Fabricating multicolored electrochromic devices using conducting copolymers

A centrosymmetric polymer precursor, 4-(2,5-di(thiophen-2-yl)-1H-pyrrol-1- yl)butan-1-amine (TPBA), was synthesized via a Knorr-Paal reaction and its copolymer with EDOT was electrochemically synthesized and characterized. While P(TPBA) has only two colors in its oxidized and neutral states, its copolymer with EDOT has eight different colors. Electrochromic devices based on P(TPBA)/PEDOT and P(TPBA-co-EDOT)/PEDOT were constructed and characterized. The oxidized state of the device shows blue color whereas it shows purple for the reduced state. At moderate potentials the device has good transparency with green and gray colors. The maximum contrast and switching time of the multielectrochromic copolymer device were measured as 25% and 0.8 s at 575 nm. Copolymerization not only increases the polymer's color scheme, but also improves its properties, such as redox stability and switching time

Improvement of carbon dioxide tolerance of PEMFC electrocatalyst by using microwave irradiation technique

The microwave irradiation technique was used to prepare platinum and platinum-ruthenium-based electrocatalysts on Vulcan for PEMFCs. The effects of microwave duration, base concentration and surfactant/precursor ratios on the properties of Pt-based catalysts were investigated. The prepared Pt-based catalysts were characterized by XRD and then PEMFC tests were performed. The particle sizes of the catalysts were ranging between 2 and 6 nm. Platinum-ruthenium-based catalysts were prepared to improve the carbon dioxide tolerance of the PEMFCs. The power losses arising from carbon dioxide in hydrogen feed were decreased by using the prepared PtRu-based catalysts when 30% carbon dioxide including hydrogen was sent to the fuel cell. (c) 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved

Effects of membrane electrode assembly components on proton exchange membrane fuel cell performance

The objective of this study is to determine the effects of various factors on the performance of proton exchange membrane (PEM) fuel cell. These factors are membrane thickness, hot-pressing conditions of the gas diffusion layer (GDL) either onto the membrane or membrane electrode assembly (MEA) and Teflon:carbon ratio in the GDL on PEM fuel cell performance. Homemade five-layer and commercial three-layer MEAs were used in the experiments. Nafion (R) 112 and 115 which have nominal thicknesses of 50 and 125 mu m, respectively, were used as membranes. It was observed that fuel cell performance is inversely proportional to membrane thickness. In the case of five-layer MEAs, optimum hot-pressing conditions of catalyst-coated GDLs onto the membrane were found as 172 N cm(-2). However, the maximum performance for three-layer MEAs was obtained with no press conditions. Also, by increasing Teflon:carbon ratio in the GDLs, PEM fuel cell performance increases up to a certain value, but further increase of this ratio worsen the performance. (C) 2007 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved

Decoration of multi-wall carbon nanotubes with platinum nanoparticles using supercritical deposition with thermodynamic control of metal loading

We demonstrate that supercritical carbon dioxide deposition is a very effective technology for decorating multi-wall carbon nano-tubes with platinum nanoparticles with an average size as small as 2 nm and with a very narrow size distribution. Platinum loading can be controlled thermodynamically based on the adsorption isotherm of the platinum precursor between the supercritical carbon dioxide phase and the carbon nanotube phase. (c) 2006 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved

Vulcan-Supported Pt Electrocatalysts for PEMFCs Prepared using Supercritical Carbon Dioxide Deposition

In this study, supercritical carbon dioxide (scCO(2)) deposition was used to prepare vulcan-supported Pt (Pt/Vulcan) electrocatalysts for proton exchange membrane fuel cells (PEMFCs), and the effects of process variables on the properties of the electrocatalysts were investigated. The two different methods used to reduce the organometallic precursor were thermal reduction in nitrogen at atmospheric pressure and thermal reduction in scCO(2). In the former method, the maximum Pt loading achieved was 9%, and this was governed by the adsorption isotherm of the Pt precursor between the scCO(2) phase and the Vulcan phase. By using the latter method, higher Pt loadings of 15% and 35% could be achieved. The Pt/Vulcan catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and cyclic voltammetry (CV). The average particle sizes for Pt/Vulcan 9%, 15%, and 35% catalysts were 1.2, 1.3, and 2nm, respectively. Electrochemical surface areas obtained from CV data were found to vary with the Pt loading

Pt-based electrocatalysts for polymer electrolyte membrane fuel cells prepared by supercritical deposition technique

Pt-based electrocatalysts were prepared on different carbon supports which are multiwall carbon nanotubes (MWCNTs), Vulcan XC 72R (VXR) and black pearl 2000 (BP2000) using a supercritical carbon dioxide (ScCO2) deposition technique. These catalysts were characterized by using X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM) and cyclic voltammetry (CV). XRD and HRTEM results demonstrated that the ScCO2 deposition technique enables a high surface area metal phase to be deposited, with the size of the Pt particles ranging from 1 to 2 nm. The electrochemical surface areas (ESAs) of the prepared electrocatalysts were compared to the surface areas of commercial ETEK Pt/C (10 wt% Pt) and Tanaka Pt/C (46.5 wt% Pt) catalysts. The CV data indicate that the ESAs of the prepared Pt/VXR and Pt/MWCNT catalysts are about three times larger than that of the commercial ETEK catalyst for similar (10 wt% Pt) loadings. Oxygen reduction activity was investigated by hydrodynamic voltammetry. From the slope of Koutecky-Levich plots, the average number of electrons transferred in the oxygen reduction reaction (ORR) was 3.5, 3.6 and 3.7 for Pt/BP2000, Pt/VXR and Pt/MWCNT, correspondingly, which indicated almost complete reduction of oxygen to water. (C) 2008 Published by Elsevier B.V

Comparison of two different catalyst preparation methods for graphene nanoplatelets supported platinum catalysts

In this study, we compared two facile and effective approaches which are supercritical carbon dioxide (scCO2) deposition and microwave irradiation methods to synthesize Pt nanoparticles uniformly dispersed on graphene nanoplatelets (G) having 750 m2/g surface area as the support material. The prepared catalysts were characterized by using XRD, TGA, TEM, CV and PEM fuel cell performance tests. Microwave irradiation (Pt/G1) and scCO2 deposition (Pt/G2) methods resulted in the particle sizes of 3.1–3.4 nm and 1.5–1.6 nm, respectively. Higher electrochemically active surface area and PEM fuel cell performance were obtained for the Pt/G2 catalyst. An accelerated aging test, carbon corrosion, is also applied to the catalysts and Tafel slope losses were determined. Pt/G1 catalyst resulted in 50 mV Tafel slope loss whereas no significant loss was observed for Pt/G2 catalyst after carbon corrosion test