No abstract

The electrochemical reduction of carbon dioxide (CO2) is a promising technology in light of energy transition and industrial electrification. In this study, two different electrolyzer configurations, flow‐through and flow‐by modes, were analyzed for the production of carbon monoxide to resolve the CO2 mass‐transfer limitation problem at high current densities in gas diffusion electrodes. These two configurations respectively state convective and diffusive flow inside the gas diffusion layer, and their effect was studied on the cathodic performance of the electrolyzer by varying the operating conditions: cathodic potential, electrocatalyst loading, and Nafion content. In flow‐through configuration, a current density of 220 mA/cm2 could be achieved at a faradaic efficiency of 90 %; whereas, in the flow‐by configuration, the current density was at the same faradaic efficiency limited to 140 mA/cm2. However, the flow‐through configuration has a few limitations, such as lower energy efficiency, owing to the higher ohmic drop and the faster deactivation caused by crystallization of electrolyte salts inside the gas diffusion electrode. Therefore, flow‐by mode is currently the most adequate configuration for the long‐term operation of electrolyzers for the reduction of CO2 to CO. This study represents an essential step toward the application of electrolyzers for the electroreduction of CO2.

A zero‐gap flow electrolyzer with a tin‐coated gas diffusion electrode as the cathode was used to convert humidified gaseous CO2 to formate. The influence of humidification, flow pattern and the type of membrane on the faradaic efficiency (FE), product concentration, and salt precipitation were investigated. We demonstrated that water management in the gas diffusion electrode was crucial to avoid flooding and (bi)carbonate precipitation, to uphold a high FE and formate concentration. Direct water injection was validated as a novel approach for water management. At 100 mA/cm2, direct water injection in combination with an interdigitated flow channel resulted in a FE of 80 % and a formate concentration of 65.4+/−0.3 g/l without salt precipitation for a prolonged CO2 electrolysis of 1 h. The use of bipolar membranes in the zero‐gap configuration mainly produced hydrogen. These results are important for the design of commercial scale CO2 electrolyzers.

Today's electrochemical reactor design is a less developed discipline as compared to electrocatalytic synthesis. Although catalysts show increasing conversion rates, they are often operated without measures for the reduction of concentration polarization effects. As a result, a stagnant boundary layer forms at the electrode‐electrolyte interface. This stagnant boundary layer presents an additional voltage drop and reduces the energy efficiency. It is generally accepted that this phenomenon is caused by a combination of fast electrode reactions and slow diffusion of the reacting species. Our earlier work demonstrated the potential of non‐conducting static mixers to reduce concentration polarization effects. However, there are few studies on conductive static mixers applied as electrodes. In this study, we present a new concept of additive manufactured flow through electrode mixers. Our electrode geometry combines a high surface area with mixing properties, diminishing concentration polarization effects of transport‐limited reactions. Mass transport properties of these conductive static mixers are evaluated in an additive manufactured electrochemical reactor under controlled conditions by applying the limiting‐current method.