R. J. Sanderson

The Electrochemical Displacement Reaction of Lithium with Metal Oxides

The electrochemical reaction of lithium with a-LiFeO2, b-Li5FeO4 , and CoO is studied by in situ X-ray diffraction and in situ Mossbauer measurements. The results of the measurements show that these metal oxides are immediately decomposed during discharge to form lithia and the reduced metal. This reaction proceeds through a single intermediate or surface phase. The reaction products are nanometer-sized, but are not amorphous as was suggested previously. During charge the metal displaces the lithium in lithium oxide to form a metal oxide and lithium. In the case of CoO, the original lithium oxide oxygen lattice is preserved and the reaction resembles an ion exchange process. This also appears to be the case for the iron oxides. Upon discharge, the reverse occurs and the lithium replaces the metal in the metal oxide, once again forming lithium oxide and reduced metal on the bottom

In Situ 119Sn Mössbauer Effect Study of the Reaction of Lithium with Si Using a Sn Probe

The reaction of lithium with amorphous Si was studied by 119 Sn Mossbauer effect spectroscopy using small amounts of Sn as probe atoms. Two powder samples, amolphous-Si 87 Sn 13 and amolphous-Si 93 Sn 7 , were prepared by magnetron sputtering and investigated using in situ and ex situ Mossbauer spectroscopy. There are two gently sloping plateaus in the voltage vs capacity of Li/Si cells whose origin has never been explained. There is a clear step between these plateaus at ∼2.3 Li atoms per Si atom, or Li 2.3 Si. The step between the plateaus is found to correlate with dramatic changes in the Mossbauer effect spectra with x in Li x Si at x ≈ 2.3, which suggest the step occurs at the point when each Si atom is surrounded only by Li atom first neighbors. The changes in the Mossbauer spectra during the delithiation of the Li/Si-Sn cells also give clues about electrode failure mechanisms.

RDE Measurements of ORR Activity of Pt1 − x Ir x ( 0 < x < 0.3 ) on High Surface Area NSTF-Coated Glassy Carbon Disks

Layered Pt 1-x Ir x (0 < x < 0.3) and Pt films were sputtered onto 0.05 μm mirror-polished and nanostructured thin film (NSTF)-coated glassy carbon (GC) disks. Rotating disk electrode (RDE) studies of oxygen reduction reaction (ORR) activity were completed for all prepared disks. The Pt 1-x Ir x film was prepared by depositing alternating layers of Pt (constant thickness) and Ir (gradient), finished with a 5 nm Pt top layer. The NSTF-supported catalysts had much higher active surface areas and reached the diffusion-limited current at higher potentials than the bare GC supported catalysts. The surface enhancement factor (SEF) of Pt on NSTF-coated disks was approximately 14. The SEF increased (reaching a maximum of 22 at x = 0.2 in Pt 1-x Ir x ) as the Ir content increased for the Pt 1-x Ir x samples on NSTF. The kinetic ORR current density also increased with increasing Ir content. A similar trend was not observed for the same catalyst coated onto bare GC disks. All of the catalyst/support combinations had identical Tafel slopes and area-specific current densities, suggesting that Pt is the active catalytic ingredient. Catalysts coated on NSTF-coated GC disks can be used to accurately examine both catalytic activities and the effects of high surface area supports in a single measurement.

Combinatorial Study of the Sn–Cu–C System for Li-Ion Battery Negative Electrode Materials

