Spinel-type Co3O4 finds applications in a wide range of fields, including clean energy conversion, where nanostructured Co3O4 may provide a cost-efficient alternative to platinum- and iridium-based ...catalysts for electrocatalytic water-splitting. We here describe a novel strategy in which basic cobalt carbonate - a precursor to Co3O4 - is precipitated as sheet-like structures and microspheres covered with fine surface protrusions, via ammonium carbonate decomposition at room temperature. Importantly, these mild reaction conditions enable us to employ bio-inspired templating approaches to further control the mineral structure. Rod-like tobacco mosaic viruses (TMV) were used as biotemplates for mineral deposition, where we profit from the ability of Co(ii) ions to mediate the ordered assembly of the virus nanorods to create complex tubular superstructures of TMV/ basic cobalt carbonate. Calcination of these tubules is then achieved with retention of the gross morphology, and generates a hierarchically-structured solid comprising interconnected Co3O4 nanoparticles. Evaluation of these Co3O4 materials as electrocatalysts for the oxygen evolution reaction (OER) demonstrates that the activity of Co3O4 prepared by calcination of ammonia diffusion-grown precursors in both, the absence or presence of TMV exceeds that of a commercial nanopowder.
We present a click chemistry approach for the synthesis of conjugated redox polymers based on highly regioregular polythiophenes with tunable amounts of pendant redox-active triphenylamine (TPA) ...groups. After solution-processing doping of homogeneous films was performed electrochemically and chemically by the acceptor F 4 TCNQ and the chemical oxidant FeCl 3 . We find that doping is accompanied by crosslinking upon electrochemical triggers or by oxidation with FeCl 3 leading to polythiophene films crosslinked via tetraphenylbenzidine (TPB) units. Cyclic voltammetry coupled with in situ absorption spectroscopy and in situ conductance measurements show similar oxidation and conductivity regimes for the backbone and the pendant redox units making the films prone to stable redox switching. Bulk conductivities as high as 8 S cm −1 are measured by four-point-probe, i.e. values comparable to doped regioregular poly(3-hexylthiophene) are reachable. The crosslinking reaction renders the films insoluble in all tested solvents, opening potential applications of the materials in direct contact with organic solvents.
The mixed conductivity behavior of polythiophene-based anionic and cationic polymers is studied under controlled atmospheres in this contribution. The conjugated polyelectrolytes are based on ...regioregular polythiophene backbones with either pendant sulfonate anions or imidazolium cations with counterbalancing tetrabutylammonium hexafluorophosphate and bromide anions, respectively. Direct current, four-point-probe measurements and impedance spectroscopy are performed to separate electronic and ionic conductivity. Optical absorption spectroscopy is used to make statements about the aggregation of the polymer chains and to visualize the electronic doping behavior. Similar to a pure conjugated polymer such as poly(3-hexylthiophene) the electronic conductivity can be tuned over a wide range from below 10−6 S/cm to 2.2 S/cm by external doping with the strong electron acceptor F4TCNQ by sequential solution doping. The ionic conductivity on the other hand is shown to be strongly dependent on the degree of water uptake. We show that values of up to 10−2 S/cm with effective ionic mobilities in the order of 10−8-10−7 cm2/(Vs) can be reached.
Display omitted
•Mixed conductivity in polymer films is elucidated.•Anionic and cationic polythiophene-based conjugated polyelectrolytes are compared.•Electronic & ionic conductivities are studied under controlled atmospheres.•Ionic conductivities can strongly be tuned via humidity control.•Electronic conductivities can be manipulated upon chemical doping with F4TCNQ.
We highlight the influence of processing conditions on polymorphism and structure formation on the mesoscale for the family of PCPDTBT polymers with branched alkyl side chains. Direct correlations of ...morphology to the chemical structure and to transistor device performance are established. We found that up to four different packing motifs could be realized depending on the polymer derivative and the processing conditions: amorphous, π-stacked, cross-hatched and dimer-containing polymorphs. While C- and F-PCPDTBT display similar packing behavior organizing in π-stacked and dimer-like structures, Si-PCPDTBT gives rise to cross-hatched structures upon simple deposition from solution. The observed differences in chain packing for C-/F-PCPDTBT versus Si-PCPDTBT are attributed to differences in backbone conformations and aggregation behavior in solution. The effect of polymorphism on charge transport is probed using field-effect transistors, in which both π-stacked and cross-hatched polymer chain arrangements yield the highest hole mobilities. Mesoscopic morphology and mobility simulations rationalize our experimental findings by relating mobility to distributions of electronic coupling elements between the chains.
We report on the oxidation potential of partially fluorinated (C42F14H14, F14-RUB) and perfluorinated rubrene (C42F28, PF-RUB) studied by cyclic voltammetry (CV) in solution as well as by ...spectroscopic ellipsometry and near edge X-ray absorption fine structure (NEXAFS) spectroscopy in thin films in combination with density functional theory computations. Due to their different electronic structure, the fluorinated derivatives have a higher oxidation potential and are more stable than rubrene (C42H28, RUB).
