Eletrocatalisadores de PtAu/C para Oxidação de Formiato: Estudos Eletroquímicos e de Célula Unitária

The increasing in the atmospheric CO2 is attributed to the burning of fossil fuels for our energy needs. The excess of CO2 in atmosphere causes environmental pollution, green house effect and it is found to be a major cause for the global warming process1. In order to address these issues, different strategies are being considered and most of them involve a deep change in the current energy supply. Therefore, CO2 valorization are in the interest of many researchers which are looking forward to the conversion of CO2 in valuable products (such as formic acid and formate) and its use as fuels in direct liquid fuel cells (DLFC) 2,3. Actually, numerous organic, inorganic and bioorganic fuels have been studied for using in DLFC. Nevertheless, the use of formate in alkaline solutions has been intensely studied for fuel cell applications since the change from the acid media to the alkaline can dramatically improve kinetics of the oxygen reduction reaction (ORR) and also formate oxidation. Furthermore, formate salts are stable, have low toxicity, are easily handled and relatively inexpensive and is a carbon-neutral fuel which can be produced from reduction of carbon dioxide4. In order to improve DLFC efficiency, this study reports the use of PtAu/C electrocatalysts with different atomic ratios (90:10, 70:30 and 50:50) supported on Vulcan XC 72 carbon and prepared by the sodium borohydride method toward formate electro-oxidation in alkaline media. The materials were characterized by X-ray diffraction, showing peaks characteristics of Pt and Au face-centered-cubic structures, and also by transmission electron micrographs that show the nanoparticles well dispersed on carbon and a mean particle size between 4 and 5 nm for all electrocatalysts. Electrochemical experiments show PtAu/C as promising catalysts toward formate oxidation, while single cell experiments reveal PtAu/C 90:10 as the best material since it provides a power density higher than Pt/C. The incorporation of Au could increase formate oxidation for more than one reason: (i) a facilitated rupture of C–H bond; (ii) the Au/oxide interface or (iii) by regenerating active sites.