The most recent investigations of operating conditions in a forward-bias bipolar-membrane zero-gap electrolyser using a silver cathode catalyst for the reduction of CO 2 to CO at low temperatures and near-ambient pressures are reported. First, the CO 2 electrolyser performance was investigated as a function of cathode feed humidification and composition. The highest CO partial current density was 127 mA cm −2 , which was obtained at an iR-corrected cell voltage of 2.9 V, a cathode feed humidification of 50%RH, CO 2 feed concentration of 90% and a CO Faradaic efficiency of 93%. The cells were tested continuously for 12 h at 3 V and 8 h at 3.4 V cell voltage to investigate system stability. While Faradaic efficiencies were maintained during the measurements at 3.0 V, a shift in selectivity was observed at 3.4 V, while a deterioration in current densities occurred in both cases. Using a specially designed electrochemical cell with an integrated reversible hydrogen reference electrode, it was found that the cathode catalyst is the main responsible for the observed loss in performance. It was furthermore determined via post-mortem SEM and EDX investigations that cathode deterioration is caused by catalyst agglomeration and surface poisoning.

The electrochemical reduction of carbon dioxide (CO 2 ) constitutes an increasingly important scientific topic and research on novel electrocatalysts for this demanding reaction is constantly increasing. One of the most important properties to be inferred for such electrocatalysts is their product selectivity and potential dependence thereof. However, the wide range of materials currently employed in CO 2 electroreduction (e.g., Ag, Cu, Pd) entails a large variety of gaseous and/or liquid reaction products for which accurate quantification implies a major challenge. With this motivation, in this study we present an online gas chromatography cell setup specifically designed for the accurate and reproducible determination of the product selectivities of CO 2 -reduction electrocatalysts. Therewith, we assess the parameters influencing the cell's performance and point out important design features, such as reproducible electrode alignment, minimized contact resistances and a low ratio among electrolyte volume and the electrodes' geometrical surface area. The setup was validated by performing measurements on a Pt nanoparticle catalyst for which H 2 is the only expected reduction product, while a Pd nanoparticle catalyst was subsequently used to verify its capabilities for CO 2 electroreduction selectivity measurements involving multiple liquid and gaseous products.

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We report on an electrochemically driven CO 2 separation process employing commercial anion exchange membranes to directly remove CO 2 from a dilute gas mixture and transport it across a cell. This methodology exploits the carbonation behavior of alkaline membrane systems to react CO 2 with hydroxide ions generated through the hydrogen evolution reaction and form (bi)carbonate ions. Electrochemically pumped (bi)carbonate then evolves as CO 2 on the anode side through the hydrogen oxidation reaction with H 2 . The resulting mixture of CO 2 and residual H 2 could be utilized for downstream valorization processes. Cell polarizations with 0.1−100% CO 2 in N 2 as the feed gas were performed with current densities of up to 50 mA• cm −2 , and CO 2 concentrations were monitored using online gas analysis. Further experiments examining the effect of pumping against pressure and concentration gradients were performed, along with Pd wire reference electrode experiments to discern cathode and anode overpotentials. Additional fundamental techno-economic considerations are presented to explore the cost dynamics of the system and the relevant targets for cell operation. The results show the complex interactions between cell input and performance parameters, as well as some of the critical limitations that must be overcome to allow for process scale-up to become viable.

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