, Yu, Sunmoon, Kim, Dohyung, Gao, Mengyu, Yang, Peidong, Roh, Inwhan, Louisia, Sheena

2022

Overview

SignificanceThe electroconversion of CO2 to value-added products is a promising path to sustainable fuels and chemicals. However, the microenvironment that is created during CO2 electroreduction near the surface of heterogeneous Cu electrocatalysts remains unknown. Its understanding can lead to the development of ways to improve activity and selectivity toward multicarbon products. This work introduces a method called on-stream substitution of reactant isotope that provides quantitative information of the CO intermediate species present on Cu surfaces during electrolysis. An intermediary CO reservoir that contains more CO molecules than typically expected in a surface adsorbed configuration was identified. Its size was shown to be a factor closely associated with the formation of multicarbon products. Despite the importance of the microenvironment in heterogeneous electrocatalysis, its role remains unclear due to a lack of suitable characterization techniques. Multistep reactions like the electroconversion of CO2 to multicarbons (C2+) are especially relevant considering the potential creation of a unique microenvironment as part of the reaction pathway. To elucidate the significance of the microenvironment during CO2 reduction, we develop on-stream substitution of reactant isotope (OSRI), a method that relies on the subsequent introduction of CO2 isotopes. Combining electrolytic experiments with a numerical model, this method reveals the presence of a reservoir of CO molecules concentrated near the catalyst surface that influences C2+ formation. Application of OSRI on a Cu nanoparticle (NP) ensemble and an electropolished Cu foil demonstrates that a CO monolayer covering the surface does not provide the amount of CO intermediates necessary to facilitate C-C coupling. Specifically, the C2+ turnover increases only after reaching a density of ∼100 CO molecules per surface Cu atom. The Cu NP ensemble satisfies this criterion at an overpotential 100 mV lower than the foil, making it a better candidate for efficient C2+ formation. Furthermore, given the same reservoir size, the ensemble’s intrinsically higher C-C coupling ability is highlighted by the fourfold higher C2+ turnover it achieves at a more positive potential. The OSRI method provides an improved understanding of how the presence of CO intermediates in the microenvironment impacts C2+ formation during the electroreduction of CO2 on Cu surfaces.

• Publisher: National Academy of Sciences
• Subject: Carbon dioxide / Catalysts / Chemistry / Coupling / Coupling (molecular) / Electrowinning / Intermediates / Isotopes / Mathematical models / Metal foils / Microenvironments / Nanoparticles / Numerical models / Physical Sciences / Reservoirs / Substitution reactions