Effects of the boundary conditions at the gas-liquid interface on single hydrogen bubble growth in alkaline water electrolysis

Alkaline water electrolysis is important for green hydrogen production. We simulate the growth of a single hydrogen bubble on a cathode in a 30 wt% KOH solution in a narrow channel. We develop and use a sharp interface method to solve the Navier-Stokes equations, the species transport equations, and the potential equation for a tertiary current distribution. To investigate the role of the mobility of the bubble interface, three different boundary conditions are used: the no-slip, the free-slip, and the Marangoni stress condition. The surface tension depends on the local electrolyte concentration. The simulation results show that different boundary conditions lead to minor changes in electrochemical quantities but significantly affect the force on the bubble. The Marangoni boundary condition leads to a relatively large force on the bubble, which is expected to accelerate bubble detachment. This result makes plausible why the hydrogen bubbles in alkaline electrolysis are relatively small. • An immersed boundary method to simulate Marangoni flow at a bubble has been developed. • A single growing hydrogen bubble on a macroelectrode in alkaline water electrolysis has been simulated. • The effects of different boundary conditions are compared, for the no-slip, free-slip and Marangoni stress condition. • The Marangoni effect due to the gradient in the electrolyte concentration has been simulated. • This effect causes a relatively large force on the hydrogen bubble, promoting detachment.