There has been increasing interest in the electrochemical reduction of CO2 as it can store electrons into stable chemicals and potentially reduce the amount of CO2 in the atmosphere. We studied gas-fed CO2 electrolysis which circumvents the slow diffusion of the CO2 gas in aqueous environment that usually leads to &lt; 30 mA/cm2 limiting current density. For gas-fed electrolysis, ionic management in the solid electrolyte has traditionally been a problem. The use of a bipolar membrane (BPM) enables sustainable ionic flux and diminished product crossover. However, the acidic environment created by the water dissociation in a BPM facilitates the hydrogen evolution reaction (HER). In this work, we used the layer-by-layer (LBL) assembly method to deposit a weak acidic cation exchange layer onto a BPM. A pH-responsive dye was constructed to precisely monitor the local surface pH. It revealed a pH transition from &lt;2 to 4.5 within 50 nm of the LBL region. Interestingly, the CO2 reduction test showed that a higher surface pH in the LBL modified BPM has a similar CO2 reduction current to that of the pristine BPM, but with apparently suppressed HER current. Thus, we confirmed the CO2 reduction has a rate-determining step that does not involve proton in our BPM based gas-fed CO2 electrolyzer. The method of monitoring local pH can be extended to other types of gas-fed electrolyzer as well as fuel cells, and the knowledge learnt from this work may help to design better gas-fed CO2 electrolyzers.

Bipolar membrane with weak acid cation exchanger for CO2 electrolysis

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.