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The role of nickel in sustainable hydrogen

As society transitions toward renewable energy, green hydrogen produced via water electrolysis is expected to play a central role in energy storage and distribution. However, current systems rely heavily on expensive noble metals, and their long-term efficiency is limited by catalyst degradation.

Nickel is an attractive alternative: inexpensive and catalytically active under alkaline conditions. But its performance depends strongly on its structure, composition, and surface chemistry. Haghverdi鈥檚 research systematically explores how these parameters influence the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), the two half鈥憆eactions that split water into hydrogen and oxygen.

Tailoring nickel oxide with atomic layer deposition

Using atomic layer deposition (ALD), Haghverdi created ultra-thin, uniform layers of nickel oxide (NiO) on both flat and three鈥慸imensional nickel substrates. This technique allowed precise control over thickness and composition, enabling detailed studies of how NiO films activate during OER.

Electrochemical activation of ALD鈥慻rown NiO improved OER performance significantly, lowering the overpotential by a factor of 3.5 to 5 compared to pristine nickel. This enhancement was linked to controlled alterations in surface energy and chemistry that promoted the creation of catalytically active 狈颈鲁鈦� species.

Engineering nickel sulphides for efficient hydrogen production

In parallel, Haghverdi explored gas鈥憄hase sulphurization to convert nickel electrodes into well鈥慸efined nickel sulphide (NixSy) phases for HER. By tuning sulphurization temperature, duration, and gas composition, he identified an optimal mixture of Ni鈧�S鈧�/Ni鈧�S鈧� that exhibited HER performance close to 90% of platinum, a remarkable achievement for a non鈥憂oble catalyst.

Long鈥憈erm testing showed that these sulphide catalysts naturally evolve toward the more active Ni鈧僑鈧� phase through a process of self鈥憀imited sulphur leaching. Rather than degrading, the catalyst becomes intrinsically more active and stable after activation.

Understanding catalyst evolution as a design tool

A central conclusion of the thesis is that catalytic materials do not remain static during operation, they transform. Instead of viewing these transformations as degradation, Haghverdi shows that with the right design strategy, controlled material evolution can improve performance, increasing surface area, enhancing charge transfer, and generating more active sites.

By combining ALD thin鈥慺ilm synthesis, sulphurization chemistry, and advanced electrochemical analysis, his work provides a comprehensive understanding of the interplay between structure, activation, and catalytic function.

Toward scalable green hydrogen technologies

The insights gained from this research offer rational guidelines for designing efficient, stable, and low鈥慶ost nickel鈥慴ased electrodes for alkaline water electrolysis. These advances help accelerate the development of sustainable hydrogen technologies and support the broader transition to a clean鈥慹nergy future.