Electrochemical capacitors, also called supercapacitors, store energy using either ion adsorption (electrochemical double layer capacitors) or fast surface redox reactions (pseudo-capacitors). They can complement or replace batteries in electrical energy storage and harvesting applications, when high power delivery or uptake is needed. A notable improvement in performance has been achieved through recent advances in understanding charge storage mechanisms and the development of advanced nanostructured materials. The discovery that ion desolvation occurs in pores smaller than the solvated ions has led to higher capacitance for electrochemical double layer capacitors using carbon electrodes with subnanometre pores, and opened the door to designing high-energy density devices using a variety of electrolytes. Combination of pseudo-capacitive nanomaterials, including oxides, nitrides and polymers, with the latest generation of nanostructured lithium electrodes has brought the energy density of electrochemical capacitors closer to that of batteries. The use of carbon nanotubes has further advanced micro-electrochemical capacitors, enabling flexible and adaptable devices to be made. Mathematical modelling and simulation will be the key to success in designing tomorrow's high-energy and high-power devices.

https://hal.archives-ouvertes.fr/hal-02417326/document

Materials for electrochemical capacitors

This paper provides a detailed overview of developments in transducer materials technology relating to their current and future applications in micro-scale devices. Recent advances in piezoelectric, magnetostrictive and shape-memory alloy systems are discussed and emerging transducer materials such as magnetic nanoparticles, expandable micro-spheres and conductive polymers are introduced. Materials properties, transducer mechanisms and end applications are described and the potential for integration of the materials with ancillary systems components is viewed as an essential consideration. The review concludes with a short discussion of structural polymers that are extending the range of micro-fabrication techniques available to designers and production engineers beyond the limitations of silicon fabrication technology.

/pdf/new-materials-for-micro-scale-sensors-and-actuators-an-21qnaonn0l.pdf

New materials for micro-scale sensors and actuators An engineering review

Supercapacitors have become the most significant energy conversion and storage system in recent renewable and sustainable nanotechnology. Due to its large energy capacity and supply with relatively short time and longer lifetime, supercapacitors breakthrough in advance energy applications. This review presents a comparative study of different materials, working principles, analysis, applications, advantages and disadvantages of various technologies available for supercapacitors. The aim of this article is to discuss the possibility of hybrid supercapacitor for the next generation of energy technology. The development of composite materials containing a wide range of active constituents (e.g., graphene, activated carbon, transition metals, metal oxides, perovskites and conducting polymers) by in-situ hybridization and ex-situ recombination is also discussed. This review consecrated largely the contribution of combining all materials (electrode and electrolyte) and their synthesis process and electrochemical performance. Enduringly, the potential issues and the perspectives for future research based on hybrid supercapacitors in energy applications are also presented.

Advanced materials and technologies for hybrid supercapacitors for energy storage – A review

http://utw10193.utweb.utexas.edu/Archive/RuoffsPDFs/334.pdf

Outstanding performance of activated graphene based supercapacitors in ionic liquid electrolyte from −50 to 80 °C

We have modelled the phase diagram of magnetic shape memory alloys of the Heusler type by using the phenomenological Ginzburg–Landau theory. When fixing the parameters by realistic values taken from experiment we are able to reproduce most details of, for example, the phase diagram of Ni2+xMn1−xGa in the (T, x) plane. We present the results of ab initio calculations of the electronic and phonon properties of several ferromagnetic Heusler alloys, which allow one to characterize the structural changes associated with the martensitic instability leading to the modulated and tetragonal phases. From the ab initio investigations emerges a complex pattern of the interplay of magic valence electron per atom numbers (Hume–Rothery rules for magnetic ternary alloys), Fermi surface nesting and phonon instability. As the main result, we find that the driving force for structural transformations is considerably enhanced by the extremely low lying optical modes of Ni in the Ni-based Heusler alloys, which interfere with the acoustical modes enhancing phonon softening of the TA2 mode. In contrast, the ferromagnetic Co-based Heusler alloys show no tendency for phonon softening.

https://iopscience.iop.org/article/10.1088/0022-3727/39/5/S13/pdf

Modelling the phase diagram of magnetic shape memory Heusler alloys

Carbon nanotubes (CNTs) were synthesized from CO2 dissolved in molten salts using the novel electrolytic method developed by the authors. The electrolysis were carried out under current and potential controls. To establish the actual current and potential ranges, the electroreduction of carbon dioxide dissolved in the halide melts under an excess pressure up to 15 bar was studied by cyclic voltammetry on glassy-carbon (GC) electrode at a temperature of 550 °C. The electrochemical–chemical–electrochemical mechanism of CO2 electroreduction was offered for explanation of the obtained results. The structure, morphology, and electronic properties of the CNTs obtained were studied using SEM, TEM, X-ray and electron diffraction analysis, Raman and ESR spectroscopy. It was found that the majority of the CNTs are multi-walled (MWCNTs), have curved form, and most often agglomerate into bundles. Almost all CNTs are filled partly with electrolyte salt. Except MWCNTs the cathode product contains carbon nanofibers, nanographite, and amorphous carbon. The dependences of CNT's yield, their diameter, and structure peculiarities against the electrolysis regimes were established.

