Pt free metal and metal oxides electrocatalysts for the Oxygen Reduction Reaction in alkaline conditions

Pt free metal and metal oxides electrocatalysts for the Oxygen Reduction Reaction in alkaline conditions Alessandro Minguzzi,a Maria Luisa Foresti,b Massimo Innocenti,b Cristina Locatelli,a Fabio Meroni,a Sandra Rondinini,a Alberto Vertovaa. a Dipartimento di Chimica Fisica ed Elettrochimica, Università degli Studi di Milano Via Golgi 19, 20133 Milan, Italy alessandro.minguzzi@unimi.it b University of Florence, Department of Chemistry, via della Lastruccia 3, 50019 Sesto Fiorentino (FI) Italy Direct alcohol fuel cells (DAFCs) represent a promising energy conversion device for mobile and stationary applications. Among the key issues to be addressed for their technological exploitation, the alcohol cross-over represents a limiting factor since the alcohol can be directly oxidized on the cathode and short-circuit the cell. In parallel, the recent improvement of anion membranes makes the development of alkaline DAFCs competitive with the acid ones. In this work we present the preparation and characterization of Pt free metal and metal oxides as possible cathode materials in alkaline DAFCs. These materials are either prepared by electrodeposition or synthesised as disperse phase powders by the wet method (Ag/C) and by the sol-gel technique (IrO2-SnO2). The investigation is carried out using potentiodynamic techniques at the Rotating Ring Disk Electrode (RRDE). The electrocatalytic powders are glued to the support with thin layer of anion exchange Tokuyama membrane. The use of the RRDE allows to quantify inter alia the amount of hydrogen peroxide produced in a broad range of potentials. A comparison of the different electrode materials in term of kinetic current and amount of hydrogen peroxide produced and the starting potential of the ORR was carried out. A interesting dependence of morphology and size of the Ag nanoparticles and of the iridium content (15-70%mol) on the ORR activity is observed. The influence of the alcohol cross-over on the oxygen reduction reaction (ORR) kinetic is also presented and discussed. Finally, following recent guidelines of theoretical studies, .the synergic effect of two different metals each of them acting on different steps of ORR is also shown. Acknowledgements: The financial contributions of PRIN 2008 – “Pt-free electrocatalysts for direct alcohol fuel cells.” 2008N7CYL5 and PUR-Università degli Studi di Milano (2009 – 2010) funds are gratefully acknowledged.