Ag(e)ing and Degradation of Supercapacitors: Causes, Mechanisms, Models and Countermeasures.

The most prominent and highly visible advantage attributed to supercapacitors of any type and application, beyond their most notable feature of high current capability, is their high stability in terms of lifetime, number of possible charge/discharge cycles or other stability-related properties. Unfortunately, actual devices show more or less pronounced deterioration of performance parameters during time and use. Causes for this in the material and component levels, as well as on the device level, have only been addressed and discussed infrequently in published reports. The present review attempts a complete coverage on these levels; it adds in modelling approaches and provides suggestions for slowing down ag(e)ing and degradation.

Intrinsically Conducting Polymer Composites as Active Masses in Supercapacitors.

Intrinsically conducting polymers ICPs can be combined with further electrochemically active materials into composites for use as active masses in supercapacitor electrodes. Typical examples are inspected with particular attention to the various roles played by the constituents of the composites and to conceivable synergistic effects. Stability of composite electrode materials, as an essential property for practical application, is addressed, taking into account the observed causes and effects of materials degradation.

Overoxidation of Intrinsically Conducting Polymers.

Intrinsically conducting polymers may undergo significant changes of molecular structure and material properties when exposed to highly oxidizing conditions or very positive electrode potentials, commonly called overoxidation. The type and extent of the changes depend on the experimental conditions and chemical environment. They may proceed already at much lower rates at lower electrode potentials because some of the processes associated with overoxidation are closely related to more or less reversible redox processes employed in electrochemical energy conversion and electrochromism. These changes may be welcome for some applications of these polymers in sensors, extraction, and surface functionalization, but in many cases, the change of properties affects the performance of the material negatively, contributing to material and device degradation. This report presents published examples, experimental observations, and their interpretations in terms of both structural and of material property changes. Options to limit and suppress overoxidation are presented, and useful applications are described extensively.

Conjugated Molecules and Polymers in Secondary Batteries: A Perspective.

Intrinsically conducting polymers constituting a subclass of macromolecules, as well as a still growing family of large, conjugated molecules, oligomers, and polymers, have attracted research interest for the recent decades. Closely corresponding to the fascination of these materials, combining typical properties of organic polymers and metallic materials, numerous applications have been suggested, explored, and sometimes transferred into products. In electrochemistry, they have been used in various functions beyond the initially proposed and obvious application as active masses in devices for electrochemical energy conversion and storage. This perspective contribution wraps up basic facts that are necessary to understand the behavior and properties of the oligo and polymers and their behavior in electrochemical cells for energy conversion by electrode reactions and associated energy storage. Representative examples are presented and discussed, and an overview of the state of research and development is provided. Particular attention is paid to stability and related aspects of practical importance. Future trends and perspectives are indicated.

Interactions in Electrodeposited Poly-3,4-Ethylenedioxythiophene-Tungsten Oxide Composite Films Studied with Spectroelectrochemistry.

Cyclic voltammograms and optical absorption spectra of PEDOT/WO3 composite films were recorded in order to identify possible interactions and modes of improved performance of the composite as compared to the single materials. Changes in the shape of redox peaks related to the W(VI)/W(V) couple in the CVs of WO3 and the composite PEDOT/WO3 films indicate electrostatic interactions between the negatively charged tungsten oxide species and the positively charged conducting polymer. Smaller peak separation suggests a more reversible redox process due to the presence of the conducting polymer matrix, accelerating electron transfer between tungsten ions. Electronic absorption spectra of the materials were analyzed with respect to changes of the shapes of the spectra and characteristic band positions. There are no noticeable changes in the position of the electronic absorption bands of the main chromophores in the electronic spectra of the composite film. Obviously, the interactions accelerating the redox performance do not show up in the optical spectra. This suggests that the existing electrostatic interactions in the composite do not significantly change the opto-electronic properties of components of the composite but resulted in the redistribution of fractions of polaron and bipolaron forms in the polymer.

Fabrication of highly and poorly oxidized silver oxide/silver/tin(IV) oxide nanocomposites and their comparative anti-pathogenic properties towards hazardous food pathogens.

