Oxygen Reduction Activity and Durability of Ordered and Disordered Pt₃Co Alloy Nanoparticle Catalysts at Practical Temperatures of Polymer Electrolyte Fuel Cells

Abstract

We have succeeded in preparing ordered-and disordered-Pt 3 Co nanoparticles supported on carbon black (CB), with the nearly identical particle size distribution, by the nanocapsule method with heat-treatment at high temperatures. The temperature dependences of the oxygen reduction reaction (ORR) activities at two kinds of Pt 3 Co/CB catalysts were examined in O 2 -saturated 0.1 M HClO 4 solution by the multi-channel flow double electrode (M-CFDE) technique. For the ordered-Pt 3 Co/CB, the apparent rate constant k app (per unit active area) for the ORR increased with elevation of the temperature up to 65 • C and stabilized at nearly the same value as that for commercial c-Pt/CB at 80 • C, due to a severe dealloying of the Co component in the hot acid solution. In contrast, the k app values at the disordered-Pt 3 Co/CB were higher than those of the ordered-Pt 3 Co/CB over the whole temperature range from 30 • C to 80 • C. The disordered-Pt 3 Co/CB also exhibited higher stability than the ordered-Pt 3 Co/CB for both an accelerated durability test (ADT, by standard potential step cycles between 0.6 V and 1. The polymer electrolyte fuel cell (PEFC) is anticipated to be one of the most promising, clean, and energy-efficient power sources for fuel cell vehicles (FCVs) and stationary cogeneration systems (FCCGs). In 2014, a strategic roadmap for hydrogen and fuel cells was formulated by the Ministry of Economy, Trade, and Industry (METI) of Japan and was revised in 2016.1 For the large scale commercialization of both FCVs and FC-CGs in its Phase 1, it is necessary to reduce the system cost while maintaining the performance and durability. At the present stage, however, the use of substantial amounts of costly Pt cathode catalysts supported on carbon (Pt/C) is unavoidable to decrease the large overpotential for the oxygen reduction reaction (ORR). Hence, the development of the cathode catalysts having both high activity for the ORR and high durability is quite important. To improve the ORR activity, Pt-based catalysts alloyed with non-precious metal such as Fe, 2-6 Co, 2,4,7-11 and Ni, 2-13 have been investigated intensively. For nano-sized Pt-M alloy catalysts (Pt-M/C), the kinetically-controlled area-specific activity j k for the ORR was enhanced by ca. 2∼7 times compared to that of pure Pt. The enhancement factor has been found to depend on various properties of alloy nanoparticles, e.g., composition, 4,14-16 shape (or size), 17-21 and crystal structure. [22][23][24][25][26][27][28][29] For example, the values of j k for Pt-Co alloys showed a maximum at the atomic ratio of Pt/Co = 3. 4,5,14 It has been reported that the electronic structure of the Pt skin layer formed on Pt-M alloys could change with the composition of the underlying alloy, reaching a maximum at the optimum alloy composition or alloying metal species M. 24,[30][31][32] Because the surface is not perfectly covered with uniform Pt skin layer, j k often decreases appreciably by dealloying of M during the operation of PEFCs or electrochemical measurements...

Classification of platinum nanoparticle catalysts using machine learning

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Highly Durable and Active Pt/Sb-Doped SnO2 Oxygen Reduction Reaction Electrocatalysts Produced by Atomic Layer Deposition

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A New Accelerated Durability Test Protocol for Water Oxidation Electrocatalysts of Renewable Energy Powered Alkaline Water Electrolyzers

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