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| 6. |
- Blidberg, Andreas, 1987-, et al.
(författare)
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Electronic changes in poly(3,4-ethylenedioxythiophene)-coated LiFeSO4F during electrochemical lithium extraction
- 2019
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Ingår i: Journal of Power Sources. - : ELSEVIER SCIENCE BV. - 0378-7753 .- 1873-2755. ; 418, s. 84-89
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Tidskriftsartikel (refereegranskat)abstract
- The redox activity of tavorite LiFeSO4F coated with poly (3,4-ethylenedioxythiophene), i.e. PEDOT, is investigated by means of several spectroscopic techniques. The electronic changes and iron-ligand redox features of this LiFeSO4F-PEDOT composite are probed upon delithiation through X-ray absorption spectroscopy. The PEDOT coating, which is necessary here to obtain enough electrical conductivity for the electrochemical reactions of LiFeSO4F to occur, is electrochemically stable within the voltage window employed for cell cycling. Although the electronic configuration of PEDOT shows also some changes in correspondence of its reduced and oxidized forms after electrochemical conditioning in Li half-cells, its p-type doping is fully retained between 2.7 and 4.1 V with respect to Li+/Li during the first few cycles. An increased iron-ligand interaction is observed in LixFeSO4F during electrochemical lithium extraction, which appears to be a general trend for polyanionic insertion compounds. This finding is crucial for a deeper understanding of a series of oxidation phenomena in Li-ion battery cathode materials and helps paving the way to the exploration of new energy storage materials with improved electrochemical performances.
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| 7. |
- Blidberg, Andreas, 1987-, et al.
(författare)
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Identifying the Electrochemical Processes in LiFeSO4F Cathodes for Lithium Ion Batteries
- 2017
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Ingår i: ChemElectroChem. - : Wiley. - 2196-0216. ; 4:8, s. 1896-1907
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The electrochemical performance of tavorite LiFeSO4F can be considerably improved by coating the material with a conducting polymer (poly(3,4-ethylenedioxythiophene); PEDOT). Herein, the mechanisms behind the improved performance are studied systematically by careful electrochemical analysis. It is shown that the PEDOT coating improves the surface reaction kinetics for the Li-ion insertion into LiFeSO4F. For such coated materials no kinetic limitations remain, and a transition from solid state to solution-based diffusion control was observed at 0.6 mA cm−2 (circa C/2). Additionally, the quantity of PEDOT is optimized to balance the weight added by the polymer and the improved electrochemical function. Post mortem analysis shows excellent stability for the LiFeSO4F-PEDOT composite, and maintaining the electronic wiring is the most important factor for stable electrochemical cycling of LiFeSO4F. The insights and the methodology used to determine the rate-controlling steps are readily transferable to other ion-insertion-based electrodes, and the findings are important for the development of improved battery electrodes.
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| 8. |
- Blidberg, Andreas, 1987-, et al.
(författare)
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Monitoring LixFeSO4F (x = 1, 0.5, 0) Phase Distributions in Operando To Determine Reaction Homogeneity in Porous Battery Electrodes
- 2017
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Ingår i: Chemistry of Materials. - : American Chemical Society. - 0897-4756 .- 1520-5002. ; 29:17, s. 7159-7169
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Tidskriftsartikel (refereegranskat)abstract
- Increasing the energy and power density simultaneously remains a major challenge for improving electrochemical energy storage devices such as Li-ion batteries. Understanding the underlying processes in operating electrodes is decisive to improve their performance. Here, an extension of an in operando X-ray diffraction technique is presented, wherein monitoring the degree of coexistence between crystalline phases in multiphase systems is used to investigate reaction homogeneity in Li-ion batteries. Thereby, a less complicated experimental setup using commercially available laboratory equipment could be employed. By making use of the intrinsic structural properties of tavorite type LiFeSO4F, a promising cathode material for Li-ion batteries, new insights into its nonequilibrium behavior are gained. Differences in the reaction mechanism upon charge and discharge are shown; the influence of adequate electronic wiring for the cycling stability is demonstrated, and the effect of solid state transport on rate performance is highlighted. The methodology is an alternative and complementary approach to the expensive and demanding techniques commonly employed for time-resolved studies of structural changes in operating battery electrodes. The multiphase behavior of LiFeSO4F is commonly observed for other insertion type electrode materials, making the methodology transferable to other new energy storage materials. By expanding the possibilities for investigating complex processes in operating batteries to a larger community, faster progress in both electrode development and fundamental material research can be realized.
