Avni A. Argun

Electrochromic devices based on soluble and processable dioxythiophene polymersElectronic supplementary information (ESI) available: details of the synthesis of PProDOT(CH2OC18H37)2 and PProDOT(CH2OEtHx)2 and their polymerization. See http://www.rsc.org/suppdata/jm/b3/b306365h/

Reflective and absorptive/transmissive polymer electrochromic devices (ECDs) composed of spray-coated films of poly(3,3-bis(octadecyloxymethyl)-3,4-dihydro-2H-thieno[3,4-b][1,4]dioxepine) (PProDOT(CH2OC18H37)2) and poly(3,3-bis(2-ethylhexyloxymethyl)-3,4-dihydro-2H-thieno[3,4-b][1,4]dioxepine) (PProDOT(CH2OEtHx)2) layers as cathodically coloring polymers and poly(3,6-bis(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)-9-methyl-9H-carbazole) (PBEDOT-NMeCz) as the anodically coloring polymer have been constructed and evaluated. These devices exhibit low switching voltages (±1.2 V), high visible contrast values, sub-second switching times, and high switching stability in atmospheric conditions. The reflective ECD comprising PProDOT(CH2OEtHx)2 as the active layer demonstrates an unusual electrochromic behavior. By regulating the applied voltage, a high reflectance contrast of greater than 70% ΔT was achieved in the NIR region (2 µm) without any noticeable color change of the device.

Line patterning for flexible and laterally configured electrochromic devices

We have applied the line patterning method, which involves printing of patterns on a plastic or paper substrate using a commercial printer followed by coating of the non-printed areas by a conductive polymer, or metal conductor, to build laterally configured polymer and metallic interdigitated electrodes (IDEs) for electrochromic devices (ECDs). Selective deposition of transparent poly(3,4-ethylenedioxythiophene)–poly(styrene sulfonate) (PEDOT–PSS) or electroless gold films resulted in lateral electrode resolution values of ∼30 µm as determined by optical microscopy. These ECDs comprise complementary colored, dioxythiophene based electrochromic polymers deposited on alternating fingers of gold coated IDEs and a viscous electrolyte layer to enable ion transport between the polymers. The devices are switched by stepping the applied voltage between −1.2 V to +1.2 V and pass a maximum of 1.3 mA cm−2 and a switching charge of 1.2 mC cm−2 in ∼3 s to switch the device from a highly reflective gold state to an absorptive blue state. Three IDEs with different anode to cathode distances have been line patterned via electroless gold deposition. Electrochromic switching kinetics of 2-lane, 4-lane, and 6-lane ECDs have been studied by applying potential steps from −1.0 V to +0.8 V and monitoring the reflectance change as a function of time. The switching times to reach 85% of the full contrast are 4.3 s, 1.5 s, and 0.8 s for the 2-lane, 4-lane, and 6-lane devices, respectively. The extent of interdigitation noticeably improves the switching performance of lateral ECDs due to shorter diffusion distances for dopant ions and minimal electrolyte resistance.

Structure-property studies of highly conductive layer-by-layer assembled membranes for fuel cell PEM applications

Layer-by-layer (LbL) films composed of poly(diallyl dimethyl ammonium chloride) (PDAC) and sulfonated poly(2,6-dimethyl 1,4-phenylene oxide) (sPPO) (PDAC/sPPO) are studied as a result of the variation of the ionic strength of assembly solutions to determine the nature of the exceptionally high ionic conductivity of this system. Film growth is modulated from 6.91 nm/bilayer (BL) when assembled with no salt to 62.2 nm/BL when assembled with 0.5 M salt in all assembly solutions. However, at optimized assembly conditions of 1.0 M salt in only the sPPO solution, fully humidified PDAC/sPPO films have ionic conductivity values of 7.00 × 10−2 S cm−1 at 25 °C, which is the highest value reported for any LbL assembled system. Selectively screening charges by adding salt to the sPPO assembly solution decreases the ionic crosslink density of the films and increases the water uptake, yielding high ionic conductivity. Thickness measurements made at 0.5 BL increments indicate that the film composition can also be tuned by the ionic strength of the assembly baths. Additionally, PDAC/sPPO films fabricated using a recently developed LbL-Spray technique allow for the preliminary characterization of the mechanical properties of free-standing membranes.

Electrochromic properties of a fast switching, dual colour polythiophene bearing non-planar dithiinoquinoxaline units

The synthesis and electropolymerisation of a new terthiophene, 1,3-di-2-thienylthieno[3′,4′:5,6][1,4]dithiino[2,3-b]quinoxaline, is reported. The compound bears a quinoxaline unit fused to the central thiophene ring via a 1,4-dithiin ring; the latter unit ensures a non-planar structure for the molecule. The corresponding polymer, prepared electrochemically, has been characterized by cyclic voltammetry and UV-vis-NIR spectroelectrochemistry. The material is oxidised within the conjugated chain, but the reduction processes are complex and arise from both the polythiophene and the independent quinoxaline units. The polymer has two distinct colour states—orange in the neutral form and green–blue in the oxidised state. Electrochromic studies on poly(1,3-di-2-thienylthieno[3′,4′:5,6][1,4]dithiino[2,3-b]quinoxaline) reveal fast switching speeds that are superior to those of poly(3,4-ethylenedioxythiophene) (PEDOT) and a colouration efficiency of 381 cm2 C−1 at 650 nm.

Graphene Based Nafion® Nanocomposite Membranes for Proton Exchange Membrane Fuel Cells

Nanocomposite proton-exchange membranes are fabricated by loading graphene nanoflakes into perfluoro sulfonic acid polymer (Nafion) solutions at controlled amounts (1–4 wt%) followed by electrical and thermal characterization of the resulting membranes. Electronic and ionic conductivity values of the nanocomposites, as well as their dielectric and thermal properties improve at increased graphene loadings. Owing to graphene’s exceptionally high surface area to volume ratio and excellent physical properties, these nanocomposite are promising candidates for proton-exchange membrane fuel cell applications.Copyright