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

In this critical review, metal oxides-based materials for electrochemical supercapacitor (ES) electrodes are reviewed in detail together with a brief review of carbon materials and conducting polymers. Their advantages, disadvantages, and performance in ES electrodes are discussed through extensive analysis of the literature, and new trends in material development are also reviewed. Two important future research directions are indicated and summarized, based on results published in the literature: the development of composite and nanostructured ES materials to overcome the major challenge posed by the low energy density of ES (476 references).

/pdf/a-review-of-electrode-materials-for-electrochemical-2cok5em0bo.pdf

A review of electrode materials for electrochemical supercapacitors

Background Since at least 400 C.E., when the Mayans first used layered clays to make dyes, people have been harnessing the properties of layered materials. This gradually developed into scientific research, leading to the elucidation of the laminar structure of layered materials, detailed understanding of their properties, and eventually experiments to exfoliate or delaminate them into individual, atomically thin nanosheets. This culminated in the discovery of graphene, resulting in a new explosion of interest in two-dimensional materials. Layered materials consist of two-dimensional platelets weakly stacked to form three-dimensional structures. The archetypal example is graphite, which consists of stacked graphene monolayers. However, there are many others: from MoS 2 and layered clays to more exotic examples such as MoO 3 , GaTe, and Bi 2 Se 3 . These materials display a wide range of electronic, optical, mechanical, and electrochemical properties. Over the past decade, a number of methods have been developed to exfoliate layered materials in order to produce monolayer nanosheets. Such exfoliation creates extremely high-aspect-ratio nanosheets with enormous surface area, which are ideal for applications that require surface activity. More importantly, however, the two-dimensional confinement of electrons upon exfoliation leads to unprecedented optical and electrical properties. Liquid exfoliation of layered crystals allows the production of suspensions of two-dimensional nanosheets, which can be formed into a range of structures. (A) MoS 2 powder. (B) WS 2 dispersed in surfactant solution. (C) An exfoliated MoS 2 nanosheet. (D) A hybrid material consisting of WS 2 nanosheets embedded in a network of carbon nanotubes. Advances An important advance has been the discovery that layered crystals can be exfoliated in liquids. There are a number of methods to do this that involve oxidation, ion intercalation/exchange, or surface passivation by solvents. However, all result in liquid dispersions containing large quantities of nanosheets. This brings considerable advantages: Liquid exfoliation allows the formation of thin films and composites, is potentially scaleable, and may facilitate processing by using standard technologies such as reel-to-reel manufacturing. Although much work has focused on liquid exfoliation of graphene, such processes have also been demonstrated for a host of other materials, including MoS 2 and related structures, layered oxides, and clays. The resultant liquid dispersions have been formed into films, hybrids, and composites for a range of applications. Outlook There is little doubt that the main advances are in the future. Multifunctional composites based on metal and polymer matrices will be developed that will result in enhanced mechanical, electrical, and barrier properties. Applications in energy generation and storage will abound, with layered materials appearing as electrodes or active elements in devices such as displays, solar cells, and batteries. Particularly important will be the use of MoS 2 for water splitting and metal oxides as hydrogen evolution catalysts. In addition, two-dimensional materials will find important roles in printed electronics as dielectrics, optoelectronic devices, and transistors. To achieve this, much needs to be done. Production rates need to be increased dramatically, the degree of exfoliation improved, and methods to control nanosheet properties developed. The range of layered materials that can be exfoliated must be expanded, even as methods for chemical modification must be developed. Success in these areas will lead to a family of materials that will dominate nanomaterials science in the 21st century.

/pdf/liquid-exfoliation-of-layered-materials-3l83x6zg7f.pdf

Liquid Exfoliation of Layered Materials

Layered double hydroxides (LDHs) are a class of ionic lamellar compounds made up of positively charged brucite-like layers with an interlayer region containing charge compensating anions and solvation molecules. Delamination of LDHs is an interesting route for producing positively charged thin platelets with a thickness of a few atomic layers, which can be used as nanocomposites for polymers or as building units for making new designed organic-inorganic or inorganic-inorganic nanomaterials. The synthesis of nanosized LDH platelets can be generally classified into two approaches, bottom-up and top-down. It requires modification of the LDH interlamellar environment and then selection of an appropriate solvent system. In DDS intercalated LDHs, the aliphatic tails of the DDS- anions exhibit a high degree of interdigitation in order to maximize guest-guest dispersive interactions. Bellezza reported that the LDH colloids can also been obtained by employing a reverse microemulsion approach.

Recent advances in the synthesis and application of layered double hydroxide (LDH) nanosheets.

The charge storage mechanism in MnO2 electrode, used in aqueous electrolyte, was investigated by cyclic voltammetry and X-ray photoelectron spectroscopy. Thin MnO2 films deposited on a platinum substrate and thick MnO2 composite electrodes were used. First, the cyclic voltammetry data established that only a thin layer of MnO2 is involved in the redox process and electrochemically active. Second, the X-ray photoelectron spectroscopy data revealed that the manganese oxidation state was varying from III to IV for the reduced and oxidized forms of thin film electrodes, respectively, during the charge/discharge process. The X-ray photoelectron spectroscopy data also show that Na+ cations from the electrolyte were involved in the charge storage process of MnO2 thin film electrodes. However, the Na/Mn ratio for the reduced electrode was much lower than what was anticipated for charge compensation dominated by Na+, thus suggesting the involvement of protons in the pseudofaradaic mechanism. An important finding o...

