The presence and role of the intermediary CO reservoir in heterogeneous electroreduction of CO ₂

Abstract

Significance The electroconversion of CO 2 to value-added products is a promising path to sustainable fuels and chemicals. However, the microenvironment that is created during CO 2 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.

Probing the Dynamics of Low-Overpotential CO2-to-CO Activation on Copper Electrodes with Time-Resolved Raman Spectroscopy

“…20,36,47,59 Recently, Roldan-Cuenya et al have shown that these vibrations can be used as a probe to measure the surface coverage of CO by taking the ratio of the two low-Raman shift vibrations (280 and 360 cm −1 ), 20 which is also possible through onstream substitution of the reactant isotope. 60 In the potential window of −0.55 to −0.85 V RHE , it is observed that the high-frequency-band (HFB) CO band at 2090 cm −1 dominates and has a lowfrequency-band (LFB) CO tail centered around 2050 cm −1 . These potential-and time-dependent CO stretching vibrations are attributed to the stochastic behavior of adsorbed CO and are extensively described in our previous work, where we studied the time-dependent behavior of adsorbed CO at fixed cathodic biases.…”

“…Around −0.55 V RHE , vibrations at 2090, 360, and 280 cm –1 appear simultaneously. These vibrations are typically assigned to the linear CO stretching, Cu-C stretching, and Cu-CO bending of adsorbed (linear) CO on Cu, respectively. ,,, Recently, Roldan-Cuenya et al have shown that these vibrations can be used as a probe to measure the surface coverage of CO by taking the ratio of the two low-Raman shift vibrations (280 and 360 cm –1 ), which is also possible through onstream substitution of the reactant isotope . In the potential window of −0.55 to −0.85 V RHE , it is observed that the high-frequency-band (HFB) CO band at 2090 cm –1 dominates and has a low-frequency-band (LFB) CO tail centered around 2050 cm –1 .…”

Photoelectrochemical CO2 Reduction toward Multicarbon Products with Silicon Nanowire Photocathodes Interfaced with Copper Nanoparticles

“…25 This was attributed to having to build up a necessary concentration of intermediates (carbon monoxide) in its microenvironment for carbon-carbon coupling. 26 Systems using planar silicon for wet-side illumination CO2R (incident light, catalyst, and electrolyte on same side) show low current densities and selectivity toward multi-carbons due to low mass loading 27,28 while a microwire array with large mass loading (>300 µg/cm 2 ) showed limited stability (≤1 hour) likely due to catalyst deactivation. 29 Considering that practical applications require long term operations with high current densities (mA scale), 30 it remains a major challenge to discover more durable and selective PEC CO2R systems.…”

“…High selectivity toward multicarbon products can be achieved by controlling the current density at a given potential by modulating the surface area of copper, the only known metal capable of carbon–carbon coupling, and by using nanostructures with undercoordinated sites . This was attributed to having to build up a necessary concentration of intermediates (carbon monoxide) in its microenvironment for carbon–carbon coupling . Systems using planar silicon for wet-side illumination CO 2 R (incident light, catalyst, and electrolyte on the same side) show low current densities and selectivity toward multicarbons due to low mass loading, , while a microwire array with large mass loading (>300 μg/cm 2 ) showed limited stability (≤1 h) likely due to catalyst deactivation .…”

Designing Cu-Based Tandem Catalysts for CO2 Electroreduction Based on Mass Transport of CO Intermediate

“…The residence time of the reactor determined the further conversion ratio of CO produced from CO 2 reduction. Furthermore, Louisia et al revealed the presence of a reservoir of unadsorbed CO intermediate near the catalyst surface through an on-stream isotope substitution experiment (Figure b) . If such a reservoir does not exist in the proximity of the Cu surface and all C 2+ products are derived from adsorbed *CO intermediates, a monolayer of *CO does not provide adequate CO intermediates to facilitate the formation of C 2+ products.…”