Conversion of a CO–CO2 co-feed with a porous tubular copper catalyst at low potential

In the electrochemical reduction of CO₂, copper electrodes are well known to be active and selective for a variety of products, depending on process conditions. However, the effect of feed composition on performance has not been extensively investigated, especially with respect to the conversion of CO₂ to CO. We now show for copper electrodes in a porous tubular configuration (Hollow Fibre Electrodes, HFEs) at a relatively low working potential (−1.1 V vs Ag/AgCl), that an increasing concentration of CO in the feed results in a decreasing CO₂ conversion rate to CO. Contrary, it is observed that the concomitant hydrogen production rate does not depend on the concentration of CO in the feed. These observations are in good agreement with thermodynamic predictions applying the equation for the Gibbs energy of reaction. On the basis of this conclusion, we anticipate that mass transfer limitations are minimized by the tubular morphology and flow-through mode of operation. Most importantly, this study shows the necessity of a low CO concentration in the feed, to obtain a high CO₂ conversion rate.