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Eric W McFarland

Publications and source records attributed to Eric W McFarland.

17 recordsLinked to original sources
PubMed2006

Efficient electrocatalyst utilization: electrochemical deposition of Pt nanoparticles using nafion membrane as a template.

We deposit Pt particles electrochemically on an electrode covered with a Nafion membrane. Platinum ions travel through the hydrophilic channels of the membrane, and platinum deposits are formed at the place where the channels make contact with the planar electrode. This procedure deposits the catalyst only at the end of the hydrophilic channels that cross the membrane; no catalyst is placed under the hydrophobic domains, where it would not be in contact with the electrolyte. By performing a series of cyclic voltammograms with this system, we show that deposition of the platinum through the membrane achieves better platinum utilization than deposition of platinum on the naked electrode followed by the placement of the membrane on top.

Journal Article↗
PubMed2005

Synthesis and characterization of Pt-WO3 as methanol oxidation catalysts for fuel cells.

Several compositions of Pt-WO3 catalysts were synthesized and characterized for the electro-oxidation of methanol and CO. The surface morphologies of the catalysts were found to be dependent on the composition. X-ray energy dispersive spectroscopy and X-ray photoelectron spectroscopy results suggest a surface enrichment of WO3 in the codeposited Pt-WO3 catalysts. Cyclic voltammetry and chronoamperometry in methanol show an improvement in catalytic activity for the Pt-WO3 catalysts. A significant improvement in the poison tolerance toward CO and other organic intermediates was observed in the mixed metal-metal oxide catalyst. The catalytic performance of the different compositions was directly compared by normalization of the current to active sites. CO-stripping voltammetry suggests the involvement of WO3 in the catalytic process as opposed to a mere physical effect as suggested by previous work. A possible mechanism for this improvement is proposed based on the electrochemical data.

Journal Article↗
PubMed2005

Electrolithographic investigations of the hydrophilic channels in Nafion membranes.

Nafion membranes are used as semisolid electrolytes in methanol and hydrogen fuel cells. The ion conduction takes place through those hydrophilic channels in the Nafion that can provide continuous pathways through the membrane. There is as yet limited information about the density, the size, and the shape of these channels. We have developed two electrochemical methods of visualizing the pore structure which involve the creation of metal lithographs using the membrane pores as templates. In the experiments, the membrane is supported on a flat solid surface on one side, and is in contact with an electrolyte on the other side. Using hydrogen-terminated n-doped Si(111), we deposited gold from an electrolyte containing a gold salt. The Au ions traverse the membrane through the pores, reach the silicon surface, and are spontaneously reduced. A metallic Au deposit is formed on the silicon surface, at the base of the hydrophilic channel. The Au deposits are imaged after the membrane is dissolved. Another method involves supporting the membrane on a Pt surface and depositing silver wires through the hydrophilic channels of the membrane. The scanning electron microscope pictures of these wires provide an image of the size and the shape of the hydrophilic channels.

Journal Article↗
PubMed2004

Parallel synthesis and characterization of photoelectrochemically and electrochromically active tungsten-molybdenum oxides.

Single phase tungsten-molybdenum mixed oxide films (W(1-x)Mo(x)O(3)) were successfully synthesized by automated parallel electrodeposition, and distinct structural changes were observed as a function of composition. A monoclinic structure (beta-phase) was observed in mixed oxides with less than 90% Mo, and above 90% Mo, orthorhombic structure (alpha-phase) was identified.

Journal Article↗
PubMed2003

Size- and support-dependent electronic and catalytic properties of Au0/Au3+ nanoparticles synthesized from block copolymer micelles.

Supported Au nanoclusters synthesized from diblock copolymer micelles can be reliably prepared with well-controlled sizes and dispersions. For particles with diameters between approximately 1 and 6 nm, the particle size and the support were found to strongly influence the oxygen reactivity, the formation and stabilization of a metal-oxide, and the catalytic activity for electrooxidation of carbon monoxide. The smallest particles studied (1.5 nm) were the most active for electrooxidation of CO and had the largest fraction of oxygen associated with gold at the surface as measured by the Au(3+)/Au(0) X-ray photoemission intensities. Conducting and semiconducting substrates, ITO-coated glass and TiO(2), respectively, were associated with greater stabilization of Au(3+) oxide as compared to insulating, SiO(2), substrates.

Journal Article↗
PubMed2003

An integrated process for partial oxidation of alkanes.

The partial oxidation of alkanes via bromination followed by the reaction with solid metal oxide mixtures (MO) is shown to give an array of products that can be tuned by varying the MO and the reaction conditions.

Journal Article↗
PubMed2003

Catalytic activity of supported Au nanoparticles deposited from block copolymer micelles.

Quasi-ordered, highly dispersed, gold nanoclusters of tightly controlled particle size were synthesized by dip-coating substrates with gold precursors encapsulated by block-copolymer micelles. By this method, gold particles (4.8 +/- 1.3 nm) were deposited on ITO-coated glass and shown to be catalytically active for electro-oxidation of carbon monoxide. XPS confirmed the catalytically active particles were predominantly Au0; however, a large fraction existed as Au3+. Whereas bulk gold is inert, these results demonstrate that catalytically active Au nanoparticles can be derived from micelle encapsulation.

Journal Article↗
PubMed2003

A photovoltaic device structure based on internal electron emission.

