Eco-friendly synthesis of bimetallic AuAg nanoparticles and their application in direct alcohol fuel cell

Full text: In this work we reported the synthesis of nanosized gold, silver and gold-silver particles that can be chemically accomplished in alkaline medium by any molecule containing a hydroxyl group like glycerol capable of generating it. The mechanism of the process was also investigated and we propose that the alkoxide generated in high-pH medium is the actual responsible for the reduction. Ultraviolet spectroscopy and the transmission electron microscopy confirmed the formation of colloidal NPs. The nanoparticles were also directly produced onto carbon to yield Au/C, Ag/C and AuAg/C. Extended X-ray absorption fine-structure (EXAFS) spectroscopy at the Au L₃ edge evidenced surface segregation of silver in the AuAg/C material. Also the X-ray absorption near edge structure (XANES) region indicated a slight reduction in the Au 5d band occupancy due the presence of silver. Since Fuel Cell is a potent source of energy for the future, the catalytic properties of the NPs were then investigated for anodic glycerol electro-oxidation reaction and results for AuAg NPs are compared with those for monometallic Au and Ag NPs. We observed that the presence of Ag in the bimetallic materials provided a more efficient catalyst for glycerol electro-oxidation in terms of the energy efficiency, reducing by 120 mV the onset potential for glycerol electro-oxidation. On the other hand, the bimetallic catalysts were found to be less promising than the Au/C catalyst with respect to the reaction rate. Ag addition influenced the mechanism of glycerol electro-oxidation, favoring the C-C-C bond breaking, as evidenced by the selective formation of formic acid on the bimetallic catalysts. The impact of Ag on the glycerol electro-oxidation over AuAg/C may be driven by electronic modifications and Ag segregation on the catalysts surface. (author)