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| 10. |
- Hedman, Jonas, et al.
(författare)
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Fiber Optic Monitoring of Composite Lithium Iron Phosphate Cathodes in Pouch Cell Batteries
- 2022
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Ingår i: ACS Applied Energy Materials. - : American Chemical Society (ACS). - 2574-0962. ; 5:1, s. 870-881
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Tidskriftsartikel (refereegranskat)abstract
- - Developing techniques for real-time monitoring of the complex and dynamic environment in lithium-ion batteries is crucial for optimal use of the cells and to develop the next generation of batteries. In this work, we demonstrate the use of fiber optic evanescent wave (FOEW) sensors for monitoring lithium iron phosphate (LFP) composite cathodes in pouch cells. The fiber optic sensors were placed on top of the LFP electrodes, and the pouch cells were found to cycle well with significantly improved electrochemical performance compared to fully embedded fibers in Swagelok cells. Galvanostatic, voltammetric, and pulsed current techniques demonstrated that the optical response correlated well with the capacity, and a clear difference in sensor response was seen when the sensors were placed at the surface of composite electrodes compared to fibers embedded in the cathode. The optical response from LFP at different rates was also investigated, but no apparent influence on intensity output was found even though polarization was observed in the voltage profiles at higher currents. It was also demonstrated that the electrolyte itself functioned as a fiber cladding and that the salt concentration in the electrolyte did not influence the optical signal. In addition, given the short penetration depth of the evanescent waves, the sensor response is most likely dominated by the surface conditions of electrode particles near the sensing region. These findings provide further insight into the application and performance of FOEW sensors integrated into batteries, as well as the possibility of developing low-cost fiber optic sensors for battery monitoring under working conditions.
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| 11. |
- Hedman, Jonas, et al.
(författare)
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Fiber Optic Sensor for Detection of Sodium Plating in Sodium-ion Batteries
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Optical fiber sensors integrated into sodium-ion batteries could provide a battery management system (BMS) with information to identify early warning signs of plating, preventing catastrophic failure and maintaining safe operation during fast charging. This work shows the possibility to directly detect plating of sodium metal in electrochemical cells by means of operando fiber optic evanescent wave (FOEW) spectroscopy. The results include measurements with FOEW sensors on bare copper substrates as well as on hard carbon anodes during operation in both half- and full-cell configurations. Full-cells using hard carbon anodes and Prussian white cathodes with high areal capacities (>1.5 mAh cm−2) and integrated FOEW sensors are shown to cycle well in pouch cells. The results also include measurements to demonstrate plating on hard carbon during sodiation at different rates.
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| 12. |
- Hedman, Jonas, et al.
(författare)
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Fiber Optic Sensors for Detection of Sodium Plating in Sodium-Ion Batteries
- 2022
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Ingår i: ACS Applied Energy Materials. - : American Chemical Society (ACS). - 2574-0962. ; 5:5, s. 6219-6227
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Tidskriftsartikel (refereegranskat)abstract
- Optical fiber sensors integrated into sodium-ion batteries could provide a battery management system (BMS) with information to identify early warning signs of plating, preventing catastrophic failure and maintaining safe operation during fast charging. This work shows the possibility of directly detecting plating of sodium metal in electrochemical cells by means of operando fiber optic evanescent wave (FOEW) spectroscopy. The results include measurements with FOEW sensors on bare copper substrates as well as on hard carbon anodes during operation in both half- and full-cell configurations. Full cells using hard carbon anodes and Prussian white cathodes with high areal capacities (>1.5 mAh cm(-2)) and integrated FOEW sensors are shown to cycle well in pouch cells. The results also include measurements to demonstrate plating on hard carbon during sodiation at different rates.
