Bubble dynamics in water electrolysis using multiphase Lattice Boltzmann Method

Abstract

Hydrogen, as an energy carrier, is of paramount importance in the energy transition. At the industrial level, it can be derived from various sources, including fossil fuels, biomass, or electrolysis. In Alkaline Water Electrolysis (AWE), the growth of hydrogen bubbles directly impacts system efficiency. Understanding and simulating this growth, attributed to the diffusion of dissolved hydrogen in the supersaturated electrolyte near nucleation sites via diffusive and convective mass transfer, is a crucial step towards advancing knowledge in this field and unlocking new possibilities.

This research focuses on simulating the growth of a single hydrogen bubble in a supersaturated domain, both far from and near the cathode, in a 30 wt% KOH solution. Bubble growth, a mesoscale phenomenon, is investigated using the Lattice Boltzmann Method (LBM). A comprehensive comparison of the Shan-Chen (SC), Colour Gradient (RK), and Interface Tracking Phase-Field (HZC) methods was conducted to measure the intricacies of the multiphase system accurately. The Laplace Law equation served as a benchmark, demonstrating that the HZC method produced the most accurate results.

A continuous species transfer method is employed to track hydrogen transport from the supersaturated electrolyte into the bubble, validated with Newman's analytical solution of mass transfer controlled by pure diffusion inside a sphere. Two cases are then analyzed: one of a single bubble far from an electrode in a supersaturated domain and another of a single bubble near an electrode with a constant hydrogen flux. For the first case, bubble growth follows a power law equivalent to R ∼ t^0.5, while in the second case, growth follows R ∼ t^0.7, matching results from previous studies. Finally, this method is extended to a 3D model; however, the results cannot be directly compared to the 2D model due to the shorter runtime resulting from computational cost.