Scalable and Efficient H2S Treated Nickel Foam Electrocatalyst for Alkaline Water Electrolysis Under Industrial Conditions
Authors: Olesen Soffi Ester Sola , Jensen Anders Westergaard , Iversen Bo Brummerstedt , Fenini Filippo , Nielsen Lars Pleth , Bentien Anders 
Published: December 2024

With the foreseen orders of magnitude increase of green hydrogen production from electrolysis in the coming decade [1], electrolyzer stacks must be produced in a scalable and efficiently manner based on abundant materials, while still maintaining high energy efficiency. This study explores a novel synthesis route utilizing reactive Chemical Vapor Deposition (CVD) of hydrogen sulfide (H2S) gas to enhance the catalytic activity of nickel foam for alkaline water electrolysis. The synthesis involves sulfiding the nickel foam at temperatures ranging from 100 °C to 140 °C in an H2S atmosphere for durations of 1 to 17 hours. The resulting electrodes exhibit a uniform film with distinctive nanostructural modification [2].
Electrochemical performance evaluations were conducted under industrial conditions, in 30 wt% KOH electrolytes at 85 °C with current densities ranging from 200 to 500 mA/cm2 for up to two weeks. Testing under high current densities and elevated temperatures is essential to meet industrial requirements [3]. The tests were made in an immersed single cell setup with 4 cm2 electrodes on both sides [4]. Remarkably, the H2S-CVD modified electrodes demonstrate a cell potential reduction of 0.4 V@200 mA/cm2, corresponding to an 18% increase in the overall efficiency for water splitting compared to pristine nickel foam. Electrochemical analysis reveals a substantial 30-fold higher surface area following the H2S-CVD treatment. [2].
Structural and compositional analyses of the modified nickel foam electrodes were conducted using various techniques including X-Ray Photoelectron Spectroscopy (XPS), Scanning Electron Microscopy (SEM), Energy Dispersive X-Rays (EDX) analysis, and synchrotron powder X-ray diffraction (XRD) both before and after running alkaline electrolysis. These analyses reveal the presence of Ni3S2 with a film thickness ranging from 1 to 4 μm post-H2S treatment. Characterization of the synchrotron data XRD shows 14 wt% Ni3S2 for the H2S-CVD treated samples. Furthermore, prolonged reaction times reveal the continuous reaction and emergence of NiS, elucidating the evolution of surface morphology under sulfidation conditions [2].
Post-electrolysis characterizations indicate either the absence or minimal presence of sulfur on the modified electrodes, suggesting that the enhanced performance is likely attributed to alterations in the surface morphology rather than sulfur-assisted increase in the catalytic activity. This study provides insights into the surface-sensitive characterization, synthesis conditions, activity assessments, and degradation analyses, showing the potential of H2S-mediated surface modification as electrocatalytic material in alkaline water electrolysis systems.

Bibliography

[1] International Energy Agency. Global Hydrogen Review 2021. www.iea.org/report s/global-hydrogen-review-2021.
[2] Olesen, S. E. et al. Scalable and Efficient H2S Treatment of Nickel Foam Electrocatalyst for Alkaline Water Electrolysis under Industrial Conditions. 2024. In preparation.
[3] Ehlers, J. C.; Feidenhans’l, A. A.; Therkildsen, K. T.; Larrazábal, G. O. Affordable Green Hydrogen from Alkaline Water Electrolysis: Key Research Needs from an Industrial Perspective. ACS Energy Letters. American Chemical Society March 10, 2023, pp 1502–1509. doi.org/10.1021/acsenergylett.2c02897.
[4] Frederiksen, M. L.; Kragh-Schwarz, M. V.; Bentien, A.; Nielsen, L. P. Improved Performance of Electrodes for Alkaline Electrolysis. Transactions of the Institute of Metal Finishing. 2023. 10.1080/00202967.2023.2196850.

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