The Department of Natural Sciences is located on Thornton Science Park, a modern expressly-designed site that profits from a recently-completed multi-million pound renovation that has created a state-of-the-art teaching and research facility. The site was home to Shell UK’s exploration and research centre since the 1940s, and its takeover by the University heralded the opportunity to apply its legacy to the continuation of world-class innovation and research in the North West.

Recent Submissions

  • Insights into HOx and ROx chemistry in the boreal forest via measurement of peroxyacetic acid, peroxyacetic nitric anhydride (PAN) and hydrogen peroxide

    Crowley, John; Pouvesle, Nicolas; Phillips, Gavin; Axinte, Raoul; Fischer, Horst; Petaja, Tuukka; Noelscher, Anke; Williams, Jonathan; Hens, Korbinian; Harder, Hartwig; Martinez-Harder, Monica; Novelli, Anna; Kubistin, Dagmar; Bohn, Birger; Lelieveld, Jos; Max Planck Institute for Chemistry; Forschungzentrum Juelich; University of Chester (European Geosciences Union, 2018-09-21)
    Unlike many oxidised atmospheric trace gases, which have numerous production pathways, peroxyacetic acid (PAA) and PAN are formed almost exclusively in gas-phase reactions involving the hydroperoxy radical (HO2), the acetyl peroxy radical (CH3C(O)O2) and NO2 and are not believed to be directly emitted in significant amounts by vegetation. As the self-reaction of HO2 is the main photochemical route to hydrogen peroxide (H2O2), simultaneous observation of PAA, PAN and H2O2 can provide insight into the HO2 budget. We present an analysis of observations taken during a summertime campaign in a boreal forest that, in addition to natural conditions, was temporarily impacted by two biomass-burning plumes. The observations were analysed using an expression based on a steady-state assumption using relative PAA-to-PAN mixing ratios to derive HO2 concentrations. The steady-state approach generated HO2 concentrations that were generally in reasonable agreement with measurements but sometimes overestimated those observed by factors of 2 or more. We also used a chemically simple, constrained box model to analyse the formation and reaction of radicals that define the observed mixing ratios of PAA and H2O2. After nudging the simulation towards observations by adding extra, photochemical sources of HO2 and CH3C(O)O2, the box model replicated the observations of PAA, H2O2, ROOH and OH throughout the campaign, including the biomass-burning-influenced episodes during which significantly higher levels of many oxidized trace gases were observed. A dominant fraction of CH3O2 radical generation was found to arise via reactions of the CH3C(O)O2 radical. The model indicates that organic peroxy radicals were present at night in high concentrations that sometimes exceeded those predicted for daytime, and initially divergent measured and modelled HO2 concentrations and daily concentration profiles are reconciled when organic peroxy radicals are detected (as HO2) at an efficiency of 35%. Organic peroxy radicals are found to play an important role in the recycling of OH radicals subsequent to their loss via reactions with volatile organic compounds.
  • Fibre laser treatment of martensitic NiTi alloys for load-bearing implant applications: Effects of surface chemistry on inhibiting Staphylococcus aureus biofilm formation

    Smith, Graham C.; Chan, Chi-Wai; Carson, Louise; Queens University Belfast; University of Chester (Elsevier, 2018-06-15)
    Biofilm infection is one of the main reasons for implant failure. It is extremely difficult to cure due to its high resistance to antibiotic treatments, and can result in substantial healthcare costs. In this study, the important shape memory NiTi alloy, in its martensitic state, was laser-treated using our newly-developed surface modification technique, aiming to tackle the biofilm infection problem. Martensitic NiTi was chosen for investigation because of its potential advantages in terms of (i) lower elastic modulus and (ii) higher damping capacity over its austenitic counterpart, giving rise to a lower risk of stress shielding and maximum stress between bones and load-bearing implants. The surfaces after laser treatment were systemically analysed using a series of surface measurement (i.e. surface roughness and water contact angle) and material characterisation (i.e. SEM-EDX, XRD and XPS) techniques. The antibacterial performance of the laser-treated surfaces was evaluated using the Staphylococcus aureus (or S. aureus) cells in-vitro cultured at 37 oC for 24h. Fluorescence microscopy accompanied by Live/Dead staining was employed to analyse the cell culture results. The surfaces in their as-received states and after polishing were also tested and compared with the laser-treated surfaces in order to gain a deeper insight in how different surface conditions would influence biofilm formation. Our results indicate that the surfaces after laser treatment can mitigate bacterial attachment and biofilm formation effectively. The antibacterial performance was mainly attributable to the laser-formed oxides which brought desirable changes to the surface chemistry of NiTi. The laser-induced changes in surface roughness and topography, on a micrometre scale, only played a minor role in influencing bacterial attachment. The findings of this study demonstrated for the first time that martensitic NiTi with laser treatment could be a promising choice for the next-generation implants given its superior antimicrobial resistance and favourable mechanical properties for loading bearing applications.
  • Oxidation processes in the eastern Mediterranean atmosphere: evidence from the modelling of HOx measurements over Cyprus

