The electrochemical reduction of CO2 is a pivotal technology for the defossilization of the chemical industry. Although pilot-scale electrolyzers exist, water management and salt precipitation remain a major hurdle to long-term operation. In this work, we present 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 a cell voltage of 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 salt accumulation under the cathode channel of the flow field compared to the land.

Anion-exchange membrane water electrolyzers (AEMWEs) have seen a significant rise in performance and durability in recent years. However, systematic studies of membrane-electrode assembly parameters such as ionomer and catalyst contents...

Direct catalyst coating of membranes is an obvious membrane‐electrode assembly (MEA) fabrication approach. Nevertheless, it bears significant challenges related to excessive swelling of the wetted membranes and catalyst layers during coating. Thermal decaling, which is currently used in proton exchange electrolysis, cannot be used with typical hydrocarbon‐based anion‐exchange membranes due to the lack of a glass transition point. In this work, a novel direct‐coating approach for MEAs for anion‐exchange membrane water electrolysis is proposed. An additional adhesive foil is used to minimize membrane swelling during the coating of the second catalyst layer. The resulting cell efficiency (1 A cm−2 at 1.8 V with ≥ 1.9 mgIr cm−2) is comparable to spray‐coated cells, while the mass transport is reduced at higher current densities (2.11 V vs 2.27 V at 2.7 A cm−2). A fully self‐casted catalyst‐coated membrane with low thickness (35 µm) achieves promising performance of 1.4 A cm−2 at 1.8 V in 0.1 m KOH and 2.0 A cm−2 in 1 m KOH. Constant current holds at 1 A cm−2 in 1 m KOH further shows a comparably low degradation rate of both spray‐ and bar‐coated cells (≈1 mV h−1) after a stabilization period.

Dry cathode operation is a desired operation mode in anion-exchange membrane water electrolyzers, but water management is crucial. This is visualized using high-resolution neutron radiography and the ion-exchange capacity of the cathode ionomer is varied.

Schematic diagram of the K-GF fabrication process. Step 1: deposition of MnOx layers onto the P-GF electrode surface using acidified KMnO4 solutions. Step 2: removal of MnOx layers using an acidified H2O2 solution to produce the K-GF electrode.

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.

No abstract