Synthesis, Structure and Electrochemical Performance of New Pt-Rh Carbon Nitride Electrocatalysts for the Oxygen Reduction Reaction

Polymer electrolyte membrane fuel cells (PEMFCs) are a class of energy conversion devices operating at low temperatures (T<150°C) which have recently drawn great interest from both the academic world and the industry. The reasons lie in their high efficiency and low environmental impact. Direct methanol fuel cells (DMFCs) operating using a methanol solution as fuel, are particularly interesting for applications in the automotive industry and in portable electronics. Nevertheless, fuel cell systems still suffer from serious drawbacks including high costs, durability issues and, on a more fundamental level, significant shortcomings in the performances of their component materials, i.e. the electrolyte membrane and the catalysts. In particular, the catalyst materials used at the cathode to enhance the rate of the oxygen reduction reaction (ORR) pose significant challenges. In order to achieve a sufficient activity towards the ORR at the temperatures of operation found in PEMFCs, the supported platinum metal has been the most used catalyst. Recently, several attempts have been made to enhance its activity by alloying Pt with other metals such as V, Cr, Fe, Co and Ni. Indeed, the resulting alloy catalysts show a slightly lower overpotential for the ORR in comparison with platinum, and in some instances a higher tolerance towards methanol contamination was reported.