Editorial pubs.acs.org/JPCL
The Magic of Electrocatalysts
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E
lectrochemically activated catalytic processes are the heart of energy conversion and storage, as well as sensing applications. Electrochemistry will play a major role in energizing electronic devices and future transportation.1 Whether it is for a fuel cell or glucose sensing,2,3 the design of the electrocatalyst plays an important role in attaining the selectivity and efficiency of an electrochemical reaction. In a proton exchange membrane (PEM) fuel cell, for example, nanometer-sized metal catalyst particles are dispersed on a carbon support in order to carry out redox processes. The recent surge in electrocatalytic research activity has exploited use of new materials emerging from nanoscience.4,5 The size, shape, composition, and substrate all play important roles in modulating the properties of electrocatalysts. The ability to probe surface reactions and size- and shape-selective catalysts has enabled scientists to establish structure−activity relationships. The quest to achieve greater efficiency and selectivity using less catalyst continues. For example, nonmetal catalysts, such as carbon nanotubes and graphene-based assemblies, have been found to be effective in carrying out ORR.6,7 A major thrust in electrocatalyst development is in the area of the oxygen reduction reaction (ORR). The electrochemical reduction of O2 can proceed via two- or four-electron transfer to produce H2O2 or H2O. Careful electrocatalyst design is important to driving the proton-coupled four-electron-transfer process. Basic understanding of the ORR has implications in designing efficient photocatalytic systems for the oxygen evolution reaction (water-splitting reaction). Pt-, Pd-, Au-, and Co-based metal alloy and core−shell structures have been the topic of many recent ORR investigations.8−10 The Perspective by Wong and co-workers, which appears in this issue, focuses on the experimental and theoretical aspects of one-dimensional (1D) noble metal electrocatalyst nanostructures in oxygen reduction [Wong, S.; Koenigsmann, C.; Scofield, M.; Liu, H. Designing Enhanced One-Dimensional Electrocatalysts for the Oxygen Reduction Reaction: Probing Size-and Composition-Dependent Electrocatalytic Behavior in Noble Metal Nanowires. J. Phys. Chem. Lett. 2012, 3, 3385− 3398]. Using the example of Pt−Pd1−xAux nanowires, the authors point out that rational tuning of both wire size and composition in a bimetallic 1D noble metal is crucial for achieving significant enhancements in electrocatalyst activity and durability. Another intriguing aspect of electrocatalysis can be found in the reduction of CO2 to alcohols and hydrocarbons. Peterson and Norskov11 recently explained how binding energies dictate the formation of intermediates in CO2 electrochemical reduction at various metal electrodes. Protonation of the adsorbed CO intermediate is singled out as the most important step in determining the overpotential of CO2 reduction. A basic understanding of surface interactions is key to screening electrocatalysts for selectivity of electrochemical reactions.
AUTHOR INFORMATION
Notes
Views expressed in this Editorial are those of the author and not necessarily the views of the ACS.
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REFERENCES
(1) Wagner, F.; Lakshmanan, B.; Mathias, M. Electrochemistry and the Future of the Automobile. J. Phys. Chem. Lett. 2010, 1, 2204−2219. (2) Gregg, B. A.; Heller, A. Redox Polymer Films Containing Enzymes. 2. Glucose Oxidase Containing Enzyme Electrodes. J. Phys. Chem. 1991, 95, 5976−5980. (3) Barton, S. C.; Kim, H. H.; Binyamin, G.; Zhang, Y. C.; Heller, A. The “Wired” Laccase Cathode: High Current Density Electroreduction of O2 to Water at +0.7 V (NHE) at pH 5. J. Am. Chem. Soc. 2001, 123, 5802−5803. (4) Chen, A. C.; Holt-Hindle, P. Platinum-Based Nanostructured Materials: Synthesis, Properties, and Applications. Chem. Rev. 2010, 110, 3767−3804. (5) Stamenkovic, V. R.; Mun, B. S.; Arenz, M.; Mayrhofer, K. J. J.; Lucas, C. A.; Wang, G. F.; Ross, P. N.; Markovic, N. M. Trends in Electrocatalysis on Extended and Nanoscale Pt−Bimetallic Alloy Surfaces. Nat. Mater. 2007, 6, 241−247. (6) Dai, L.; Yu, D.; Nagelli, E.; Du, F. Metal-Free Carbon Nanomaterials Become More Active than Metal Catalysts and Last Longer. J. Phys. Chem. Lett. 2010, 1, 2165−2173. (7) Qu, L. T.; Liu, Y.; Baek, J. B.; Dai, L. M. Nitrogen-Doped Graphene as Efficient Metal-Free Electrocatalyst for Oxygen Reduction in Fuel Cells. ACS Nano 2010, 4, 1321−1326. (8) Koh, S.; Strasser, P. Electrocatalysis on Bimetallic Surfaces: Modifying Catalytic Reactivity for Oxygen Reduction by Voltammetric Surface Dealloying. J. Am. Chem. Soc. 2007, 129, 12624−12625. (9) Sasaki, K.; Naohara, H.; Cai, Y.; Choi, Y. M.; Liu, P.; Vukmirovic, M. B.; Wang, J. X.; Adzic, R. R. Core-Protected Platinum Monolayer Shell High-Stability Electrocatalysts for Fuel-Cell Cathodes. Angew. Chem., Int. Ed. 2010, 49, 8602−8607. (10) Xing, Y.; Cai, Y.; Vukmirovic, M. B.; Zhou, W.-P.; Karan, H.; Wang, J. X.; Adzic, R. R. Enhancing Oxygen Reduction Reaction Activity via Pd−Au Alloy Sublayer Mediation of Pt Monolayer Electrocatalysts. J. Phys. Chem. Lett. 2010, 1, 3238−3242. (11) Peterson, A. A.; Norskov, J. K. Activity Descriptors for CO2 Electroreduction to Methane on Transition-Metal Catalysts. J. Phys. Chem. Lett. 2012, 3, 251−258.
Prashant V. Kamat, Deputy Editor University of Notre Dame
© 2012 American Chemical Society
Published: November 15, 2012 3404
dx.doi.org/10.1021/jz301767a | J. Phys. Chem. Lett. 2012, 3, 3404−3404
