Kevin Van Droogenbroek

Computational fluid dynamics simulations of gas-electrolyte behaviour in alkaline water electrolysis cells

In today’s world, concern is growing about the future of energy. Despite very ambitious international climate goals by 2050, global energy-related carbon dioxide (CO₂) emissions keep increasing. In order to tackle this problem, hydrogen (H₂) might become a significant part of the solution since it is a way to produce, store, move and use energy in a clean way. However, more than 95% of the actual hydrogen production is made of grey hydrogen, i.e. H₂ produced from fossil fuels, which leads to high CO₂ emissions. One way to decarbonise this energy vector is to use renewable energies (solar panels, wind turbines, etc) to produce green hydrogen via water electrolysis. This is where the HeCO₂ project funded by the Walloon region comes in, focusing on the production of green hydrogen via Alkaline Water Electrolysis (AWE).

In general, AWE is characterised by the use of two planar electrodes separated by a certain distance and operating in a liquid alkaline electrolyte solution (i.e. KOH, potassium hydroxide). However, the efficiency of the process can be improved by using 3D electrodes in a zero-gap cell configuration and by forcing the electrolyte flow through the cell. This configuration is the one that will be used in the scope of the HeCO₂ project and it is depicted in the figure below. The chemical reactions taking place at the cathode and at the anode are also highlighted.

In more details, the work will consist in the fluid mechanical modelling of liquid and gaseous flows within an industrial scale alkaline electrolyser, especially in the cathodic chambers where hydrogen will be produced. The geometry considered in this project is the one of the pilot located in the laboratories of UCLouvain. The figure hereunder gives an overview of this industrial scale pilot. The pumps used to force the flow and one of the stacks are also highlighted. An exploded view of one specific cell of the stack is shown on the top right, as well as the simplified geometry used to model the cathodic half-cell. 

The study of liquid electrolyte flow and of gaseous hydrogen bubble formation and escape will allow to optimise the performance of the electrolyser. Computational Fluid Dynamics (CFD) is a powerful numerical tool that will be used during this project to determine the optimal configuration required to homogenise the electrolyte flow (to take advantage of the whole specific area provided by the electrodes) while favouring hydrogen bubble removal from the complex 3D structures. As an example, the added value of a numerical simulation for a better understanding of the electrolyte flux distribution within a cell is shown below where the velocity field of the electrolyte (in m/s) is compared with KOH deposits that were found on one of the bipolar plates of the pilot after a bench of tests. Note that these numerical results were generated with the OpenFOAM software.