Surface Alloying in Silver-Cobalt through a Second Wave Solution Combustion Synthesis Technique.

Herein, we report the synthesis of silver-cobalt nanopowders using three different modes of solution combustion synthesis, and we present the effects of the synthesis conditions on particle morphology. The synthesized nanoparticles were characterized using X-ray diffraction (XRD), Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), UV-Visible spectrophotometer (UV-vis), Transmission electron microscopy (TEM), and X-Ray Photoelectron Spectroscopy (XPS) to understand the structural and elemental properties. When Co is synthesized over Ag in a second wave of combustion, peak shifts observed in XRD and XPS show a change in the cell parameters and prove the existence of a strong electronic interaction between Ag and Co. Better control of mixing and alloying through the second wave combustion synthesis mode (SWCS) was evident. The sequence of combustion affects the structure and composition of the material. SWCS reduces the amount of carbon content, as compared to single-stage combustion, and the combustion of carbon is followed by a rearrangement of atoms.

Synthesis of Highly Efficient Bifunctional Ag/Co3O4 Catalyst for Oxygen Reduction and Oxygen Evolution Reactions in Alkaline Medium.

Ag/Co3O4 catalysts using three different modes of solution combustion synthesis were developed and characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, and transmission electron microscopy to identify crystallite size, oxidation state, composition, and morphology. Cyclic voltammetry and linear sweep voltammetry measurements for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) confirm the bifunctionality of the electrocatalysts. The electrochemical evaluation indicates that a synergic effect between Ag and Co enhances the activity through the fast breaking of O-O bond in the molecular oxygen to enhance the reduction mechanism. The high content of cobalt (Co) in the catalyst Ag/Co3O4-12, synthesized by second wave combustion, improves the activity for ORR, and the reaction mechanism follows a 3.9 number of electron transfer in overall reaction. The kinetic and limiting current densities of Ag/Co3O4-12 are maximum when compared to those of other Ag/Co3O4 catalysts and are very close to commercial Pt/C. Moreover, the maximum current density of OER for Ag/Co3O4-12 makes it a promising candidate for various bifunctional electrocatalytic applications such as fuel cells and metal-air batteries.