Single atom Pt on Pd@Au and Pd shell on AuPt nanowire: application in electrocatalysis

Abstract text (incl. figure legends and references)

Off late, research in nanoscience emerged as front-runner due to its tremendous industrial applications including application in renewable energy resources. Due to depleting fossil fuel reserves and ever-growing demand for environment friendly renewable energy resources, researchers are trying to develop efficient catalyst for energy conversion. Catalysts based on nanomaterials is one of the focused areas of research. Specifically, one dimensional nanomaterial is widely explored in catalytic applications due to high surface area. Ultrathin Au nanowires have been explored for several applications, but the fragile nature at high temperature, and in polar medium limits its catalytic applications. Instability of these nanowires under the electron beam possess difficulties for its microstructural study. Alloying of Au nanowire with Pd and Pt increases the stability as well as improves electrocatalytic efficiency with faster kinetics due to bifunctional mechanism. In our current investigation, ultrathin single crystalline AuPdPt trimetallic nanowires with different composition have been synthesized using microwave assisted synthesis at liquid-liquid interface. By changing the order of second and third metal reduction on Au nano wire template, single atom Pt on Pd@Au nanowire and Pd shell on AuPt nanowire have been synthesized. Interestingly, these trimetallic nanowires retains single crystalline nature after successive reduction of second and third metal on Au nanowire. Using z-contrast high angle annular dark field imaging (HAADF-STEM), x-ray photoelectron spectroscopy (XPS) and cyclic voltammetry surface atomic distribution as well as chemical environment have been elucidated. Annealing under control atmosphere, e.g., Ar and CO, was performed to modify the surface of these nanowires. Surface atomic distribution has been further visualized and explained using z-contrast HAADF-STEM, and electrocatalysis. Single atom Pt on Pd@Au nanowire showed highest activity with moderate onset potential compared to bimetallic Pd@Au nanowire. After Ar-annealing, alloying improvement led to vanishing Pt single atom rom surface. Whereas CO-annealing caused PdPt segregation on surface leading to improved potential and activity. Ar-annealed Pd shell on AuPt nanowire showed better kinetics than as-synthesized one resulting lower onset potential. CO-annealed Pd shell on AuPt nanowire showed highest activity with higher potential. These nanowires were explored as catalyst for electrocatalytic methanol oxidation. Further, changes in activity with surface atomic distribution has been visualised and explained by electron microscopy.