Probing promoting effects of alkali cations on the reduction of CO at the aqueous electrolyte/copper interface

Abstract

The catalytic selectivity and reactivity of an electrocatalytic interface can profoundly depend on the identity of the supporting electrolyte's cation. In the case of CO reduction on copper electrodes, these cation effects have been utilized to suppress undesired hydrogen evolution and to promote the formation of C reduction products. However, to more effectively steer the catalytic selectivity of the electrolyte/copper interface by cations, it is crucial to reveal the various physical mechanisms by which cations impact the catalytic properties of this prototypical interface for CO reduction. Herein, we employ surface-sensitive infrared spectroscopy to probe how alkali cations (Li, K, and Cs) control the coverage of CO, a key intermediate in CO reduction, on a polycrystalline copper electrode. We find that surface-adsorbed CO experiences an increasingly larger interfacial electric field with increasing cation size. The reduction of CO is further promoted by the two larger cations, leading to a significant drop of the CO coverage at high cathodic potential around -1 V vs. RHE. Our results demonstrate for the first time that the coverage of CO on the electrode is very sensitive to the identity of the cation. Since the relative coverage of CO and hydrogen on the copper surface affects the catalytic rates of CO reduction and hydrogen evolution, our results represent an essential step towards a better understanding of how cation effects control the product distribution.

Hydrogen bonding steers the product selectivity of electrocatalytic CO reduction

“…The pH of these solutions slightly drifts during the measurements (Materials and Methods). It is well established that adsorption of CO on Cu is pH independent (55,95). Further, our previous work established that the CO stretch frequency is only slightly affected by pH (95).…”

In‐Situ Infrared Spectroscopy Applied to the Study of the Electrocatalytic Reduction of CO2: Theory, Practice and Challenges

“…all rest on cation‐induced differences in the electric field felt by solvent and intermediate species at the electrical double layer. Gunathunge et al . have studied these effects by examining the effect of the cations on the stretching frequency of CO on Cu using ATR‐SEIRAS.…”

Ion‐Enhanced Conversion of CO2 into Formate on Porous Dendritic Bismuth Electrodes with High Efficiency and Durability

“…Some halides specifically adsorbed on metal cathodes were found to influence CO selectivity by increasing the negative charge at the surface and thereby altering the proton consumption (i.e., local pH change) . However, a large cation decreases the pH near the electrode surface, increases the local concentration of available CO 2 , and affects the selectivity for hydrocarbons …”

“…[18][19][20] However,al arge cation decreases the pH near the electrode surface, increases the local concentration of available CO 2 ,a nd affects the selectivityf or hydrocarbons. [21][22][23] With the above findings in mind, we synthesized porous dendrite-type Bi electrodes and examined their electrocatalytic activity toward the CO 2 RR under various experimentalc onditions. In addition, the elementary CO 2 RR steps on Bi were simulatedc omputationally.O nt he basis of the experimental and computational results,a s-synthesized porous Bi dendrite electrodes paired with IrO 2 anodes weretested at an optimized electrolyte composition for3 60 ha taJ FM value of 15 mA cm À2 .…”