Double-layer-type devices

Most of the devices described up to now are based on materials that tend to crystallize [phthalocyanines, porphyrins and perylenetetracarboxydiimids, (59)] [276, 277], or form liquid crystalline phases [278, 279]. With respect to amorphous glasses, light sensitive donor-acceptor type molecules, for example, the p-type triarylamines tris [4-methylphenyl(4-nitrophenyl)ammo]triphenylamine and tris[5-(dimesitylboryl)thiophen-2-yl]triphenylamine have been combined with an n-type material in a double-layer heterostructure [280]. The cells respond to visible light from 400 to 800 nm with overall efficiencies of 0.1%. 

ECs are another promising electrical energy storage device with a higher energy density than electrical capacitors, and a better rate capability and cycling stability than LIBs [32]. Carbon-based electric double layer capacitors and metal oxide- or polymer-based pseudocapacitors are two main types of ECs. The charge-... 

In addition to conventional pressure driven flow, electrokinetic flow is also a commonly used means of transporting liquids in microfluidic devices. One type of electrokinetic flow, electroosmotic flow, relies on the presence of an electrical double layer at the solid-liquid interface. A negatively charged surface in a flow channel will attract cationic species from the fluid to form an electrical double layer at the surface. Application of an external voltage can pull those cationic species through the flow channel inducing bulk flow. The electroosmotic flow velocity can be described... 

It is most convenient to use Ragone diagrams for the comparison of the main characteristics of electrochemical devices. Figure 30.1 shows a Ragone diagram for diverse commercial electrochemical devices conventional electrolytic capacitors, electrochemical supercapacitors (ECSCs), batteries, and fuel cells (Pandolfo and Hollenkamp, 2006). One should point out that it is mainly electric double-layer capacitors (EDLCs) of all the available ECSC types that are produced at present. 

Conway, B. E., and W. G. Pell. 2003. Double-layer and pseudocapacitance types of electrochemical capacitors and their applications to the development of hybrid devices. Journal of Solid State Electrochemistry 7 637-644. 

There has been growing interest in the field of supercapacitors due to their possible applications in medical devices, electrical vehicles, memory protection of computer electronics, and cellular communication devices. Their specific energies are generally greater than those of electrolytic capacitors and their specific power levels are higher than those of batteries. Supercapacitors can be divided into redox supercapacitors and electrical double layer capacitors (EDLCs). The former uses electroactive materials such as insertion-type compounds or conducting polymers as the electrode, while the latter uses carbon or other similar materials as the blocking electrode. 

The terms supercapacitor and ultracapacitor are used to describe any double layer or redox capacitor with specific energy and specific power intermediate to batteries and traditional capacitors. Typically, ultracapacitor refers to a device comprised of two carbonaceous electrodes whereas supercapacitor refers to a similar device in which the two carbonaceous electrodes are catalyzed with metal oxides such as Ru02. This chapter will use the term supercapacitor to describe EAP-based capacitors, since that seems to be the most commonly used term for such materials. Another charge storage configuration uses an EAP electrode and a battery-type carbonaceous electrode in what is known as a hybrid device (however, outside of the EAP-based supercapacitor field, hybrid may refer to the combination of a battery electrode such as nickel hydroxide with a carbon electrode) [1]. 

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