Dark electrochemistry

While it might seem surprising that rather large (/xm-scale) particles can be characterized as slurries in solution by electrochemical techniques, there have been many papers concerned with the dark electrochemistry of suspended solids. For example, voltammetric studies of suspensions of AgBr are possible (84). In addition, there have been numerous studies of solid particles mounted on electrode surfaces (85). 

The electrochemistry of single-crystal and polycrystalline pyrite electrodes in acidic and alkaline aqueous solutions has been investigated extensively. Emphasis has been laid on the complex anodic oxidation process of pyrite and its products, which appears to proceed via an autocatalytic pathway [160]. A number of investigations and reviews have been published on this subject [161]. Electrochemical corrosion has been observed in the dark on single crystals and, more drastically, on polycrystalline pyrite [162]. Overall, the electrochemical path for the corrosion of n-EeS2 pyrite in water under illumination has been described as a 15 h" reaction ... 

In articles on spectroscopy and electrochemistry one can find discussions abouf fhe purification of ILs. Thoroughgoing approach to that problem is presented by Gordon in Ref. 32 where he is discussing about the synthesis of ILs and fhe purification methods, including the purification by charcoal, alumina columns, and the precautions on purity to be taken for fhe starting materials. It is evident that to obtain pure ILs, carefully purified reactants have to be used and the reagents should be stored in the dark. One latest article completely devoted to purification of ILs is given in Ref. 33. 

The flat band potential in electrochemistry of semiconductors is equivalent to the zero-charge potential in electrochemistry of metals (more exactly, to the potential of the zero free charge—see Frumkin, 1979). As with the zero-charge potential in the electrochemistry of metals, the flat band potential is rather important in the kinetics of both dark and photoelectrochemical reactions at semiconductor electrodes. Several methods, including photoelectrochemical ones, have been developed to determine q>tb (see Section 7). 

Because this is similar to the dark J-V curves of conventional solar cells, it has led to suggestions that the current in DSSCs is controlled by a p-n electrical junction. This was used as one justification for modeling DSSCs as p-n junctions (Sec. V.D). However, such J-V data can be fit just as well to the Butler-Volmer equation, a mainstay of electrochemistry [48], as to the diode equation. The... 

Tubandt was a pioneer of - solid state electrochemistry. He introduced a methodology to determine the - transport numbers of ions in -> solid electrolytes [i], which is now referred to as -> Tubandt method. Together with his co-workers he performed seminal studies of conductivities and transport numbers of solid electrolytes, e.g., of silver, lead, and copper halides, and silver sulfide. He showed for the first time that the entire dark current of silver bromide is transported by silver ions, and also that slightly below the melting point silver iodide has a higher conductivity than the melt. 

The electrochemistry of Ge and Si porphyrins with o-bonded alkyl and aiyl groups has been investigated by Kadish and Guilard The reactions are complicated and must be carried out both in the dark and in the strict absence of O2. An insertion of O2 into the Ge-carbon bond of Ge(Por)(R)2 has been postulated but later studies show that these reactions are actually more complicated than initially suggested The reduction of Ge(Por)(R)2 and Si(Por)(R)2 occurs in either one or two single electron transfer steps. E1/2 values of —1.45 V and —1.48 V are obtained for the first reduction of Ge(OEP)(CH3)2 and Si(OEP)(CH3)2 in PhCN and no second reduction is observed in this solvent In contrast, Ge(TPP)(CeHs)2 is reduced in two steps which occur at - 1.10 and - 1.65 V in PhCN. Similar values of - 1.17 V and -1.72 vs. SCE are measured for the reduction of Ge(TPP)(CH2CsH5)2. First and second reduction poten-... 

The first electrochemical oxidation of aniline to emeraldine salt was reported by Letheby in 1862 [1] as a dark-green precipitate under aqueous acidic condition. This green powdery material soon became known as "aniline black . Almost a himdred years later interest in the electrochemistry of aniline black was revived in 1962. When Mohilner et al. [23] reported mechanistic aspects of aniline oxidations. Buvet et al. [6] studied die conductivity of prepared polyaniline and the influence of water on conductivity measurements. 

Poly(3,4-ethylenedioxythiophene) is one of the most durable and transparent conducting polymers with a very good thermal stability and high conductivity (ca. 200 S cm ). The bandgap of PEDOT can be varied between 1.4 and 2.5 eV. In the state of complete oxidation, its conductivity decreases and the polymer behaves hke a semiconductor. Moreover, PEDOT demonstrates an electrochromic effect. In the reduced state it has dark blue color, and while oxidized it is colorless (Groenendaal et al., 2000). Apart from apphcations in electrochemistry, such as batteries, fuel cells, organic solar cells, sensors, and biosensors, PEDOT is widely used in optoelectronics (Krzyczmonik and Socha, 2013). 

In the following, we will foeus on one popular example of a semiconductor nanostructure, the electrochemieal formation of self-organized nanotubular Xi02 nanostructures, as well as the electrochemistry involved on these nanostructures both in the dark (e.g., used for ion intercalation, electrochemical tube filling and dark photocatalysis) and under illumination (e.g., used for photocatalysis and solar cells). 

---