Catalytic Pt-on-Au nanostructures: why Pt becomes more active on smaller Au particles.

Platinum is a widely used precious metal in many catalytic nanostructures. Engineering the surface electronic structure of Pt-containing bi- or multimetallic nanostructure to enhance both the intrinsic activity and dispersion of Pt has remained a challenge. By constructing Pt-on-Au (Pt^Au) nanostructures using a series of monodisperse Au nanoparticles in the size range of 2-14 nm, we disclose herein a new approach to steadily change both properties of Pt in electrocatalysis with downsizing of the Au nanoparticles. A combined tuning of Pt dispersion and its surface electronic structure is shown as a consequence of the changes in the size and valence-band structure of Au, which leads to significantly enhanced Pt mass-activity on the small Au nanoparticles. Fully dispersed Pt entities on the smallest Au nanoparticles (2 nm) exhibit the highest mass-activity to date towards formic acid electrooxidation, being 2 orders of magnitude (75-300 folds) higher than conventional Pt/C catalyst. Fundamental relationships correlating the Pt intrinsic activity in Pt^Au nanostructures with the experimentally determined surface electronic structures (d-band center energies) of the Pt entities and their underlying Au nanoparticles are established.

[1]  D. J. Mowbray,et al.  Trends in CO Oxidation Rates for Metal Nanoparticles and Close-Packed, Stepped, and Kinked Surfaces , 2009 .

[2]  P. Claus,et al.  The influence of real structure of gold catalysts in the partial hydrogenation of acrolein , 2003 .

[3]  Bo-Qing Xu,et al.  Platinum covering of gold nanoparticles for utilization enhancement of Pt in electrocatalysts. , 2006, Physical chemistry chemical physics : PCCP.

[4]  N. Marković,et al.  Structural effects in electrocatalysis: Oxygen reduction on the Au (100) single crystal electrode , 1984 .

[5]  H. Sakurai,et al.  Effect of electronic structures of Au clusters stabilized by poly(N-vinyl-2-pyrrolidone) on aerobic oxidation catalysis. , 2009, Journal of the American Chemical Society.

[6]  Younan Xia,et al.  Nanocrystals with unconventional shapes--a class of promising catalysts. , 2007, Angewandte Chemie.

[7]  Yushan Yan,et al.  Highly efficient submonolayer Pt-decorated Au nano-catalysts for formic acid oxidation. , 2008, Chemical communications.

[8]  Zhong Lin Wang,et al.  Synthesis of Tetrahexahedral Platinum Nanocrystals with High-Index Facets and High Electro-Oxidation Activity , 2007, Science.

[9]  Jens K. Nørskov,et al.  Theoretical surface science and catalysis—calculations and concepts , 2000 .

[10]  J. Bokhoven,et al.  d Electron density and reactivity of the d band as a function of particle size in supported gold catalysts , 2007 .

[11]  Xiulei Ji,et al.  Nanocrystalline intermetallics on mesoporous carbon for direct formic acid fuel cell anodes. , 2010, Nature chemistry.

[12]  V. Radmilović,et al.  Formic acid oxidation on Pt–Au nanoparticles: Relation between the catalyst activity and the poisoning rate , 2012 .

[13]  M. Arenz,et al.  Oxygen electrocatalysis in alkaline electrolyte: Pt(hkl), Au(hkl) and the effect of Pd-modification , 2002 .

[14]  J. Nørskov,et al.  How a gold substrate can increase the reactivity of a Pt overlayer , 1999 .

[15]  D. Tripković,et al.  Kinetic study of formic acid oxidation on carbon-supported platinum electrocatalyst , 2005 .

[16]  Roger Parsons,et al.  The oxidation of formic acid at noble metal electrodes Part III. Intermediates and mechanism on platinum electrodes , 1973 .

[17]  Kimihisa Yamamoto,et al.  Size-specific catalytic activity of platinum clusters enhances oxygen reduction reactions. , 2009, Nature chemistry.

[18]  M. El-Sayed,et al.  Changing catalytic activity during colloidal platinum nanocatalysis due to shape changes: electron-transfer reaction. , 2004, Journal of the American Chemical Society.

[19]  Masashi Nakamura,et al.  Structural effects of electrochemical oxidation of formic acid on single crystal electrodes of palladium. , 2006, Journal of Physical Chemistry B.

[20]  B. Steele,et al.  Materials for fuel-cell technologies , 2001, Nature.

[21]  J. Parks.  Less Costly Catalysts for Controlling Engine Emissions , 2010, Science.

