bluuebunny/crossref_metadata_2025 huggingface dataset:
Hybrid Electrodes of Conducting Polymers and Two-Dimensional Ti3C2 (MXene) for Li and Na Ion Storage
Authors: VahidMohammadi Armin , Beidaghi Majid
Published: February 2020

High-rate lithium and sodium storage devices that can deliver energy densities considerably higher than those of conventional aqueous or non-aqueous electrochemical capacitors have recently received considerable attention [1]. Li-ion capacitors (LICs) and sodium-ion capacitors (NACs) can combine the high-energy density of batteries and with a high-power density of supercapacitor by utilizing electrode materials that are capable of fast intercalation of Li+ and Na+ [1-4]. 2D transition metal carbides and/or carbonitrides called MXenes are a new family of 2D materials that are produced by selective etching and liquid exfoliation of MAX phases, a large group of ternary carbides and/or nitrides, where M is an early transition metal, A is a group A element and X is carbon and/or nitrogen [5]. Two-dimensional (2D) Ti3C2, which is produced by selective removal of Al atoms from Ti3AlC2 MAX phase, is the most studied MXene material which presents an excellent volumetric capacitance of around 900 F cm-1 in some aqueous electrolytes [5]. However, like other 2D materials, Ti3C2 shows much lower capacitance in Li and Na ion containing organic electrolytes mainly due to the restacking of Ti3C2 sheets that decrease the accessibility of Li+ and Na+ ions to the electrode surface, thus hindering the redox reactions at the surface of the electrodes. Herein, we address this issue by reporting freestanding hybrid electrodes of Ti3C2 and polyaniline (PANI) synthesized by oxidant-free polymerization of aniline monomers on the surface of individual MXene sheets. The results show that a few-nanometer-thick PANI coating on the surface of single layer MXene sheets increases the layer spacing of the freestanding electrodes. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and Raman analysis confirmed the formation of PANI thin films on the surface of Ti3C2 nanosheets. The conducting and electrochemically active PANI also contribute to the overall capacity of the electrodes, resulting in specific capacities as high as 200 Fg-1 when tested as an LIC electrode. The PANI/Ti3C2 electrodes were also investigated as anode material for both Li-ion and Na-ion batteries and showed highly improved capacities compared to bare Ti3C2 electrodes.

 

Keywords: Ti3C2, MXene, 2D materials, Lithium capacitor, Batteries

 

References

1. A. Byeon et al., J. Power Sources. 326, 686-694 (2016).

2. C. E. Ren et al., ChemElectroChem. 3, 689-693 (2016).

3. X. Xie et al., Nano Energy26, 513-523 (2016).

4. J. Luo et al., ACS Nano11 (3), 2459-2460 (2017).

5. B. Anasori, M. R. Lukatskaya, Y. Gogotsi, Nat. Rev. Mater. 2, 16098 (2017).
Tracking Electrochemical Double Layer Effects Modulated By the Solvent Composition in Lithium Ion Batteries: A Combined Theoretical and Experimental Investigation
Authors: El kharbachi Abdel , Thangavel Vigneshwaran , Nguyen Trong-Khoa , Xue Kan-Hao , Quiroga Matias , Franco Alejandro A. , Larcher Dominique
Published: February 2020

The study of the response of Lithium Ion Batteries (LIBs) to fast transient power solicitations is a crucial topic which may depend on the specificity of each application. In fact, LIBs can be present in different connection-configurations and their response performances will depend on the nature of the electrical engines, high dynamics power regulators and other electrochemical systems devoted to battery recharging [1]. One of the key aspects in the resulting transient response of LIBs is the ionic transport phenomena taking place at the interface between the liquid electrolyte and the solid active material (electrochemical double layer –EDL– region) [2]. However, characterization of the capacitive interfaces, as well as dynamic properties, as function of the electrolyte composition in Li-ion batteries remains a challenge owing to the change in the electrode/electrolyte environment from one cell component to another.

In this work, we present an investigation, combining experimental and computational modeling approaches, of the electrolyte/active material interfaces with focus on the EDL using LiFePO4 as a model electrode. In particular, the aim is to track the effect of the electrolyte solvent composition on the transient electrochemical behavior of the electrodes. A successful Swagelok® type setup probing interface liquid modifications is adapted for that purpose, in which the change of the solvent is made in-situ without cell disassembling. Such experimental cell allows the capture on how the electrolyte composition can affect the electrode potential dynamics. Coupling experimental results to computational modelling is addressed first for binary carbonate-based solvents (EC/DMC) with emphasize on the stability of the measurements using impedance spectroscopy. Mechanistic insights on the EDL structure and dynamics are also provided and discussed for ternary systems (EC/PC/DMC).

Acknowledgements

This work is funded by the French National Research Agency (ANR) through the project “ALIBABA” under the contract reference ANR-11-PRGE-0002.

References

[1] N. Legrand, S. Raël, B. Knosp, et al., J
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Power Sources251, 370 (2014).

[2] M.A. Quiroga, K.H. Xue, T.K. Nguyen, M. Tułodziecki, H. Huang, A.A. Franco, Journal of The Electrochemical Society, 161(8), E3302 (2014).

