Alloy-Carbon Nitride “core-shells” ORR electrocatalysts

The high efficiency, power density and compatibility with the environment of proton exchange membrane fuel cells (PEMFCs) make them highly attractive for a variety of applications including light-duty vehicles and distributed power generation. The operation of PEMFCs requires suitable electrocatalysts to achieve the optimum performance. This issue is of great relevance for the electrocatalysts meant to promote the oxygen reduction reaction (ORR). A new and unique three-step protocol was recently devised to prepare advanced ORR electrocatalysts. In the first step, a hybrid inorganic-organic precursor is synthesized; subsequently, the material undergoes a multi-step pyrolysis process; the final electrocatalyst is obtained after suitable chemical/electrochemical activation procedures. This protocol is extremely flexible, allowing a good control of the chemical composition and morphology of the electrocatalyst. Electrocatalysts characterized by an improved turnover frequency in comparison with pristine platinum nanoparticles are obtained. In addition, nitrogen atoms are introduced in the graphite-like support, giving so rise to a carbon nitride matrix. The latter is able to better coordinate and stabilize the alloy nanoparticles bearing the active sites, improving the performance and the tolerance of the electrocatalysts to oxidizing environments such as that found at the cathode of a PEMFC. A major improvement in the performance of the proposed family of ORR electrocatalysts is achieved by adding to the starting precursors suitable electron-conducting nanoparticles as “cores”. The final materials show an improved dispersion of the active sites in the “shell” of systems with a “core-shell” morphology. With respect to the corresponding “bulk” electrocatalysts, an enhanced performance in single-cell configuration is obtained due to an easier mass transport of reagents and products