Nitrogen-Doped Carbon Shells as a Protective Molecular Sieve for Poison-Tolerant PEMFC Anodes

Pt/C and Pt50Ru50/C materials with a protective nitrogen(N)-doped carbon shell are synthesized by a green thermal reduction method using citric acid as the reducing agent and carbon shell source, and urea as the N-doping agent. Physicochemical characterizations show that the materials consist of nanoparticles with actual composition and metal loading close to nominal ones, but a low level of alloying for bimetallic catalysts, indicating a Pt core–Ru shell structure coated with a N-doped carbon shell. The structure of the carbon shell depends on the core metal, interacting strongly with Pt and rapidly blocking most of the Pt surface active sites, while the Ru-rich surface in PtRu catalysts is less affected by its interaction with the carbon shell. Electrochemical measurements indicate that Pt50Ru50/C catalysts covered by a N-doped carbon shell present higher tolerance to poisoning by carbon monoxide and carbon dioxide than commercial Pt/C and PtRu/C catalysts, while maintaining activity toward the hydrogen oxidation reaction at the same level or even higher than uncapped catalysts. Varying the concentration of reagents in the synthesis could tune the catalyst activity and poison tolerance. Identical location transmission electron microscopy analysis did not demonstrate degradation of the best capped PtRu catalyst structure, and electrochemical tests showed activity retention.