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| 13. |
- Hedman, Jonas, 1992-
(författare)
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Fiber Optic Sensors for Monitoring of Lithium- and Sodium-ion Batteries
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Rechargeable batteries, particularly lithium-ion batteries, have rapidly evolved since their introduction and now dominate the market, owing primarily to their high energy and power densities. With growing demand for high-performance batteries in portable electronics and electric vehicles, the need for safe, efficient, and reliable batteries is crucial. Conventional battery management systems, which generally rely on parameters such as current, voltage, and temperature, provide limited information on the chemical and physical processes taking place in the battery during operation. The understanding of degradation processes and how they evolve with time is also limited due to the complex nature of batteries. In order to enhance the battery lifetime, safety, and reliability of current batteries as well as for emerging battery technologies, more detailed information from the cells is required. Developing sensors that can be used to probe the batteries could allow for optimized performance and a more accurate determination of cell state. In this regard, fiber optic sensors are promising candidates.This work explores the use of fiber optical evanescent wave (FOEW) sensors for monitoring chemical and electrochemical reactions in lithium- and sodium-ion batteries under working conditions. The sensor response and battery performance were compared with the sensor either fully embedded in a lithium iron phosphate cathode or positioned at the electrode surface. The optical response was further linked to the oxidation and reduction of the active material during cycling by means of galvanostatic and voltammetric experiments. The influence of cycling rate, sensor position, and electrolyte salt concentration was also discussed. The work also shows the ability of the FOEW sensors to detect lithium and sodium plating, both as a result of insufficient storage capacity and high cycling rates. This is an important finding as plating poses a serious risk for short circuit in batteries. A correlation with the sensor response and lithium staging in graphite anodes could also be seen.These findings highlight the value of optical sensors for monitoring batteries under working conditions. The concept of fiber optic sensing in batteries is still in its early stages, but the research field is gaining more interest. This work has aimed to advance the understanding of FOEW sensors in particular, and the results could help to provide directions for the research community for the realization of fiber optic sensing in commercial batteries.
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| 14. |
- Hedman, Jonas, et al.
(författare)
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Fiber Optical Detection of Lithium Plating at Graphite Anodes
- 2023
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Ingår i: Advanced Materials Interfaces. - : Wiley-VCH Verlagsgesellschaft. - 2196-7350. ; 10:3
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Tidskriftsartikel (refereegranskat)abstract
- Avoiding the plating of metallic lithium on the graphite anode in lithium-ion batteries, potentially leading to aging and the formation of dendrites is critical for long term and safe operation of the cells. In this contribution, in operando detection of lithium plating via a fiber optical sensor placed at the surface of a graphite electrode is demonstrated. The detection is based on the modulation of light at the sensing region, which is in direct contact with the graphite particles. This is first demonstrated by the intentional deposition of lithium on a copper electrode, followed by experiments with graphite electrodes in pouch cells where plating is initiated both as a result of over-lithiation and excessive cycling rates. The plating resulted in a significant loss of light from the fiber, and the findings correlated well with previous experiments on the detection of sodium plating. The modulated light is also found to correlate well with the graphite staging via changes in the optical properties of the graphite during slow (de)intercalation of lithium ions. In a practical application, the fiber optical sensor may provide a battery management system (BMS) with input to optimize the charging procedure or to warn for cell failure.
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| 15. |
- Hedman, Jonas, et al.
(författare)
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Fibre Optic Sensor for Characterisation of Lithium-Ion Batteries
- 2020
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Ingår i: ChemSusChem. - : Wiley. - 1864-5631 .- 1864-564X. ; 13:21, s. 5731-5739
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Tidskriftsartikel (refereegranskat)abstract
- The interaction between a fibre optic evanescent wave sensor and the positive electrode material, lithium iron phosphate, in a battery cell is presented. The optical-electrochemical combination was investigated in a reflection-based and a transmission-based configuration, both leading to comparable results. Both constant current cycling and cyclic voltammetry were employed to link the optical response to the charge and discharge of the battery cells, and the results demonstrated that the optical signal changed consistently with lithium ion insertion and extraction. More precisely, cyclic voltammetry showed that the intensity increased when iron was oxidised during charge and then decreased as iron was reduced during discharge. Cyclic voltammetry also revealed that the optical signal remained unchanged when essentially no oxidation or reduction of the electrode material took place. This shows that optical fibre sensors may be used as a way of monitoring state of charge and electrode properties under dynamic conditions.
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| 18. |
- Högström, Jonas, et al.
