At the center of this process is the hydrogen evolution reaction (HER). An electrochemical cell does the job of water splitting. Here, hydrogen gas surfaces at the negatively charged electrode. Catalysts play a pivotal role, making the reaction efficient by lowering the overpotential, which is essentially the difference between the theoretical and actual voltage required for the reaction.
A recent entry in the line-up of catalysts is an alloy consisting of gold (Au) and nickel (Ni), which has demonstrated remarkable HER activity. While its electrochemical attributes have been researched extensively, the alloy's surface structure and atomic composition, crucial for determining a catalyst's electrocatalytic potential, have remained elusive.
Aiming to unravel this mystery, a research group from Chiba University has dived deep into the characteristics of the AuNi electrocatalysts. This team, helmed by Associate Professor Masashi Nakamura of the Graduate School of Engineering, encompassed other notable members such as doctoral student Syunnosuke Tanaka and Professor Nagahiro Hoshi. Their findings, delineated in their recent publication in ChemElectroChem dated 28 June 2023, probed the atomic arrangement, surface structure, and HER performance of AuNi surface alloys formed at varying temperatures on single-crystal Au electrodes.
Addressing their research's driving force, Dr. Nakamura said, "While metals like platinum have been the go-to choice for water electrolysis, their rarity and cost make them less favorable. Gold, though more chemically stable than platinum, hasn't showcased high HER activity. This is where AuNi nanoparticles can offer a compelling non-platinum alternative. Our goal was to amplify their HER prowess."
To assess the alloy's capabilities, the team shifted the AuNi/Au electrode into an electrochemical cell with 0.05 M sulfuric acid. Cyclic voltammogram (CV) and linear sweep voltammogram (LSV) measurements were then conducted. Additionally, X-ray photoelectron spectroscopy (XPS) and surface X-ray diffraction (SXRD) techniques illuminated the catalyst's surface properties.
Findings from CVs and LSVs uncovered that the efficiency of the AuNi/Au alloy in HER varied with the Au substrate's surface structure. The (110) surface was identified as the most active, trailed by (111) and (100) surfaces. A pivotal insight was that Ni's extraction from the alloyed layer enhanced the HER activity. XPS and SXRD analyses corroborated this by indicating a reduced atomic presence on the alloy's top layer, attributed to Ni's removal. This removal process led to surface defects, enhancing HER at the gold sites neighboring Ni.
This work shines a light on the intricacies of the AuNi surface alloy, setting the stage for the creation of superior Au-based catalysts that can revolutionize electrolysis and fuel cell technologies. "A future where non-platinum electrocatalysts reduce water electrolysis costs and boost energy conversion is not far," remarks Dr. Nakamura, emphasizing the study's implications.
Research Report:Hydrogen Evolution Reaction on AuNi Surface Alloy Formed on Single Crystal Au Electrodes
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