Submicrometer LiCoO 2 films have been prepared on silicon substrates with RF sputtering and pulsed laser deposition ͑PLD͒. The electrochemical activity of both types of thin film electrodes is compared using scanning cyclic voltammetry, galvanostatic and potentiostatic intermittent titration, and electrochemical impedance spectroscopy. The RF films exhibit a axis orientation and have an accessible diffusion plane alignment, unlike the c axis oriented PLD films. The preferential orientation of the host crystal lattice toward the electrolyte solution is critical for the intercalation rate and cycling efficiency. The RF films show superior electrochemical performance and faster relaxation characteristics than the PLD films. Based on the analysis of the time and frequency domain measurements a model for the electrode response is proposed. Apparently, the intercalation rate of the RF films is not diffusion-limited, but hindered by the large charge-transfer resistance, the phase boundary movement, and the hindrance by the solid electrolyte interface.

Gold nanoparticles supported on hydrous tin-oxide ͑Au-SnO x ͒ are active for the four-electron oxygen reduction reaction in an acid electrolyte. The unique electrocatalytic of the Au-SnO is confirmed by the low amount of peroxide detected with rotating ring-disk electrode voltammetry and Koutecký-Levich analysis. In comparison, 10 wt % Au supported on Vulcan carbon and SnO x catalysts both produce significant peroxide in the acid electrolyte, indicating only a two-electron reduction reaction. Characterization of the Au-SnO x catalyst reveals a high-surface area, amorphous support with 1.7 nm gold metal particles. The high catalytic activity of the Au-SnO is attributed to metal support interactions. The results demonstrate a possible path to non-Pt catalysts for proton exchange membrane fuel cell cathodes.

Submicrometer LiCoO 2 films were prepared with pulsed laser deposition ͑PLD͒ and rf sputtering using stoichiometric targets. The influences of both substrate material and annealing procedure on the polycrystalline microstructure of the LiCoO 2 films were investigated. XRD analysis revealed strong preferential orientation: annealed films deposited with PLD had their ͑00l͒ planes parallel to the surface, while rf sputtered films had their ͑110͒ planes in this orientation. The rf-film also developed the ͑003͒ reflection typical of PLD-films, but only after prolonged annealing at 600°C. The degree of preferential orientation is influenced significantly by the annealing procedure and only little by the substrate material and the thickness of the deposited film. Pulsed laser deposition on an rf-sputtered seed layer revealed the PLD-film reflections. Extinction of the otherwise dominating ͑003͒ reflection indicated a random cationic distribution in LiCoO 2 with an NaCl-type structure.The lithium intercalation ability of LiCoO 2 was discovered 20 years ago by Goodenough and has been exploited by Sony with the introduction of their rechargeable C/LiCoO 2 battery in 1991. Presently, this technology finds large-scale commercial application as a power source for numerous handheld devices. Extensive research has been conducted to explore alternative materials, which are more cost effective and less toxic. 1 Until now, lithium cobalt oxide based electrodes exhibit superior properties in terms of cycle stability and energy density, a favorable combination for a reliable power source. 2,3 There is a growing interest in the production of secondary lithium batteries of smaller dimensions; microbatteries are very suitable to provide backup power for on-chip static memory modules. Integrated memory is encountered frequently due to a growing tendency in the microelectronics industry toward complete integration of all functions onto a single chip designed for one specific purpose. For example, a motor controller chip will contain everything from controller to the power regulation in one module called a multichip module ͑MCM͒. The functions can subsequently be implemented on a separate silicon substrate, interconnected, and stacked in a single housing. 4 The addition of a single microbattery allows the digital memory states to remain unaffected during power failure or long time storage.The common composite powder electrodes are unsuitable for microbattery application due to their porosity and the necessity for additives. The indistinct characteristics of powder-based electrodes also make modeling of the electrochemical intercalation behavior difficult. The present paper describes preparation and properties of dense, submicron films of polycrystalline LiCoO 2 on a silicon wafer with pulsed laser deposition ͑PLD͒ and rf sputtering. The welldefined composition, microstructure, and dimensions of the deposited layers make these samples suitable for fundamental electrochemical studies of the lithium intercalation process. Eventually, these f...

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Proton exchange membrane fuel cells ͑PEMFCs͒ depend on platinum at the cathode to catalyze the oxygen reduction reaction ͑ORR͒ and maintain high performance. This report shows that the electrocatalytic activity of Pt is enhanced when it is dispersed in a matrix of hydrous iron phosphate ͑FePO͒. The Pt-FePO has 2 nm micropores with Pt dispersed as ions in Pt 2ϩ and Pt 4ϩ oxidation states. Increased ORR performance is demonstrated for the Pt-FePO ϩ Vulcan carbon ͑VC͒ materials compared to a standard 20 wt % Pt-VC catalyst on rotating disk electrodes with Pt-loadings of 0.1 mg͑Pt͒ cm Ϫ2 . The improvement in the ORR is attributed to the adsorption/storage of oxygen on the FePO, presumably as iron-hydroperoxides. The ORR activity of the Pt-FePO in air is close to that in oxygen at low current density, and therefore this catalyst has a distinctly unique behavior from Pt-VC. Contrary to Pt-VC, the Pt-FePO catalyst shows activity towards hydrogen and CO oxidation, but does not exhibit their characteristic adsorption peaks, suggesting that Pt ions in the iron phosphate structure are less sensitive to poisoning than metallic Pt. The results present opportunities for new low-Pt catalysts that extend beyond the current capabilities of Pt-VC.Proton-exchange membrane fuel cells ͑PEMFCs͒ are electrochemical conversion devices that can produce electricity at high fuel efficiencies, and they are currently in development for a wide range of commercial applications. Before the fuel cells become practical for wide-scale consumer use, several technological problems must be solved. For instance, the activity of the electrodes must be improved to increase efficiency, while the amount of platinum ͑Pt͒ catalyst in the electrodes must be lowered to reduce the cost of the devices. The issues of activity and Pt loading are greatest at the cathode where the oxygen reduction reaction ͑ORR͒ suffers from high overpotentials. 1 The oxygen reduction reaction ͑ORR͒ at a fuel cell cathode is given in Eq. 1 and the hydrogen oxidation reaction ͑HOR͒ at the anode is given in Eq. 2Pt is an ideal catalyst for both these reactions, and the catalytic efficiency per unit weight of Pt is generally improved by decreasing the particle size of the catalysts, as smaller particles exhibit a larger catalytic surface area per unit of volume. However, the success gained by size reduction is limited by three effects. First, the catalytic activity drops with decreasing particle size, because active Pt crystal facets disappear. 2 For example, the fraction of the surface having the most active ͑100͒ facets drops rapidly for particles less than 6 nm in diameter and disappears completely at 1.8 nm. Pt particles smaller than 2 nm are formed almost entirely from ͑111͒ facets, 3 which exhibit two orders of magnitude lower activity than ͑100͒ facets, as shown on single-crystal Pt in sulfuric acid electrolyte. 4 Second, the surface energy increases with the decrease in particle diameter. As a result the reactants are more strongly adsorbed and not easily released. Hence, Pt n...