Investigation of microstructure and hydrogen absorption properties of bulk immiscible AgRh alloy nanoparticles

• Published in: Journal of alloys and compounds 2021-07, Vol.869, p.159268, Article 159268
• Main Authors: Tayal, Akhil, Seo, Okkyun, Kim, Jaemyung, Kusada, Kohei, Kobayashi, Hirokazu, Kitagawa, Hiroshi, Sakata, Osami
• Format: Article
• Language: English
• Subjects: Ag-Rh alloy nanoparticles; Bimetals; Charge transfer; Fine structure; Heterogeneous alloy; Hydrogen; Hydrogen absorption; Hydrogen storage; Microstructure; Miscibility; Nanoalloys; Nanoparticles; Solid solutions; X ray absorption; X-ray diffraction; XAFS
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2021.159268

•The local structure around Ag and Rh environment and active sites for the H2 storage was investigated.•On the contrary to the XRD, the XAFS analysis reveals a distinct local environment of Ag and Rh in the sample.•Rh local environment has a higher degree of the disorder as compared to the Ag.•Formation of nano/sub-nano alloy clusters occurs in the sample with atomic-level mixing at the interfacial region.•The interfacial region acts as the active sites for hydrogen storage. Bimetallic alloy nanoparticles (NPs) exhibit superior catalytic and chemical storage properties relative to the monometallic NPs. Previously, it has been reported that bimetallic AgRh forms solid-solution alloy NPs that have unusual hydrogen storage properties not commonly observed in individual Ag and Rh NPs. Here, we use a combination of X-ray diffraction (XRD) and X-ray absorption fine structure spectroscopy (XAFS) techniques to investigate the microstructure and unique hydrogen absorption properties of bulk immiscible AgRh alloy NPs. XRD analysis reveals that the long-range structure of the alloy sample can be estimated as a single fcc phase with a slightly smaller lattice parameter than that of the bulk Ag and larger than that of bulk Rh. XAFS analysis reveals that charge transfer between Rh and Ag occurs in this interfacial region. The near-edge profile reveals a variety of local environments for Ag and Rh, including distinct atomic pair distances and disorder. The atomic pair distances were compressed around Ag and elongated around Rh. A substantial fraction of the sample is an alloy phase formed by mixing of nano/sub-nanosized domains of Rh and Ag NPs. Mixing at the atomic level mainly occurs in the interfacial region. Consequently, the interfacial region has an important influence over the microstructure and provides active sites for hydrogen absorption.