(författare)
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On the evaluation of corrosion resistances of amorphous chromium carbide thin-films
- 2014
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Ingår i: Electrochimica Acta. - : Elsevier BV. - 0013-4686 .- 1873-3859. ; 122:SI, s. 224-233
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Tidskriftsartikel (refereegranskat)abstract
- The possibilities of evaluating the corrosion resistance of amorphous chromium carbide (Cr-C) films containing nanometre-sized carbide grains embedded in an amorphous carbon matrix on the basis of polarization curves, voltammograms and the oxidation charge have been studied for Cr-C films with different carbon concentrations. The films, which were manufactured by non-reactive directcurrent magnetron sputtering, were studied in 1.0 mM H2SO4 at both 22 °C and 80 °C, and with scanning electron microscopy and X-ray photoelectron spectroscopy prior to and after the electrochemical experiments. It is demonstrated that the oxidation of these Cr-C films gives rise to a surface composed of Cr2O3 and partially oxidized carbon and that the non-corroding oxidation current due to the carbon oxidation increases with increasing carbon concentration in the films as well as with the electrolyte temperature. Since the oxidation current is composed of contributions from both Cr-C and carbon oxidation it is not straightforward to evaluate the corrosion resistances of these films based on the current in the passive region, the mixed potential (i.e., the corrosion potential) or the open circuit potential. The present results in fact indicate that Cr-C films with high carbon concentrations may have better corrosion resistances than the corresponding films with lower carbon concentrations although larger currents in the passive region can be seen in polarization curves.
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| 19. |
- Ihrfors, Charlotte, 1989-
(författare)
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Electrochemical characterisations of TiO2 nanotube and lithium-metal electrodes for lithium-based batteries
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Lithium-ion batteries have since their introduction on the commercial market in the early 1990s played an important role within the field of energy storage. In this thesis both titanium dioxide, TiO2, and lithium metal are investigated based on their properties as anodes for lithium-based battery technologies. TiO2 nanotubes with lengths between 4.5 and 40 µm were synthesized through a two-step anodization of titanium metal foil in a fluoride containing electrolyte. The formed nanotubes were investigated using scanning electron microscopy and electrochemically evaluated in pouch-cell batteries. For the long nanotubes, especially the 40 µm long ones, the results indicate that the lithiation and delithiation processes are limited by the solid state diffusion of lithium ions within the electrode material for the employed cycling conditions. Studies of the TiO2 nanotubes at elevated temperatures, 80 °C, showed a good temperature stability both in a conventional organic electrolyte and in an ionic liquid based electrolyte. In full cells the ionic liquid electrolyte was needed to get a good performance mainly due to the LiFePO4 cathode. Despite a good general performance, the TiO2 nanotubes show capacity losses during high rate cycling. This effect was studied using galvanostatic cycling including open circuit periods and analyses of the cycled electrodes with inductive coupled plasma atomic emission spectroscopy. The results indicate the presence of a lithium trapping effect in the TiO2 electrodes caused by the lithium diffusion within the electrode material. The trapping effect was also seen in a comparative study involving TiO2 nanoparticles and nanotubes. The comparison also showed that the electrochemical performance depended on the electrode design.Enabling of 2D lithium growth and avoiding lithium dendrite formation are of great importance for both battery research and practical applications. In this thesis an approach based on formation of a large amount of equally sized lithium nuclei on the surface in combination with a diffusion controlled deposition is described. To achieve this an electrolyte with a low lithium ion concentration, where the migrations is taken care of by a supporting salt, was used in combination with an initial potentiostatic pulse. This approach was found to yield a homogeneous coverage of lithium nuclei and dendrite-free deposition.
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| 20. |
- JOHANSSON, DAVID, et al.
(författare)
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Nanoplasmonic sensing of Pb-acid and Li-ion batteries
- 2016
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Ingår i: Presented at the 2nd International Conference on Sensors and Electronic Instrumental Advances (SEIA), Barcelona, Spain, September 22 – 23, 2016. - : INT FREQUENCY SENSOR ASSOC-IFSA. ; , s. 57-59, s. 57-59
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Konferensbidrag (refereegranskat)abstract
- The increasing sophistication and performance of batteries are connected with more complex chemical and physical battery processes and increase the need of more direct and informative measurements, both in the R&D phase and for monitoring and control during operation of vehicles. Todays potentiometric based measurement sensors are not sufficiently accurate for optimal battery sensing. To avoid the built in wide safety margins new, more informative monitoring signals are therefore desired or needed. In this study the optical technology NanoPlasmonic Sensing (NPS) has been used to in-situ monitor the charge and discharge processes of lead-acid and Li-ion batteries. The optical signals were found to correlate well with charging/discharging of both battery technologies.
