Enhancing the efficiency of industrial water electrolysis for green hydrogen production is vital for the energy transition. The formation of gas bubbles at the electrode-electrolyte interface and their accumulation in the bulk affect the electrolysis efficiency by reducing the active surface area, obstructing the ionic pathways, hindering the mass transport to the electrode, and increasing the ohmic resistance. Our research focus on understanding the (H2, O2) bubble dynamics and developing efficient bubble removal methods, thus for highly efficient and cost-competitive alkaline water electrolysers (AWE).
Direct Numerical Simulations of Electrolytic Bubble Growth
A sharp-interphase Immersed Boundary Method (IBM) is developed for direct numerical simulations of the growth of electrolytic hydrogen (or oxygen) bubbles. The growth of a bubble is determined by diffusive and convective mass transfer across the immersed boundary. With this numerical tool we work on the following topics:
- Comparing the bubble growth at different boundary conditions: no-slip (clean water), free-slip (with contamination), Marangoni stress boundary (with Marangoni flow)
- Understanding the bubble growth at different operation environment: flow rate, pressure, potential, current density
- Understanding bubble detachment
Euler-Lagrange Simulations of Bubbly Flows in AWE
The performance of an AWE is closely linked to the hydrodynamics of the gas-liquid flow in each cell. We employed a Euler-Lagrange method to simulate bubbly flow in an AWE cell, with direct implementation of insights gained from DNS of bubble growth. Using this numerical approach we work on the following topics:
- Understanding the flow dynamics at different operation environment: flow rate, pressure, current density
- Determining the relation between bubble dynamics and the cell performance
- Designing and optimizing the cell configuration: zero gap, electrode pattern, voltage pulsing
Void fraction measurement using X-ray visualization techniques
Measuring the gas fraction and its distribution in electrolysers is challenging due to opaque dense bubbly flows and the required high spatial resolution. The latter is particularly difficult in case of zero-gap or narrow-gap configurations. We utilize advanced X-ray visualization techniques to measure the void fraction in an in-house electrolyser with adjustable gap size, with a resolution of 15 microns. With these experimental investigations, we work on the following topics:
- Measuring the gas distribution in the cell at different configurations under different operating conditions
- Understanding the contribution of bubble presence/dynamics to the cell overpotential
- Understanding liquid crossover phenomenon