A deeper understanding of flooding dynamics in gas diffusion electrodes for CO2 electrolyzer: how interfacial pressure shapes gas–liquid stability

Gas-fed CO2 electrolyzers are a promising technology for sustainable fuel and chemical production, but their industrial deployment is limited by the instability of gas diffusion electrodes (GDEs), particularly in microfluidic flow cells (MFCs). A key failure mechanism is electrode flooding, which discontinues CO2 transport and favours hydrogen evolution. Although pressure control across the gas–liquid interface has emerged as a strategy to mitigate flooding, the precise role of differential pressure (ΔP) between gas and liquid side of the GDE remains poorly understood and inconsistently defined in literature. In this work, we systematically explore how gas and liquid pressure management alters the GDE interface, focusing on the understudied “flow-by” regime. Using Cu nanoparticles as a model catalyst and operating at industrially relevant current densities (0.5 A cm−2), we monitor flooding dynamics through real-time pressure readings, product selectivity analysis, electrochemical impedance spectroscopy (EIS) and field emission scanning electron microscopy (FE-SEM) in different electrochemical setups with several commercial Gas Diffusion Layers (GDL). Our results demonstrate that a ΔP of 30 mbar can fully suppress flooding, preserving catalyst performance and enabling selective CO2 reduction for over 6 h at 0.5 A cm−2, almost an order-of-magnitude improvement over uncontrolled system. The experimental ΔP value is confirmed by multiphysics simulations, by modelling capillary-driven liquid invasion and gas transport, in which a predicted onset value of 20 mbar is defined as the required value to prevent the flooding. This work provides the first integrated framework combining pressure tuning, diagnostics, and multi-physics simulation to define and optimize flow-by operation, offering actionable insights for designing robust, high-performance CO2 electrolyzers.