Researchers at Japan’s Chiba University have developed a better understanding of an alloy of gold (Au) and nickel (Ni) that showed promising hydrogen evolution reaction (HER) activity.
HER is what takes place when an electrochemical cell is used to split water, and hydrogen gas gets released at the negatively charged electrode.
In a paper published in the journal ChemElectroChem, the scientists explain that they investigated the surface structure, atomic arrangement, and HER activity of AuNi surface alloys prepared at different alloying temperatures on single-crystal Au electrodes.
“Rare and highly expensive metals like platinum are commonly used as catalysts for water electrolysis. While Au shows high chemical stability as a catalyst compared to platinum, it suffers from low HER activity,” lead researcher Masashi Nakamura said.
“Now, AuNi nanoparticles have emerged as a promising non-platinum alternative, and it is crucial to improve their HER activity further.”
To get to this finding, Nakamura and his team transferred the AuNi/Au electrode to an electrochemical cell with 0.05 M sulfuric acid to perform cyclic voltammogram (CV) and linear sweep voltammogram (LSV) measurements, evaluating its HER activity. The surface properties of the AuNi/Au catalyst were also analyzed using X-ray photoelectron spectroscopy (XPS) and surface X-ray diffraction (SXRD) techniques.
CVs and LSVs revealed that the HER activity of AuNi/Au depended on the surface structure of the Au substrate, with (110) surface resulting in the highest activity followed by (111) and (100), respectively.
Also, the surface alloy improved the HER activity via Ni dealloying. This was verified by XPS and SXRD, wherein the group observed a decrease in the atomic occupancy on the topmost layer of the surface caused by the dissolution of Ni from the surface-alloy layer. The Ni dealloying process created defects on the surface, and the low-coordination Au sites adjacent to Ni activated the HER.
In the researchers’ view, these insights into the structural and electrochemical properties of AuNi surface alloy pave the way for highly active and durable Au-based catalysts for practical electrolysis and fuel cell applications.
“Designing effective non-platinum electrocatalysts can reduce the cost of water electrolysis and also improve its energy conversion efficiency, which is crucial for accelerating toward a hydrogen-driven society,” Nakamura said.