    Mallik, Chinmay; Tomsche, Laura; Bourtsoukidis, Efstratios; Crowley, John; Derstroff, Bettina; Fischer, Horst; Haferman, Sascha; Hueser, Imke; Javed, Umar; Kessel, Stephan; Lelieveld, Jos; Martinez, Monica; Meusel, Hannah; Novelli, Anna; Phillips, Gavin; Pozzer, Andrea; Reiffs, Andreas; Sander, Rolf; Taraborrelli, Domenico; Sauvage, Carina; Schuladen, Jan; Su, Hang; Williams, Jonathan; Harder, Hartwig; Max Planck Institute for Chemistry; Cyprus Institute; Forschungzentrum Juelich; University of Chester (Copernicus Publications, 2018-07-31)
    The Mediterranean is a climatically sensitive region located at the crossroads of air masses from three continents: Europe, Africa, and Asia. The chemical processing of air masses over this region has implications not only for the air quality but also for the long-range transport of air pollution. To obtain a comprehensive understanding of oxidation processes over the Mediterranean, atmospheric concentrations of the hydroxyl radical (OH) and the hydroperoxyl radical (HO2) were measured during an intensive field campaign (CYprus PHotochemistry EXperiment, CYPHEX-2014) in the northwest of Cyprus in the summer of 2014. Very low local anthropogenic and biogenic emissions around the measurement location provided a vantage point to study the contrasts in atmospheric oxidation pathways under highly processed marine air masses and those influenced by relatively fresh emissions from mainland Europe. The CYPHEX measurements were used to evaluate OH and HO2 simulations using a photochemical box model (CAABA/MECCA) constrained with CYPHEX observations of O3, CO, NOx, hydrocarbons, peroxides, and other major HOx (OH+HO2) sources and sinks in a low-NOx environment (<100pptv of NO). The model simulations for OH agreed to within 10% with in situ OH observations. Model simulations for HO2 agreed to within 17% of the in situ observations. However, the model strongly under-predicted HO2 at high terpene concentrations, this under-prediction reaching up to 38% at the highest terpene levels. Different schemes to improve the agreement between observed and modelled HO2, including changing the rate coefficients for the reactions of terpene-generated peroxy radicals (RO2) with NO and HO2 as well as the autoxidation of terpene-generated RO2 species, are explored in this work. The main source of OH in Cyprus was its primary production from O3 photolysis during the day and HONO photolysis during early morning. Recycling contributed about one-third of the total OH production, and the maximum recycling efficiency was about 0.7. CO, which was the largest OH sink, was also the largest HO2 source. The lowest HOx production and losses occurred when the air masses had higher residence time over the oceans.
  • Effect of Temperature and Catholyte Concentration on the Performance of a Chemically Regenerative Fuel Cell POM-based catholytes for platinum-free polymer electrolyte fuel cells

    Ward, David B.; Davies, Trevor J.; University of Chester (JOHNSON MATTHEY, plc, 2018-04-01)
    Chemically regenerative redox cathode (CRRC) polymer electrolyte fuel cells (PEFCs) are attracting more interest as a platinum-free PEFC technology. These fuel cells utilise a liquid catalyst or catholyte, to perform the indirect reduction of oxygen, eliminating the major degradation mechanisms that plague PEFC durability. A key component of a CRRC PEFC system is the catholyte. This article reports a thorough study of the effect of catholyte concentration and temperature on CRRC PEFC system performance for H7PV4Mo8O40 and Na4H3PV4Mo8O40, two promising polyoxometalate (POM)-based catholytes. The results suggest 80ºC and a catholyte concentration of 0.3 M provide the optimum performance for both H7PV4Mo8O40 and Na4H3PV4Mo8O40 (for ambient pressure operation).
  • Gastrointestinal Stents: Materials and Designs

    Black, Steven J.; Edwards, Derek W.; Smith, Graham C.; Laasch, Hans-Ulrich; MDECON Ltd.; The Christie NHS Foundation Trust; University of Chester (Thieme Publishing, 2018-05-09)
    Over the last 25 years stents have developed into an established way of restoring luminal patency throughout the gastrointestinal tract. Materials used as well as the construction of these devices have become more and more sophisticated in order to comply better with the complex environment they are inserted. The requirements vary greatly from organ to organ and stent behavior differs significantly between stent constructions. However this is not necessarily understood by many operators, as the choice of devices is now vast and in many cases decisions are made on availability and cost. An increasing challenge in malignant conditions is the improving survival of incurable patients, which now exceeds the traditional life expectancy of a stent by a factor of 2 to 3. Consequently more patients experience failure of their stent and require repeat interventions. This has a poor impact on patients’ quality of life and potentially on their survival. Re-intervention is often more difficult, carries the risk of additional complications and presents an additional economic burden to the health systems. This article illustrates current stent designs, their different behavior and their limitations.
  • Bioinspired bactericidal surfaces with polymer nanocone arrays

