Recent experiments on the chlorite-iodide-malonic acid-starch reaction in a gel reactor give the first evidence of the existence of the symmetry breaking, reaction-diffusion structures predicted by Turing in 1952. A five-variable model that describes the temporal behavior of the system is reduced to a two-variable model, and its spatial behavior is analyzed. Structures have been found with wavelengths that are in good agreement with those observed experimentally. The gel plays a key role by binding key iodine species, thereby creating the necessary difference in the effective diffusion coefficients of the activator and inhibitor species, iodide and chlorite ions, respectively.

https://science.sciencemag.org/content/sci/251/4994/650.full.pdf

Modeling of turing structures in the chlorite--iodide--malonic Acid--starch reaction system.

A 7.4% power conversion efficiency at air mass (AM) 1.5 full sunlight was reached with a mesoscopic solar cell employing a new binary ionic liquid electrolyte composed of 1-propyl-3-methylimidazolium iodide and 1-ethyl-3-methylimidazolium tricyanomethanide in conjunction with the amphiphilic ruthenium complex NaRu(4-carboxylic acid-4‘-carboxylate)(4,4‘-dinonyl-2,2‘-bipyridine)(NCS)2, coded as Z-907Na. Ultramicroelectrode voltammetric, nanosecond laser transient absorbance, and photovoltaic measurements show that a high iodide concentration is required for dye regeneration to compete efficiently with charge recombination. A surprisingly fast reductive quenching process is turned on in pure iodide melts. This channel is unproductive, explaining the lower photocurrents observed under these conditions.

Charge separation and efficient light energy conversion in sensitized mesoscopic solar cells based on binary ionic liquids.

A redox hydrogel with an apparent electron diffusion coefficient (Dapp) of (5.8 ± 0.5) × 10-6 cm2 s-1 is described. The order of magnitude increase in Dapp relative to previously studied redox hydrogels results from the tethering of redox centers to the backbone of the cross-linked redox polymer backbone through 13 atom spacer arms. The long and flexible tethers allow the redox centers to sweep electrons from large-volume elements and to collect electrons of glucose oxidase efficiently. The spacer arms make the collection of electrons from glucose oxidase so efficient that glucose is electrooxidized already at −0.36 V versus Ag/AgCl, the reversible potential of the redox potential of the FAD/FADH2 centers of the enzyme at pH 7.2. The limiting current density of 1.15 mA cm-2 is reached at a potential as low as −0.1 V versus Ag/AgCl. The novel redox center of the polymer is a tris-dialkylated N,N‘-biimidazole Os2+/3+ complex. Its redox potential, −0.195 V versus Ag/AgCl, is 0.8 V reducing relative to that o...

Long tethers binding redox centers to polymer backbones enhance electron transport in enzyme "Wiring" hydrogels.

Quasi-solid-state dye-sensitized solar cells were fabricated using low-molecular-weight gelators. They showed comparable photoenergy conversion efficiencies to the liquid cell at high illumination intensity up to AM 1.5 (1 sun). Conductivity measurements of the electrolyte phases revealed that the gelation does not affect the conductivity of the electrolyte and that the conductivity increased with an increase of iodine in both gel electrolytes and liquid electrolyte. The formation of polyiodide ions, such as I3- and I5-, caused by addition of iodine was confirmed by Raman spectroscopic measurement. The self-diffusion of iodide species in the gel electrolyte was found about a quarter of that of I- in acetonitrile. The formation of less-mobile polyiodide ions in electrolyte increased the conductivity in the mesoporous phase, which should be rationalized as due to the Grotthuss-type electron exchange mechanism caused by rather packed polyiodide species in the electrolytes. The optimized quasi-solid-state cel...

Quasi-Solid-State Dye-Sensitized TiO2 Solar Cells: Effective Charge Transport in Mesoporous Space Filled with Gel Electrolytes Containing Iodide and Iodine

V. J. Friedrich

Papers

Transfer diffusion. II. Kinetics of electron exchange reaction between ferrocene and ferricinium ion in alcohols

Transfer diffusion. III. Kinetics and mechanism of the triiodide-iodide exchange reaction