Facetted Platinum Electrocatalysts for Fuel Cells Applications

RAMOS SILVINA GABRIELA; ANDREASEN GUSTAVO; TRIACA WALTER

Buenos Aires

Simposio; The Fifth International Symposium Enviromental Biotechnology and Engineering (5ISEBE); 2016

5ISEBE

The oxygen electroreduction overpotential is one of the main contributions to the losses in efficiency and power density in low temperature fuel cells. Platinum (Pt) is an effective electrocatalyst for electrodic reactions involved in hydrogen/oxygen proton exchange membrane (PEM) fuel cell systems, particularly the oxygen electroreduction reaction. The morphology and crystalline orientation of Pt are very important factors to be considered for understanding the effect of the electrocatalyst surface structure on the kinetics of electrocatalytic reactions. In this work, the preparation and characterisation of (111)-type facetted Pt crystallites electrodeposited onto carbon-supported for using in PEM fuel cell are described. High surface area facetted Pt crystallites were obtained by applying a square wave potential pulse of high frequency in aqueous chloroplatinic acid at 25°C. The influence of upper potential limits, changing between 1,2 V and 1,38 V at fixed lower potential limit of -0,2 V, on the characteristics of the facetted Pt electrocatalyst as a function of electrodeposition time was evaluated. The development of facetting with preferential crystal orientation of the electrodeposited Pt nanoparticles was followed through the changes in the relative height of weakly and strongly bound H-adatom voltammetric current peaks1. The surface morphology of the Pt nanoparticles was examined by using SEM and TEM techniques, and the characteristics of the crystalline structure were determined by X-ray diffractometry. The electrochemical active surface area of the Pt electrodeposits was determined through the hydrogen electrosorption charge by voltamperometric techniques. The characterization studies of metal electrodeposits revealed the presence of highly facetted Pt nanoparticles having a predominant (111) preferential crystal orientation, which have shown a greater catalytic activity for the oxygen electroreduction reaction. The Pt nanoparticles look like polyhedrons with predominance of triangular faces and acute angles, which is consistent with the development of the (111) preferential crystal orientation. The net charge for the electrodeposition process was determined through an electronic coulometer and the amount of Pt deposited was measured by using a spectrophotometric method with a colour developing agent of SnCl2 2. The results show that the amount of dissolved Pt during the anodic hemicycles of applied electric perturbation increases on increasing the upper potential limit as expected for an activation-controlled process of electrodissolution.