Figure 1
Electrochemical Peformance of Lithium-Ion Capacitors Evaluated Under High Temperature and High Voltage Stress Using Redox Stable Electrolytes and Additives
Authors: Boltersdorf Jonathan , Delp Samuel A. , Zheng Jim P , Jow T Richard , Read Jeffrey A.
Published: February 2020

Lithium-ion capacitors (LICs) were investigated for high power, moderate energy density applications for operation in extreme environments with prolonged cycle life performance. The LICs were prepared as three-layer pouch cells with an asymmetric configuration employing Faradaic pre-lithiated hard carbon anodes and non-Faradaic anion adsorption−desorption activated carbon (AC) cathodes. The studies were conducted in order to develop and improve the LIC cell design, the cell formation procedure, the stability of the electrolytes and additives, and the long-term capacity retention under high stress conditions. The LIC cells have been evaluated using critical performance tests under the following conditions: long-term cycling stability at room temperature (2.2-3.8 V), high temperature holds at 3.8 V, and high upper cut-off potential conditions (2.2 V to 3.8-5.0 V). The rate performance of different electrolytes and additives were measured after the LIC cell formation by charging at a 1C rate and discharging at a 1C, 2C, 4C, 6C, 10C, and again 1C rate from 2.2 V to 3.8 V. The performance of the energy storage devices were evaluated in terms of the specific discharge capacity, operational voltage/temperature window, coulombic efficiency, and cycling stability under different conditions using various electrolytes and additives. The presence of electrolyte additives were found to be essential to the improved performance of the LIC cells at room temperature, at high temperature, and at higher cut-off potentials.
Novel Redox Gel Electrolytes for All-Solid-State Supercapacitors
Authors: Kundu Arpan , Fisher Timothy
Published: February 2020

The conventional technique to fabricate high energy density supercapacitors is to use pseudocapacitive materials such as metal oxides, conducting polymers as supercapacitor electrodes. However, the fabrication process of such electrodes is often complex and they suffer from low power density and short cycle life due to their low electrical conductivity and mechanical fragility. An innovative approach has recently been developed with the introduction of a redox additives into the electrolyte to boost the capacitance. In this work, a couple of new stable and effective redox-mediated gel electrolytes have been prepared by doping FeCl2/FeCl3 and K3Fe(CN)6/K4Fe(CN)6 into polyvinyl alcohol (PVA), and high performance solid-state supercapacitors have been fabricated using light commercial nanotube paper electrodes and the prepared gel polymer as electrolyte and separator. Vertical graphene petals have been grown on the carbon nanotube paper to enhance the available surface area. During charge/discharge, the redox species in the electrolytes exchange electrons with the electrode while undergoing fast, reversible reactions which leads to high capacitance and low internal resistance. The devices are mechanically robust and exhibit high volumetric capacitance (based on the total device volume) due to their extremely low thickness. A comparison study has been performed for PVA-K3Fe(CN)6-K4Fe(CN)6 redox gel electrolyte and PVA-H2SO4 gel electrolyte devices. The redox electrolyte device shows a three-fold higher capacitance and superior charge/discharge stability. After 3000 cycles, its capacitance retention is 78% which is nominally smaller than the PVA-H2SO4 device (81%). In summary, the new redox-mediated gel electrolytes have been demonstrated as simple, scalable ingredients for achieving high energy density with minute penalty in cyclic stability.
A Molecular Dynamics Study of Concentrated Aqueous Solutions of Lithium Salts at Charged Electrodes
Authors: Vatamanu Jenel , Borodin Oleg
Published: February 2020

Li-ion batteries (LiBs) are widely used in very diverse set of applications from portable electronics, to electric vehicle transportation. Hence, improving LiBs’ power and energy while not compromising safety, remains a hot research topic. Organic solvents permit higher operating voltages; however, they have the disadvantage of being volatile and flammable. Aqueous solvents, on the other hand, are inexpensive and non-flammable but they are typically stable only at low voltages (<1V) resulting in relatively low energy density (<100Wh/kg). Recently, an intriguing paradigm shift regarding the extending electrochemical stability window of aqueous electrolytes was reported for the aqueous electrolytes.(1-4) Specifically, highly concentrated aqueous solutions of electrolytes (i.e. “water in salt”) were shown to have electrochemical stability window above 3V, despite the presence of water in the system.

In this presentation we explore an intriguing supposition that the electrochemical stability of these systems can be correlated with the electrolyte structure near surface. Using classical molecular dynamics simulations we investigate the electrolyte partition near the electrode, as a function of the applied potential. The studied system consisted of a highly concentrated solution of two salts LiTFSI and LiCF3SO3in water that was recently shown to have one wide electrochemical stability.(2) The electrolyte structuring near the electrode was found to be strongly dependent on the applied potential. Specifically, at the positively charged electrode water is displaced from the surface by the voluminous anions, while at the negatively charged electrode a large accumulation of water is observed in the interfacial layer. Interestingly, the water is displaced rapidly from the negative surface as the potential increases from -2V to 0V, and surprisingly elevated densities of F groups were found next to surface at -1V.

In such concentrated electrolytes, the Li ions are only partly coordinated with water (2-2.6 water molecules per Li). The partly desolvated Li+ can drag the TFSI anion near the negative electrode. In agreement with this observation, our simulations confirmed the presence of F groups in the proximity of the interfacial Li+ at the negative electrode. The presence of Li+and F next to the negative charged surface can trigger electrochemical reactions that kinetically passivate the negative electrode surface.

