Local analysis of oxygen reduction catalysis by scanning vibrating electrode technique : a new approach to the study of biocorrosion

The scanning vibrating electrode technique (SVET)was employed to investigate oxygen reduction catalysis by the presence of enzyme in an aerobic medium. Heme protoporphyrin (hemin) was chosen as a model of the enzymes that are able to catalyze oxygen reduction. A strict experimental protocol was defined for preparing the graphite surface by deposition of hemin with a simple configuration mimicking the presence of enzyme on the samples. The same configuration was adapted to a stainless steel electrode. Different geometric arrangementswere investigated by SVET to approach the local conditions. The results demonstrated that hemin deposited on the electrode surface led to an increase in the cathodic current, which indicated a catalytic effect. Based on the SVET analysis, itwas demonstrated that hemin caused the appearance of galvanic cells on the material surface. The SVET proved able to locate active catalytic centres and therefore to foresee the contribution of the enzyme to the creation of galvanic cells, thus leading to localized corrosion. The application of SVET to the study of the interaction between biological molecules and material provides a newapproach for visualizing and understanding microbially influenced corrosion (MIC) in an aerobic medium

Optimization of Full Cell Formulation Factors Based on Silicon – Graphite Composite Negative Electrode

Battery Science & TechnologyIn the state of the art progress in improving the performance of the Lithium Ion Batteries (LIB) full cell, the formulation engineering has received little attention, compared to new structures and new compositions of the electrochemically active material so far. However, much attention is paid to the formulation engineering in the field of battery industry, because it is critically significant in order to manufacture efficient full cells which can be commercialized. Such efforts are quite restricted to access or publication, because they are the proprietary information of the manufacturing companies. This study is focused on the optimization of full cell formulation factors based on silicon-natural graphite composite negative electrode. The considered factors were composition of active materials, binder, electrolyte and cutoff voltage in a full cell. The effect of different particle sizes of natural graphite within the composite, which is composed of silicon and natural graphite, was investigated, in which the composite with smaller natural graphite showed the superior electrical conductive network. The experiment showed that the silicon based composite electrode keeps higher voltage profile than that of natural graphite, especially during delithiation in the half cell. And, the simulation result, computed out of the experimental result, envisioned that it is better to shift cutoff voltage to the lower voltage during discharge in the full cell consisting of silicon–natural graphite composite electrode in order to use the maximum capacity of each electrode, comparing with that of natural graphite electrode. Additionally, a design method of calculating initial discharge capacity in a full cell was investigated. A statistical analysis method making use of Design of Experiments (DOE) was applied to search for the optimized condition for the weight ratio of binder mixture and the electrolyte kind, which showed that the cycle life of silicon-natural graphite composite electrode with the PAA or CMC binders is superior to that with SBR binder. This experimental result enabled me to argue that those binders, which have mechanically high ‘proportional limit stress’ like PAA and CMC, provide more robust bonds among expansive active materials (Si) which, in turn, can be adhered solidly to current collector substrate, compared with SBR and PVDF which have low ‘proportional limit stress’. Such strong bonds are also formed even between Si and Natural graphite of active materials, which contributed to the preservation of electrical conductivity of a composite negative electrode despite under repeated dimensional changes during cycles.ope

Ab initio study of sodium cointercalation with diglyme molecule into graphite

The cointercalation of sodium with the solvent organic molecule into graphite can resolve difficulty of forming the stage-I Na-graphite intercalation compound, which is a predominant anode of Na-ion battery. To clarify the mechanism of such cointercalation, we investigate the atomistic structure, energetics, electrochemical properties, ion and electron conductance, and charge transferring upon de/intercalation of the solvated Na-diglyme ion into graphite with {\it ab initio} calculations. It is found that the Na(digl)$_2$C$_n$ compound has the negatively lowest intercalation energy at $n\approx$21, the solvated Na(digl)$_2$ ion diffuses fast in the interlayer space, and their electronic conductance can be enhanced compared to graphite. The calculations reveal that the diglyme molecules as well as Na atom donates electrons to the graphene layer, resulting in the formation of ionic bonding between the graphene layer and the moiety of diglyme molecule. This work will contribute to the development of innovative anode materials for alkali-ion battery applications

