Experimental and theoretical study on the gas holdup feature in a 1.5-m tall alkaline water electrolytic cell

Abstract

Gas–liquid two-phase flow in alkaline water electrolysis critically influences current density and efficiency, yet quantitative insights remain limited. This work examines gas holdup and bubble size distribution in a custom-designed 1.5-m high-electrolytic cell, mimicking an industrial press-filter design. Results reveal that gas holdup increases with cell height and current density due to cumulative gas production, while higher electrolyte flow velocity reduces holdup by accelerating bubble transport. The average electrolytic bubble size d₄₃ evolves significantly from ~100 μm near the bottom to ~300 μm at the top of the cell, driven by coalescence and influenced by electrolysis current. A one-dimensional drift-flux model identified cell height, current density, electrolyte circulation rate, and bubble size as critical determinants of gas holdup. Theoretical predictions demonstrate that increasing d₄₃ from 130 to 270 μm can halve gas holdup, highlighting bubble size regulation as a key strategy for reducing gas holdup to enhance electrolyzer performance.