Electropolishing of p-type silicon has been investigated over a wide range of HF concentrations (0.01-11 wt. %) by potentiodynamic polarization. Oxide dissolution rates were determined from the plateau current densities observed in the electropolishing region during the reverse sweeps; i.e. where the growth and dissolution rates of the anodic oxide film are believed to be equal. Based on the shape of the CV curves the oxide dissolution process was treated as a corrosion process controlled by the dissolution of a salt film, that is its rate controlled by removal of dissolved products away from the surface rather than reactants to the surface as previously proposed. Although a contribution from HF from bulk to surface cannot be completely ruled out, because the removal of the initial dissolution product can be by either mass transport or further chemical reaction with HF species in solution this mechanism is capable of explaining the dependence of the dissolution rate on HF concentration for the whole range investigated.

Periodic hybrid-exchange density functional theory (DFT) simulations are used to develop a predictive model of the structure of water on the rutile TiO2(110) surface (Θ ≤ 1 ML). A description of the adsorbed species is given: dissociated water molecules and either mixed or dissociative dimers. The behaviour of the adsorbates is rationalised by considering both direct intermolecular and surface-mediated interactions. Some of these results are then compared with those from water adsorption on the rutile SnO2(110) sur- face, isostructural to TiO2(110). Lastly, the electronic structure of the surface in contact with monolayer water (Θ = 1 ML) reveals the contributions of adsorbate states involved in the photocatalytic reaction that controls the water oxidation process.

The efficacy of vertically aligned defect engineered multi-walled carbon nanotube (MWCNT) arrays as electrochemical double layer capacitors (EDLCs) was investigated using standard electrochemical techniques such as cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). We report a ∼ 200% improvement in specific double layer capacitance of MWCNT arrays by extrinsically introducing defects using argon plasma irradiation. The capacitance-voltage characteristics of argon irradiated MWCNTs provide insights into the nature of the defects and their influence on the specific capacitance (capacitance/area).

Using the recently developed Cahn-Hilliard reaction (CHR) theory, we present a simple mathematical model of the transition from solid-solution radial diffusion to two-phase shrinking-core dynamics during ion intercalation in a spherical solid particle. This general approach extends previous Li-ion battery models, which either neglect phase separation or postulate a spherical shrinking-core phase boundary under all conditions, by predicting phase separation only under appropriate circumstances. The effect of the applied current is captured by generalized Butler-Volmer kinetics, formulated in terms of the diffusional chemical potential in the CHR theory. We also consider the effect of surface wetting or de-wetting by intercalated ions, which can lead to shrinking core phenomena with three distinct phase regions. The basic physics are illustrated by different cases, including a simple model of lithium iron phosphate (neglecting crystal anisotropy and coherency strain).

We have studied the electrochemical reduction of CO2 to produce short chain hydrocarbons and alcohols using supported Cu2O electrocatalysts. The catalysts are prepared using Cu2O nanoparticles formed by chemical reduction of aqueous CuCl2 mixed with polyethylene glycol surfactant, followed by addition of NaOH and L-ascorbic acid (sodium). The nanoparticles are then added to a Nafion/ethanol solution and coated onto a carbon fiber support. When tested used for CO2 electroreduction at −1.5 V(NHE), the Cu2O particles are reduced to metallic Cu, but the hydrocarbon product distribution remains different from that reported for conventional metallic Cu electrodes. Ethylene is the major hydrocarbon produced, with a Faradaic efficiency around 25%, while the efficiency for CH4 formation is reduced to around 1%. The major alcohol product is ethanol, with a Faradaic efficiency around 6%. The relative formation rates of the individual products are discussed in terms of the relevant branch points in recent computational models for the overall reaction mechanism.

In this study Sr2+ diffusion along Ce0.8Gd0.2O2-δ (CGO) grain boundaries is investigated. Model samples with different grain boundary densities were prepared by different thin film tech-niques. Diffusion experiments were performed by annealing and subsequent ToF-SIMS analysis. The activation energy of grain boundary diffusion is determined as 492 kJ/mol, which is 2/3 of the bulk diffusion activation energy 739 kJ/mol, deduced from literature data [1-5].

The formation of an electrical blocking SrZrO3 layer due to grain boundary diffusion of Sr2+ through a CGO barrier layer may limit the long term stability of Solid Oxide Fuel Cells based on Zr0.85Y0.15O2-δ electrolytes and La0.58Sr0.4Co0.2Fe0.8O3-δ cathodes. The grain boundary diffusivity and the CGO grain boundary density highly influence the kinetic of the SrZrO3 formation. Aim of this study is to gain data for a prediction of the maximum lifetime of a SOFC system, limited by the increasing cell resistivity due to SrZrO3 formation. Specifications for the CGO barrier layer preparation concerning grain boundary density are determined.

