Deniz Yiğit

Heterostructured poly(3,6-dithien-2-yl-9H-carbazol-9-yl acetic acid)/TiO2 nanoparticles composite redox-active materials as both anode and cathode for high-performance symmetric supercapacitor applications

Herein, a facile and simple method is reported for preparation of composite electrode materials based on conducting polymer/nano metal oxide combination for supercapacitor applications. The heterostructured composite redox-active electrode materials, having both p- and n-doping ability, were fabricated using poly(3,6-dithien-2-yl-9H-carbazol-9-yl acetic acid) and nano sized TiO2 particles without any binder and conducting additives. The heterostructured composite electrodes exhibited remarkable a specific capacitance (Cspec = 462.88 F g−1), specific power (SP = 266.96 kW kg−1), specific energy (SE = 89.98 W h kg−1), good cycling performance and excellent reversible capability (81.7% capacitance retention after 8000 charge/discharge cycles) at 2.5 mA cm−2 current density within a 1.2 V potential window with two-electrode symmetric cell configuration. Besides, heterostructured composite electrode materials were fabricated using different particle sized TiO2 (3–5 nm, average 21 nm and bulk), and the effect of the particle size on supercapacitor performances was investigated and compared in detail. Our symmetric pseudo-capacitor device lighted a LED for 4.7 min with 42 s charge time at 2.5 mA cm−2 even after 8000 charge/discharge cycles.

N-Substituted poly(3,6-dithienylcarbazole) derivatives: a new class of redox-active electrode materials for high-performance flexible solid-state pseudocapacitors

Herein, we present the design and synthesis of novel poly(3,6-dithienylcarbazole) derivatives, namely poly(tert-butyl 2-(3,6-di(thiophen-2-yl)-9H-carbazol-9-yl)acetate) (PTTBCbz) and poly(tert-butyl 2-(3,6-bis(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)-9H-carbazol-9-yl)acetate) (PETBCbz), as redox-active materials for high performance electrochemical energy storage applications. Symmetric flexible solid-state pseudocapacitor devices were assembled by using PTTBCbz or PETBCbz and a polymer gel electrolyte based on LiClO4. The electrochemical characteristics of the pseudocapacitor devices were evaluated by cyclic voltammetry (CV), galvanostatic charge/discharge measurements (GCD) and electrochemical impedance spectroscopy (EIS). The fabricated supercapacitor devices delivered superior specific capacitances (Cspec = 640 F g−1 and Cspec = 554 F g−1), energy densities (E = 1280 W h kg−1 and E = 1108 W h kg−1) and power densities (P = 36 kW kg−1 and P = 32.7 kW kg−1). Furthermore, these flexible supercapacitors exhibited good cycling stability and excellent capacitance retentions (92.5% and 90.5%) after 10000 successive charge/discharge cycles at a current density of 1 mA cm−2. The electrochemical characterization studies confirmed that these novel poly(3,6-dithienylcarbazole)-based redox-active materials have significant potential for utilization as redox-active electrode materials in high performance flexible and portable energy storage devices.

Novel poly(2,5-dithienylpyrrole) (PSNS) derivatives functionalized with azobenzene, coumarin and fluorescein chromophore units: spectroelectrochemical properties and electrochromic device applications

Three novel 2,5-dithienylpyrrole (SNS) derivatives containing strong chromophore units such as azobenzene, coumarin and fluorescein were synthesized to investigate the effects of chromophore substituents on the electrochemical and spectroelectrochemical properties of resulting polymers. Electrochemical and optoelectronic characteristics of the homopolymers, poly(1-(2-(4-(phenyldiazenyl)phenoxy)ethyl)-2,5-di(thiophen-2-yl)-1H-pyrrole) (PTPTAz), poly(4-(2-(2,5-di(thiophen-2-yl)-1H-pyrrol-1-yl)ethoxy)-2H-chromen-2-one) (PTPTCo) and poly(methyl 2-(6-(2-(2,5-di(thiophen-2-yl)-1H-pyrrol-1-yl)ethoxy)-3-oxo-3H-xanthen-9-yl)benzoate) (PTPTFlo), were investigated in detail. The combination of a strong chromophore pendant group with a poly(2,5-dithienylpyrrole) (PSNS) backbone significantly influences the electronic and optoelectronic behaviors of conducting polymers. PTPTAz and PTPTCo exhibited different colors in their neutral and oxidized states while PTPTFlo showed a yellow color in all states. The optical band gap (Eg) values of PTPTAz, PTPTCo and PTPTFlo films were calculated as 2.81 eV, 2.44 eV and 2.31 eV respectively. Moreover, a PTPTFlo/PEDOT based dual type solid state electrochromic device (ECD) was constructed. The ECD exhibited quite good long-term stability with reasonable optical memory performance under ambient conditions.

Microwave-Assisted Synthesis of Furo[3,2-c]-1,8-naphthyridines

Abstract Microwave-assisted ring-conversion reactions of some pyrido[1,2-a]pyrimidine derivatives to 1,8-naphthyridines have been investigated. Novel furo[3,2-c]-1,8-naphthyridine compounds were synthesized in good yields under thermal reaction conditions. Both microwave and classical heating methods have been found to be satisfactory for the synthesis of new 1,8-naphthyridines.

Carbon nanofiber/poly(tetrahydro[1,4]dioxino[2,3-b]thieno[3,4-e][1,4]dioxine) binder-free composite redox-active electrode for electrochemical energy storage applications

We report the preparation and supercapacitive properties of a novel composite electrode material based on carbon nanofiber (CNF) and poly(tetrahydro[1,4]dioxino[2,3-b]thieno[3,4-e][1,4]dioxine) (PTDTD) for electrochemical energy storage applications. The CNF/PTDTD composite electrode was directly prepared by electrodeposition of PTDTD on the CNF coated substrate without any binder or conductive additives. The symmetric solid-state supercapacitor device was assembled by using these CNF/PTDTD composite electrodes. In addition, CNF/CNF and CNF/poly(3,4-ethylenedioxythiophene) (PEDOT) symmetric supercapacitor devices were also fabricated to make a detailed performance comparison. The electrochemical characteristics of all supercapacitor devices were comprehensively evaluated by CV, GCD and EIS measurements. The CNF/PTDTD composite electrodes delivered a maximum specific capacitance of 332 F g−1, energy density of 166 W h kg−1, power density of 4.9 kW kg−1 and an excellent cycling stability with 89% capacitance retention after 12 500 cycles at 2 mA cm−2 current density while CNF/PEDOT electrodes were able to reach a specific capacitance of 254 F g−1, energy density of 128.8 W h kg−1 and power density of 5.45 kW kg−1 in those supercapacitor devices. These results confirmed that PTDTD has significant potential to be a good alternative redox-active material and CNF/PTDTD composite structure is a promising candidate for supercapacitor applications.