David L. Officer

University of Wollongong, City of Greater Wollongong, New South Wales, Australia

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Publications (182)702.95 Total impact

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    ABSTRACT: An integrated solar energy conversion and storage system is presented using a dye sensitized electrode in a redox battery structure. A stable discharge voltage is shown with high areal energy storage capacity of 180 μWh/cm2 by choosing iodide/polysulfide as the pair of active materials matched with permeable porous electrodes. The solar rechargeable battery system offers a higher round-trip efficiency and potential cost savings on fabrication compared to individual devices.
    No preview · Article · Feb 2016 · Journal of Materials Chemistry A
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    ABSTRACT: A series of zinc porphyrins substituted at adjacent β-positions with a CN group and para-substituted ethenyl/ethynyl-phenyl group have been studied using electronic absorption spectroscopy, resonance Raman spectroscopy and DFT calculations. The oxidative nucleophilic substitution of hydrogen was utilized for the introduction of a cyano substituent on the porphyrin ring. This modification has a remarkable electronic effect on the ring. The resulting porphyrin cyanoaldehyde was further modified in Wittig condensations to give series of arylalkene- and arylalkyne-substituted derivatives. This substitution pattern caused significant redshifting and broadening of the B band, tuning from 433-446 nm. Additionally the Q/B band intensity ratios show much higher values than observed for the parent porphyrin ZnTPP (0.20 vs. 0.03). Careful analysis of the electronic transitions using DFT and resonance Raman spectroscopy reveal that the substituent does not significantly perturb the electronic structure of the porphyrin core, which is still well described by Gouterman's four-orbital model. However, the substituents do play a role in elongating the conjugation length and this results in the observed spectral changes.
    No preview · Article · Sep 2015 · Chemistry - A European Journal
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    ABSTRACT: A series of Zn(II) porphyrins which have asymmetrically substituted meso groups have been studied with UV-vis, resonance Raman, emission spectroscopies, and density functional theory (DFT) calculations. Dye-sensitized solar cells (DSSCs) of these materials have also been fabricated and their performance parameters measured. DFT calculations show perturbation of frontier molecular orbitals, and redox-active substituents cause greater perturbation than nonredox active substituents. All substituents cause a broadening of the B band, as is common for substituted porphyrins. TD-DFT calculations and resonance Raman spectroscopy suggest the donor and acceptor substituents play a small role in transitions of the B band. The meso donor substituent is electronically isolated and does not significantly perturb the molecular orbitals (MOs), while the meso cyanoacrylic acid TiO2 binding group has a much larger effect on the eg MO in particular. However, in the oxidized porphyrin species, the hole is located on the meso substituent, localizing it away from the semiconductor surface, which should reduce recombination and also improve performance. They show modest efficiency when incorporated into solar cells; however, the pattern of behavior is consistent with localization of charge at the meso unit.
    No preview · Article · Sep 2015 · The Journal of Physical Chemistry C
  • S. Sayyar · E. Murray · S. Gambhir · G. Spinks · G. G. Wallace · D. L. Officer
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    ABSTRACT: Chitosan, a naturally derived polysaccharide, was covalently linked to chemically converted graphene (CCG) and the properties of the resulting composites were investigated. The composites were prepared using a stable dispersion of CCG in aqueous solvent. The CCG sheets are stabilised in solution by a small number of peripheral charged groups that can be used to form amide linkages with the polymer matrix. Apart from processability and swellability, the synthesized composites exhibited improved mechanical properties and conductivity by the addition of graphene. Graphene incorporation also introduced a control over the extent of swelling in the composites. The synthesized graphene/composites are promising materials for a variety of applications, for example as conducting substrates for the electrically stimulated growth of cells.