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| 22. |
- Masunaga, Kumi, et al.
(författare)
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Development of sensor surface with recognition of molecular substructure
- 2008
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Ingår i: Sensors and actuators. B, Chemical. - : Elsevier BV. - 0925-4005 .- 1873-3077. ; 130:1, s. 330-337
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Tidskriftsartikel (refereegranskat)abstract
- A biological olfaction system is one of the highest performance chemical sensing systems for low-molecular-weight compounds. An ability of recognizing a various molecular properties based on their structures is essential for a biological odor recognition process. For the development of a sensor mimicking the olfactory system, we have formed benzene-patterned self-assembled monolayer (SAM) on the sensor surface using SAMs with nanostructure that serves as adsorption sites for benzene ring, which is representative substructure of aromatics. The structure of the benzene-patterned SAM surface was analyzed by contact-angle measurement, ellipsometry, cyclic voltammetry (CV) and atomic force microscopy (AFM). Moreover, the electrodes evaluated as sensor surfaces with cyclic surface-polarization impedance (cSPI) sensor that measures changes in impedance of the electrode surface by adsorption of substances. The results of cSPI indicated the benzene-patterned SAM surface could distinguish benzene by recognizing of the hydrophobicity and the molecular size. © 2007 Elsevier B.V. All rights reserved.
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| 23. |
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| 24. |
- Ulrich, Christian, 1976-, et al.
(författare)
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Evaluation of industrial cutting fluids using electrochemical impedance spectroscopy and multivariate data analysis
- 2012
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Ingår i: Talanta. - : Elsevier BV. - 0039-9140 .- 1873-3573. ; 97, s. 468-472
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Tidskriftsartikel (refereegranskat)abstract
- In this paper we explore the combination of electrochemical impedance spectroscopy (EIS) and multivariate data analysis to evaluate the concentration and pH of an industrial cutting fluid. These parameters are vital for the performance of for instance tooling processes, and an on-line quality monitoring system would in such applications be very beneficial. It is shown that both the total impedance and the phase angle contain information that allows the simultaneous discrimination of the concentration and the pH. The final evaluation was conducted using the regression technique partial least squares (PLS), and this approach provided a way to quickly and easily find the correlation between EIS data and the sought parameters. The possibility to estimate both the concentration and pH level clearly indicates the potential of this method to be implemented for on-line evaluation.
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| 27. |
- Ulrich, Christian, 1976-, et al.
(författare)
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Surface Gradients on Bipolar Electrodes
- 2008
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Ingår i: presented at the 12<sup>th</sup> International Conference on Electroanalysis of the European Society for ElectroAnalytical Chemistry (ESEAC), Prague, 16-19 June, 2008..
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Konferensbidrag (refereegranskat)
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| 28. |
- Uvdal, Kajsa, 1961-, et al.
(författare)
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Metal ion interaction with phosphorylated tyrosine analogue monolayers on gold
- 2006
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 110:46, s. 23410-23416
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Tidskriftsartikel (refereegranskat)abstract
- Phosphorylated tyrosine analogue molecules (pTyr-PT) were assembled onto gold substrates, and the resulting monolayers were used for metal ion interaction studies. The monolayers were characterized by X-ray photoelectron spectroscopy (XPS), infrared reflection−absorption spectroscopy (IRAS), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS), both prior to and after exposure to metal ions. XPS verified the elemental composition of the molecular adsorbate and the presence of metal ions coordinated to the phosphate groups. Both the angle-dependent XPS and IRAS results were consistent with the change in the structural orientation of the pTyr-PT monolayer upon exposure to metal ions. The differential capacitance of the monolayers upon coordination of the metal ions was evaluated using EIS. These metal ions were found to significantly change the capacitance of the pTyr-PT monolayers in contrast to the nonphosphorylated tyrosine analogue (TPT). CV results showed reduced electrochemical blocking capabilities of the phosphorylated analogue monolayer when exposed to metal ions, supporting the change in the structure of the monolayer observed by XPS and IRAS. The largest change in the structure and interfacial capacitance was observed for aluminum ions, compared to calcium, magnesium, and chromium ions. This type of monolayer shows an excellent capability to coordinate metal ions and has a high potential for use as sensing layers in biochip applications to monitor the presence of metal ions.
