Carita Kvarnström

Preparation of Supercapacitors on Flexible Substrates with Electrodeposited PEDOT/Graphene Composites

Composite films consisting of poly(3,4-ethylenedioxythiophene) (PEDOT) and graphene oxide (GO) were electrochemically polymerized by electrooxidation of EDOT in ionic liquid (BMIMBF4) onto flexible electrode substrates. Two polymerization approaches were compared, and the cyclic voltammetry (CV) method was found to be superior to potentiostatic polymerization for the growth of PEDOT/GO films. After deposition, incorporated GO was reduced to rGO by a rapid electrochemical method of repetitive cathodic potential cycling, without using any reducing reagents. The films were characterized in 3-electrode configuration in BMIMBF4. Symmetric supercapacitors with aqueous electrolyte were assembled from the composite films and characterized through cyclic voltammetry and galvanostatic discharge tests. It was shown that PEDOT/rGO composites have better capacitive properties than pure PEDOT or the unreduced composite film. The cycling stability of the supercapacitors was also tested, and the results indicate that the specific capacitance still retains well over 90% of the initial value after 2000 consecutive charging/discharging cycles. The supercapacitors were demonstrated as energy storages in a room light energy harvester with a printed organic solar cell and printed electrochromic display. The results are promising for the development of energy-autonomous, low-power, and disposable electronics.

Electrochemical reduction of graphene oxide and its in situ spectroelectrochemical characterization

The electrochemical properties of self-assembled films of graphene oxide (GO) on mercaptoethylamine (MEA) modified rough Au-surfaces were studied. The film deposition process on MEA primed gold was followed by surface plasmon resonance measurements and the film morphology on 3-aminopropyltriethoxysilane primed Si(100)-surface was studied by atomic force microscopy. The deposited few layer thick GO films on gold were electrochemically reduced by cyclic voltammetry simultaneously as the structural changes in the film were recorded by in situ vibrational spectroscopies. In situ surface enhanced infrared spectroscopy results indicate that the effect of the applied potential on the GO structure could be divided into two parts where the changes occurring at moderate negative potentials are mainly related to changes in the double layer at the film-electrolyte interface and to hydrogen bonding of intercalated water between the GO sheets. At potentials more negative than -0.8 V vs. Ag/AgCl the reduction of GO starts to take place with concomitant conversion of the different functional groups of the film.

The Nature of the Charge Carriers in Polyazulene as Studied by in Situ Electron Spin Resonance -UV -Visible -Near-Infrared Spectroscopy

In situ spectroelectrochemistry is of high importance for the characterization of doping reactions in pi-conjugated polymers. In this paper we present the results of simultaneous ESR and UV-vis-NIR measurements performed in situ during electrochemical p- and n-doping of polyazulene (PAz). In previous studies on p-doping of PAz the assignment of the optical absorption bands to specific charge carriers have been somewhat controversial, therefore the aim of this study is to clarify the nature of the doping-induced charge carriers and their corresponding optical absorption bands by in situ ESR-UV-vis-NIR spectroelectrochemistry. PAz was polymerized in two different potential ranges in order to obtain films with different structures and morphologies. On the basis of our spectroelectrochemical results we propose that polarons and polaron pairs are formed during p-doping in the two different types of PAz films electrodeposited on ITO. For studying n-doping of PAz, a Pt electrode was used. The ESR signal first decreased in intensity at low doping levels and then increased in intensity at higher doping levels pointing to the formation of new paramagnetic species. At high negative potentials there occurred an additional line broadening of the ESR signal indicating the existence of rather localized negative charge carriers.

ESR/UV-Vis-NIR spectroelectrochemical study and electrochromic contrast enhancement of a polythiophene derivative bearing a pendant viologen

The importance of viologens in the field of electrochromic materials is well recognized due to their intensely colored radical cation formation. In this study, 1-[6-[(4-methyl-3-thienyl)oxy]hexyl]-4,4′-bipyridium hexafluorophosphate (Th-V) was synthesized and electropolymerized in a solvent mixture comprising water and acetonitrile (v/v; 50u2006:u200650) with 0.1 M lithium perchlorate (LiClO4) as an electrolyte salt, yielding a viologen bearing polythiophene (PTh-V) film on an electrode surface. The resulting polymer shows electrochemical activity from both the redox active viologen and the conjugated polythiophene moieties. The redox behavior of the polymer was studied by multi in situ spectroelectrochemical technique by means of simultaneous recording of electron spin resonance and UV-Vis-near infrared (ESR/UV-Vis-NIR) spectra. The results indicate that only polaron charge carriers are created during both n- and p-doping of the PTh-V film. The polymer film shows enhanced electrochromic contrast due to the introduction of a pendant viologen group into the thiophene unit. The film switched reversibly between dark violet (at −0.6 V) and almost transparent (at 1.0 V) showing good optical contrast with a coloration efficiency of ca. 305 cm2 C−1 at 610 nm. The switching transmittance kinetics demonstrate fast response times to attain a bleached state and excellent operational stability with repeatable voltage switching between colored/bleached states for 1000 cycles. The polythiophene backbone was found to strengthen the thermal stability of the conjugated PTh-V redox polymer. The excellent optical contrast with sharp color changes and high color efficiency combined with adequate thermal behavior suggests the potential of PTh-V in the electrochromic device (ECD) application.

