Local pH Effect in the CO₂Reduction Reaction on High-Surface-Area Copper Electrocatalysts

Abstract

The local pH on electrode surfaces is known to play an important role in the electrochemical reduction of CO 2 , which could alter the chemical kinetics and molecular transport under the reaction conditions. Here we report the study of local pH effect on the catalytic performance of high-surface-area Cu electrocatalysts. The electroreduction of CO 2 was systematically investigated on three types of Cu nanowires with distinct surface roughness factors and nanostructures. The measured electrocatalytic activities and selectivities were further correlated to the simulated local pH on the electrode surface. It was revealed that the high local pH induced by the production of hydroxide from the reaction beneficially suppresses the evolution of hydrogen and enhances the selectivity toward multi-carbon products, but detrimentally limits the transport of CO 2 molecules at large current densities. An optimal range of local pH is determined for the electroreduction of CO 2 , which is insightful for improving the design of electrodes for more efficient energy conversion and chemical transformations.

Oxygen induced promotion of electrochemical reduction of CO2 via co-electrolysis

“…At −1.0 V RHE , the increases of C 2+ product formation rates become less than ten times at 20% O 2 . This could be attributed to the enhanced ORR kinetics at higher overpotentials reducing the surface coverage of its intermediates that facilitate the C-C coupling chemistry in the CO 2 RR, as well as the reduced local CO 2 concentration caused by the increased proton consumption rate 33,34 . These mechanistic aspects will be discussed in the following sections.…”

“…This challenge is circumvented by providing a continuous supply of oxidant in the CO 2 RR, i.e., co-electrocatalysis of CO 2 and O 2 , to stabilize the surface oxidized Cu species, i.e., surface hydroxyl group. Co-electrolysis could also be viewed as coupled reactions, with the ORR supplying reactive oxygen species to form and replenish the surface hydroxyl species vital to the enhancement of the 33,34 . The increase of electrolyte pH has been demonstrated to not affect C 2+ product formations because the RDS does not involve any proton transfer 28,44,54,55 .…”

System Design Rules for Intensifying the Electrochemical Reduction of CO2 to CO on Ag Nanoparticles

“…Anion effects are interpreted on the basis of specific adsorption and/or pH, whereas cation effects are explained using promoter effects, Frumkin effects, cation hydrolysis, and electrical double layer (EDL) stabilization . Studies have also examined the effects of electrolyte pH on eCO 2 RR . More specifically, for Ag catalysts, studies show that high pH suppresses the competing hydrogen evolution reaction (HER), gives higher CO partial current densities (j CO ), shows better FEs for CO production, decreases the onset potentials (V vs. RHE), and decreases the overpotential required for eCO 2 RR to CO .…”

Si photocathode with Ag-supported dendritic Cu catalyst for CO2reduction

“…23 A number of studies have shown that high surface area, dendritic catalysts, can support relatively high current densities for CO2R. [57][58][59][60] For example, Urbain et al reported that Ag dendrites formed on Cu foam have high activity (>27 mA cm -2 ) and selectivity (85-96%) for CO formation. 57 Here, we will show that an integrated photocathode can achieve overall CO2R with faradaic efficiencies (FEs) of over 80%, with faradaic efficiencies (FEs) to C2-C3 products as high as 70%.…”