References

1. L. Suo, O. Borodin, T. Gao, M. Olguin, J. Ho, X. Fan, C. Luo, C. Wang and K. Xu, Science, 350, 938 (2015).

2. L. Suo, O. Borodin, W. Sun, X. Fan, C. Yang, F. Wang, T. Gao, Z. Ma, M. Schroeder, A. von Cresce, S. M. Russell, M. Armand, A. Angell, K. Xu and C. Wang, Angew. Chem. Int. Ed, 55, 7136 (2016).

3. F. Wang, Y. Lin, L. Suo, X. Fan, T. Gao, C. Yang, F. Han, Y. Qi, K. Xu and C. Wang, Energy Environ. Sci.,, 9, 3666 (2016).

4. Y. Yamada, K. Usui, K. Sodeyama, S. Ko, Y. Tateyama and A. Yamada, Nature Energy, 1, 16129 (2016).

Figure 1
Investigating the Electrode-Electrolyte Behaviour of Carbon Materials in Various Non-Aqueous Electrolytes
Authors: Cameron Amanda , Donne Scott W
Published: February 2020

Charge storage in electrochemical capacitors has been shown to be via charge separation at the electrode-electrolyte interface (so called electrical double layer charge storage) and via pseudo-capacitance, which is often described as fast redox reactions through the same interface. Charge storage via both of these mechanisms depends heavily on the interaction between the electrode morphology (electrochemically active surface area, pore size distribution, etc.) and the solvated ion in the electrolyte. In this work the interaction between a series of carbon-based substrates and various electrolyte species has been investigated.

Electrolytes examined include tetraethylammonium bis(trifluoromethane)sulfonimide (Et4NTFSI), 1-butyl-1-methylpyrrolidinium tetrafluoroborate (PYR14BF4), 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR14TFSI), and tetraethylammonium tetrafluoroborate (Et4NBF4) in acetonitrile. The interaction between these electrolytes and various carbon-based substrates was examined using a combination of cyclic voltammetry (CV) and step potential electrochemical spectroscopy (SPECS). These techniques have enabled differentiation of the charge storage mechanisms based on ion size, solvated ion size and charge density, as well as substrate surface area and porosity.
Low-Temperature Performance of Symmetric MnOx-Carbon Nanofoam-Based Ecs with Mild-pH Aqueous Electrolytes
Authors: Sassin Megan B. , Wallace Jean , Ko Jesse , Long Jeffrey W.
Published: February 2020

Electrochemical capacitors, ECs, should provide high performance over the broadest range of operating temperatures which is primarily determined by the properties of the electrolyte (freezing and boiling points, ionic conductivity and salt solubility as a function of temperature, flash point for flammable solvents). In the case of mild-pH aqueous electrolytes, where flammability is a non-issue, the sub-ambient temperature performance is the most critical factor. En route to demonstrating the performance of aqueous-electrolyte ECs at low temperature, we have characterized both the bulk thermal properties of single and multi-component electrolytes and their behavior when used in EC pouch cells. The ionic conductivities of bulk electrolytes with a fixed cation concentration of 5 M for single-component (e.g. Li2SO4, NaNO3) and multi-component electrolytes (e.g. Li2SO4 + NaNO3) ranged from 63 to 136 mS cm-1 at 20oC. The freezing points of these electrolytes were measured with differential scanning calorimetry. It was found that the anion dominates the freezing-point behavior, with sulfate-based electrolytes supporting freezing points down to –45oC and nitrate-based electrolytes down to –35oC. To assess the impact of temperature on performance as a function of electrolyte composition, we fabricated symmetric pouch cells comprising MnOx-carbon nanofoam electrodes and tested them over the temperature range of 25oC to –45oC in an environmental chamber. All ECs exhibited a gradual decrease in capacitance as the temperature decreased; however, upon re-warming to 25°C, the capacitance was recovered, indicating that freezing does not cause significant degradation to electrode or separator components. Aqueous electrolytes comprising mixtures of Li2SO4 and NaNO3 yielded the best combination of depressed freezing point and ionic conductivity among the compositions evaluated in EC pouch cells.
Printed Planar Supercapacitors (SCs) Having High Energy Density
Authors: Hsieh Bing R
Published: February 2020

Although SCs (Fig. 1a) are known for their very high power density, very long cycle life, and being relatively innocuous, their energy densities are about 10 - 25X lower as compared to lithium ion batteries (LIBs). Despite this shortcoming, replacement of traction LIBs with SCs in hybrid electric vehicles is now commonplace but the opposite is not. However, SCs have rather long road ahead. For example, the specific energy of the recently launched Maxwell 2.85V DuraBlue SC cell is only 7.7 Wh/kg which is one fourth of that for the lead acid batteries (35 Wh/kg), the capacity target for the next generation of SCs. Recently, graphene or activated carbon based microsupercapacitors having planar interdigitated electrodes and current collectors (Fig. 1b) showed high energy densities rivaling or surpassing those of thin film LIBs and lead acid batteries were reported by several groups [1]. These results gave us a glimpse of the possibility of competing with LIBs in both consumer electronics and EVs in the future and inspired us to invent new planar SC designs in order to achieve even higher energy density.

