Plurimetallic alloys bonded in carbon nitride “shells” supported on “cores” of conducting nanoparticles as electrocatalysts for the oxygen reduction reaction (ORR)

Proton exchange membrane fuel cells (PEMFCs) are an advanced family of energy conversion devices characterized by a high efficiency and a low environmental impact. The electrochemical reactions involved in PEMFC operation must be promoted by suitable electrocatalysts to achieve a sufficient performance level. This issue is of particular relevance for the electrocatalysts meant to improve the kinetics of the oxygen reduction reaction (ORR). The ORR is sluggish, and even the best state-of-the-art electrocatalysts suffer from a variety of drawbacks including large overpotentials, a relatively poor durability and a high cost. Indeed, the best performance is afforded by materials characterized by platinum nanoparticles supported on conductive carbons showing a large surface area. Over the course of several years, our research group has devised and optimized a new and unique three-step protocol for the preparation of 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 proved extremely flexible, allowing a good control of the chemical composition and morphology of the electrocatalyst. In particular, active sites based on plurimetallic alloys of the PGM-X type (PGM → platinum-group metal: Pt, Pd…; X → other metal: Fe, Co, Ni, Rh…) are obtained easily. These systems may show an improved turnover frequency in comparison with pristine platinum nanoparticles. Furthermore, 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.