Gas bubble removal from a zero-gap alkaline electrolyser with a pressure swing and why foam electrodes might not be suitable at high current densities

Gas bubble removal from a zero-gap alkaline electrolyser with a pressure swing and why foam electrodes might not be suitable at high current densities

Bleeker, J.J. (TU Delft ChemE/Transport Phenomena)
van Kasteren, Celine (Student TU Delft)
van Ommen, J.R. (TU Delft ChemE/Product and Process Engineering)
Vermaas, D.A. (TU Delft ChemE/Transport Phenomena)

2024

To make green hydrogen more economically attractive, the energy losses in alkaline electrolysis need to be minimized while operating at high current densities (1 A cm⁻²). At these current densities the ohmic resistance and gas bubbles effects contribute largely to the energy losses. To mitigate the gas bubbles losses, we demonstrate, for the first time, a pressure swing to remove gas bubbles in a zero-gap alkaline water electrolyzer. The pressure swing leverages the ideal gas law to increase the volume of gas in the system periodically, for a short duration (<2 s). This temporal volume increase effectively removes bubbles from the electrolyzer. We show that pressure swing can be used to measure the effect of bubbles on the ohmic resistance (R_Bubbles). Our results reveal that foam electrodes have a significantly larger R_Bubbles than perforated plate electrodes (1.8 Ω cm² vs 0.3 Ω cm²). The time-averaged cell voltage reduces by 170 mV when applying pressure swings to an electrolyzer operating at 200 mA cm⁻² in 1 M KOH with foam electrodes. The bubble resistance further depends on the electrolyte conductivity (inversely proportional) and is only moderately affected by operating pressure (25 % lower when increasing pressure amplitude from 1–2 to 1–5 bar). By implementing these findings in a model, we estimate that the pressure swing could reduce the cell voltage by ∼0.1 V for an electrolyzer operating at industrial conditions (6 M KOH, 80 °C, 1 A cm⁻²) for foam electrodes. For perforated plate electrodes, however, the reduced cell voltage is lower and does not outweigh the additional compression energy.

Alkaline water electrolysis
Gas bubbles
Hydrogen
Pressurized
Zero-gap

http://resolver.tudelft.nl/uuid:6d851c18-203b-4c97-a56c-99ba178cbcbd

https://doi.org/10.1016/j.ijhydene.2024.01.147

0360-3199

International Journal of Hydrogen Energy, 57, 1398-1407

Institutional Repository

journal article

© 2024 J.J. Bleeker, Celine van Kasteren, J.R. van Ommen, D.A. Vermaas