The first question we asked was "Is the MSC design shown in Fig. 1b scalable?" And our initial response was “unlikely” because the driving force for ion movement between the positive and negative carbon electrodes is limited to the relatively weak fringe electric field (shown as the yellow dash lines in Fig. 1b) which cannot effectively drive the ion movement through the entire thickness of the carbon electrode (t2) as it increases into the micron range.

In order to overcome the lack of driving force for facile ion movement, we came up with several new designs in a recent patent application [2]. One of them is shown in Fig. 2 as an example, wherein the current collectors are coated on the sidewalls of the carbon electrodes and gives raise to the direct electric field, as indicated by the purple arrow. In this presentation we will discuss other planar designs, their corresponding pack designs, as well as low cost fabrication methods involving printing processes.

1. (a) D. Pech et al., Nature Nanotech. 2010, 5, 651; (b) W. Gao et al. ibid., 2011, 6, 496; (c) M. F. El-Kady et al., Science, 2012, 335, 1326; (d) M. F. El-Kady; R. B. Kaner, Nature Comm. 2013, 4, 1475; (e) Z.-S. Wu et al., ibid., 2013, 4, 2487; (f) T. Lin et al., Science, 2015, 350, 1508.

2. B. R. Hsieh, US patent application US20160133396A1 (2016).

Figure 1
(Invited) Controlling Electrochemical Energy Storage Kinetics with Structural Water in Tungsten Oxides
Authors: Mitchell James , Lo William , Wang Ruocun , Gao Qiang , LeBeau James , Balke Nina , Augustyn Veronica
Published: February 2020

The ability of structural water to act as an ‘internal electrolyte’ for ion transport within transition metal oxides is an intriguing concept for improving the kinetics of energy storage, particularly to enable high volumetric capacitance. Crystalline tungsten oxide dihydrate (WO3·2H2O) is a model compound to investigate whether interlayer structural water can lead to fast proton intercalation. This material can be readily precipitated under acidic conditions and contains two types of structural water: one that is directly bound to tungsten, and another that exists in the interlayer. These waters form a hydrogen-bonded network within the interlayer. Using cyclic voltammetry and in situ Raman spectroscopy, we find that hydrated tungsten oxide offers better capacity retention and energy efficiency over the anhydrous, crystalline tungsten oxide at sweep rates up to 200 mV s-1. These results are obtained with particles that are more than 100 nm in diameter and with high mass loading, slurry-cast electrodes suggesting that the rapid kinetics are intrinsic to the hydrated phase. We further characterize the electrochemical performance of both the hydrated and anhydrous tungsten oxides using in situ scanning probe microscopy to determine whether the proton intercalation occurs within the hydrated layers and leads to any appreciable structural deformation.
Simultaneous Analysis of Thin-Film MnO2 Deposits Using Cyclic Voltammetry (CV), Step Potential Electrochemical Spectroscopy (SPECS), Electrochemical Quartz Crystal Microbalance (EQCM) and Electrochemical Impedance Spectroscopy (EIS)
Authors: Cameron Hayden , Donne Scott W
Published: February 2020

As a population the reliance on portable electronics and rapid development in electric vehicles in order to combat global warming has caused researchers to search for materials that exhibit excellent energy storage properties. Thin film manganese dioxide deposits have been observed to exhibit excellent behaviour and have become a popular research material for electrochemical capacitors and batteries.

In this project a method was developed in which the mass change for a thin film of manganese dioxide during electrochemical experiments could be observed. Manganese dioxide was electrodeposited onto a platinum EQCM electrode allowing for the mass change throughout the deposition process to be recorded providing a better understanding of the electrodeposition mechanism. Once the manganese dioxide was prepared the EQCM was used as a working electrode throughout further electrochemical testing which included cyclic voltammetry (CV), step potential electrochemical spectroscopy (SPECS), and electrochemical impedance spectroscopy (EIS) while recording the mass change throughout each test.

Cyclic voltammetry was conducted with a 25 mV/s sweep in 0.5 M K2SO4 from 0-0.8V vs SCE for 250 cycles. By doing this the capacitive performance of the material was determined, and by recording the mass change throughout the experiment it was possible to determine if there were faradaic, non-faradaic process occurring on the surface of the electrode affecting the charge storage mechanism and to observe sample stability throughout cycling.

SPECS and EIS immediately followed the cycling which allowed for the observation of the maximum charge storage capability of the material and the mechanism in which the material stores charge. The impedance data allows for the analysis of the charge transfer mechanism and the various interfacial resistance and capacitance at the electrode-electrolyte interface.

This combination of techniques has allowed for significantly greater understanding of the processes that the electrode materials are undergoing throughout the experiments and can be used as a powerful tool in various aspects of electrochemical analysis.
Interfacial Phenomena at the Junction of Conductive Carbon with Pseudocapacitive Metal Oxides and Polymers: Implications for Electrochemical Capacitors
Authors: Long Jeffrey W. , Ko Jesse , Parker Joseph F. , Sassin Megan B. , Rolison Debra R.
Published: February 2020