    No preview · Article · Aug 2015 · JOM: the journal of the Minerals, Metals & Materials Society
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    ABSTRACT: The formation of a poly(2,6-carbazole) derivative during an electrochemical polymerization process is shown. Comparison of 3,5-bis(9-octyl-9H-carbazol-2-yl)pyridine and 3,5-bis(9-octyl-9H-carbazol-3-yl)pyridine by electrochemical and UV-Vis-NIR spectroelectrochemical measurements and DFT (density functional theory) calculation prove the formation of a poly(2,6-carbazole) derivative. Both of the compounds form stable and electroactive conjugated polymers. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    Full-text · Article · Jun 2015 · Macromolecular Rapid Communications
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    ABSTRACT: Graphene, a nanocarbon with exceptional physical and electronic properties, has the potential to be utilized in a myriad of applications and devices. However, this will only be achieved if scalable, processable forms of graphene are developed along with ways to fabricate these forms into material structures and devices. In this review, we provide a comprehensive overview of the chemistries suitable for the development of aqueous and organic solvent graphene dispersions and their use for the preparation of a variety of polymer composites, materials useful for the fabrication of graphene-containing structures and devices. Fabrication of the processable graphene dispersions or composites by printing (inkjet and extrusion) or spinning methods (wet) is reviewed. The preparation and fabrication of liquid crystalline graphene oxide dispersions whose unique rheologies allow the creation of graphene-containing structures by a wide range of industrially scalable fabrication techniques such as spinning (wet and dry), printing (ink-jet and extrusion) and coating (spray and electrospray) is also reviewed.
    Full-text · Article · Jun 2015 · NPG Asia Material
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    ABSTRACT: Graphene-based polymer composites are a very promising class of compounds for tissue engineering scaffolds. However, in general the methods of synthesis are environmentally hazardous and residual toxic materials can affect the biocompatibility significantly. In this paper a simple, scalable, environmentally-friendly, microwave-assisted synthesis is described that results in conducting graphene/polycaprolactone composites that retain the processability and biocompatibility of the pristine polymer without introducing possibly hazardous reducing agents. Composites of polycaprolactone and graphene oxide were synthesised in a single step by the ring-opening polymerisation of ε-caprolactone in the presence of dispersed graphene oxide nanosheets under microwave irradiation. The graphene oxide provides a nucleation centre for the crystallisation of the polymer resulting in polymer-functionalised nanosheets. During polymerisation, the graphene oxide was also reduced to conducting graphene. The resulting graphene/polymer composites were comparable to composites prepared by blending previously highly chemically reduced graphene into polycaprolactone, and they could be easily dispersed in a number of solvents or melt extruded for further processing. These three-dimensional melt extruded materials showed excellent biocompatibility and are promising substrates for tissue engineering scaffolds.
    Full-text · Article · May 2015 · RSC Advances
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    ABSTRACT: In this study, binder-free TiO2 colloidal pastes have been prepared using a variety of heterocyclic bases with diverse characteristics to produce robust photoanodes for dye-sensitized solar cells (DSSC) from a single cast film thickness of 5 micron. The influence of the base on the electrode structure and film morphology, including its electron donor characteristics are investigated after low temperature thermal treatment and high temperature sintering. The results show that quinoline in the TiO2 paste is retained within the electrode structure in comparison to piperidine and pyridine after a short thermal treatment of 150 °C for 15 minutes. The presence of organic additives with π-conjugation in the photoanode enhances both electron injection efficiency and charge carrier lifetime resulting in higher Jsc and Voc. This formulation in combination with low temperature processing yields an energy conversion efficiency of over 5% in DSSC devices. In devices where high temperature sintering is permitted, the performance of TiO2 electrodes converges towards an efficiency of over 6%, irrespective of the organic additive within the paste. This formulation offers a high degree of versatility in casting electrodes onto polymer, glass or metal foil substrates from a single source of TiO2 paste, for the many variants of low-cost solar cells. This journal is
    Full-text · Article · Mar 2015 · RSC Advances
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    ABSTRACT: The photo-conversion efficiency and stability of back-illuminated dye sensitised solar cells with titanium foil based photoanodes are enhanced by a simple nitric acid treatment through which the foil is passivated. This treatment changes the morphology of the titanium foil and increases its electrochemical double layer capacitance.
