High-resolution neutron imaging of salt precipitation and water transport in zero-gap CO2 electrolysis

Abstract The electrochemical reduction of CO2 is a pivotal technology for the defossilization of the chemical industry. Although first pilot-scale electrolyzers exist, water management and salt precipitation remain a major hurdle to long-term operation. In this work, we present the first high resolution neutron imaging (6 µm) of a zero-gap CO2 electrolyzer to uncover water distribution and salt precipitation under application-relevant operating conditions (200 mA cm− 2 at 2.8 V with a Faraday efficiency for CO of 99%). Precipitated salts penetrating the cathode gas diffusion layer can be observed, which are believed to block the CO2 gas transport and are therefore the major cause for the commonly observed decay in Faraday efficiency. Neutron imaging further shows higher carbonate accumulation under the cathode channel of the flow field compared to the land. In fact, a higher local reaction rate under the land compared to the channel can be estimated from the gas bubble generation on the opposing anode side.