Effects of cycling on lithium-ion battery hysteresis and overvoltage

Currently, lithium-ion batteries are widely used as energy storage systems for mobile applications. However, a better understanding of their nature is still required to improve battery management systems (BMS). Overvoltages and open-circuit voltage (OCV) hysteresis provide valuable information regarding battery performance, but estimations of these parameters are generally inaccurate, leading to errors in BMS. Studies on hysteresis are commonly avoided because the hysteresis depends on the state of charge and degradation level and requires time-consuming measurements. We have investigated hysteresis and overvoltages in Li(NiMnCo)O2/graphite and LiFePO4/graphite commercial cells. Here we report a direct relationship between an increase in OCV hysteresis and an increase in charge overvoltage when the cells are degraded by cycling. We fnd that the hysteresis is related to difusion and increases with the formation of pure phases, being primarily related to the graphite electrode. These fndings indicate that the graphite electrode is a determining factor for cell efciency.Peer ReviewedPostprint (published version

Ion sputter textured graphite

A specially textured surface of pyrolytic graphite exhibits extremely low yields of secondary electrons and reduced numbers of reflected primary electrons after impingement of high energy primary electrons. An ion flux having an energy between 500 eV and 1000 eV and a current density between 1.0 mA/sq cm and 6.0 mA/sq cm produces surface roughening or texturing which is in the form of needles or spines. Such textured surfaces are especially useful as anode collector plates in high efficiency electron tube devices

Polymeric foams as the matrix of voltammetric sensors for the detection of catechol, hydroquinone, and their mixtures

Producción CientíficaPorous electrodes based on polymethylmethacrylate and graphite foams (PMMA_G_F) have been developed and characterized. Such devices have been successfully used as voltammetric sensors to analyze catechol, hydroquinone, and their mixtures. The presence of pores induces important changes in the oxidation/reduction mechanism of catechol and hydroquinone with respect to the sensing properties observed in nonfoamed PMMA_graphite electrodes (PMMA_G). The electropolymerization processes of catechol or hydroquinone at the electrode surface observed using PMMA_G do not occur at the surface of the foamed PMM_G_F. In addition, the limits of detection observed in foamed electrodes are one order of magnitude lower than the observed in the nonfoamed electrodes. Moreover, foamed electrodes can be used to detect simultaneously both isomers and a remarkable increase in the electrocatalytic properties shown by the foamed samples, produces a decrease in the oxidation potential peak of catechol in presence of hydroquinone, from +0.7 V to +0.3 V. Peak currents increased linearly with concentration of catechol in presence of hydroquinone over the range of 0.37·10−3 M to 1.69·10−3 M with a limit of detection (LOD) of 0.27 mM. These effects demonstrate the advantages obtained by increasing the active surface by means of porous structures.Ministerio de Economía, Industria y Competitividad - Fondo Europeo de Desarrollo Regional (project AGL2015-67482-R)Junta de Castilla y Leon - Fondo Europeo de Desarrollo Regional (project VA-011U16

Extracellular electron transfer mechanism in Shewanella loihica PV- 4 biofilms formed at indium tin oxide and graphite electrodes

Electroactive biofilms are capable of extracellular electron transfer to insoluble metal oxides and electrodes; such biofilms are relevant to biogeochemistry, bioremediation, and bioelectricity production. We investigated the extracellular electron transfer mechanisms in Shewanella loihica PV-4 viable biofilms grown at indium tin oxide (ITO) and graphite electrodes in potentiostat-controlled electrochemical cells poised at 0.2 V vs. Ag/AgCl. Chronoamperometry and confocal microscopy showed higher biofilm growth at graphite compared to the ITO electrode. Cyclic voltammetry, differential pulse voltammetry, along with fluorescence spectroscopy showed that direct electron transfer through outer membrane c type cytochromes (Omcs) prevailed at the biofilm/ITO interface, while biofilms formed at graphite electrode reduced the electrode also via secreted redox mediators, such as flavins and quinones. The biofilm age does not affect the prevalent transfer mechanism at ITO electrodes. On the other hand, secreted redox mediators accumulated at biofilm/graphite interface, thus increasing mediated electron transfer as the biofilm grows over five days. Our results showed that the electrode material determined the prevalent electron transfer mechanism and the dynamic of secreted redox mediators in S. loihica PV-4 biofilms. These observations have implications for the optimization of biofilm-based electrochemical systems, such as biosensors and microbial fuel cells

Ion sputter textured graphite electrode plates

A specially textured surface of pyrolytic graphite exhibits extremely low yields of secondary electrons and reduced numbers of reflected primary electrons after impingement of high energy primary electrons. Electrode plates of this material are used in multistage depressed collectors. An ion flux having an energy between 500 iV and 1000 iV and a current density between 1.0 mA/sq cm and 6.0 mA/sq cm produces surface roughening or texturing which is in the form of needles or spires. Such textured surfaces are especially useful as anode collector plates in high tube devices