PtRu Nanoparticle Catalytic Activity Enhanced by the Ligand Effect
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1127-T07-01
PtRu Nanoparticle Catalytic Activity Enhanced by the Ligand Effect
Shuji Goto, Yuli Li, Naomi Nagasawa, Tadashi Senoo and Kazuhiro Noda Environment & Energy Technology Lab, Advanced Materials Laboratories, Sony Corporation, 4-16-1 Okata, Atsigi-shi, 243-0021, Japan Yoshihiro Kudo and Akihiro Maesaka Materials Analysis Center, Advanced Materials Laboratories, Sony Corporation, 4-16-1 Okata, Atsigi-shi, 243-0021, Japan Tsuyonobu Hatazawa Vanguard Material Research Lab, Advanced Materials Laboratories, Sony Corporation, 4-16-1 Okata, Atsigi-shi, 243-0021, Japan
ABSTRACT We synthesized a methanol electrocatalyst with high activity and low noble metal content. The electrocatalyst consists of carbon-supported PtRu nanoparticles, which have 1–2 Pt monoatomic layers on Ru nanocores. In spite of the pure Pt surface, the catalyst showed high catalytic activity when used in the anode of a direct methanol fuel cell. Clearly the underlying Ru atoms modified the property of the surface Pt atoms, bringing about the high catalytic activity. INTRODUCTION Direct methanol fuel cells (DMFCs) are a promising power source for portable applications owing to their system simplicity and high-energy-density fuel. Higher power, higher durability and cost reduction are necessary, however, to satisfy the requirements of the latest mobile electronic devices. To solve these challenging issues, a novel methanol electrocatalyst is required. PtRu alloy catalysts are widely used in DMFCs. The catalytic activity of PtRu alloys for methanol electro-oxidation is generally attributed to the bifunctional mechanism [1]. Ru promotes the oxidation of CO, which is formed by the dehydrogenation of methanol and is strongly bound to the adjacent Pt, by supplying an oxygen source. The oxidation of CO is the rate-determining step. Homogeneous PtRu alloys should therefore have the most Pt–Ru pairs and high catalytic activity [2]. The ligand effect, on the other hand, holds that the heterometallic bonding between Pt and Ru modifies the Pt electronic structure so that the binding strength of adsorbed CO is weakened, thereby reducing the oxidation overpotential [3]. The ligand effect makes it possible to adopt inhomogeneous nanostructures. In particular, Pt-coated bimetallic nanoparticles are of practical importance [4], in that they could prevent Ru from leaching out during DMFC operation [5]. We report here a PtRu catalyst with a nanostructure which takes full advantage of the ligand effect. An extremely thin Pt layer was formed on the large surface area of extremely small Ru cores. The platinum surface exhibited high catalytic activity for methanol electro-oxidation.
EXPERIMENTAL Catalyst preparation Carbon-supported Ru nanoparticles (Ru/C) and PtRu nanoparticles (PtRu/C) were synthesized by chemical reduction of Pt and Ru precursors. 1.09 mL of 0.98 M aqueous ruthenium(III) trichloride solution and 18 mL of 7.35 M aqueous sodium acetate solution were mixed using a magnetic stirrer to obtain a homogeneous solution. 200 mg of carbon black (Ketjenbla
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