Modelling of finite-gap and zero-gap alkaline water electrolyser configurations for gas bubble management and optimisation

Gas evolution in classical alkaline water electrolysers strongly influences electrochemical performance through bubble accumulation at electrode surfaces and within electrolyte channels. Multiphysics modelling using COMSOL software is employed to systematically investigate gas bubble behaviour in both classical finite-gap and zero-gap alkaline water electrolyser configurations. The effects on gas bubble formation of key cell design parameters, including electrode height, as well as operating conditions, such as pressure, electrolyte flow rate, and electrolyte concentration, are analysed. The results show that these parameters affect gas accumulation significantly and, consequently, electrochemical performance. A new zero-gap cell design is proposed. It exhibits approximately four times higher current density than a classical finite-gap cell (∼ 0.4 A/cm2 vs 0.1 A/cm2 at 1.9 V), while also substantially reducing gas bubble accumulation (gas volume fraction εg ∼ 0.015 to 0.045 vs ∼ 0.25 to 0.35). The influence of porous structure and surface properties of gas diffusion electrodes on bubble accumulation and cell performance is systematically investigated. Comparisons between finite-gap and zero-gap designs reveal distinct bubble transport mechanisms, which affect electrochemical performance. This analysis provides insights for the optimisation of electrode and cell design in alkaline water electrolysers.