We present a systematic study of the morphology and absorption properties of a typical donor–acceptor polymer (PCPDTBT) with semicrystalline behavior in solution and in thin films. In-situ ...spectroelectrochemical data give information about the evolution of the absorption spectra from neutral to charged species. The experimental data are supported by theoretical calculations in the framework of the density functional theory (DFT). Regarding thin film structures, we show that the choice of the solvent has significant influence on the morphology in thin films: whereas CS2 and CHCl3 give rather structureless (amorphous) morphologies, films from 1-CN exhibit a clear crystalline nanofiber morphology. Accompanying UV/vis/NIR spectra of films are highly dependent on the morphology and therefore on the choice of the processing solvent. The absorption of fiber morphologies is strongly red-shifted compared to the structureless films.
Herein, we present a quasi-living Negishi-type catalyst-transfer polycondensation of a zinc–organic DTS-based monomer which provides an access to narrowly distributed ...poly(4,4-bis(2-ethylhexyl)dithieno3,2- b :2′,3′- d silole (PDTS) with controlled molecular weight. The synthesis of well-defined all-conjugated diblock copolymers containing a PDTS block was accomplished by a combination of Kumada and Negishi catalyst-transfer polycondensations (KCTP and NCTP, respectively). Particularly, it was shown that living P3HT chains obtained by KCTP of magnesium–organic thiophene-based monomer efficiently initiate NCTP of zinc–organic DTS-based monomer. The purity of the DTS-based monomer was found to be a crucial factor for achieving a clean chain-growth polymerization process. A combination of physico-chemical methods was used to prove the success of the block copolymerization.
Ultrafast transient absorption spectroscopy is performed on a novel donor-acceptor-donor triad made of two identical bisthiophene derivatives as electron donors and a central perylenediimide moiety ...as electron acceptor. The triad is extended at both ends by covalently bound siloxane chains that confer self-organisation into thin smectic films at ambient temperature. When diluted in chloroform, selective excitation of the donor moiety leads to resonance energy transfer within 130 fs to the acceptor moiety, followed by the formation of a charge transfer (CT) state in ~3 ps. The CT state recombines entirely on a 55 ps time scale. In the liquid crystal films, excitonic intermolecular coupling leads to significant changes in the dynamics. Most remarkably, ultrafast intra- and intermolecular CT state formation occurs in about 60 fs, i.e. on a time scale comparable to electronic coherence times. While the intra-molecular CT states recombine on the same time scale as in solution or even faster, inter-molecular CT states live for about 1 ns. Last, triplet states of the perylenediimide moiety dominate the differential absorption after ~1 ns. We anticipate that the fast recombination of intra-molecular CT states and the triplet state formation may severely limit the photo-current in these materials.
Spinel-type Co
O
finds applications in a wide range of fields, including clean energy conversion, where nanostructured Co
O
may provide a cost-efficient alternative to platinum- and iridium-based ...catalysts for electrocatalytic water-splitting. We here describe a novel strategy in which basic cobalt carbonate - a precursor to Co
O
- is precipitated as sheet-like structures and microspheres covered with fine surface protrusions, via ammonium carbonate decomposition at room temperature. Importantly, these mild reaction conditions enable us to employ bio-inspired templating approaches to further control the mineral structure. Rod-like tobacco mosaic viruses (TMV) were used as biotemplates for mineral deposition, where we profit from the ability of Co(ii) ions to mediate the ordered assembly of the virus nanorods to create complex tubular superstructures of TMV/ basic cobalt carbonate. Calcination of these tubules is then achieved with retention of the gross morphology, and generates a hierarchically-structured solid comprising interconnected Co
O
nanoparticles. Evaluation of these Co
O
materials as electrocatalysts for the oxygen evolution reaction (OER) demonstrates that the activity of Co
O
prepared by calcination of ammonia diffusion-grown precursors in both, the absence or presence of TMV exceeds that of a commercial nanopowder.
The influence of the molecular shape on the charge transport in the columnar mesophases of bi-centred crown ether based mesogens is studied. Even though a bent shaped bridging of two aromatic cores ...promotes the stability and the width of the columnar liquid crystal phase, the quality of the intra-columnar packing and thus the charge carrier mobility are reduced. Keeping instead a linear arrangement of the cores and increasing the molecular flexibility by enlarging the crown is detrimental to the liquid crystal phase stability while the charge carrier mobility is only slightly affected. This leads to the conclusion that the optimal molecular geometry for crown ether based mesogens providing a stable mesophase with good charge transport properties is achieved by using small crown ether bridges connecting two pi -systems as linear as possible. We used discotic mesogens based on 12-crown-4, 15-crown-5, 18-crown-6 and 21-crown-7 moieties linking two triphenylene cores. The inter- and intra-columnar structure is studied by detailed small- and wide-angle X-ray scattering experiments, respectively. To study the electronic properties temperature dependent photoconductivity and mobility measurements in the organic field effect transistor setup are carried out.
PDF
