ARTICLE pubs.acs.org/JPCC
Electrochemical Characterization of PtRu Nanoparticles Supported on Mesoporous Carbon for Methanol Electrooxidation Federico A. Viva,† Mariano M. Bruno,*,†,‡ Matías Jobbagy,§ and Horacio R. Corti†,§ †
Grupo Celdas de Combustible, Departamento de Física de la Materia Condensada, Centro Atomico Constituyentes, Comision Nacional de Energía Atomica (CNEA), Av General Paz 1499 (1650), San Martín, Buenos Aires, Argentina ‡ Escuela de Ciencia y Tecnología, Universidad de Gral. San Martín, Martin de Irigoyen 3100 (1650), San Martín, Buenos Aires, Argentina § Instituto de Química Física de los Materiales, Medio Ambiente y Energía (INQUIMAE), Universidad de Buenos Aires CONICET, Ciudad Universitaria, Pabellon II, 1428 Buenos Aires, Argentina ABSTRACT: Nanoparticles of PtRu supported on mesoporous carbon were obtained by the impregnation and reduction method with NaBH4. The highsurface-area mesoporous carbon was obtained by carbonization of a resorcinolformaldehyde polymer with a cationic polyelectrolyte as a soft template. Surface characterization performed by transmission electron microscopy and powder X-ray diffraction showed a homogeneous distribution and high dispersion of metal particles. The PtRu catalyst shows an electrochemical active surface area, determined by CO stripping, 45% higher than PtRu catalyst synthesized by the same method on Vulcan. This translated in a 25% increase in the methanol oxidation current as well as a lower poisoning rate and higher turnover frequency, as was assessed by cyclic voltammetry and chronoamperometry. Differential electrochemical mass spectroscopy indicated an 8% higher conversion efficiency of methanol to CO2, demonstrating the benefits of using a mesoporous carbon as catalyst support.
1. INTRODUCTION The improvement of the efficiency of methanol electrooxidation continues to be a key research interest due to the role played by this reaction in direct methanol fuel cell (DMFC), which is envisioned as a convenient energy source for portable applications. PtRu alloy has known to be the best electrocatalyst for the methanol electro-oxidation reaction for more than 30 years14 and has been used in fuel cells fed directly with methanol5 for ∼25 years. However, DMFC still strives for a major breakout due to the slow kinetics of methanol oxidation and the high catalyst loadings needed to sustain reasonable power densities.6 Commonly, the catalyst is supported over carbon particles to have a good dispersion, increase the metal particles surface area, and reduce the metal content.710 The carbon support also has to provide an electrical connectivity between the metal particles and the gas diffusion layer or current collector. Evidence demonstrates that the nature of the support and the interaction between support and metal particles influence the morphology, dispersion, and stability of the final catalyst,1113 thus affecting the catalytic activity of the metal particles.8,10,1418 Recently, mesoporous carbon with controlled structure was used as support for fuel cell electrocatalyst exhibiting promising activities in both half cell and single cell configuration.10,1926 The control of structural parameters, such as surface area, pore size, and particle morphology, provides extra fine-tuning of the final catalyst electroactivity.7,8,10 In contrast, carbon powders like Vulcan XC-72, the most common electrocatalyst carbon r 2011 American Chemical Society
support used in fuel cells have a much simple particle structure and lower surface area, which might not provide the best substrate for the metal particles. Structured carbons allow the preparation of highly dispersed catalytic nanoparticles, whereas the mesoporosity guarantees facile diffusion path for reactants and byproducts.10,27 Moreover, the inherent surface microporosity provides good physical anchoring sites for the deposited catalyst layer.28 There are several methods to obtain structured carbon.2931 One of the most used is by replication of inorganic template, which produces carbon particles with small size and narrow mesopore distribution (15 nm).33,34 In the present work, we describe the preparation and characterization of PtRu catalyst, prepared by the impregnationreduction method, supported on a carbon with high surface area. The substrate, prepared by carbonization of a resorcinol-formaldehyde polymer with a soft template, has micropores (