The technological push to dramatically shorten the charge/discharge times of electrochemical energy-storage (EES) devices while still providing significant energy content requires rethinking how we design and assemble EES, from the choice of particular types of charge-storing materials to how those materials are spatially translated into a high-performance, yet still practical, electrode architecture. Materials that exhibit “pseudocapacitance,” with fast faradaic charge-storage mechanisms that mimic the current–voltage characteristics of a conventional capacitor, promise to satisfy both energy and power needs when incorporated into electrochemical capacitor (EC) devices. The poor electronic conductivity of most pseudocapacative materials (e.g., manganese oxides, MnOx) dictates that they must be integrated with a better electronic conductor, typically porous, nanostructured carbons, in order to minimize ohmic losses and to reasonably utilize innate faradaic capacity. The past decade has seen great advancements in the development of new electrode architectures that incorporate oxides or polymers at carbon substrates, accompanied by promising electrochemical results. Yet our experience with such multifunctional materials shows that we may still be “leaving on the table” too much energy and power performance, due to suboptimal electronic/chemical/physical interactions at the junction of carbon (with its semimetal character) and nanoscale overlayers of pseudocapacitive materials (often semiconductors or hopping conductors). In order to explore these fundamental questions, we step back from the complexity of 3D electrode architectures to planar electrode configurations that otherwise mimic the material characteristics of practical electrode structures. Carbon films prepared by chemical vapor deposition (CVD) that are based on the pyrolysis of benzene and related monomers serve as model substrates on which we deposit pseudocapacitive metal oxides and electroactive polymers. The resulting 2D interfaces are characterized by classical electroanalytical methods to determine fundamental properties such as electron-transfer kinetics. In conjunction with electrochemical characterization, we apply surface-sensitive techniques such as photoelectron spectroscopy and scanning probe microscopy to query electronic, chemical, and physical structure as those properties are tuned by variations in synthesis/deposition of each phase: carbon and pseudocapacitive coating. Lessons learned from these model 2D interfaces are readily applied to the redesign of practical 3D electrode structures in next-generation electrochemical capacitors and batteries.
Synthesis and Characterization of Platinum Monolayers on Graphenated, Three-Dimensional Structures
Authors: Alamgir Faisal M , Arnold Christopher , Buntin Parker , Abdelhafiz Ali
Published: February 2020

The purpose of this work is to explore the concept and properties of a novel design for Pt based catalysts. Highly porous Ni foam capped with a layer of graphene was utilized as a substrate for layer by layer Pt growth through a surface-limited redox replacement (SLRR) scheme. A survey of literature reveals seems to indicate that ours is the first instance of graphene/metal-foam being used as a template for the electrochemical deposition of Pt wetted few-monolayer films. Based on XPS, CV, SEM/EDS and high-resolution TEM analysis, it has been shown that the graphene deposition covers much of the Ni foam and that the Pt subsequently grows epitaxially on the graphene. This scheme leads to Pt utilization that approaches theoretical limits. This catalyst synthesis approach may prove extremely valuable for high-utilization and low-loading catalyst applications. We present here a thorough investigation of the atomic/electronic structure and of the related evolution of electrocatalytic properties as a function of the graphene-templated layer-by-layer growth.
Supercapacitor Electrode from Electrospray of Polymeric Sol As Carbon Precursor on Current Collector
Authors: Chavhan Madhav Prabhakar , Ganguly Somenath
Published: February 2020

This presentation describes a process, involving electrospray of carbonaceous polymer sol on a current collector-substrate, followed by in situ curing, drying and carbonization. The electrospray process splits the precursor sol into fine droplets by Coulombic fission, prior to the deposition on the substrate. The pyrolysis of cured and dried gel film provides the active layer with enhanced internal surface area for the double layer capacitance, and lower resistance to charge transport. The choices of different methods and parameters e.g., sol composition, electrospray voltage, drying method, pyrolysis and pore activation protocols make possible the tuning of pore structure.

The carbonaceous precursor sol, considered in this work is resorcinol formaldehyde (RF). The sol-gel transition involves addition and polycondensation reactions respectively, where the latter step contributes to crosslinks. Upon pyrolysis, the crosslinks develop into micropores. RF gel can be prepared in either aqueous or organic solvent, and the choice of solvent may affect the morphology of the deposited film. Further, the method of solvent removal for the drying of cured RF gel film contributes to the mesopore formation in the carbon film. In particular, the simultaneous evaporation of organic solvent at the time of curing vis-à-vis the lyophilization of aqueous gel film can lead to distinctly different pore structure. The hierarchical structure with connected mesopores enables better access to the micropores. The presentation addresses these aspects using experimental measurements. The nitrogen adsorption-desorption experiment on bulk carbon powder showed the pore size distribution and specific surface area. The carbon powder is also analyzed here using XRD, FTIR, and Raman spectroscopy.

Carbon paper is used in this work as the current collector. Sufficient adhesion between the deposited film and the carbon paper enabled handling of the composite through curing, solvent removal, and carbonization steps without peel. The morphology of the film is studied under SEM, and the pore size is calculated using the image analysis software. The electrochemical performance of the electrode is studied in a symmetric cell using KCl and KOH respectively as electrolytes. The cyclic voltammetry, chronopotentiometry, and impedance spectroscopy are performed to estimate specific capacitance, electrolyte resistance at different extents of ion penetration into the pore. The retention of capacitance and coulombic efficiency after several charge-discharge cycles are reported here.
Fluorescently Active Carbon Nanostructures from Neurotransmitter Family Precursors
Authors: Ozhukil Kollath Vinayaraj , Mayer Francis D , Mudigonda Thanmayee , Islam Muhammad Naoshad , Karan Kunal
Published: February 2020