    Preview · Article · Jan 2015
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    ABSTRACT: Composites of graphene in a chitosan-lactic acid matrix were prepared to create conductive hydrogels that are processable, exhibit tunable swelling properties and show excellent biocompatibility. The addition of graphene to the polymer matrix also resulted in significant improvements to the mechanical strength of the hydrogels, with the addition of just 3 wt % graphene resulting in tensile strengths increasing by over 200 %. The composites could be easily processed into three-dimensional scaffolds with finely controlled dimensions using additive fabrication techniques and fibroblast cells demonstrate good adhesion and growth on their surfaces. These chitosan-graphene composites show great promise for use as conducting substrates for the growth of electro-responsive cells in tissue engineering.
    Full-text · Article · Nov 2014
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    ABSTRACT: A study was conducted to demonstrate the first example of photo-driven chemopropulsion in which photo irradiation in close proximity to the micro-vehicle, a lipophilic droplet initiated a rapid pH change in the aqueous channel fluid in which the vehicle sat, as a result of the photo-induced dissociation of a water soluble organic acid. This led to a cascade of events involving protonation of the 2-hexyldecanoate ion in the fuel, rapid solubilization in the channel fluid of the released lipophilic CI-H+ , and an immediate change in surface tension of the fluid surrounding the droplet resulting in fast movement of the droplet away from the light source. The studied lipophilic droplet, typically contained a 1:1 (v:v) mixture of 2-hexyldecanoic acid (HDA) and 0.02 M chromoionophore I (CI) in dichloromethane (DCM), giving a large molar excess of HDA within the droplet.
    Full-text · Article · Nov 2014 · Advanced Materials
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    ABSTRACT: A novel donor-acceptor poly(terthiophene) derivative bearing a C-60 pendant was electropolymerizated from N-methy1-2-(2-[4,4 ''-didecyloxy-2,2 ';5 ',2 '']terthiophen-3 '-yI-ethenyl)fullero[3,4]pyrrolidine (TTh-C-60) solution. The electroreduction of TTh-C-60 and poly(TTh-C-60) showed the presence of complex peaks related to fulleropyrrolidine reduction. The dual nature of these redox couples may be related to increasing Coulombic repulsion or coupling between C-60 substituents. Electrochemical, X-Ray photoelectron spectroscopy (XPS), Ultra-Violet photoelectron (UPS) and UV-Vis spectroscopy also confirm the nature of poly(TTh-C-60). Electrochemical band gap of poly(TTh-C-60) is 0.63 +/- 0.20 eV in TBAP electrolyte and propylene carbonate (PC) solution. Furthermore, we obtained the value of optical energy band gap (E-opt = 0.59 +/- 0.03 eV), the transport energy band gap (E-g (trans) = 1.17 +/- 0.20 eV) and the exciton binding energy (E-b = 0.58 +/- 0.20 eV) for poly(TTh-C-60). The ionization energy values (IE) were determined using UPS spectroscopy (IE = 4.92 +/- 0.10 eV) and electrochemical investigations of the poly(TTh-C-60) polarized in TBAP/DCM (IE = 5.01 +/- 0.10 eV) and TBAP/PC solution (IE = 4.95 +/- 0.10 eV) demonstrating good coincidence of the value. The electrochemical method revealed, that the location of the Fermi level relative to the valence and conduction bands indicates p-type character of semiconducting poly(TTh-C-60). On the other hand photoemission spectroscopy manifests n-type behavior of examined sample. In turn, the UV-Vis result showed that the charge transfer (CT) between poly(TTh) and C-60 unit can suggest, that these chromophores are not entirely independent.
