Onset and Consequences of Streamwise Depletion in Zero-Gap CO2 Electrolyzers

Lourenço Vieira^a^,^b, Pedro Villarroel^c^,^d, Roman Schärer^a, Egon Kecsenovity^d, Jürgen Schumacher^a

^aTeam of Electrochemical Cells and Energy Systems, Institute of Computational Physics (ICP), Zürcher Hochschule für Angewandte Wissenschaften (ZHAW), Winterthur 8400, Switzerland

^bDepartment of Chemical and Process Engineering, Karlsruher Institut für Technologie (KIT), Karlsruhe 76131, Germany

^cDepartment of Physical Chemistry and Materials Science, University of Szeged, Szeged 6720, Hungary

^deChemicles Zrt, Szeged, Hungary

Materials for Sustainable Development Conference (MATSUS)
Proceedings of MATSUS Fall 2026 Conference (MATSUSFall26)

C3 Current bottlenecks of the industrial application of CO2 electrolysis

Palma, Spain, 2026 October 26th - 30th

Organizers: Balazs Endrodi and Kevinjeorjios Pellumbi

Poster, Lourenço Vieira, 517
Publication date: 22nd July 2026

Zero-gap membrane electrode assemblies enable high-rate CO₂-to-CO electrolysis, but scale-up generates streamwise gradients that can culminate in local CO₂ depletion. Here, we develop a two-dimensional, non-isothermal continuum scale model to determine what controls the onset of depletion and how the cell responds once it is reached. The model resolves the projected flow direction and through-plane MEA structure and is assessed against local current-density and gas-composition measurements from a segmented cell. Within the cathode catalyst layer, CO₂ supply couples gas-phase transport and dissolution with ionic-strength-dependent salting-out, carbonate chemistry, and capillary water saturation. Increasing saturation promotes depletion by restricting gas transport and the CO₂-accessible Ag surface, while increasing the liquid-accessible surface available for hydrogen evolution. We examine how current density, gas residence time, pressure, and hydration determine where this transition occurs. Once CO₂ supply no longer sustains its electrochemical consumption, CO formation becomes transport-limited, activity shifts upstream, and hydrogen evolution increasingly carries the downstream current, lowering CO selectivity and current-density uniformity. Concurrent changes in pH and carbonate speciation connect depletion to carbon crossover and membrane transport. The framework distinguishes reactant depletion from flooding and ionic limitations, providing a mechanistic basis for operating and scaling zero-gap CO₂ electrolyzers.

Acknowledgements:

This work is funded by the Swiss State Secretariat for Education, Research and Innovation (SERI) and is part of the European Commission’s Marie Skłodowska-Curie doctoral network MiEl. Under the HORIZON programme, the MiEl project received funding by the European Union via the Grant Agreement No. 101073003.

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