Three biologically significant molecules – dopamine, epinephrine and norepinephrine, all fall under the neurotransmitter category of molecules, upon liquid-phase polymerization gave rise to sphere, petal and nanodot shapes in a water-alcohol mixture under basic conditions. The size and uniformity of these nanostructures can be controlled by varying the reaction solvents. An extrapolation of size control in the case of dopamine nanospheres showed a minimum achievable diameter of 30 nm. Zetapotential measurements of the resulting nanostructure suspensions showed -40 mV, -18 mV and -11 mV respectively for dopamine, epinephrine and norepinephrine nanostructures. The current consensus on the formation mechanism of dopamine nanospheres in alkaline water-alcohol mixture cannot explain the nanostructures formed from epinephrine and norepinephrine. All three nanostructures showed inherent fluorescence, which makes them interesting candidates for shape and size controlled carbon nanostructures that can be employed for imaging structures in complex fluids. The resulted nanostructures were tested as precursor for carbon nanostructures, and characterized for structure integrity and fluorescence properties. The presentation will discuss the results of synthesis and characterization of basic properties.
Transformation of Plant Biomass Waste into Resourceful Activated Carbon Materials for Mixed-Assembly Type Electrochemical Capacitors
Authors: Momodu Damilola , Okafor Chimaka , Manyala Ncholu , Bello Abdulhakeem , Zebaze-Kana Martiale Gaetan , Ntsoenzok Esidor
Published: February 2020

Activated carbon (AC) was obtained from three different plant biomass wastes sources (coconut shell, pine cones and rice husk) via hydrothermal treatment followed by carbonization at 800 °C. The morphological and structural characteristics of the transformed carbon material revealed a porous network suitable for energy storage application. The asymmetric cells fabricated exhibited EDLC behaviour in all material sample combinations using all three transformed activated carbons. The mixed assembly device worked comfortably in a voltage window of 1.5 V in a neutral electrolyte. A specific capacitance (C
S) of ∼110 F g-1 was obtained with a corresponding energy density of 8.5 W h kg-1 and power density of 380 W kg-1 at a current density of 0.5 A g-1. An excellent stability was exhibited with a coulombic efficiency of a 99.7% and capacitance retention of 80% after 10000 continuous cycling at 5.0 A g-1. Furthermore, subjecting the device to a floating test for ∼48 h (2 days) at the optimum voltage (1.5 V) revealed a drop in the initial capacitance value but still without any recorded device failure. Remarkably, the asymmetric design showed a potential for adopting EDLC materials of different carbon sources in order to capture the entire properties for efficient and stable energy storage devices.

Keywords: Plant waste; Energy storage materials; Activated carbon; Mixed-assembly; Supercapacitors

Figure 1
Influences of Chloride and Fluoride Ions on Localized Corrosion of Stainless Steels at Anodic Polarization
Authors: Tsukioka Chinatsu , Ueyama Meiko , Hoshi Yoshinao , Shitanda Isao , Itagaki Masayuki , Takata Satoshi , Kogure Tomonari
Published: February 2020

Polymer electrolyte fuel cells (PEFCs) are environmentally friendly generators and operate at relatively low temperatures, so they have been put into practical use as power sources for automobiles. A carbon plate is generally used for the separator of PEFC. However, there are problems in using carbon separator such as low mechanical strength and cost, thus metal separators are used for automotive PEFC. Stainless steels are considered to be suitable metal among several candidates for material of metal separator because it is highly corrosion resistant, high workable and relatively reasonable. Since the inside of the PEFC becomes particular corrosive environments, dissolution of metallic ions due to localized corrosion of stainless steel is feared. Typical conditions of the particular corrosive environments assumed in this research are as follows, chloride ion concentration: 10 ppm, fluoride ion concentration: 30 ppm, pH 3, electrode potential: 0.8 V vs. SSE, temperature: 80 degree centigrade. A schematic diagram of the anodic polarization curve of stainless steels is shown in Fig. 1. The anodic polarization curve is divided into three potential regions and they are defined as a passive region, a first transpassive region, and a second transpassive region. Anodic polarization curves of SUS 447 in three kinds of solutions are shown in Fig. 2. The following three solutions were used for measurements. A: pH 3 1 M H2SO4 (80℃) without halide ions, B: 1 M H2SO4 containing 10 ppm NaCl, C: 1 M H2SO4 containing 30 ppm NaF. The anodic polarization curve of SUS 447 in solution A without halide ion shows the passive region and the second transpassive region at nobler potential than 1.2 V vs. SSE. The anodic polarization curve of SUS 447 in the solution B containing chloride ions shows the first transpassive region and the current increase above 0.8 V vs. SSE is observed. If the potential of the PEFC cathode is assumed to be 0.7 ~ 0.8 V vs. SSE, it is near the boundary between the passive region and the first transpassive region, and metallic ions dissolution may occur. Furthermore, in the anodic polarization curve in SUS447 in a solution C containing fluoride ions, the current value in the first second transpassive regions is much larger than that in the solution B, indicating the acceleration of the dissolution rate. It is considered that corrosion protections such as surface treatment and inhibitor addition are necessary when stainless steels are used in the particular corrosive environment in PEFC. In this study, we investigated the influences of chloride and fluoride ions on localized corrosion of stainless steel by electrochemical measurements, and discuss the corrosion protection method of stainless steel as a metal separator of PEFC.

