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

https://www.chem.ccu.edu.tw/~joyce/referance/gump/IL/Chem.%20Rev.%201999,%2099,%202071.pdf

Room-Temperature Ionic Liquids. Solvents for Synthesis and Catalysis

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

Fuel cells convert chemical energy directly into electrical energy with high efficiency and low emission of pollutants. However, before fuel-cell technology can gain a significant share of the electrical power market, important issues have to be addressed. These issues include optimal choice of fuel, and the development of alternative materials in the fuel-cell stack. Present fuel-cell prototypes often use materials selected more than 25 years ago. Commercialization aspects, including cost and durability, have revealed inadequacies in some of these materials. Here we summarize recent progress in the search and development of innovative alternative materials.

Materials for fuel-cell technologies

Supercapacitors, also called ultracapacitors or electrochemical capacitors, store electrical charge on high-surface-area conducting materials. Their widespread use is limited by their low energy storage density and relatively high effective series resistance. Using chemical activation of exfoliated graphite oxide, we synthesized a porous carbon with a Brunauer-Emmett-Teller surface area of up to 3100 square meters per gram, a high electrical conductivity, and a low oxygen and hydrogen content. This sp 2 -bonded carbon has a continuous three-dimensional network of highly curved, atom-thick walls that form primarily 0.6- to 5-nanometer-width pores. Two-electrode supercapacitor cells constructed with this carbon yielded high values of gravimetric capacitance and energy density with organic and ionic liquid electrolytes. The processes used to make this carbon are readily scalable to industrial levels.

/pdf/carbon-based-supercapacitors-produced-by-activation-of-1wqrpq3luo.pdf

Carbon-based Supercapacitors Produced by Activation of Graphene

A device to produce electricity by a chemical reaction without the addition of liquid electrolyte comprises an anode electrode, a polymer membrane electrolyte fabricated to conduct hydroxyl (OH—) ions, the membrane being in physical contact with the anode electrode on a first side of the membrane, and a cathode electrode in physical contact with a second side of the membrane. The anode electrode and cathode electrode contain catalysts, and the catalysts are constructed substantially entirely from non-precious metal catalysts. Water may be transferred to the cathode side of the membrane from an external source of water.

Alkaline membrane fuel cells and apparatus and methods for supplying water thereto

Chromium addition improves the performance of carbon‐supported Pt electrodes for oxygen reduction in phosphoric acid fuel cells. To clarify the role of chromium and its chemical nature at the electrode surface, we have performed a combined electrochemical/surface science investigation of a series of bulk PtxCr1−x alloys (0≤x≤1). In this paper we report the surface characterization of the starting electrodes by XPS, electrochemical results from cyclic voltammetry in 85% phosphoric acid, and postelectrochemical surface characterization. For Cr contents less than 40%, the electrodes were quite stable up to +1.6 V versus dynamic hydrogen electrode (DHE). The surface Cr was largely oxidized to Cr+3 for surfaces at open circuit and those exposed at potentials <+1.4 V. For intermediate Cr levels, Cr was leached from the surface region by +1.5 V, leaving a porous Pt electrode with increased electrochemical hydrogen adsorption capacity. For Pt0.2 Cr0.8, treatments at +1.4 V and above led to the appearance of Pt+4 ...

/pdf/combined-electrochemical-surface-science-investigations-of-2cz2ri6dwc.pdf

Combined electrochemical/surface science investigations of Pt/Cr alloy electrodes

A conformable fuel cell is provided which includes a basic structure that provides flexibility while providing a high compression along the active surface of the fuel cell's membrane electrode assembly, which can be achieved by an injection-molded frame. A suitable fuel is delivered to the anode aspect of the fuel cell. Effective water management could also be provided by appropriate diffusion layers. The fuel cell can be contour-molded to a desired shape, or can be constructed of an array of flexibly connected individual fuel cells that overall have a curvilinear shape, or can be constructed as a pliable fuel cell that can be incorporated into an application device or an article of clothing.

Conformable fuel cell

Thin-film fuel cells

The dehydrogenation of C60 · H18.7 was studied using thermogravimetric and powder x-ray diffraction analysis. C60 · H18.7 was found to be stable up to 430 °C in Ar at which point the release of hydrogen initiated the collapse of a fraction of fullerene molecules. X-ray diffraction analysis performed on C60 · H18.7 samples dehydrogenated at 454, 475, and 600 °C displayed an increasing volume fraction of amorphous material. The decomposition product comprises randomly oriented, single-layer graphite sheets. Evolved gas analysis using gas chromatograph (GC) mass spectroscopy confirmed the presence of both H2 and methane upon dehydrogenation. Attempts to improve reversibility or reduce hydrogenation/ dehydrogenation temperatures by addition of Ru and Pt catalysts were unsuccessful.

Shimshon Gottesfeld

Papers

Alkaline membrane fuel cells and apparatus and methods for supplying water thereto

Combined electrochemical/surface science investigations of Pt/Cr alloy electrodes

Conformable fuel cell

Thin-film fuel cells

Irreversible hydrogenation of solid c60 with and without catalytic metals