Iodide/triiodide redox couple

Kawano et al. used a microelectrode technique and the Dahms-Ruff equation to explore the diffusion mechanism of the iodide/triiodide redox couple and explain the physical diffusion accompanying an exchange reaction [22]. They showed that when high concentrations of iodide and tiiiodide are added to a RTCL as the solvent, the diffusion coefficient derived from the exchange reaction, expressed by / + —> /f + / , become significant and superior to the simple physical dif-... 

In most cases, the iodide-triiodide redox couple has been employed (presumably because of its success in shuttling the photo-oxidized dye in the sensitization experiments) although other redox electrolytes e.g., SCN /(SCN)2 , [342] have also been employed. For the chalcogenide films, sodium selenosulfite was employed [319]. It must be noted that, aside from losses due to the surface recombination and back-reactions, an additional loss component from the increase in film resistance must also be recognized especially as the film thickness is increased. The resistance loss manifests as a deterioration in the photovoltage and fill factor. 

In the vast majority of cases, the iodide/triiodide redox couple has been employed (presumably because of its success in shuttling the photooxidized dye in the... 

Langmuir ME, Parker MA, Rauh MD (1982) Electrochemical photovoltaic cells based on n-GaAs and the triiodide/iodide redox couple in acetonitrile. J Electrochem Soc 129 1705-1710... 

Using the tri-iodide/iodide redox couple and the sensitizers (22) and (56), several groups have reported up to 8-10% solar cell efficiency where the potential mismatch between the sensitizer and the redox couple is around 0.5 V vs. SCE. If one develops a suitable redox couple that decreases the potential difference between the sensitizer and the redox couple, then the cell efficiency could increase by 30%, i.e., from the present value of 10% up to 13%. Towards this goal, Oskam et al. have employed pseudohalogens in place of the triiodide/iodide redox couples, where the equilibrium potential is 0.43 V more positive than that of the iodide/iodide redox couple.17 Yamada and co-workers have used cobalt tris-phenanthroline complexes as electron relays (based on the CoII/m couple) in dye-sensitized solar cells.95... 

In general, the modest efficiencies of Cu(I)/(II) redox couples compared to the iodide/triiodide can be explained by a slow dye reduction, which could be reasonably anticipated, given the slow kinetics that are associated to the Cu(I)/(H) redox chemistry. On the other hand, using a suitably built photoanode equipped with a compact Ti02 underlayer and an appropriate heteroleptic dye like Z907, the detrimental electronic... 

Figure 11. Principle of operation of the dye-sensitized nanocrystalUne solar cell. Photoexcitation of the sensitizer (S) is followed hy electron injection into the conduction band of an oxide semiconductor film. The dye molecule is regenerated by the redox system, which itself is regenerated at the counter-electrode by electrons passed through the load. Potentials are referred to the normal hydrogen electrode (NHE). The energy levels drawn match the redox potentials of the standard N3 sensitizer ground state and the iodide/triiodide couple. (Redrawn from Gratzel [187] with permission from publisher, Elsevier. License Number 2627070632803).

The electrochemical activity of the counter electrode can be checked by cychc voltammetry (CV) with respect to the triiodide/iodide redox couple in a sample electrolyte. Comparison of the peak potentials of reduction and oxidation and current densities thereof with those of various platinum electrodes gives preliminary assessment of the cathode material for use in DSSCs. PPDOT-Et2 conter electrodes, as well as the above-described PEDOT-PSS counter electrodes, demonstrated peak potentials and redox current densities close to those of the platinum electrode. In Figure 3.8, the redox behavior of PPDOT-Et2 in a triiodide/iodide-based electrolyte (ImM D, lOmM Lil, 0.1 M LiC104 in AN) is compared with that of the sputtered platinum electrode, where a PPDOT-Et2 film was deposited by a charge capacity of 40mCcm for polymerization. The two anodic and cathodic peaks in the CV curves represent the following two reactions [31] ... 

Nanofiber can be considered as promising candidate for preparation o f solid or semi solid electrolyte. This is mostly because of the inherent longterm instability of electrolyte used in DSSCs usually consists of triiodide/ iodide redox coupled in organic solvents [42], Many solid or semi-solid viscous electrolytes with low level of penetration to TiO layer such as ionic liquids [43], and gel electrolytes [44] utilized to triumph over these problems. However, nanofiber with may increase the penetration of viscous polymer gel electrolytes through large and controllable pore sizes. 

Figure 14-2. Schematic drawing showing the use of dye derivatized semiconductor nanocrystals as light harvesting units. The sensitizer is cis-Ru(SCN)2L2 L = 2,2 -bipyridyl-4,4 -dicurboxylnte) The redox system use to regenerate the dye and transport the positive charges to the counter electrode is the iodide/triiodide couple dissolved in an organic electrolyte or in a room temperature ionic liquid.

Zhao Y, Wang L, Byon HR (2013) High-performance rechargeable lithium-iodine batteries using triiodide/iodide redox couples in an aqueous cathode. Nat Commun 4 1896... 

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