Alkaline high-pressure electrolysis

Since 2009, the H2 group has been working in cooperation with ITBA from Argentina on the design and development of a high-pressure electrolyzer. The main advantage of synthetizing hydrogen at high pressure is the simplification of system by omitting a posterior mechanical compression, which is the most critical and expensive element at hydrogen refueling stations. This has also a positive impact on the overall efficiency and the compactness of the facility, and allows a higher flexibility and robustness to volatile power inputs.

Two defined branches can be found within this project, where the individual progress in one branch allows refining the results of the other.

The experimental branch of the project currently aims to optimize the H2 solubility, with the following goals:

• Producing single bubbles at needle electrodes
• Observing of correct bubble formation, growing, detachment and interaction with the free surface
• Obtaining simultaneous formation of H2 and O2 bubbles.

Prototypes at 200 bar and 350 bar operated successfully at partner locations in Argentina, who will also provide a test chamber to continue with the experiments.

The theoretical branch of the project aims to develop a numerical tool for the simulation of bubble flow inside the electrolyzer. A self-developed code, implemented in OpenFOAM, is framed into the following approach for a two-phase flow:

• Modelling of bubble formation at electrode surface depending on supersaturation of dissolved hydrogen
• Bubble detachment based on balance of forces with a stochastic disturbance
• Transport of dispersed phase with an Euler-Euler approach
• Bubble coalescence/break up with Interfacial Area Transport Equation