Determination of elastic properties of a MnO2 coating by surface acoustic wave velocity dispersion analysis

MnO2 is a material of interest in the development of high energy-density batteries, specifically as a coating material for internal 3D structures, thus ensuring rapid energy deployment. Its electrochemical properties have been mapped extensively, but there are, to the best of the authors' knowledge, no records of the elastic properties of thin film MnO 2. Impulsive stimulated thermal scattering (ISTS), also known as the heterodyne diffraction or transient grating technique, was used to determine the Young's modulus (E) and porosity (ψ) of a 500nm thick MnO2 coating on a Si(001) substrate. ISTS is an all optical method that is able to excite and detect surface acoustic waves (SAWs) on opaque samples. From the measured SAW velocity dispersion, the Young's modulus and porosity were determined to be E=25±1GPa and ψ = 42 ± 1 %, respectively. These values were confirmed by independent techniques and determined by a most-squares analysis of the carefully fitted SAW velocity dispersion. This study demonstrates the ability of the presented technique to determine the elastic parameters of a thin, porous film on an anisotropic substrate. © 2014 AIP Publishing LLC.status: publishe

The importance of charge redistribution during electrochemical reactions: a density functional theory study of silver orthophosphate (Ag 3 PO 4)

The structural sensitivity of silver orthophosphate (Ag3PO4) for photo-electrochemical water oxidation on (100), (110) and (111) surfaces has recently been reported by experimental studies (D. J. Martin et al., Energy Environ. Sci., 2013, 6, 3380–3386). The (111) surface showed the highest performance with an oxygen evolution rate of 10 times higher than the other surfaces. The high performance of the (111) surface was attributed to high hole mobility, high surface energy and, in a recent theoretical study (Z. Ma et al., RSC Adv., 2017, 7, 23994–24003), to a lower OH adsorption energy and the band structure. The investigations are based on a few structures and a full atomistic picture of the Ag3PO4 under electrochemical reactions is still missing. Therefore, we report here a systematic study of the oxygen evolution reaction (OER) of Ag3PO4 (100), (110), and (111) surfaces by density functional theory (DFT) calculations. Through a detailed investigation of the reaction energies and the overpotentials of OER on all possible surface orientations with all possible terminations and different involvement of Ag adsorption sites, we can confirm that (111) surfaces are highly active. However, surface orientation was not found to exclusively determine the electrochemical activity; neither did the number of Ag atoms involved in the adsorption of the intermediate species nor the type of surface termination or the different potential determining reaction steps. By using Bader charge analysis and investigation of the charge redistribution during OER, we found that the highest activity, i.e. lowest overpotential, is related to the charge redistribution of two OER steps, namely the Oad and the HOOad formation. If the charge redistribution between these steps is small, then the overpotential is small and, hence, the activity is high. Charge redistributions are usually small for the (111) surface and therefore the (111) surface is usually the most active one. The concept of charge redistribution being decisive for the high activity of Ag3PO4 may open a new design strategy for materials with highly efficient electrochemical surfaces

Investigation of a cholera outbreak in a tea garden of Sivasagar district of Assam

Background: In late May 2012, Bagjan division of Borbam tea estate, of Sivasagar district of Assam was affected by an outbreak of acute watery diarrhea, subsequently confirmed as Vibrio cholerae O1. Objectives: Our objective is to investigate and control the acute diarrheal disease outbreak in Sivasagar district of Assam. Materials and Methods: A physician-epidemiologist-led team did rapid outbreak investigation to confirm the outbreak and instituted treatment and control measures. Quantitative data collection was done using standard schedule and qualitative data by using key informant interview schedule. Results: Spot mapping of cases was done along the garden residential lines. About 120 suspected cases were line listed; with 1:1.23 male: female ratio. Ages ranged from 3 to 70 years (median - 40.5 years). Attack rate was 4.79% with one death; case fatality rate was 0.83%. Open air defecation was practiced by 94.6%. Rectal swabs were positive for V. cholerae O1 (Ogawa). All the piped water samples were class IV unsatisfactory for domestic use. Conclusions: There is a need to improve water and sanitation facility in the tea garden lines along with implementation of a strengthened disease surveillance system through integrated disease surveillance project covering all tea estates

Nanometer-thin graphitic carbon buffer layers for electrolytic MnO₂ for thin-film energy storage devices

In this study, nanometer thin graphitic carbon coatings were applied as an adhesion layer for the growth of submicron to micron thick electrolytic manganese dioxide (EMD) films for thin-film energy storage devices. The graphitic carbon coating served not only as current collector and adhesion layer between the EMD and the substrate, but also prevented the oxidation of the non-noble TiN substrate during the anodic deposition process. The EMD films consisted of a network of interconnected nanometer-size particles with around 50% porosity. The ability to grow a few hundred nanometer thick EMD film with good adhesion to the current collector is critical for reliable thin-film batteries on high aspect ratio microstructured surfaces. Thin EMD films grown on our graphitic carbon coated TiN substrates showed improved reversible Li-ion intercalation kinetics and increased cycle life compared to similar films deposited on noble metal platinum substrates, thus demonstrating the improved interface properties using the graphitic carbon buffer layer.status: publishe

The electrochemistry of iron oxide thin films nanostructured by high ion flux plasma exposure

Photo-electrochemical (PEC) water splitting of hematite photoanodes suffers from low performance and efficiency. One way to increase the performance is to increase the electrochemically active surface area available for the oxygen evolution reaction. In this study, we use high ion flux, low energy helium plasma exposure to nanostructure sputtered iron thin films. Subsequent annealing in air at 645 \ub0C leads to the formation of PEC active hematite (?-Fe2O3) phase in these films. The surface area, as derived from electrochemical impedance spectroscopy (EIS), was seen to increase 10–40 times with plasma exposure. The photocurrent density increased by 2–5 times for the plasma exposed films as compared to the unexposed films. However, the less nanostructured film showed a higher photocurrent density. These findings were explained by detailed chemical and structural characterization in combination with electrochemical characterization and attributed to the presence of secondary elements in the film as well as to the presence of secondary iron oxide phases apart from hematite. This work demonstrates the complex effect of plasma exposure on both film morphology and chemical composition of PEC thin films and provides further understanding on how this technique can be used for nanostructuring of other functional films

Statistika penelitian dengan SPSS 24

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Electrochemistry of Sputtered Hematite Photoanodes: A Comparison of Metallic DC versus Reactive RF Sputtering

The water splitting activity of hematite is sensitive to the film processing parameters due to limiting factors such as a short hole diffusion length, slow oxygen evolution kinetics, and poor light absorptivity. In this work, we use direct current (DC) magnetron sputtering as a fast and cost-effective route to deposit metallic iron thin films, which are annealed in air to obtain well-adhering hematite thin films on F:SnO2-coated glass substrates. These films are compared to annealed hematite films, which are deposited by reactive radio frequency (RF) magnetron sputtering, which is usually used for depositing metal oxide thin films, but displays an order of magnitude lower deposition rate. We find that DC sputtered films have much higher photoelectrochemical activity than reactive RF sputtered films. We show that this is related to differences in the morphology and surface composition of the films as a result of the different processing parameters. This in turn results in faster oxygen evolution kinetics and lower surface and bulk recombination effects. Thus, fabricating hematite thin films by fast and cost-efficient metallic iron deposition using DC magnetron sputtering is shown to be a valid and industrially relevant route for hematite photoanode fabrication