Thin-film combinatorial sputter-deposited Sn-Cu-C alloys for negative electrodes of Li-ion batteries were characterized using electron microprobe (energy-dispersive spectroscopy), X-ray diffraction, electrochemical methods, and 119 Sn Mossbauer effect spectroscopy. Combinatorial libraries with nominal compositions Sn x Cu y C 1―x―y , with x = 0.49, x = 0.39, and x = 0.25 (0 < y < 1 - x) and Sn x Cu y C 1―x―y with y/x = 6/5 (0 < 1 ― x ― y < 0.45) were investigated. The addition of carbon was responsible for a decrease in grain size and an increase in specific capacity, which approached the calculated value (based on 4.4Li/Sn + 0.5Li/C). Mossbauer effect spectra were compared with differential capacity (dQ/dV vs V) and it was determined that the sample with the best capacity retention most closely resembled nanostructured Cu 6 Sn 5 grains embedded in a C matrix, yielding over 90% capacity retention after 30 cycles. However, changes in dQ/dV vs V suggested that regions of Cu 6 Sn 5 were steadily growing or aggregating as Li was cycled, which may be a limiting factor in later cycles.

Alternative Catalyst Supports Deposited on Nanostructured Thin Films for Proton Exchange Membrane Fuel Cells

A series of platinum-coated underlayer materials, alumina, gold, titanium carbide, and titanium disilicide, deposited by a high throughput magnetron sputtering method have been investigated as cathode catalyst supports in fuel cells. Orthogonal thickness gradients of the underlayer materials (0-100 nm planar equivalent) and the platinum top layer (0-75 nm planar equivalent) made up the 76 × 76 mm libraries. The resulting catalyst films were characterized by surface profilometry, X-ray diffraction, scanning electron microscopy, and X-ray photoelectron spectroscopy. The electrochemical properties of the catalyst composition spreads were investigated simultaneously in 64-electrode proton exchange membrane fuel cells with emphasis placed on the determination of the electrochemical surface area (ECSA) as a function of underlayer thickness and chemistry. The present study shows that gold and titanium disilicide used as underlayers on 3Ms nanostructured thin film supports lead to a loss of ECSA during operation. Migration and surface accumulation were observed when gold was used as underlayer material. For titanium disilicide, alloying and the generation of platinum silicide phases occurred. Alumina and titanium carbide were found to be potentially acceptable underlayer materials as well as alternative support materials on the basis of their influence on the catalyst surface area.

Impact of Rare Earth Additions on Transition Metal Oxides as Negative Electrodes for Lithium-Ion Batteries

Transition metal oxides have been proposed as negative electrode material candidates for lithium-ion batteries because they can reversibly react with lithium via a displacement reaction to deliver two to three times the specific capacity of graphite. However, the practical application of transition metal oxides has been frustrated by their inconvenient working potential. Here, the impact of the addition of rare earth (RE) elements to transition metal (TM) oxides as negative electrodes was studied. Thin films of pseudobinary misch-metal-Fe-O libraries (misch metal is a mixture of common RE elements) were prepared by combinatorial sputtering methods. Powdered perovskite-structured RE-TM-O 3 samples, including LaFeO 3 , CeFeO 3 , and LaCoO 3 , were synthesized by solid-state methods. The structural and electrochemical characterizations of these samples are presented here. It was found that the addition of RE elements decreases the working potential of TM oxides. However, the specific capacity is undesirably lowered.

Photocatalytic oxidation of DBP precursors using UV with suspended and fixed TiO2

French River water (Nova Scotia, Canada) was separated into six different natural organic matter (NOM) fractions, including hydrophobic acids, bases and neutrals and hydrophilic acids, bases and neutrals. The raw water, as well as each of the NOM fractions were analysed for disinfection by-product (DBP) formation potential before and after advanced oxidation with UV/TiO(2) to determine the efficacy of this treatment for the removal of DBP precursors. The UV/TiO(2) treatment was carried out with a nanostructured thin film (NSTF), coated with TiO(2) which is compared with the use of a TiO(2) suspension. For the raw river water, removals of total trihalomethane formation potential (TTHMFP) and total haloacetic acid formation potential (THAA(9)FP) were found to be approximately 20% and 90%, respectively, with 50 mJ/cm(2) UV exposure and 1mg/L TiO(2). For the fractionated samples, approximately 75% of both trihalomethane (THM) and haloacetic acid (HAA) precursors were found to be associated with the hydrophobic acid fraction. For this individual fraction the same UV/TiO(2) treatments exhibited approximately 20-25% removal of both TTHMFP and THAA(9)FP, suggesting that the fractionation process may have affected the treatability of HAA precursors or may have altered the results of the oxidation processes.