    Full-text · Article · Sep 2014 · Electrochimica Acta
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    ABSTRACT: A straightforward, systematic approach to the reduction of graphene oxide (GO) that affords dispersions of chemically converted graphene (CCG) in anhydrous organic solvents with decreasing basal plane defects is reported. The extent of reduction can be controlled and optimized, resulting in highly reduced dispersible chemically converted graphene (hrCCG) having an O1S/C1S ratio of 0.06, which approaches that of graphite. The hrCCG dispersion in anhydrous dimethylformamide (DMF) was stable for several months at a concentration of 0.5–0.6 mg mL−1. This process was found to be easily scalable and could be exploited for the large scale production of hrCCG in DMF and its dispersion in other anhydrous organic solvents. This study demonstrates that the stability of the graphene dispersion is critically dependent on the exfoliation process. The improved elimination of basal defects and the restoration of aromaticity, while maintaining dispersion stability on a large scale in an anhydrous organic solvent, greatly increase the potential of this material for a wide variety of applications.
    No preview · Article · Sep 2014 · Carbon
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    ABSTRACT: Different nanocarbons, that is, single-wall carbon nanotubes, graphene, single-wall carbon nanohorns (SWCNHs), and their respective oxidized analogs have been used to fabricate novel doped TiO2 electrodes for DSSCs. Our results indicate that all of the nanocarbons significantly enhance the device characteristics when compared to standard TiO2 electrodes. Overall, our most outstanding finding is that SWCNH derivatives are also a plausible material for developing highly-efficient DSSCs.
    Full-text · Article · Dec 2013 · Advanced Materials
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    ABSTRACT: Dye sensitized solar cells (DSSCs) employing a dimer porphyrin, which was synthesised with two porphyrin units connected without conjugation, have shown that both porphyrin components can contribute to photocurrent generation, that is, more than 50 % internal quantum efficiency. In addition, the open-circuit voltage (Voc) of the DSSCs was higher than that of DSSCs using monomer porphyrins. In this paper, we first optimized cell structure and fabrication conditions. We obtained more than 80% incident photon to current conversion efficiency from the dimer porphyrin sensitized DSSCs and higher Voc and energy conversion efficiency than monomer porphyrin sensitized solar cells. To examine the origin of the higher Voc, we measured electron lifetime in the DSSCs with various conditions, and found that the dimer system increased the electron lifetime by improving the steric blocking effect of the dye layer, whilst the lack of a conjugated linker prevents an increase in the attractive force between conjugated sensitizers and the acceptor species in the electrolyte. The results support a hypothesis; dispersion force is one of the factors influencing the electron lifetime in DSSCs.
    Full-text · Article · Nov 2013 · ACS Applied Materials & Interfaces
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    ABSTRACT: In this work fibres and complex three-dimensional scaffolds of a covalently linked graphene-polycaprolactone composite were successfully extruded and printed using a melt extrusion printing system. Fibres with varying diameters and morphologies, as well as complex scaffolds were fabricated using an additive fabrication approach and were characterized. It was found that the addition of graphene improves the mechanical properties of the fibres by over 50% and in vitro cytotoxicity tests showed good biocompatibility indicating a promising material for tissue engineering applications.
    No preview · Article · Nov 2013 · Materials Science Forum
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    ABSTRACT: A series of 2,5-bis(2-thien-2-ylethenyl) thiophene-based oligomers with a para-R-arylethenyl substituent have been subjected to electrochemical (cyclic voltammetry and electronic absorption spectroscopy) and density functional theory characterization. The primary aim of this investigation is to characterize the behavior of these oligomers in the oxidized state. Oligomers without methyl ‘end-caps’ undergo facile σ-dimerization; however there is no evidence for the formation of higher oligomers. The oxidized σ-dimers exist in both cationic and dicationic form. Oligomers with methyl ‘end-caps’ do not show any evidence of σ-dimerization. The inductive capacity of the para-R substituent has a significant bearing on the electronic properties of the oligomer, in particular, oligomers with more electron-withdrawing substituents have charge transfer character associated with the dominant electronic excitations.
