Operando Neutron Imaging for Improved Understanding of Gas Distributions in an Alkaline Electrolyzer
Authors: Kragh-Schwarz Marcus , Bentien Anders , Birk Jonas Okkels , Huss-Hansen Mathias K. , Olesen Soffi Ester Sola , Hjelme Sara , Jacobsen Andreas Nørgaard , Forooghi Pourya , Nielsen Lars Pleth 
Published: December 2024

Optimizing hydrogen and oxygen transport within porous electrodes is essential for improving the efficiency of industrial alkaline electrolyzers. Current commercial electrodes, such as nickel foam, are limited by insufficient gas management. Research suggests that at least 5% efficiency improvements can be obtained by enhancing bubble removal in electrolyzers1,2. This challenge is particularly pronounced in large-scale industrial alkaline electrolyzers, with electrode diameters upwards of two meters3.

In this study, we present quasi-dynamic operando neutron radiographic measurements conducted on an alkaline electrolysis cell equipped with commercial nickel foam electrodes. The imaging measurements involved a parametric study examining the impact of various operational parameters including pore density, current density, flow rate, and electrolyzer configuration (comparing zero gap versus non-zero gap assembly). All imaging experiments were conducted at NEUTRA at the Paul Scherrer Institute.

Operando neutron imaging offers a unique approach for direct monitoring of the spatial distribution of hydrogen and oxygen gases inside the nickel foam during electrolysis. Utilizing the high contrast in attenuation between the electrolyte and gas, it is possible to identify transport-related bottlenecks, active regions of the electrodes during operation, and immobilized bubbles.

Our findings suggest that the hydrogen and oxygen evolution reactions primarily occur near the electrode-membrane interface. Specifically, imaging of the bottom part of the electrolysis cell indicates that approximately 50% of hydrogen and oxygen is produced in the innermost quarters of both the cathode and anode. Additionally, stroboscopic operando neutron imaging reveals that 5 - 10% of the volume within the electrode compartments remains occupied by trapped gas bubbles even after system flush-out, underscoring the critical need for enhanced gas management within electrolyzers.

In this talk, we will present the experimental method applied in our study, discuss our findings, and detail how these results can lead to further optimization of electrolyzers. We will also demonstrate how the experimental results can be used as input for numerical modelling, and thus providing a practical framework for improving electrolyzer design and operation. Through this work, we aim to contribute to the development of more efficient and effective electrolyzer technologies by combining neutron imaging with numerical modelling.

Acknowledgements

This work was supported by Innovation Fund Denmark under Case no. 2077-00021A and Case. No. 2040-00025B.

References

[1] K. Mazloomi, N. B. Sulaiman, and H. Moayedi, “Electrical Efficiency of Electrolytic Hydrogen Production,” Int J Electrochem Sci, vol. 7, no. 4, pp. 3314–3326, Apr. 2012.

[2] S. De Li, C. C. Wang, and C. Y. Chen, “Water electrolysis in the presence of an ultrasonic field,“ Electrochim Acta, vol. 54, no. 15, pp. 3877–3883, Jun. 2009.

[3] Frederiksen, M. L., Kragh-Schwarz, M. V., Bentien, A., and Nielsen, L. P., “Improved performance of electrodes for alkaline electrolysis,“ Transactions of the IMF, 101(3), 115–117, 2023.

Figure 1