Figure 1
Iron Sulfides Electroactivity in Environments in the Presence of Strong Acid, Carbonic Acid and Aqueous Hydrogen Sulfide
Authors: Navabzadeh Esmaeely Saba , Nesic Srdjan
Published: February 2020

Iron sulfides, particularly the two most stable polymorphs: pyrite and pyrrhotite, have captured the attention of scholars due to their semi-conductive properties. Their semi-conductive nature allows for the corrosive species to be reduced at their surface while electrons are transported from the steel surface via their network. Thus, as a corrosion product layer, pyrite or pyrrhotite do not offer sufficient protection to the steel underneath in the form of a mass transfer barrier for corrosive species. In addition, these layers could accelerate the corrosion rate via an enhancement of reduction of corrosive species rate on their surface. The electrochemistry of iron sulfide layers as it is related to the field of corrosion is unclear and the reported data in the literature has not reached a conclusion. Most of the available literature about electrochemistry of iron sulfides reports on their anodic, rather than cathodic behavior. However, it is noteworthy that in the mechanism related to a mild steel corrosion under such layers, the mild steel is the anode, and the iron sulfide layers are the cathode. A much higher cathodic surface area emerges due to the porous nature of these layers, which results in a higher corrosion currents of the mild steel. Therefore, in order to understand their main role on mild steel corrosion, it is important to study the rate of reduction of corrosive species such as: hydrogen (H+), carbonic acid (H2CO3) and hydrogen sulfide (H2S) on their surface to investigate their electroactivity. This would extend the current understanding of galvanic corrosion of a mild steel under iron sulfide layers.

In the current study, pyrite and pyrrhotite electrodes made from geological specimens were polarized negatively and the results were compared with the data obtained from a mild steel electrode. The experiments were conducted in deaerated aqueous solutions with and without H2S at different pH at a room temperature.

The experimental results revealed the significance of electroactivity of pyrite and pyrrhotite related to H+, H2CO3 and H2S reduction rates. A comparison of their polarization data with a bare mild steel data showed a similar level of electroactivity.

The measured data were compared with the calculated data from an electrochemical model developed and validated for a mild steel electrode exposed to aqueous environments with and without H2S.

The experimental results from the pyrrhotite electrode showed an extra wave on the polarization curves with a distinct limiting current, it remains unclear what this wave represents. The nature of this wave is still under investigation.

Figure 1
Sulfide Scaling and Corrosion of Carbon Steel in a Sour Medium
Authors: Al-Qahtani Noora , Qi Jiahui , Abdullah Aboubakr Moustafa , Laycock Nick , Ryan Mary P
Published: February 2020

The damage caused by the building up of scale inside wellbores and pipelines costs millions of pounds each year. A better understanding of scale formation and the kinetic nature of the process is essential, for asset management in general and the development of new protection approaches. Surface scale formation is one of the important factors related to the corrosion rate. The internal corrosion of carbon steel in the presence of hydrogen sulfide represents a significant problem for both oil refineries and gas treatment facilities/pipelines. Many studies have revealed that the system is complex since more than one iron sulfide compound may form. However, the kinetics of scale formation, such as the nucleation and growth processes of the scale are not at all well-understood and how corrosion inhibitors interact with scales. The kinetics of the scale formation will be investigated by using a variety of methods, some more successful than others. The methods employed include SEM, TEM, EDX, and Raman analysis, and this was done with the aim of obtaining the physical structure, the chemical composition and the crystal structure of the iron sulfide scale formed at different time scales.
Overview of U.S. Department of Energy Office of Fossil Energy’s Solid Oxide Fuel Cell Program
Authors: Vora Shailesh D , Lundberg Wayne L. , Pierre Joseph F.
Published: February 2020

The primary mission of the U.S. Department of Energy’s Office of Fossil Energy (FE) is to ensure the nation can continue to rely on its indigenous fossil fuel resources for clean, secure, and affordable energy. A component of that effort is the Solid Oxide Fuel Cell (SOFC) Program, administered by FE’s National Energy Technology Laboratory (NETL). The SOFC Program is committed to: developing efficient, low-cost electricity from natural gas or coal with intrinsic carbon capture capabilities for distributed generation and central power generation applications; maintaining cell development and core technology research to increase the reliability, robustness, and durability of cell, stack, and system technology; and providing the technology base to permit cost-competitive distributed generation applications. The program recently initiated two focused efforts: addressing cell and system reliability and an Innovative Concepts initiative.

Based on feedback from several program participants, chromium contamination of cathode was identified as a major contributor to performance degradation and reduced system reliability. NETL has launched an initiative to address the issue of chromium contamination. The SOFC Program portfolio presently has 13 projects addressing this critical issue.

The SOFC Program is also funding an Innovative Concepts initiative that supports the research, development, and demonstration (RD&D) of SOFC technology that has the potential to surpass current anode supported planar SOFC technology in terms of cost and reliability. Program participants are developing novel cell and stack architectures and/or material sets. This next-generation SOFC technology development in the near-term includes nominally 5-10 kWe-scale stack tests using cells envisioned in the developer’s future commercial systems.

