Pt-Fe and Pt-Ni Carbon Nitride-Based 'Core-Shell' ORR Electrocatalysts for Polymer Electrolyte Membrane Fuel Cells

This report describes the preparation of new bimetal carbon nitride (CN)-based 'core-shell' electrocatalysts for the oxygen reduction reaction (ORR) for application in polymer electrolyte membrane fuel cells. The 'core' consists of graphitic carbon nanoparticles and the 'shell' of CN electrocatalysts. These latter are based on Pt-Fe and Pt-Ni active sites which, with respect to pure Pt, are devised for their improved ORR performance. This morphology allows to stabilise the active sites of the electrocatalysts by a chemical coordination process with the support as the coordinating agent. The wt% of N is lower than 2% to obtain electrocatalytic 'shells' with a good electron conductivity. The electrocatalysts with a 'core-shell' morphology were extensively characterised from the chemical, thermogravimetric and morphological points of view. Electrochemical measurements carried out by cyclic voltammetry using a thin-film rotating ring-disk electrode (CV-TF-RRDE) method allowed to study the specific surface area of the active sites and to determine the ORR performance and the reaction mechanism. Finally, the materials were mounted at the cathode of single fuel cells and their performance was tested in operative conditions. The Pt mass required to achieve 1 kW was as low as 0.3 g, versus 1.11 g of the reference membrane-electrode assembly.