[22]  H. Gasteiger,et al.  Activity benchmarks and requirements for Pt, Pt-alloy, and non-Pt oxygen reduction catalysts for PEMFCs , 2005 .

[23]  Zhenmeng Peng,et al.  PtAu bimetallic heteronanostructures made by post-synthesis modification of Pt-on-Au nanoparticles , 2009 .

[24]  A. Gross,et al.  Local reactivity of supported metal clusters: Pdn on Au(1 1 1) , 2004 .

[25]  J. Yi,et al.  Surface-specific overgrowth of platinum on shaped gold nanocrystals. , 2009, Physical chemistry chemical physics : PCCP.

[26]  Hubert A. Gasteiger,et al.  Methanol electrooxidation on well-characterized Pt-Ru alloys , 1993 .

[27]  M. W. Ruckman,et al.  Monolayer Metal Films on Metallic Surfaces: Correlation between Electronic Structure and Molecular Chemisorption , 1994 .

[28]  Bo-Qing Xu,et al.  Pt Flecks on Colloidal Au (Pt∧Au) as Nanostructured Anode Catalysts for Electrooxidation of Formic Acid , 2009 .

[29]  Bo-Qing Xu,et al.  Enhancement of Pt utilization in electrocatalysts by using gold nanoparticles. , 2006, Angewandte Chemie.

[30]  Pascal Granger,et al.  Catalytic NO(x) abatement systems for mobile sources: from three-way to lean burn after-treatment technologies. , 2011, Chemical reviews.

[31]  Bo-Qing Xu,et al.  Surprisingly strong effect of stabilizer on the properties of Au nanoparticles and Pt^Au nanostructures in electrocatalysis. , 2010, Nanoscale.

[32]  Eric van Steen,et al.  Intrinsic reactivity of gold nanoparticles: Classical, semi-empirical and DFT studies , 2007 .

[33]  Bjørk Hammer,et al.  Structure sensitivity in adsorption: CO interaction with stepped and reconstructed Pt surfaces , 1997 .

[34]  R. Masel,et al.  Size effects in electronic and catalytic properties of unsupported palladium nanoparticles in electrooxidation of formic acid. , 2006, The journal of physical chemistry. B.

[35]  B. Yan,et al.  Manipulation of Pt∧Ag Nanostructures for Advanced Electrocatalyst , 2009 .

[36]  Hee-Young Park,et al.  Surface Structure of Pt-Modified Au Nanoparticles and Electrocatalytic Activity in Formic Acid Electro-Oxidation , 2007 .

[37]  Philip N. Ross,et al.  Improved Oxygen Reduction Activity on Pt3Ni(111) via Increased Surface Site Availability , 2007, Science.

[38]  D. Goodman,et al.  The Nature of the Metal-Metal Bond in Bimetallic Surfaces , 1992, Science.

[39]  A. Wiȩckowski,et al.  Formic Acid Decomposition on Polycrystalline Platinum and Palladized Platinum Electrodes , 1999 .

[40]  Bo-Qing Xu.  Electro-oxidation of Formic Acid on Nanostructured Pt-on-Au(Pt^ Au) Electrocatalysts , 2008 .

[41]  J. Nørskov,et al.  Surface electronic structure and reactivity of transition and noble metals , 1997 .

[42]  E. Roduner.  Size matters: why nanomaterials are different. , 2006, Chemical Society reviews.

[43]  B. Yan,et al.  Proper alloying of Pt with underlying Ag nanoparticles leads to dramatic activity enhancement of Pt electrocatalyst , 2008 .

[44]  D. Su,et al.  Platinum-monolayer shell on AuNi(0.5)Fe nanoparticle core electrocatalyst with high activity and stability for the oxygen reduction reaction. , 2010, Journal of the American Chemical Society.

[45]  Y. Tong,et al.  Electrocatalytic properties of Au@Pt nanoparticles: effects of Pt shell packing density and Au core size. , 2011, Physical chemistry chemical physics : PCCP.

[46]  O. Petrii,et al.  Real surface area measurements in electrochemistry , 1991 .

[47]  Jens K Nørskov,et al.  Changing the activity of electrocatalysts for oxygen reduction by tuning the surface electronic structure. , 2006, Angewandte Chemie.

[48]  Bongjin Simon Mun,et al.  Trends in electrocatalysis on extended and nanoscale Pt-bimetallic alloy surfaces. , 2007, Nature materials.

[49]  M. J. Weaver,et al.  Electrocatalytic Pathways on Carbon-Supported Platinum Nanoparticles: Comparison of Particle-Size-Dependent Rates of Methanol, Formic Acid, and Formaldehyde Electrooxidation , 2002 .