Insensitive cation effect on single-atom Ni catalyst allows selective electrochemical conversion of captured CO2 in universal media

Abstract

The direct electroconversion of captured CO2 is attracting attention as an alternative to the current energy-demanding CO2 separation processes. In conventional capturing media, the reaction inevitably takes place in the presence of bulky ammonium, leading to steric hindrance and low CO selectivity. Here, for the first time, we present a single atom Ni catalyst (Ni–N/C) exhibits superior activity for the electroconversion of captured CO2, without the need for additives. In a CO2-captured monoethanolamine-based electrolyte, Ni–N/C achieves a notably high CO selectivity of 64.9% at −50 mA cm−2 integrated with a membrane electrode assembly. We also propose that Ni–N/C demonstrates weak cation sensitivity to the CO2 reduction reaction, maintaining high CO production activity in various capturing solutions, while Ag shows a gradual decrease depending on the bulkiness of the amine. These trends provide insights into selective catalyst design for the electroconversion of captured CO2 in universal media.

Advancing integrated CO2 electrochemical conversion with amine-based CO2 capture: a review

“…Similarly, Kim et al 75 also observed that the CO partial current densities reach peak values when the temperature is moderate (40 °C vs. 60 °C) in 5 M MEA aqueous solutions.…”

“…Compared to the development of the gas-diffusion electrodes, the requirement for the electrode development is less stringent on maintaining a stable wetting condition and gas-liquid interfaces within the electrode. 75,80,84,85 In the field of direct bicarbonate reduction, for example, when the Berlinguette group directly incorporated Ag foam instead of carbon-based Ag gas-diffusion electrodes, the bicarbonate electrolyser can achieve a further improvement of the performance. 79,86 As bicarbonate is the main source of CO 2 reduction in tertiary amines, we could also apply the advances in the development of direct bicarbonate reduction to improve the performance further.…”

“…In addition to the electrode, a local reaction environment close to the catalyst surface is essential to provide sufficient reactants and suppress unwanted side reactions such as hydrogen evolution reactions. As mentioned earlier, the local chemical speciation could vary vastly with the amines 61,71,75 , CO 2 loading 60 , local pH, proton supply 45,75 , alkali cations 37,69,75 , temperatures 37,61 , and electrochemical operating conditions 62 . An ideal local reaction environment should maintain sufficient catalytically active species, minimise surface coverage of protonated amines and protons that leads to hydrogen formation, facilitate fast ion conduction and charge transfer, and provide a benign environment for amine recovery.…”

“…Such configuration can further reduce ohmic loss arising from electrolyte ion conduction. Kim et al 75 employed such cell configuration and significantly improved the rates of CO 2 conversion. Similarly, Zhang et al 79 demonstrated that a membrane electrode assembly with porous flow-through the electrode could also boost the overall CO 2 conversion selectivity at industrially relevant rates from concentrated bicarbonate solutions.…”

“…11b, point out that the improvement could be correlated with an easier desolvation and more rapid pairing kinetics with carbamate over K + than over Li + . Interestingly, Kim et al 75 report that the effects of cations vary with the catalyst types: Ni single-atom catalyst is less sensitive to cation effects than a metallic catalyst. The authors attributed such trend to the high potential of zero charges of single-atom catalysts that can maintain a high surface charge density no matter the size of the alkali cations.…”