Synthesis, characterization and electrochemical performance of tri-metal Pt-free carbon nitride electrocatalysts for the oxygen reduction reaction

This paper reports the preparation of two families of platinum-free carbon nitride electrocatalysts with general formula PdCoX-CNy. These materials were synthesized through innovative protocols which permitted to control the stoichiometry of the active sites and the concentration of nitrogen in the carbon nitride support. The electrocatalysts were extensively characterized in terms of chemical, thermal, morphological and electrochemical points of view. The materials characterized by a nitrogen concentration >15%, with respect to the platinum reference exhibited an improved tolerance toward the thermal degradation under oxidizing conditions. Electrochemical measurements, performed with the cyclic voltammetry-thin film rotating disk electrode method (CV-TF-RDE), showed that the oxygen reduction reaction (ORR) of proposed materials occurs through a mechanism similar to that of the platinum reference both in the high- and in the low-potential regimes. In addition, results demonstrated that, with respect to the platinum reference, the overpotential in the ORR of proposed materials increases as the N concentration in the support is raised. The most important figures of merit accounting for the performance of the electrocatalysts were determined by assembling the materials in single PEMFCs which were tested under operative conditions. Finally, it was determined that selected electrocatalysts required 0.69 g of palladium to produce 1 kW of power; in the same conditions the reference MEA needed 1.12 g of platinum.