Catalytic Activity of Pt1-xNix (0 < x < 0.8) Measured on High Surface Area NSTF-Coated GC Disks

Intermixed Pt1-xNix (0 < x < 0.8) and Pt were sputter-deposited onto high surface area, NSTF-coated GC disks and studied for oxygen reduction reaction (ORR) activity by rotating disk electrode (RDE). NSTF-coated GC disks used in RDE experiments is a viable alternative to the regular mirror-polished GC disks in screening catalyst activities because both the catalytic activities and the effects of high-surface area support can be examined in a single measurement. The sputtered Pt-Ni samples have a much higher Surface Enhancement Factor (SEF) and kinetic current density. The impact of potential cycling is also included in this work.

Surface characteristics and protein adsorption on combinatorial binary Ti-M (Cr, Al, Ni) and Al-M (Ta, Zr) library films

Systematic studies of protein adsorption onto metallic biomaterial surfaces are generally lacking. Here, combinatorial binary library films with compositional gradients of Ti(1-x)Cr(x), Ti(1-x)Al(x), Ti(1-x)Ni(x) and Al(1-x)Ta(x), (0 <x < 1) and Al(1-y)Zr(y) (0 < y <0.5) as well as corresponding pure metal films were sputtered onto clean Si surfaces. Bulk and surface chemistry, film microstructure, and surface roughness were subsequently correlated to fibrinogen or albumin adsorption measured using a high throughput wavelength dispersive spectroscopy technique. X-ray diffraction revealed these binary films to have crystalline phases present primarily at either extreme of the compositional library and an amorphous zone dominating along the gradient. These mirror-like films were generally found by atomic force microscopy to have a roughness of less than 8 nm, with any relative increases in roughness consistent with the development of crystalline phases. Surface chemistry by quantitative high-resolution X-ray photoelectron spectroscopy differed significantly from bulk film composition as measured by electron microprobe, with TiO(2) and Al(2)O(3) preferentially forming on the binary film surfaces. Correspondingly, protein adsorption onto these films closely correlated with their surface oxide fractions. Aluminum deposited as either a constant-composition film or as part of a binary library consistently adsorbed the least amount of albumin and fibrinogen, with alumina-enrichment of the surface oxide correlating with this adsorption. Overall, this combinatorial materials approach coupled with high-throughput surface analytical methods provides an efficient method of screening potential metallic biomaterials that may enable as well systematic studies of surface properties driving protein adsorption on these metal / metal oxide systems.

Mössbauer effect studies of Fe–C combinatorially sputtered thin films

Alloys of Fe1− x C x were produced using combinatorial sputtering methods. The composition of the films as a function of position was determined using electron microprobe techniques and the results have shown that a composition range of about 0.35 < x < 0.75 was obtained. X-ray diffraction methods were employed to study the structure of the thin films and showed that all portions of the films were amorphous or nanostructured. Room temperature 57Fe Mössbauer spectroscopy was utilized to study the atomic environment around the Fe atoms. Hyperfine field distributions of ferromagnetic alloys, as extracted from the Mössbauer analysis, suggested the existence of two classes of Fe sites: (1) classes of Fe sites that have primarily Fe neighbours corresponding to a high-field component in the distribution and (2) classes of Fe sites that have a greater number of C neighbours, corresponding to a low-field component. The magnetic splitting decreased as a function of increasing carbon concentration and alloys with x greater than about 0.68 were primarily paramagnetic in nature. These spectra exhibited distributions of quadrupole splitting with mean splitting in excess of 1.0 mm/s. This indicates a higher degree of local asymmetry around the Fe sites than typically seen in other Fe-metalloid systems.