    No preview · Article · Sep 2013 · Journal of Molecular Structure
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    ABSTRACT: Four novel nanographene/porphyrin hybrids were prepd., characterized, and probed in solar energy conversion schemes. Exfoliation of graphite by means of immobilizing four different porphyrins onto the basal plane of graphene is accompanied by distinct electronic interactions in both the ground and the excited states. In the ground state, a strong loss in oscillator strength goes hand-in-hand with a notable broadening of the porphyrin transitions and, as such, attests to the shift of electron d. from the electron donating porphyrins to nanographene. In the excited state, a nearly quant. quenching of the porphyrin fluorescence is indicative of full charge transfer. The latter is corroborated by femtosecond transient absorption measurements, which reveal the generation of the one-electron oxidized radical cation of the porphyrins with absorption maxima at 490 and 625 nm in the visible region and conduction band electrons in nanographene with features at 890 and 1025 nm in the near IR region. We have demonstrated the applicability of the new nanographene/porphyrin hybrids in, for example, solar cells. In this regard, the presence of flakes is crucial in terms of influencing the injection processes, preventing aggregation, and reducing recombination losses, which are commonly encountered in porphyrin-based DSSCs.
    No preview · Article · Aug 2013 · Chemical Science
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    ABSTRACT: The origin of simultaneous improvements in the short-circuit current density (Jsc) and open-circuit voltage (Voc) of porphyrin dye-sensitized TiO2 solar cells following white light illumination was studied by systematic variation of several different device parameters. Reduction of the dye surface loading resulted in greater relative performance enhancements, suggesting open space at the TiO2 surface expedites the process. Variation of the electrolyte composition and subsequent analysis of the conduction band potential shifts suggested that a light-induced replacement of surface-adsorbed lithium (Li+) ions with dimethylpropylimidazolium (DMPIm+) ions was responsible for an increased electron lifetime by decreasing the recombination with the redox mediator. Variation of the solvent viscosity was found to affect the illumination time required to generate increased performance, while similar performance enhancements were not replicated by application of negative bias under dark conditions, indicating the light exposure effect was initiated by formation of dye cation molecules following photoexcitation. The substituents and linker group on the porphyrin chromophore were both varied, with light exposure producing increased electron lifetime and Voc for all dyes; however, increased Jsc values were only measured for dyes containing binding moieties with multiple carboxylic acids. It was proposed that the initial injection limitation and/or fast recombination process in these dyes arises from the presence of lithium at the surface, and the improved injection and/or retardation of fast recombination after light exposure is caused by the Li+ removal by cation exchange under illumination.
    Full-text · Dataset · Jul 2013
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    ABSTRACT: Polythiophenes are attractive candidate polymers for use in synthetic cell scaffolds as they are amenable to modification of functional groups as a means by which to increase biocompatibility. In the current study we analysed the physical properties and response of primary myoblasts to three thiophene poly-mers synthesized from either a basic bithiophene monomer or from one of two different thiophene monomers with alkoxy functional groups. In addition, the effect of the dopants pTS − and ClO 4 − was investigated. In general, it was found that pTS − doped polymers were significantly smoother and tended to be more hydrophilic than their ClO 4 − doped counterparts, demonstrating that the choice of dopant significantly affects the polythiophene physical properties. These properties had a significant effect on the response of primary myoblasts to the polymer surfaces; LDH activity measured from cells harvested at 24 and 48 h post-seeding revealed significant differences between numbers of cells attaching to the different thiophene polymers, whilst all of the polymers equally supported cell doubling over the 48 h period. Differences in morphology were also observed, with reduced cell spreading observed on polymers with alkoxy groups. In addition, significant differences were seen in the polymers' ability to support myo-blast fusion. In general pTS − doped polymers were better able to support fusion than their ClO 4 − doped counterparts. These studies demonstrate that modification of thiophene polymers can be used to promote specific cellular response (e.g. proliferation over differentiation) without the use of biological agents.
    Full-text · Dataset · Jul 2013

Publication Stats

5k Citations
702.95 Total Impact Points

Institutions

  • 2006-2015
    • University of Wollongong
      • • Intelligent Polymer Research Institute
      • • ARC Centre of Excellence for Electromaterials Science
      City of Greater Wollongong, New South Wales, Australia
  • 2013
    • Rowan University
      Camden, New Jersey, United States
  • 1994-2012
    • Massey University
      • Institute of Fundamental Sciences
      Palmerston North City, Manawatu-Wanganui, New Zealand