Chemists uncover the true active surface of nickel catalysts
Nickel is a promising, cost-effective and robust catalyst for alkaline water electrolysis—a key technology for the climate-neutral production of hydrogen. However, the actual structure of the active surface of such nickel electrodes under reaction conditions had not yet been conclusively determined. A research team at Ulm University has now refuted a decades-old assumption: The catalytically…
Scientists at Ulm University have discovered that nickel catalysts used in alkaline water electrolysis do not have a nickel oxyhydroxide (NiOOH) surface as previously thought, but instead have a nickel dioxide (NiO₂) surface. This finding, published in Nature Catalysis, is significant because the oxygen evolution reaction, where oxygen is produced during water splitting, is a key part of the electrolysis process and often experiences energy losses.
The active surface of nickel catalysts during oxygen evolution was previously assumed to consist of NiOOH. However, the Ulm researchers used isotope labeling, in situ Raman spectroscopy, electrochemical investigations, and density functional theory calculations to test this assumption. They discovered that when hydrogen is replaced by deuterium, there are no characteristic changes in the Raman spectra if the surface is NiOOH.
Instead, the experimentally observed spectra could be reconstructed, leading to the conclusion that the surface is NiO₂, not NiOOH. This difference is crucial as NiOOH contains hydrogen atoms, while NiO₂ does not, meaning that the chemical properties and reaction pathways on the surface need to be reassessed. Additionally, the study provides insights into the interpretation of Raman spectra of catalytic materials, showing that certain bands previously attributed to reaction intermediates are actually overtones, a physical phenomenon rarely observed in materials composed of two-dimensional layers.
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