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| 29. |
- Valiokas, Ramunas, 1970-, et al.
(författare)
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Structural and kinetic properties of laterally stabilized, oligo(ethylene glycol)-containing alkylthiolates on gold : A modular approach
- 2006
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Ingår i: Biointerphases. - : American Institute of Physics (AIP). - 1934-8630 .- 1559-4106. ; 1:1, s. 22-34
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Tidskriftsartikel (refereegranskat)abstract
- The formation of highly ordered self-assembled monolayers (SAMs) on goldfrom an unusually long and linear compound HS(CH2)15CONH(CH2CH2O)6CH2CONH(CH2)15CH3 is investigated by contact angle goniometry, ex situ null ellipsometry, cyclic voltammetry and infrared reflection-absorption spectroscopy. The molecules are found to assemble in an upright position as a complete monolayer within 60 min. The overall structure of the SAM reaches equilibrium within 24 h as evidenced by infrared spectroscopy, although a slight improvement in water contact angles is observed over a period of a few weeks. The resulting SAM is 60 Å thick and it displays an advancing water contact angle of 112° and excellent electrochemicalblocking characteristics with typical current densities about 20 times lower as compared to those observed for HS(CH2)15CH3 SAMs. The dominating crystalline phases of the supporting HS(CH2)15 and terminal (CH2)15CH3 alkyl portions, as well as the sealed oligo(ethylene glycol) (OEG) “core,” appear as unusually sharp features in the infrared spectra at room temperature. For example, the splitting seen for the CH3 stretching and CH2 scissoring peaks is normally only observed for conformationally trapped alkylthiolate SAMs at low temperatures and for highly crystalline polymethylenes. Temperature-programmed infrared spectroscopy in ultrahigh vacuum reveals a significantly improved thermal stability of the SAM under investigation, as compared to two analogous OEG derivatives without the extended alkyl chain. Our study points out the advantages of adopting a “modular approach” in designing novel SAM-forming compounds with precisely positioned in plane stabilizing groups. We demonstrate also the potential of using the above set of compounds in the fabrication of “hydrogel-like” arrays with controlled wetting properties for application in the ever-growing fields of protein and cell analysis, as well as for bioanalytical applications.
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| 30. |
- Wei, Wei, et al.
(författare)
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Capacity Limiting Effects for Freestanding, Monolithic TiO2 Nanotube Electrodes with High Mass Loadings
- 2020
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Ingår i: ACS Applied Energy Materials. - : American Chemical Society (ACS). - 2574-0962. ; 3:5, s. 4638-4649
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Tidskriftsartikel (refereegranskat)abstract
- Galvanostatic and cyclic voltammetric experiments have been used to identify the main capacity limiting phenomenon for TiO2 nanotube electrodes with nanotube lengths between 4.5 and 40.5 mu m and mass loadings up to 10.5 mg cm(-2). The results for the nanotube electrodes, which were synthesized by using a two-step anodization and evaluated in pouch cell batteries containing lithium metal counter electrodes, show that higher capacities could be obtained by using voltammetric rather than galvanostatic cycling and that the capacity is limited by the TiO2 lithiation step. The maximum average TiO2 lithiation degree (which correspond to an average composition of about Li0.55TiO2) is a result of a decrease in the lithium ion diffusion rate with an increasing concentration of LixTiO2 in the nanotubes. This saturation effect is also responsible for the diffusion-controlled decrease in the capacity seen when increasing the constant current cycling rate. The different electrochemical lithiation and delithiation behaviors are explained based on the differences between the LixTiO2 and TiO2 concentration profiles obtained in the nanotubes. During the lithiation, the increasing LixTiO2 concentration in the nanotubes gives rise to a decreasing lithiation voltage when the LixTiO2 concentration becomes sufficiently high. The areal capacity of the nanotube electrodes can be increased from 0.18 to 1 mAh cm(-2) (at a rate of C/5) by increasing the length of the nanotubes from 4.5 to 40.5 mu m. Although the cell resistance is shown to be practically independent of the nanotube length, the increasing mass loading and hence current required at a given cycling rate result in larger iR drops for the longer nanotubes. The data also indicate the presence of a lithium-ion trapping effect due to two-way diffusion of lithium ions in the lithiated nanotubes in analogy with the behavior previously found for lithium-alloy-forming electrode materials.
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