Charge Storage Mechanism of MnO2 Electrode Used in Aqueous Electrochemical Capacitor

Using an ab initio molecular orbital (MO) method, the normal frequencies are calculated for perfluorinated lithium sulfonate and carboxylate membranes by construction of a cluster model, which seve...

Theoretical studies on the structure of hydration in perfluorinated lithium salt membranes.

PURPOSE:To concentrate uranium from a dilute uranium solution, and to recover the acid or alkali contained in the solution, with a simple procedure, in high efficiency, by filtering the solution under pressure with an organic polyelectrolyte membrane. CONSTITUTION:Dilute U solution containing an acid or an alkali is separated into a solution of the acid or alkali and a concentrated U solution by filtering with a polyelectrolyte membrane under pressure. The polyelectrolyte used as the filter membrane is a polymer compound having dissociable group such as carboxylic acid residue, sulfonic acid residue, phenolic hydroxyl group, phosphoric acid residue, ammonium residue, etc. in the molecule. An ultrafiltration membrane such as acetyl cellulose membrane or polycarbonate membrane bonded with polyelectrolyte and charged pigment, etc. may also be used as the filter membrane. The acid or alkali, and U are concentrated in the filtrate and in the remaining liquid, respectively, by the filtration treatment under pressure.

Treatment of uranium solution

マンガン酸化物には様々なトンネル構造と層状構造を持つ化合物が報告されている。これらのトンネル構造及び層状構造を持つマンガン酸化物はイオンや分子とホスト・ゲスト反応することができる。そのホスト・ゲスト反応において, イオンふるいや分子ふるい効果を示すので, 選択吸着剤, 触媒及びリチウム二次電池材料等として注目されている。本解説はボアサイズの異なるトンネル構造や層状構造を持つ一連のマンガン酸化物イオンふるい結晶の合成, 金属イオンの抽出/挿入反応及びイオンふるい特性について, 著者らの最近の研究結果を中心に概説した。これらのマンガン酸化物における金属イオンの抽出/挿入反応は酸化還元反応とイオン交換反応で進み, 反応サイトは酸化還元サイトとイオン交換サイトに分類することができる。金属イオンに対する吸着選択性はマンガン酸化物の結晶構造に依存する。スピネル型マンガン酸化物, ホランダイト型マンガン酸化物及びバーネサイト型マンガン酸化物はそれぞれLi+, K+及びRb+イオンに対して高い選択性を示す。これらのマンガン酸化物のトンネルサイズ或いは層間距離はそれぞれこれらのイオンの大きさに対応する。従って, スピネル型, ホランダイト型, バーネサイト型及びトドロカイト型マンガン酸化物の有効ボア半径はそれぞれ0.7, 1.4, 1.5及び2.7となる。種々のトンネル構造を持つマンガン酸化物は水熱ソフト化学法という従来の方法と異なる新規なイオンふるい合成法を用いて合成できる。

Manganese Oxide Ion-Sieves (1) Syntheses and Ion Adsorptive Properties

A long silver nanowire with a high aspect ratio of at least 3000 could be obtained from Ag+-exchanged inorganic ion-exchanger with NASICON structure by electron beam irradiation. Nanowires formed frequently at the exchanger with more than ca. 15 wt% of silver content. The minimum silver content threshold that enables the formation of nanowire was 9.4 wt%. For less than 15 wt% of silver content, nanoparticles as well as nanoprecipitates that cause splitting of particles formed more frequently than did the nanowires.

Synthesis of Long Silver Nanowires by Electron Beam Irradiation on Ag-exchanged Material

Since coordination polymers (CPs) are generally obtained as fine powders, the fabrication of a CP is an issue that should be addressed. A monolithic CP was successfully prepared through the lyophilization of a cyclohexane organogel of [Sm(dehp)3] consisting of Sm3+ and di-(2-ethylhexyl)phosphoric acid. The crystalline domains of the CP possibly act as cross-linking points, and the crystallization of cyclohexane is likely to generate the void space in the resulting cryogels. The architecture of the material can be varied by changing the volume ratio of cyclohexane to [Sm(dehp)3]. While the morphology observed through the scanning electron microscope was completely different from the as-synthesized material, powder X-ray diffraction analysis revealed that the crystalline structure did not change. The distribution coefficient and kinetic constant of ion exchange in the lanthanide series were improved by cryogel formation.

Kenta Ooi

Papers

Theoretical studies on the structure of hydration in perfluorinated lithium salt membranes.

Treatment of uranium solution

Manganese Oxide Ion-Sieves (1) Syntheses and Ion Adsorptive Properties

Synthesis of Long Silver Nanowires by Electron Beam Irradiation on Ag-exchanged Material

Fabrication of a monolithic cryogel from the cyclohexane organogel of a coordination polymer based on a phosphoester