Herein, we report the fabrication of highly oxidized silver oxide/silver/tin(IV) oxide (HOSBTO or Ag3+-enriched AgO/Ag/SnO2) nanocomposite under a robust oxidative environment created with the use of concentrated nitric acid. Tin(IV) hydroxide nanofluid is added to the reaction mixture as a stabilizer for the Ag3+-enriched silver oxide in the nanocomposite. The formation of Ag nanoparticles in this nanocomposite originates from the decomposition of silver oxides during calcination at 600 °C. For comparison, poorly oxidized silver oxide/silver/tin(IV) oxide (POSBTO with formula AgO/Ag/SnO2) nanocomposite has also been prepared by following the same synthetic procedures, except for the use of concentrated nitric acid. Finally, we studied in detail the anti-pathogenic capabilities of both nanocomposites against four hazardous pathogens, including pathogenic fish bacterium (Stenotrophomonas maltophilia stain EP10), oomycete (Phytophthora cactorum strain P-25), and two different strains of pathogenic strawberry fungus, BRSP08 and BRSP09 (Collectotrichum siamense). The bioassays reveal that the as-prepared HOSBTO and POSBTO nanocomposites exhibit significant inhibitory activities against the tested pathogenic bacterium, oomycete, and fungus in a dose-dependent manner. However, the degree of dose-dependent effectiveness of the two nanocomposites against each pathogen largely varies.

Composites and Copolymers Containing Redox-Active Molecules and Intrinsically Conducting Polymers as Active Masses for Supercapacitor Electrodes-An Introduction.

In this introductory report, composites and copolymers combining intrinsically conducting polymers and redox-active organic molecules, suggested as active masses without additional binder and conducting agents for supercapacitor electrodes, possibly using the advantageous properties of both constituents, are presented. A brief overview of the few reported examples of the use of such copolymers, composites, and comparable combinations of organic molecules and carbon supports is given. For comparison a few related reports on similar materials without intrinsically conducting polymers are included.

Increased Capacitance of Metal Oxide-Based Supercapacitor Electrodes Caused by Surfactant Addition to the Electrolyte Solution.

Suggested beneficial effects of surfactants added to the electrolyte solution of supercapacitors have been studied with the aim of improving wetting of the metal oxide electrode surface possibly enhancing material utilization and overall performance. Using representative non-ionic and anionic surfactants such improvements in terms of increased specific capacitance, capacitance retention with current density and improved stability were found. Further examination of type of surfactant and optimum surfactant concentration are recommended.

Ultrathin Mesoporous RuCo2 O4 Nanoflakes: An Advanced Electrode for High-Performance Asymmetric Supercapacitors.

A new ruthenium cobalt oxide (RuCo2 O4 ) with a unique marigold-like nanostructure and excellent performance as an advanced electrode material has been successfully prepared by a simple electrodeposition (potentiodynamic mode) method. The RuCo2 O4 marigolds consist of numerous clusters of ultrathin mesoporous nanoflakes, leaving a large interspace between them to provide numerous electrochemically active sites. Strikingly, this unique marigold-like nanostructure provided excellent electrochemical performance in terms of high energy-storage capacitance (1469 F g-1 at 6 A g-1 ) with excellent rate proficiency and long-lasting operating cycling stability (ca. 91.3 % capacitance retention after 3000 cycles), confirming that the mesoporous nanoflakes participate in the ultrafast electrochemical reactions. Furthermore, an asymmetric supercapacitor was assembled using RuCo2 O4 (positive electrode) and activated carbon (negative electrode) with aqueous KOH electrolyte. The asymmetric design allowed an upgraded potential range of 1.4 V, which further provided a good energy density of 32.6 Wh kg-1 (1.1 mWh cm-3 ). More importantly, the cell delivered an energy density of 12.4 Wh kg-1 even at a maximum power density of 3.2 kW kg-1 , which is noticeably superior to carbon-based symmetric systems.

Correction: An acid-free rechargeable battery based on PbSO4 and spinel LiMn2O4.

Correction for 'An acid-free rechargeable battery based on PbSO4 and spinel LiMn2O4' by Yu Liu et al., Chem. Commun., 2014, 50, 13714-13717.

Low-Cost Al2O3 Coating Layer As a Preformed SEI on Natural Graphite Powder To Improve Coulombic Efficiency and High-Rate Cycling Stability of Lithium-Ion Batteries.

Coulombic efficiency especially in the first cycle, cycling stability, and high-rate performance are crucial factors for commercial Li-ion batteries (LIBs). To improve them, in this work, Al2O3-coated natural graphite powder was obtained through a low-cost and facile sol-gel method. Based on a comparison of various coated amounts, 0.5 mol % Al(NO3)3 (vs mole of graphite) could bring about a smooth Al2O3 coating layer with proper thickness, which could act as a preformed solid electrolyte interface (SEI) to reduce the regeneration of SEI and lithium-ions consumption during subsequent cycling. Furthermore, we examined the advantages of Al2O3 coating by relating energy levels in LIBs using density functional theory calculations. Owing to its proper bandgap and lithium-ion conduction ability, the coating layer performs the same function as a SEI does, preventing an electron from getting to the outer electrode surface and allowing lithium-ion transport. Therefore, as a preformed SEI, the Al2O3 coating layer reduces extra cathode consumption observed in commercial LIBs.

Hybrid system for rechargeable magnesium battery with high energy density.

