Redox-Active Electrolytes

Recently, redox-active electrolytes have been proposed to be used for ESs to provide addition pseudocapacitive contribution, which utilized the faradaic reactions originated from the electrolyte to store charge [905-907]. Therefore, both the electrode materials and electrolytes contribute to the overall capacitance [908]. 

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The ability to manipulate the anodic corrosion problem using high concentrations of redox active electrolyte also makes possible the sustained oxidation of Br" at illuminated metal dichalcogenide-based cells, Figure 1.(15) The use of high concentrations of electrolyte has proven valuable in situations involving other photoanode materials, notably n-type Si.(36,37)... 

Dye-sensitized solar cells (DSSCs) are photoelectrochemical solar devices, currently subject of intense research in the framework of renewable energies as a low-cost photovoltaic device. DSSCs are based upon the sensitization of mesoporous nanocrystalline metal oxide films to visible light by the adsorption of molecular dyes.5"7 Photoinduced electron injection from the sensitizer dye (D) into the metal oxide conduction band initiates charge separation. Subsequently, the injected electrons are transported through the metal oxide film to a transparent electrode, while a redox-active electrolyte, such as I /I , is employed to reduce the dye cation and transport the resulting positive charge to a counter electrode (Fig. 17.4). 

Photoelectrochemical cell concepts based on light absorption in a semiconductor and charge transfer to a redox-active electrolyte (Figure 4.1a) have been studied extensively as an alternative to the cells based on semiconductor junctions [23, 28]. 

Some Data from the Selected Literature Concerning the Redox-Active Electrolyte-Based ESs... 

Noticeably, Chen et al. [923] reported that ESs using the HQ-based redox-active electrolyte suffered from a much faster self-discharge process, which was due to the transfer of redox-active species in the electrolytes between positive and negative electrodes. The authors also proposed two strategies to address this issue (a) the selection of a redox-active electrolyte that could be reversibly converted into insoluble species during the charging/discharging process and (b) the use of a suitable separator membrane such as Nafion. 

Su, L., L. Gong, H. Lii, and Q. Xii. 2014. Enhanced low-temperature capacitance of MnOj nanorods in a redox-active electrolyte. Journal of Power Sources 248 212-217. 

Frackowiak, E., K. Fic, M. Meller, and G. Lota. 2012. Electrochemistry serving people and nature High-energy ecocapacitors based on redox-active electrolytes. ChemSusChem 5 1181-1185. 

Mai, L. Q., A. Minhas-Khan, X. Tian et al. 2013. Synergistic interaction between redox-active electrolyte and binder-free functionalized carbon for ultrahigh supercapacitor performance. Nature Communications 4 1-7. 

Roldan, S., M. Granda, R. Menendez, R. Santamarfa, andC. Blanco. 2011. Mechanisms of energy storage in carbon-based supercapacitors modified with a quinoid redox-active electrolyte. Journal of Physical Chemistry C 115 17606-17611. 

Chen, W., R. B. Rakhi, and H. N. Alshareef. 2013. Capacitance enhancement of polyaniline coated curved-graphene supercapacitors in a redox-active electrolyte. Nanoscale 5 4134-4138. 

With regard to the redox-active electrolyte, Lota and Frackowiak [63] found the cycling stability of the electrode in the 1 M KI electrolyte to be significantly affected by the type of the metallic current collector. After 10,000 cycles, a moderate decrease of the specific capacitance (<20%) was observed for the Au current collector, whereas an increase of specific capacitance from 235 to 300 F was found for the stainless-steel current collector. Meller et al. [64] also pointed ont that it is not suitable to use an Au current collector in iodide electrolytes dne to its reaction with iodides, while it is appropriate to use a stainless-steel cnrrent collector since it resulted in good long-term stability of ES. 

Bidikoudi M, Znbeir LF, Falaras P (2014) Low viscosity highly condnctive ionic liqnid blends for redox active electrolytes in efficient dye-sensitized solar cells. J Mater Chem A 2 15326-15336... 

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