Templating effects onto electrocatalytic properties of Pt-free carbons for oxygen reduction reaction

The aim of this work was to investigate morphologic effects that templating may exert on the synthesis of nitrogen-doped Pt-free carbons and any resulting variation in the electrochemical behavior of these products for the oxygen reduction reaction (ORR). This latter reaction is kinetically slow and limits the energy efficiency of currently investigated Polymer Electrolyte Membrane Fuel Cells. The starting point of this work was a silica templating method, in which organic precursors reacted at high temperature in the presence of high surface area silica. Other simple templating methods were projected and developed. Among these, some catalyst synthesis procedures required solid supports as shape-imprinting materials. The aim was to obtain a replica of template porosity and surface features in the synthesized products. In other synthesis, auto-templating processes of catalyst precursors, e.g. freeze-drying and in-situ generation of gas, were studied. Synthesized catalysts have been characterized by physico-chemical methods as surface area analysis and cyclic voltammetry, which allowed the study of the kinetics of the electrochemical ORR by rotating disk electrode and rotating ring disk electrode in acidic and alkaline solutions. A relation between pore size distribution and electrochemical activity of the synthesized materials seemingly exists. Overall, a BET porosity analysis suggests that templating procedure can be actually effective to improve the electrocatalytic behaviour for ORR, only if it ensures a homogeneous distribution of macropores and small and medium mesopores (Figure 1). This surface feature is necessary to catalyst performances because it favours mass transport processes to/from the electrode surface.