Electrolytic synthesis of carbon nanotubes from carbon dioxide in molten salts and their characterization

Thermally grown SiO2 on Si substrates implanted with Si+ ions with a dose of 6×1016 cm−2 were studied by the techniques of photoluminescence, electron paramagnetic resonance (EPR), and low-frequency Raman scattering. Distinct oxygen-vacancy associated defects in SiO2 and nonbridging oxygen hole centers were identified by EPR. The luminescence intensity in the 620 nm range was found to correlate with the number of these defects. The low-frequency Raman scattering technique was used to estimate the average size of the Si nanocrystallites formed after the implantation and thermal annealing at T>1100 °C, which are responsible for the photoluminescence band with a maximum at 740 nm. The intensity of this band can be significantly enhanced by an additional treatment in a low-temperature rf plasma.

Optical and electron paramagnetic resonance study of light-emitting Si+ ion implanted silicon dioxide layers

The influence of the substitutional atoms Cr, Mn, Ni, Cu, Mo in iron-based alloys on the stability of the crystalline fcc structure and the change of the electron state density at the Fermi surface are studied by means of conduction electron spin resonance (CESR). The temperature dependence of the CESR g-factor and of its integral intensity is measured and analysed in relation to theoretical predictions. It is shown that Cr, Mn and Mo decrease the state density at the Fermi surface in the fcc iron, whereas Ni and Cu increase it. The study singles out the contributions of three electron subsystems (conduction s electrons, localized isolated d electrons and those included in superparamagnetic clusters) to g(T) and traces the important role of substitutional alloying elements in the formation of clusters in fcc solid solution.

The influence of substitutional atoms upon the electron structure of the iron-based transition metal alloys

The effect of nitrogen and carbon on the electronic and magnetic properties of the iron-base Fe56Cr18Ni16Mn10 3d-alloy with f.c.c. lattice (austenite) is studied by means of the magnetic resonance. It is shown that the electron state density on the Fermi surface in the nitrogen austenite is one order of magnitude higher than that in the carbon one. Based on measurements of the temperature dependence of the g-factor the existence of superparamagnetic clusters is stated, the latter being obviously clusters of substitutional solutes. Signs and values of the exchange interaction between conduction electrons and other magnetic subsystems are obtained from the analysis of the temperature dependence of the paramagnetic susceptibilities. The exchange interaction between conduction electrons and isolated localised spins has antiferromagnetic character, while conduction electron—cluster interaction is ferromagnetic. The size of the clusters is markedly higher in the carbon austenite. This difference in structural homogeneity can be used for an explanation of the higher thermodynamic stability of the nitrogen austenite as compared to the carbon one.



Der Einflus von Stickstoff und Kohlenstoff auf die magnetischen Eigenschaften der Fe56Cr18Ni16Mn10 Eisenlegierung mit k.f.z. Gitter (Austenit) wird mit Hilfe der magnetischen Resonanz untersucht. Es wird gezeigt, das die Dichte der Elektronenzustande auf der Fermi-Oberflache im Stickstoffaustenit um eine Grosenordnung hoher als die im Kohlenstoffaustenit ist. Aus den Messungen der Temperatur-abhangigkeit des g-Faktors wird auf die Existenz von superparamagnetischen Clustern, d. h. Clustern von gelosten, substitutionellen Atomen, geschlossen. Vorzeichen und Werte der Austauschwechselwirkung zwischen freien Elektronen und anderen magnetischen Systemen werden aus der Analyse der Temperaturabhangigkeit der paramagnetischen Suszeptibilitat erhalten. Die Austauschwechselwirkung zwischen freien Elektronen und isolierten, lokalisierten Spins hat antiferromagnetischen Charakter, wahrend die Wechselwirkung zwischen freien Elektronen und Clustern ferromagnetisch ist. Die Grose der Cluster ist merklich hoher im Kohlenstoffaustenit. Dieser Unterschied in der strukturellen Homogenitat kann zur Erklarung der hoheren thermodynamischen Stabilitat des Stickstoffaustenits im Vergleich zum Kohlenstoffaustenit herangezogen werden.

A. A. Konchits

Papers

Electrolytic synthesis of carbon nanotubes from carbon dioxide in molten salts and their characterization

Optical and electron paramagnetic resonance study of light-emitting Si+ ion implanted silicon dioxide layers

The influence of substitutional atoms upon the electron structure of the iron-based transition metal alloys

Exchange interaction between electron subsystems in iron-based F.C.C. alloys doped by nitrogen or carbon

Diamond-like carbon films: electron spin resonance (ESR) and Raman spectroscopy