Spectroelectrochemical study of polyphenylene by in situ external reflection FT-IR spectroscopy I. Polymerization of biphenyl

Abstract In situ spectroelectrochemical measurements with external reflection FT-IR are performed at different stages of polymerization of 0.05, 0.1 and 0.8 M biphenyl in 0.1 M TBABF 4 in acetonitrile. The biphenyl concentration is not found to have any effect on the structure of the polymer formed. Formation of oligomers and the ratio of ortho/para -substituted polymer chains during film growth are studied. The first coupling of dimers to oligomers is found to take place in the vicinity of the electrode surface and at a later stage of polymerization the oligomers start to form polymer film on the electrode. A mixed para and ortho coupling resulting in crosslinking between chains is observed already at the early stage of polymerization. However, when a lower current density is used a more ordered polymer structure is obtained. A breakdown of the polymer film due to overoxidation can be seen when the potential is increased to 2.0 V.

Redox reactions in a linear polyviologen derivative studied by in situ ESR/UV-vis-NIR spectroelectrochemistry

It is well-known that reductive electropolymerization of cyanopyridinium moieties yields to viologenic materials. In this work, a monomer with two electropolymerizable cyanopyridinium groups separated by a six carbon spacer (CNP) has been synthesized. Its electropolymerization in aqueous electrolyte results in a linear polyviologen (PV) derivative, a purple-colored film deposited on the electrode surface. Cyclic voltammetry (CV) of PV films displays two well-resolved one-electron redox processes at c.a. −0.5 and −1.0xa0V vs. Ag/AgCl. Fourier transform infrared (FTIR) spectral analysis shows successful polymerization of PV from the CNP monomer. In situ electron spin resonance (ESR)/UV-vis-NIR spectroelectrochemistry was used in order to simultaneously determine the polycation radical as well as the magnetic and optical response of the redox PV system. The single-line ESR spectrum observed at the first reduction peak of PV film was assigned to the formation of stable viologen cation radical species within the polymer matrix, exhibiting the characteristic UV-vis-NIR viologen cation radical absorption bands. The electrosynthesized linear PV system represents a promising stable redox active n-type material for organic rechargeable devices.

One-pot synthesis of an Au/Au2S viologen hybrid nanocomposite for efficient catalytic applications

We report a facile one-pot synthesis of Au/Au2S multicomponent nanoparticles supported on viologen (V) as a hybrid nanocomposite. Sodium dithionite was used as the reducing agent for both Au and V precursors and SDS as the stabilizing agent for Au nanoparticles in aqueous reaction medium. Spectroscopy, microscopy and electrochemical measurements confirm the successful composite formation. The as-prepared flower-like composite showed excellent catalytic properties towards the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP). The catalytic activity factor of the Au/Au2S–V hybrid was highest in comparison to those reported for polymer supported Au nanoparticle catalysts. The enhanced catalytic performance can be attributed to the strong adsorption of 4-NP molecules onto the cationic V matrix and Au2S nanoparticle surface along with effective donor–acceptor interactions between Au–Au2S nanoparticles and V facilitating the electron transfer at the hybrid interface.

Preparation of Multi-Walled Carbon Nanotube/Amino- Terminated Ionic Liquid Arrays and Their Electrocatalysis towards Oxygen Reduction

Arrays of aligned multi-walled carbon nanotube-ionic liquid (MIL) were assembled on silicon wafers (Si-MIL). Formation of Si-MIL was confirmed by FTIR, AFM and Raman techniques. The electrochemical measurements indicated that Si-MIL showed good electrocatalysis towards oxygen reduction compared with MIL drop-cast on a glassy carbon electrode.

In situ Resonance Raman Spectroscopy of Polyazulene on Aluminum

Polyazulene (PAz) has been electrochemically deposited on different electrode substrates. The films were characterized with Raman and UV-vis spectroscopy. The spectroelectrochemical studies were performed in situ during p- and n-doping (electrochemical oxidation and reduction, respectively). The focus of this work was mainly on the charging and discharging reactions of PAz on Al substrates. The results were compared to the corresponding results obtained from PAz on Pt substrates. Three different excitation wavelengths (514, 633, and 780 nm) were used in the Raman experiments and the resonance enhancement effect was observed when changing the wavelength of the excitation line. The vibrational behavior of PAz deposited on Al was very similar to that of PAz deposited on Pt during p-doping. Furthermore, it was found that the vibrational responses during p- and n-doping are different indicating that the electronic structure of PAz is not the same during positive and negative charging. It was concluded that PAz is not reversibly n-doped on Al. The n-doping on Pt was shown to be more reversible. In this paper, the important correlation between UV-vis and Raman spectroscopy is discussed as well as the correlation between doping-induced infrared active bands and Raman bands of neutral PAz.

Mixed ion transfer analysis in redox processes of electroactive thin films

Electrochemical quartz crystal microbalance (EQCM) technique was used to measure the ion transfer in redox processes in electroactive organic thin films, such as self-assembled monolayer (SAM) (4-pyridyl hydroquinone, abbr. 4PHQ), multilayer based on SAM and conducting polymer film (here poly-(3,4-ethylenedioxythiophene), abbr. PEDOT). A mechanism of mixed ion transfer is developed and presented. Analysis of mixed ion transfer during redox processes successfully elucidates the deviation of oscillation frequency of the quartz crystal from theoretical expectation.