The status of these strategically oriented research programs, along with the status of the program’s integrated systems tests and the roadmap to deploy a MWe-class natural gas-fueled distributed generation system, will be presented.
Metallic Thin-Film Co- and Ce/Co-Coated Steels as Interconnect Material in IT-SOFC
Authors: Falk Windisch Hannes , Svensson Jan-Erik , Froitzheim Jan
Published: February 2020

In recent years SOFC manufacturers have been able to decrease the operating temperature significantly and today several anode- and metal-supported designs are able to operate at temperatures as low as 600-700 ˚C. One of several advantages of lower operating temperatures is the possibility to use less expensive materials, for example for the interconnect. Volatilization of Cr(VI) species and the increased electrical resistance, caused by the growing oxide scale, are probably the two most detrimental degradation mechanisms associated with the use of Cr2O3-forming ferritic stainless steels as interconnect material in SOFCs. Within the last decade extensive research has been carried out investigating these two degradation mechanisms. Development of custom-made alloys as well as reactive element surface treatments have been shown to improve corrosion resistance. Additionally a wide range of spinel based coating systems have been suggested to effectively mitigate Cr vaporization. However, the vast majority of studies, which investigate the mitigation of Cr vaporization in combination with oxide scale growth, and the electrical scale resistance were carried out at significantly higher temperatures (800-900 ˚C), often to accelerate the aforementioned degradation mechanisms. Cr vaporization, oxide scale growth, and electrical resistance are, however, all differently affected by a change in temperature, especially with regard to the influence of temperature on the microstructure of the oxide scale. In this work the effect of temperature in the technologically relevant temperature range (650-850 °C) is studied with focus on Cr vaporization, oxide scale growth, microstructural and chemical evolution, as well as the effect these factors have on the electrical resistance of the oxide scale (ASR). Commercially available interconnect materials such as Sanergy HT, Crofer 22 APU and AISI 441, coated with thin-film Co- and Ce/Co-coatings are exposed in air within a typical IT-SOFC temperature regime. Chromium vaporization is measured using the denuder technique, ASR is recorded ex-situ (after the furnace exposures) using platinum as electrode material and the oxide scales are characterized using SEM/EDX. The results from this work show that thin-film Co- and Ce/Co-coatings exhibit excellent properties as interconnect materials for IT-SOFC with respect to Cr vaporization, oxide scale growth, and electrical resistance. The results also show that temperature has a significant effect on the chemical composition of the oxidized Co-coating. However, due to the high electrical conductivity of the relevant Co-spinels, in comparison to the substantially lower electrical conductivity of chromia, this change does not affect the electrical resistance of the total oxide scale.
In-Situ Observation of Co-Ce Coated Metallic Interconnect Oxidation Combined with High-Resolution Post Exposure Analysis
Authors: Poitel Stéphane , Wang Zhujun , Willinger Marc , Van herle Jan , Hébert Cécile
Published: February 2020

Several SOFC metallic interconnect coatings are based on cobalt, which is efficient to prevent chromium evaporation and to maintain the contact resistance low after prolonged exposure. The addition of a very thin cerium layer beneath the Co coating seems to reinforce its properties. The oxidation of such coated SOFC FeCr steels, which contain a considerable number of alloy additives, becomes difficult to interpret.

In this study, surface oxidation of Sanergy SSHT steel with Ce-Co coating, frequently used as interconnect material, was first observed at high temperature (900°C) under an oxygen flow, in a modified environmental scanning electron microscope (ESEM), for different durations (0-48h). After these live observations, lamellas of the observed area were precisely cut using a focused ion beam (FIB). This allowed to evaluate the final composition of the oxidation layers of the steel by scanning transmission electron microscopy (STEM) and energy dispersive x-ray analysis (EDX), to try to link the chemistry to the structures observed during in-situ observation in the ESEM.

In-situ observation up to 48h was conducted. Results show the diffusion of manganese towards the cobalt coating to form a cobalt-manganese spinel oxide layer. Under this top layer, chromia scale forms. The very thin cerium layer does not prevent the diffusion of other elements from the steel. Niobium and titanium form oxidized precipitates in the steel just below the chromia scale.

Results from shorter exposure/observation times present a time-lapse picture of the initial oxidation for a more detailed understanding. Ex-situ experiments complement the results.
High Performance (La,Sr)(Co,Fe)O3 Cathodes with Improved Adherence for Metal-Supported Fuel Cells
Authors: Bram Martin , Udomsilp David , Roehrens Daniel , Menzler Norbert H. , Opitz Alexander Karl , de Haart L.G.J. , Guillon Olivier
Published: February 2020

A novel sintering approach was developed in order to overcome the issue of insufficient adherence of (La,Sr)(Co,Fe)O3 type cathodes in metal-supported solid oxide fuel cells (MSCs). Investigation of the phase stability of the perovskite structure at high temperature in various atmospheres with low oxygen partial pressures provided the basis for the development of a sintering procedure applicable to full-cells. By investigating the layer adherence, time dependent mechanical integrity and reversibility of phase transformations, metal-supported cells with sintered cathodes could be produced reliably and were electrochemically characterized in single cell measurements. The novel sintering approach of such cathodes resulted in a significantly enhanced mechanical stability of the cathode layers. Extensive spallation of the cathode was prevented, which is a substantial improvement in comparison with state-of-the-art MSCs. Furthermore, the electrochemical measurements revealed a beneficial effect regarding the cell performance. Post-test characterization is assumed to provide further information regarding the quality of bonding between cathode and electrolyte. Further investigations cover the implementation of alternative high-performance cathode materials like LSC as well as the combination with optimized anode structures/compositions.