Direct Hydrothermal Synthesis of Carbonaceous Silver Nanocables for Electrocatalytic Applications

This study demonstrates a facile but efficient hydrothermal method for the direct synthesis of both carbonaceous silver (Ag@C core-shell) nanocables and carbonaceous nanotubes under mild conditions (<180°C). The carbonaceous tubes can be formed by removal of the silver cores via an etching process under temperature control (60-140°C). The structure and composition are characterized using various advanced microscopic and spectroscopic techniques. The pertinent variables such as temperature, reaction time, and surfactants that can affect the formation and growth of the nanocables and nanotubes are investigated and optimized. It is found that cetyltrimethylammonium bromide plays multiple roles in the formation of Ag@C nanocables and carbonaceous nanotubes including: a shape controller for metallic Ag wires and Ag@C cables, a source of Br^- ions to form insoluble AgBr and then Ag crystals, an etching agent of silver cores to form carbonaceous tubes, and an inducer to refill silver particles into the carbonaceous tubes to form core-shell structures. The formation mechanism of carbonaceous silver nanostructures depending upon temperature is also discussed. Finally, the electrocatalytic performance of the as-prepared Ag@C nanocables is assessed for the oxidation reduction reaction and found to be very active but much less costly than the commonly used platinum catalysts. The findings should be useful for designing and constructing carbonaceous-metal nanostructures with potential applications in conductive materials, catalysts, and biosensors. The direct hydrothermal synthesis of both carbonaceous silver nanocables and carbonaceous nanotubes with template-free and simple synthesis procedures are demonstrated under mild conditions. The carbonaceous nanostructures, with controllable sizes and porous walls, show potential applications in electrochemical catalysis in oxygen reduction reaction, but at a much lower cost than the commonly used platinum.