Catalysts with Pt Surface Coating by Atomic Layer Deposition for Solid Oxide Fuel Cells

Abstract

We tested the atomic layer deposition of platinum layers onto various sputtered porous metals including silver, palladium, ruthenium, and gold as catalysts for solid oxide fuel cells. We investigated thermal and chemical stability against oxidation using X-ray photoelectron spectroscopy. Fuel cell tests were conducted using the metal-atomic layer deposition platinum cathodes with 200 m thick, 8% yttria-stabilized zirconia electrolytes and sputtered platinum anodes. Performance of the fuel cells was measured by comparing the current-voltage curves and maximum power densities with varying temperature.Ceramic fuel cells have attracted recent attention as a future energy conversion system because of their potentials for high efficiency and fuel flexibility. However, the high operating temperature of ceramic fuel cells of 700-1000°C limits their practical usage. There have been several efforts to reduce the operating temperature to below 400°C by employing thin electrolyte membranes, by replacing conventional zirconia-based electrolytes with other doped oxides, which exhibit higher ionic conductivity, or by replacing conventional cathodes based on perovskite oxides with novel metal oxide cermets. 1-9 At intermediate temperatures, platinum or platinum alloys are known as the best catalysts. However, the high price of platinum has become a main bottleneck against the commercialization of fuel cells equipped with Pt-based catalysts. Recently, it was reported that several Pt metal alloys exhibited higher catalytic activities compared to pure Pt with a stable formation of a Pt skin segregated from the bulk of the cluster. 10 Atomic layer deposition ͑ALD͒ is a modified version of metallorganic chemical vapor deposition relying on the self-limiting chemistry of precursors and the interaction between substrates and precursor molecules. The ALD process enables conformal deposition along complex three-dimensional contours because the surface reaction takes place regardless of reactant flow direction. ALD films can be deposited along trenches with a high aspect ratio. 11,12 Therefore, ALD is expected to achieve good surface alloying over a nanoscale metal mesh used for current collection. Pure ALD Pt was investigated as a fuel cell catalyst in our previous work. 13 In this study, we tested metal catalysts surface-coated with Pt layers by ALD as cathodes of fuel cells to minimize the high cost of platinum and to enhance surface kinetics on the Pt metal surface alloys. ExperimentalVarious nanoporous metal meshes, including Ag, Pd, Ru, and Au, were used as template metals for cathodes. There was a prior investigation of Ag, Pd, and Au as solid oxide fuel cell ͑SOFC͒ catalysts. 14 There are also several publications reporting reasonably high or better performance of bimetallic alloys, including Ag-Pt and Pd-Pt, as cathodes for fuel cells compared to pure Pt. 15,16 The metal meshes used in our tests were produced by dc sputtering with 10 Pa of Ar background gas for 80 s of sputtering time to grow ϳ80 nm thick porous layers. On the me...

Nucleation and growth of Pt atomic layer deposition on Al2O3 substrates using (methylcyclopentadienyl)-trimethyl platinum and O2 plasma

“…15 These studies revealed that Pt ALD films thinner than 18.3 nm were discontinuous and porous. 21 Various degrees of Pt coverage on the different metals were observed that correlated with expectations from relative surface energies. Additional studies by the same group also observed that 72 cycles of thermal Pt ALD on various sputtered metals resulted in Pt clusters.…”

“…9,10 Recent research has suggested that ultrathin conformal Pt films on a high surface area support will exhibit significantly higher area-specific activity for the oxygen reduction reaction than an equivalent surface area of Pt nanoparticles. [13][14][15][16][17][18][19][20][21] However, this Pt ALD chemistry does not yield continuous and conformal films as is typical for ALD film growth. Electronic mail: steven.george@colorado.edu.…”

Atomic layer deposition of Pt nanocatalysts on graphene oxide nanosheets for electro-oxidation of formic acid

“…Atomic layer deposition (ALD) is a modified version of metalorganic chemical vapor deposition, which relies on the selflimiting chemistry of precursors and the interaction between substrates and precursor molecules [1,2]. Because it offers an atomic level control of thin-film growth using sequential and self-limiting surface reactions, the ALD process can be extensively used to deposit conformal films inside high aspect ratio structures.…”

Nanoionics and Nanocatalysts: Conformal Mesoporous Surface Scaffold for Cathode of Solid Oxide Fuel Cells

“…Here we demonstrate, for the first time, the establishment of conformal mesoporous nanoionics ZrO 2 networks on the interior surface of porous commercial SOFC cathode formed through atomic layer deposition (ALD)2930313233. By contrast to the PLD thin film deposition and chemical solution based infiltration343536, chemical vapor based ALD is uniquely suitable for depositing uniform and conformal films on SOFC cathodes possessing complex three-dimensional topographies with high aspect ratio.…”