Hydrogen Bubble Growth in Alkaline Water Electrolysis: An Immersed Boundary Simulation Study

Enhancing the efficiency of industrial water electrolysis for hydrogen production is important for the energy transition. In electrolysis, hydrogen is produced at the cathode, which forms bubbles due to the diffusion of dissolved hydrogen in the surrounding supersaturated electrolyte. Hydrogen (and oxygen) bubbles play an important role in the achievable electrolysis efficiency. The growth of the bubbles is determined by diffusive and convective mass transfer. In turn, the presence and the growth of the hydrogen bubbles affect the electrolysis process at the cathode.
In the present study, we simulate the growth of a single hydrogen bubble attached to a vertical cathode in a 30 wt KOH solution in a cathodic compartment represented by a narrow channel. We solve the Navier-Stokes equations, mass transport equations and potential equation for a tertiary current distribution. A sharp interface immersed boundary method with an artificial compressibility method for the pressure is employed. To verify the numerical accuracy of the method, we performed a grid refinement study and checked the global momentum and hydrogen mass balances. We investigate the effects of flow rate and operation pressure upon bubble growth behaviour, species concentrations, potential and current density. We compare different cases in two ways: for the same time and for the same bubble radius. We observe that increasing the flow velocity leads to a small increase in efficiency. Increasing the operation pressure causes higher hydrogen density which slows down the bubble growth. It is remarkable that, for a given bubble radius, increasing the pressure leads to a small decrease in efficiency.