Limited electrochemical performance and microstructure instability are crucial problems in Platinum electrodes for solid state electrochemical devices. YSZ infiltration into porous YSZ skeleton is a prospective method to enhance the electrochemical performance and stabilize the microstructure. In this work, the effect of Pt skeleton microstructure on the electrochemical performance and stability of Pt-YSZ electrodes prepared by infiltration was investigated. The electrode polarization resistance of YSZ infiltrated Pt electrode sintered at 800 °C was 0.060 Ohm.cm2 per electrode at 800 °C without degradation during the operation time of 51 hours. Triple phase boundary enhancement by YSZ infiltration and YSZ infiltration into Pt skeleton with smaller particle size resulted in the suppression of the electrochemical process observed at 150 Hz.

Degradation of the catalyst and catalyst support is an essential limitation of polymer electrolyte membrane (PEM) fuel cells containing commercial platinum on carbon catalysts. Catalysts based on platinum nanoparticles coated onto nanostructured TiO2 materials are presently investigated as a more stable and equally cost effective alternative. Reported here is the synthesis of two different Pt/Nb0.1Ti0.9O2 catalysts that were prepared by chemical reduction of H2PtCl6 with either sodium borohydride in ethanolic surfactant solution or ethylene glycol. X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and high-resolution transmission electron microscopy confirmed the deposition of Pt nanoparticles on the surface of the nanofibers and revealed average sizes of 5.4 nm and 7.6 nm for reduction with ethylene glycol and sodium borohydride, respectively. The formation of smaller sized Pt nanoparticles in ethylene glycol is reasoned with the passivation of the nanoparticle surface by glycolic anions. Cyclic voltammetry measurements confirmed a higher electrochemical specific surface area (ESCA) of about 5.45 m2/gPt for the catalyst with smaller nanoparticles while the other catalyst reached only 4.96m2/gPt. Both catalysts retain about 60% of their electrochemically active surface area after 1000 voltammetric cycles in the range of 0.03 to 1.4 V vs. RHE. This relatively high value of activity retention is explained with a strong interaction between Pt nanoparticles and Nb0.1Ti0.9O2 support.

Pt catalysts are the leading catalysts for use in ORR. However, Pt is an expensive catalyst and with limited supply can not be considered a sustainable material for feasible application that is scalable in the economy. This calls for new solutions for catalyst materials that either mitigate the amount of Pt used in catalysts by developing hybrid catalysts, or to replace Pt altogether with a material with similar or better catalytic activity. Perovskite LSCF and Fluorite GDC materials with proven catalytic activity in solid oxide fuel cells are herein explored for their catalytic reduction of oxygen for use at low temperatures. Since the materials lack electronic conductivity at low temperatures, we have improved their conductivity with graphene. The resulting materials are compared to Pt in their ORR catalytic capabilities and electronic conductivity.

High temperature (>550°C) applications of silver based porous composites have been limited due to relatively low melting temperature (962°C) of Ag. Incorporation of oxide particles was demonstrated as an effective approach for stabilization of the porous Ag microstructures. This study aims developing an understanding based on the relationships between the properties of the incorporated YSZ (yttria-stabilized zirconia), the developed porous microstructures and the electrochemical response of their electrodes. Minimum degradation was observed with the composite microstructure based on comparable Ag and YSZ particle sizes. The results demonstrated that YSZ incorporation into Ag matrix can increase the stable application temperature to 800°C.

In this study the strain states in alternating multilayers of an extrinsic O2− ion conductor yttria stabilized zirconia (YSZ) and an insulator RE2O3 (RE = Er, Y) are investigated as a function of the layer thickness. Multilayers with narrow columnar crystallites and coherent phase boundaries were grown by pulsed laser deposition (PLD). A detailed strain analysis is performed by X-Ray Diffraction XRD, measuring distinct reflections in and perpendicular to the interface planes. Because of small columnar crystallites in the layers, the interfacial strain decays by shear with increasing distance from the interface. The extent of the strained interface regions in the YSZ layers is estimated from XRD data. By using a quantitative analytical model based on the pressure dependence of the free migration enthalpy for vacancies the results are compared to former published experimental data on O2− ion conductivity and diffusion.

Density functional theory calculations are used to address the energetics of protons crossing “triple phase boundaries” based on Pd and barium zirconate. Our calculations show that the proton transfer reaction at these triple phase boundaries is controlled by the terminal layer of the electrolyte in contact with the metallic catalyst and gas phase. Hydrogen spilling onto the electrolyte surface is energetically favored at peripherical sites of the metal-electrolyte interface, and proton incorporation into the sub-surface region of the electrolyte involves energies of the order of 1 eV. At the triple phase boundary, the energy cost associated with the proton transfer reaction is controlled by both the nature of chemical contact and the Schottky barrier at the metal-electrolyte interface.