The electrochemical oxygen reduction reaction is the limiting half-reaction for low-temperature hydrogen fuel cells, and currently costly Pt-based electrocatalysts are used to generate adequate rates. Although most other metals are not stable in typical acid-mediated cells, alkaline environments permit the use of less costly electrodes, such as silver. Unfortunately, monometallic silver is not sufficiently active for economical fuel cells. Herein we demonstrate the design of low-cost Ag–Co surface alloy nanoparticle electrocatalysts for oxygen reduction. Their performance relative to that of Pt is potential dependent, but reaches over half the area-specific activity of Pt nanoparticle catalysts and is more than a fivefold improvement over pure silver nanoparticles at typical operating potentials. The Ag–Co electrocatalyst was initially identified with quantum chemical calculations and then synthesized using a novel technique that generates a surface alloy, despite bulk immiscibility of the constituent materials. Characterization studies support the hypothesis that the activity improvement comes from a ligand effect, in which cobalt atoms perturb surface silver sites.
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We acknowledge support from the US DOE Office of Basic Energy Sciences, Division of Chemical Sciences (FG-02-05ER15686). We also acknowledge the University of Michigan Electron Microbeam Analysis Laboratory for use of the microscopy facilities. This research is also supported as part of a user project by Oak Ridge National Laboratory (ORNL)'s Center for Nanophase Materials Sciences, which is sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, US DOE (J-C.I.). Finally, we acknowledge H. Xin and T. van Cleve for helpful discussions and experimental assistance.
The authors declare no competing financial interests.
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Holewinski, A., Idrobo, JC. & Linic, S. High-performance Ag–Co alloy catalysts for electrochemical oxygen reduction. Nature Chem 6, 828–834 (2014). https://doi.org/10.1038/nchem.2032
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