Thin nickel films boost green hydrogen production

Ultra-thin nickel oxide coatings can significantly improve the performance of anion exchange membrane (AEM) water electrolysers, a promising technology for producing green hydrogen. This was demonstrated by a team led by HZB scientist Dr. Michelle Browne. The results show that a nickel oxide film only 10 nanometres thick outperformed conventional nickel oxide powder electrodes while using less than 1% of the catalyst material. The study is published in the Journal of Materials Chemistry A,

Green hydrogen is needed in big quantities for a future fossil free economy, not only as an energy dense fuel but as well for the chemical industry. Hydrogen can be produced by electrolysis, which splits water into hydrogen and oxygen using electricity from renewable sources. Different types of electrolysers are currently used: The so called PEM electrolysers work already on an industrial scale, but they need scarce noble metals as catalysts, which presents a sort of bottleneck. AEM electrolysers are actually less efficient than PEM-electrolysers, but can do with abundant, non-precious metals such as nickel instead. However, their technology readiness level is still somewhat behind. A new study could help to change this, since it shows a way to improve the catalyst performance of nickel oxides by using a thin film instead of a powder.

Better performance with less catalyst

The HZB team compared a commercially available nickel oxide powder catalyst with an ultra-thin nickel oxide layer deposited by magnetron sputtering, a coating technique already used in industry. In laboratory tests, the thin-film catalyst required less energy to drive the reaction and remained more stable over time than the powder-based electrode.

Put into a working AEM electrolyser, the two electrodes turned out to produce hydrogen at the same rate and consume about the same electricity. What separated them was material loading: the sputtered coating needed roughly 150 times less nickel oxide than the sprayed powder to do the same job. It also needed slightly less voltage, a difference of about 4% at full output, and it aged better, with the powder electrode chemically breaking down over 65 hours of operation while the thin coating stayed largely as it started. The team reports the result as a 140-fold higher hydrogen output "per gram of catalyst." That figure is another way of stating the difference in material use rather than a difference in how much hydrogen comes out.

“We implemented our catalysts in a electrolyser cell of 4 cm² surface, to make sure that the results are useful for larger applications”, says Dr. Karuppasamy Dharmaraj, first author of the study and postdoc in the team of Michelle Browne, who leads the Young Investigator Group Electrocatalysis at HZB. 

The scientists observed that the thin film maintained its structure during long-term operation, while the powder catalyst underwent major chemical and structural changes. With advanced X-ray techniques at the synchrotron source SOLEIL, France, they could observe how the catalyst changed during the reactions. These measurements revealed that the thin-film catalyst activates mainly at its surface while preserving its internal structure. In contrast, the powder catalyst required much larger structural changes to become active.

Why catalyst architecture matters

“Not only the catalyst material itself but also its physical form plays a major role”, explains Dharmaraj. Conventional powder coatings can be uneven and often require polymer binders that may degrade during operation. The sputtered thin films form a uniform coating, improving access to active reaction sites and reducing energy losses.

“Our results show that carefully designed thin-film catalysts can achieve high performance while using much less material. Understanding how these catalysts operate and remain stable is important for developing more efficient and cost-effective green hydrogen technologies,” says Michelle Browne.