The dynamics of the growth and detachment of a single hydrogen bubble on both the horizontal and vertical microelectrode surfaces in water electrolysis were synthetically investigated by combining the numerical simulation, force balance analysis, and available experimental data. Approximately, multiple steady simulation cases with different bubble diameters for different growth instances were conducted to state the actual unsteady bubble growth and detachment behavior. The numerical simulations of the temperature distribution considering the heat transfer caused by the liquid microlayer and induced Marangoni convection effects were performed. Then, a force balance model for predicting the bubble detachment diameter was developed by fully utilizing the simulated multi-physical field parameters and the experimental results of some key bubble geometric parameters. The presented numerical model and the force balance model were validated by comparing them with previous experimental data on the potential and the bubble detachment diameter, respectively. The simulation results indicate a significantly larger potential value occurs within the microlayer, and hence, the Joule heat of the electrolyte is mainly generated in the microlayer and then transferred to the bulk flow region. Obviously, the temperature gradient distribution is formed at the bubble interface, causing unstable Marangoni convection structure. The distribution patterns and evolutions of the electrolyte temperature, Marangoni convection velocity, and microlayer thickness for the horizontal and vertical microelectrode systems are significantly different. The present force balance model presents higher prediction accuracy for the bubble detachment diameters. Moreover, the in-depth force analysis results reveal that some dominant forces influence the bubble growth and detachment.

Based on our previous visual experiments and the volume of fluid (VOF) multiphase model, the growth and detachment characteristics of a single hydrogen bubble on the horizontal microelectrode surface under the electrode-normal magnetic field have been numerically investigated. The mass transfer contributions of supersaturated dissolved hydrogen to the bubble growth from the liquid microlayer under the direct injection model and from the bulk bubble interface under the gas–liquid diffusion-controlled model are adopted. The bubble shapes and diameters predicted from the numerical investigation agree well with experimental results under the same conditions. The simulated results indicate that the supersaturated dissolved hydrogen concentration and the mass transfer source at the wedge-shaped areas adjacent to the bubble foot are obviously higher than those in the wider bulk bubble interface regions. The mass transfer contribution to the bubble growth from the liquid microlayer beneath the bubble base directly plays a dominant role. The higher current density and corresponding Lorentz force mainly appears in the wedge-shaped areas, while the higher rotational electrolyte flow velocity appear at oblique positions of the bubble equator. The bubble detachment behavior makes the rotational electrolyte flows is significantly more complex.