Effect of Gaseous Contaminants on Electrochemical CO2 Reduction to C2+ Products

Electrochemical conversion of CO₂ into valuable fuels and chemicals has gained attention owing to the mild conditions applied and the possibility to integrate renewable energy sources to power the process. One of the major drawbacks of CO₂ point sources such as the chemical industry or power plants is the presence of contaminants such as SO₂, H₂S, COS and NO_x which could be detrimental to the copper catalysts that drive the conversion of CO₂ to C₂₊ products. The industrial feedstock cleaning procedures are typically energy and capital intensive, making it desirable to study the effect of various contaminants on the CO₂RR and to determine the limits of each contaminant in order to derive an optimal feedstock cleaning procedure.

In this work, we study the influence of various concentrations of sulfur-based gaseous contaminants such as SO₂, H₂S and COS in the CO₂ feed, on the selectivity, product distribution and catalyst stability during the CO₂RR. Presence of SO₂ above 100 ppm significantly suppresses the C₂₊ products and CO at -1.0 V vs RHE, however, at -1.2 V vs RHE, this is not observed until above 1000 ppm. The main products observed under the suppressed conditions are hydrogen and formate. With H₂S, a similar effect is observed even at 10 ppm at -1.0 V vs RHE, while at -1.2 V vs RHE, this is not observed until above 100 ppm. COS proved to be the most detrimental to copper, suppressing the C₂₊ products even at 10 ppm at -1.0 V and -1.2 V vs RHE. Recovery experiments show that it takes 1-4 hours of purging with pure CO₂ and a constant voltage supply to (partially) regenerate the copper catalyst after exposure to 1 h of 10000 ppm of SO₂/H₂S/COS, making the continuous operation of CO₂RR plant difficult in the presence of these contaminants.