There has been an active search for cost-effective photovoltaic devices since the development of the first solar cells in the 1950s (refs 1-3). In conventional solid-state solar cells, electron-hole pairs are created by light absorption in a semiconductor, with charge separation and collection accomplished under the influence of electric fields within the semiconductor. Here we report a multilayer photovoltaic device structure in which photon absorption instead occurs in photoreceptors deposited on the surface of an ultrathin metal-semiconductor junction Schottky diode. Photoexcited electrons are transferred to the metal and travel ballistically to--and over--the Schottky barrier, so providing the photocurrent output. Low-energy (approximately 1 eV) electrons have surprisingly long ballistic path lengths in noble metals, allowing a large fraction of the electrons to be collected. Unlike conventional cells, the semiconductor in this device serves only for majority charge transport and separation. Devices fabricated using a fluorescein photoreceptor on an Au/TiO2/Ti multilayer structure had typical open-circuit photovoltages of 600-800 mV and short-circuit photocurrents of 10-18 micro A cm(-2) under 100 mW cm(-2) visible band illumination: the internal quantum efficiency (electrons measured per photon absorbed) was 10 per cent. This alternative approach to photovoltaic energy conversion might provide the basis for durable low-cost solar cells using a variety of materials.

Journal Article↗
PubMed2002

Electrochemical synthesis of nanostructured ZnO films utilizing self-assembly of surfactant molecules at solid-liquid interfaces.

An electrochemical synthesis strategy for the production of nanostructured films was developed by combining self-assembly of surfactant-inorganic aggregates at solid-liquid interfaces and an electrodeposition process. Through this approach high quality nanostructured ZnO films were cathodically deposited from a plating solution containing 0.1 wt % of sodium dodecyl sulfate (SDS). The resulting ZnO films possess lamellar structures with two different repeat distances, d001 = 31.7 A and d001* = 27.5 A, both of which feature well-defined long range order. Due to kinetically controlled surfactant-inorganic assembly during the deposition process, the film exhibits a wide distribution of the stacking directions of the ZnO layers, which will allow facile access of the guest molecules and analytes to the interlayers. The synthetic mechanism used here can be generalized to generate nanostructured films of other semiconducting and metallic materials with architectures that cannot be assembled by other means.

Journal Article↗
PubMed2002

Microengineering neocartilage scaffolds.

Advances in micropatterning methodologies have made it possible to create structures with precise architecture on the surface of cell culture substrata. We applied these techniques to fabricate microfeatures (15-65 microm wide; 40 microm deep) on the surface of a flexible, biocompatible polysaccharide gel. The micropatterned polymer gels were subsequently applied as scaffolds for chondrocyte culture and proved effective in maintaining key aspects of the chondrogenic phenotype. These were rounded cell morphology and a positive and statistically significant (p < 0.0001) immunofluorescence assay for the production of type II collagen throughout the maximum culture time of 10 days after cell seeding. Further, cells housed within individual surface features were observed to proliferate, while serial application of chondrocytes resulted in the formation of cellular aggregates. These methods represent a novel approach to the problem of engineering reparative cartilage in vitro.

Absorbable Implants↗
PubMedDate not supplied

High-throughput screening system for catalytic hydrogen-producing materials.

A high-throughput screening system and methodology were developed for libraries of hydrogen (H(2)) producing catalytic materials. The system is based on the chemo-optical properties of WO(3), which give rise to reflectance changes in the presence of H(2). Pd-coated WO(3) sensors were synthesized and examined for their hydrogen sensitivity, wavelength-dependent reflectance, and performance in the presence of water vapor. For high-throughput screening, a polypropylene reactor block was designed and constructed to house 8 x 12 catalyst libraries deposited as thin films. When the library and reactor block are assembled together, 96 independent microreactor units are formed. A large-area Pd/WO(3) sensor film covers and seals all microreactors, forming a 96-element 2-D H(2) sensor array. As H(2) is produced differentially across the library, the reflectance changes of the Pd/WO(3) film are monitored by reflectivity sensors that scan the surface every 30 s. The time-dependent changes in reflectance indicate relative rates of H(2) production. A library of cathode electrocatalysts was synthesized from Ti, Pt, Ni, Au, Pd, Al, Ag, Ge, and mixtures thereof to demonstrate the H(2) high-throughput screening system. The results of the electrolytic screening are in agreement with expected literature trends: mixtures of Ni and samples containing Pt and Pd generated H(2) at the greatest rates, while Ge- and Ti-based materials were the least effective electrocatalysts. A mixture of 80% Al and 20% Pt was found to have the highest rate of H(2) production. This high-throughput screening system is applicable in a variety of catalytic screening applications where hydrogen is the desired product.

Journal Article↗
PubMedDate not supplied

Automated electrochemical synthesis and photoelectrochemical characterization of Zn1-xCo(x)O thin films for solar hydrogen production.

High-throughput electrochemical methods have been developed for the investigation of Zn1-xCo(x)O films for photoelectrochemical hydrogen production from water. A library of 120 samples containing 27 different compositions (0 <or= x <or= 0.068) was synthesized by automated serial electrochemical deposition. High-throughput photoelectrochemical screening revealed improved solar hydrogen production for the cobalt-doped films, with Zn0.956Co0.044O exhibiting a 4-fold improvement over pure ZnO with no external bias. Flat-band potential, bias-dependent photocurrent, and action spectra were also measured automatically with the high-throughput screening system. The 200-nm-thick films were subsequently characterized by numerous techniques, including SEM, XRD, XPS, and UV-vis, which show that the depositions are well-controlled. Zn/Co stoichiometry in the films was controlled by the ratio of the Zn and Co precursors in each deposition bath. All films exhibited the wurtzite structure typical of pure ZnO, and the Co2+ appears to substitute Zn2+, forming a single-phase solid solution. Band gaps of the solid solutions were systematically lower than the 3.2-eV band gap typical of ZnO.

Automation↗