One of the main challenges of electrical energy storage (EES) is the development of environmentally friendly battery systems with high safety and high energy density. Rechargeable Mg batteries have been long considered as one highly promising system due to the use of low cost and dendrite-free magnesium metal. The bottleneck for traditional Mg batteries is to achieve high energy density since their output voltage is below 2.0 V. Here, we report a magnesium battery using Mg in Grignard reagent-based electrolyte as the negative electrode, a lithium intercalation compound in aqueous solution as the positive electrode, and a solid electrolyte as a separator. Its average discharge voltage is 2.1 V with stable discharge platform and good cycling life. The calculated energy density based on the two electrodes is high. These findings open another door to rechargeable magnesium batteries.

The adsorption of thiophenol on gold--a spectroelectrochemical study.

The adsorbate formed by adsorption of thiophenol on a polycrystalline gold electrode and brought into contact with aqueous solutions of 1 M HClO4 and 0.1 M KClO4 has been studied using cyclic voltammetry and surface-enhanced Raman spectroscopy. A strong adsorption is deduced from observations made using cyclic voltammetry. From the SER spectra, interactions of thiophenol with the gold surface via a gold-sulfur bond with the aromatic ring pointing away from the surface is concluded for both electrolyte solutions.

Three-Dimensional Arrays of 1D MnO2 Nanocrystals for All-Solid-State Asymmetric Supercapacitors.

Reported is the synthesis of 3D hierarchical structures based on one-dimensional MnO2 nanobuilding blocks (nanorods, nanowires, and nanoneedles) by means of a facile and scalable coprecipitation method and their use as electrodes for the assembly of all-solid-state supercapacitors. Asymmetric devices were also assembled by using these nanostructured MnO2 materials as the positive electrode and reduced graphene oxide (rGO) as the negative electrode with a polymeric gel electrolyte. The asymmetric cells successfully extend the working voltage windows beyond 1.4 V and allowed for a maximum voltage of 1.8 V. An asymmetric device based on hierarchical nanoneedle-like MnO2 and rGO achieved a maximum specific capacitance of 99 F g-1 at a scan rate of 10 mV s-1 with a stable operational voltage of 1.8 V. This high value allowed for a large specific energy of 24.12 Wh kg-1 .

Development of hybrid materials based on sponge supported reduced graphene oxide and transition metal hydroxides for hybrid energy storage devices.

Earnest efforts have been taken to design hybrid energy storage devices using hybrid electrodes based on capacitive (rGO) and pseudocapacitive (Ni(OH)2 and Co(OH)2) materials deposited on the skeleton of 3D macroporous (indicate sponge material) sponge support. Conducting framework was formed by coating rGO on macroporous sponge on which subsequent deposition of Ni(OH)2 and Co(OH)2 was carried out. The synergetic combination of rGO and Ni(OH)2 or Co(OH)2) provides dual charge-storing mechanisms whereas 3D framework of sponge allows excellent accessibility of electrolyte to hybrid electrodes. Moreover, to further increase the energy density, hybrid devices have been fabricated with SP@rGO@Ni or SP@rGO@Co and SP@rGO as positive and negative electrodes, respectively. These hybrid devices operate with extended operating voltage windows and achieve remarkable electrochemical supercapacitive properties which make them truly promising energy storage devices for commercial production.

An acid-free rechargeable battery based on PbSO4 and spinel LiMn2O4.

An acid-free lead rechargeable battery system comprising PbSO4 as the negative electrode, LiMn2O4 as the positive electrode and a neutral Li2SO4 aqueous solution as electrolyte is reported and its electrochemical performance is very good. It shows great promise to reduce the global use of lead by 50% since it is also low cost.

Surfactant-assisted morphological tuning of hierarchical CuO thin films for electrochemical supercapacitors.

Copper oxide (CuO) thin films are successfully synthesized using a surfactant assisted chemical bath deposition method for application in supercapacitors. The effect of organic surfactants such as Triton X-100 and polyvinyl alcohol (PVA) on structural, morphological, surface areas and electrochemical properties of CuO thin films is investigated. The films deposited using organic surfactants exhibit different surface morphologies. It is observed that the organic surfactants play important roles in modifying the morphology, surface area and pore size distribution. Electrochemical analysis confirms that the nanostructures of the electrode material play a vital role in supercapacitors. The cyclic voltammetry studies show a considerably improved high rate pseudocapacitance of CuO samples synthesized using organic surfactants. The maximum specific capacitance of 411 F g(-1) at 5 mV s(-1) is obtained for the CuO sample prepared using an organic surfactant (Triton X-100). Furthermore, all the CuO nanostructures exhibit high power performance, excellent rate as well as long term cycling stability. The Ragone plot ascertains better power and energy densities of CuO nanostructured samples. This is an easy and simple way to tune the morphology using surfactants which can be applied for other energy storage materials.