Probing the Mechanism of Aqueous CO₂ Reduction on Post-Transition-Metal Electrodes using ATR-IR Spectroelectrochemistry

Abstract

The role of metastable surface oxides in the reduction of CO 2 on lead, bismuth, tin, and indium electrodes was probed using in situ attenuated total reflectance infrared (ATR-IR) spectroelectrochemistry. The effect of the surface oxide on the Faradaic efficiency of CO 2 reduction to formic acid was studied by etching and anodizing the electrodes, and the results were correlated with respect to the observed spectroscopic behavior of the catalysts. A metastable oxide is observed on lead, tin, and indium cathodes under the electrochemical conditions necessary for CO 2 reduction. Spectroscopic evidence suggests that bismuth electrodes are fully reduced to the metal under the same conditions. The dynamics of the electroreduction of CO 2 at lead and bismuth electrodes appears to be different from that on on tin and indium electrodes, which suggests that these catalysts act through different mechanistic pathways. The post-transition-metal block can be divided into three classes of materials: oxide-active materials, oxide-buffered materials, and oxide-independent materials, and the mechanistic differences are discussed.

Promises of Main Group Metal–Based Nanostructured Materials for Electrochemical CO2 Reduction to Formate

“…It was proposed that the formation of this surface‐bound tin carbonate was the key step in electrochemical CO 2 RR to formate because these IR bands were absent on etched Sn that was measured to have a poor electrocatalytic activity (Figure c). The same authors later reported a similar observation about In that its oxide/hydroxide persisted during CO 2 RR and actively participated in the reaction . By contrast, even though Pb supported a metastable oxide under CO 2 RR, this oxide did not play a direct role in the formate production.…”

Understanding the Heterogeneous Electrocatalytic Reduction of Carbon Dioxide on Oxide‐Derived Catalysts

“…Recent studies have demonstrated that post‐transition metal oxides have an important impact on the electrochemistry of CO 2 reduction ,,,. This is especially interesting because the Pourbaix diagram for each of the post‐transition metals (except Hg) predicts that there is native oxide present in neutral solutions at 0 V vs. SHE…”

Reaction Mechanisms of the Electrochemical Conversion of Carbon Dioxide to Formic Acid on Tin Oxide Electrodes

“…Electrokinetic studies based on Tafel and reaction‐order analyses have proposed possible rate‐determining steps (RDS) for HCOO − formation . Furthermore, in situ IR and Raman analyses have presented direct evidence for intermediates and active sites . Even though intensive efforts have been made in many areas, it is still challenging to fully uncover the reaction mechanism.…”