Electrochemical Properties of Pt Coatings on Ni Prepared by Atomic Layer Deposition

Abstract

Presented herein is an approach to fabrication of Pt coatings on non-noble metals with ͑sub͒monolayer thickness. The Pt coatings were prepared using atomic layer deposition ͑ALD͒ in which Ni-disk substrate is exposed to MeCpPtMe 3 and H 2 in alternating cycles. The structure and electrocatalytic activity of the coatings were characterized using elemental analysis and various electrochemical techniques. We found that the ALD results in micrometer-size Pt islands up to ca 3.7 monolayers of Pt loading and continues more uniformly at higher loadings. The islandlike growth at low Pt loadings is attributed to the presence of adsorbed O on atomically rough facets of polycrystalline Ni substrate. The thin films of Pt on Ni show enhancement factors in the oxygen reduction reaction similar to what has been reported for PtNi alloys. Potential applications of the methodology demonstrated in this work for the development of the third-generation polymer electrolyte fuel cell catalytic layers with ultralow Pt loading are briefly discussed.The strategy to reduce the Pt loading in polymer electrolyte fuel cells ͑PEFCs͒ using smaller and smaller Pt nanoparticles has been actively pursued ever since the advent of the PEFC technology. 1-3 Unfortunately, it seems now that this approach has reached a plateau, because Pt nanoparticles smaller than 2-3 nm show lower electrocatalytic activity in oxygen reduction reaction ͑ORR͒ 4,5 and decreased stability. 6 An alternative approach to reduction of the Pt loading is to decrease the number of bulk ͑nonsurface͒ Pt atoms in the catalytic particles. The largest possible noble metal loading reduction without sacrifice in power density can be achieved using a ͑sub͒monolayer-thick Pt shell on a non-noble nanostructured core. 7 Adzic et al. has demonstrated some advantages of this strategy by the example of Pt ͑sub͒monolayers on Ru, 8 Pd, 9 and alloy 10 nanoparticle cores prepared via spontaneous deposition or Cu underpotential ͑UPD͒ displacement. Pt shells have also been produced through partial corrosion of Pt alloys with less noble metals 11-13 or by electroless plating. 14,15 The core-shell concept has been expanded beyond supported nanoparticles to carbon-free three-dimensional nanoporous cores. 15 In all these cases, however, the cores still contain noble metals, thus offsetting the cost reduction due to lower Pt loading. Conventional methods of preparing Pt thin films, such as UPD displacement, 9 thermal decomposition, 16 chemical vapor deposition ͑CVD͒, 17-19 and physical vapor deposition, 20,21 are not suitable for making conformal monolayer-thick Pt shells on non-noble metal cores either due to a parasitic displacement reaction 22-24 in the case of liquid-phase depositions or due to a poorly controlled conformity and thickness in the case of both liquid-and gas-phase processes affected by mass-transport of the Pt precursor. 21 Atomic layer deposition ͑ALD͒ is a gas-phase process that allows for a conformal growth even in high-aspect-ratio nanostructures with a precise deposit-thickness c...

Remote Plasma ALD of Platinum and Platinum Oxide Films

“…[1][2][3][4][5][6][7] While being less investigated, platinum oxide is of interest because of its optical properties and because PtO x can be ͑locally͒ reduced to Pt. [8][9][10] In the research efforts toward the applications of these films deposited by ALD, nucleation properties, material quality, and process temperature window are of key importance.…”

Precise control of highly ordered arrays of nested semiconductor/metal nanotubes

“…Therefore, we first explored the formation of ALDgenerated Pt covering the initial stages of the thin film nucleation process and the synthesis of high aspect ratio nanotube structures developed using rimethyl(methylcyclopentadienyl)platinum(IV), Me 3 Pt (CpMe), and oxygen as the precursors [9][10][11][12]. The penetration depth of the Pt into porous templates having various pore sizes and aspect ratios was investigated using the template replication method.…”

Core–Shell-Structured Low-Platinum Electrocatalysts for Fuel Cell Applications

“…This feature is especially attractive for the synthesis of heterostructured materials used in catalysis and nanodevices [362][363][364][365]. The ALD has also been explored as an alternative method for the preparation of advanced heterostructured and core-shell-structured electrocatalysts, such as Pd@Pt and Ni@Pt [368,374,[377][378][379][380]. For example, Cao et al [366] synthesized uniform Pd@Pt core-shell-structured electrocatalysts using the ALD technique with ODTS self-assembled monolayers as substrates (Fig.…”