Using a combination of density functional theory (DFT) calculations and an array of experimental techniques including in situ X-ray absorption spectroscopy, we identified, synthesized, and tested successfully a new class of electrocatalysts for the oxygen reduction reaction (ORR) that were based on monolayers of Pt deposited on different late transition metals (Au, Pd, Ir, Rh, or Ru), of which the Pd-supported Pt monolayer had the highest ORR activity. The amount of Pt used was further decreased by replacing part of the Pt monolayer with a third late transition metal (Au, Pd, Ir, Rh, Ru, Re, or Os). Several of these mixed Pt monolayers deposited on Pd single crystal or on carbon-supported Pd nanoparticles exhibited up to a 20-fold increase in ORR activity on a Pt-mass basis when compared with conventional all-Pt electrocatalysts. DFT calculations showed that their superior activity originated from the interaction between the Pt monolayer and the Pd substrate and from a reduced OH coverage on Pt sites, the result of enhanced destabilization of Pt–OH induced by the oxygenated third metal. This new class of electrocatalysts promises to alleviate the major problems of existing fuel cell technology by simultaneously decreasing materials cost and enhancing performance.
Density functional theory calculations Oxygen reduction reaction Platinum monolayer Fuel cells Electrocatalysis Cathode
Work at UW-Madison was supported by DOE-BES and by S. C. Johnson through a fellowship to AUN. Supercomputing time at NERSC, CI, PNNL, and National Center for Computational Sciences (NCCS; provided through the INCITE program) resources is gratefully acknowledged. Work at BNL was supported by the Divisions of Chemical and Material Sciences, U.S. Department of Energy (Contract No. DE-AC02–98CH10886). Work at ORNL was conducted at the Center for Nanophase Materials Sciences, which is sponsored by the Division of Scientific User Facilities, U.S. Department of Energy. The NCCS at ORNL is supported by the Office of Science of the U.S. DOE under Contract No. DE-AC05-00OR22725. AUN thanks Lars Grabow for his valuable help.
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