    Hazell, Gavin; Fisher, Leanne E.; Murray, W. Andrew; Nobbs, Angela H.; Su, Bo; University of Chester; University of Bristol (Elsevier, 2018-05-28)
    Infections resulting from bacterial biofilm formation on the surface of medical devices are challenging to treat and can cause significant patient morbidity. Recently, it has become apparent that regulation of surface nanotopography can render surfaces bactericidal. In this study, poly(ethylene terephthalate) nanocone arrays are generated through a polystyrene nanosphere-mask colloidal lithographic process. It is shown that modification of the mask diameter leads to a direct modification of centre-to-centre spacing between nanocones. By altering the oxygen plasma etching time it is possible to modify the height, tip width and base diameter of the individual nanocone features. The bactericidal activity of the nanocone arrays was investigated against Escherichia coli and Klebsiella pneumoniae. It is shown that surfaces with the most densely populated nanocone arrays (center-to-center spacing of 200 nm), higher aspect ratios (>3) and tip widths <20 nm kill the highest percentage of bacteria (∼30%).
  • Studies of black silicon and black diamond as materials for antibacterial surfaces

    Hazell, Gavin; May, P. W.; Taylor, P.; Nobbs, A. H. N.; Su, B.; University of Bristol; Oxford Instruments Plasma Technology (Royal Society of Chemistry, 2018-03-27)
    ‘Black silicon’ (bSi) samples with surfaces covered in nanoneedles of varying length, areal density and sharpness, have been fabricated using a plasma etching process. These nanostructures were then coated with a conformal uniform layer of diamond using hot filament chemical vapour deposition to produce ‘black diamond’ (bD) surfaces. The effectiveness of these bSi and bD surfaces in killing Gram-negative (E. coli) and Gram-positive (S. gordonii) bacteria was investigated by culturing the bacteria on the surfaces for a set time and then measuring the live-to-dead ratio. All the nanostructured surfaces killed E. coli at a significantly higher rate than the respective flat Si or diamond control samples. The length of the needles was found to be less important than their separation, i.e. areal density. This is consistent with a model for mechanical bacteria death based on the stretching and disruption of the cell membrane, enhanced by the cells motility on the surfaces. In contrast, S. gordonii were unaffected by the nanostructured surfaces, possibly due to their smaller size, thicker cell membrane and/or their lack of motility.
  • Mass-producible 2D-MoSe2 bulk modified screen-printed electrodes provide significant electrocatalytic performances towards the hydrogen evolution reaction

    Rowley-Neale, Samuel J.; Foster, Christopher W.; Smith, Graham C.; Brownson, Dale A. C.; Banks, Craig E.; Manchester Metropolitan University; University of Chester (Royal Society of Chemistry, 2017-01-25)
    We demonstrate a facile, low cost and reproducible methodology for the production of electrocatalytic 2D-MoSe2 incorporated/bulk modified screen-printed electrodes (MoSe2-SPEs). The MoSe2-SPEs outperform traditional carbon based electrodes, in terms of their electrochemical activity, towards the Hydrogen Evolution Reaction (HER). The electrocatalytic behaviour towards the HER of the 2D-MoSe2 within the fabricated electrodes is found to be mass dependent, with an optimal mass ratio of 10% 2D-MoSe2 to 90% carbon ink. MoSe2-SPEs with this optimised ratio exhibit a HER onset, Tafel value and a turn over frequency of ca. −460 mV (vs. SCE), 47 mV dec−1 and 1.48 respectively. These values far exceed the HER performance of graphite (unmodified) SPEs, that exhibit a greater electronegative HER onset and Tafel value of ca. −880 mV and 120 mV dec−1 respectively. It is clear that impregnation of 2D-MoSe2 into the MoSe2-SPEs bulk ink/structure significantly increases the performance of SPEs with respect to their electrocatalytic activity towards the HER. When compared to SPEs that have been modified via a drop-casting technique, the fabricated MoSe2-SPEs exhibit excellent cycling stability. After 1000 repeat scans, a 10% modified MoSe2-SPE displayed no change in its HER onset potential of −450 mV (vs. SCE) and an increase of 31.6% in achievable current density. Conversely, a SPE modified via drop-casting with 400 mg cm−2 of 2D-MoSe2 maintained its HER onset potential of −480 mV (vs. SCE), however exhibited a 27.4% decrease in its achievable current density after 1000 scans. In addition to the clear performance benefits, the production of MoSe2-SPEs mitigates the need to post hoc modify an electrode via the drop-casting technique. We anticipate that this facile production method will serve as a powerful tool for future studies seeking to utilise 2D materials in order to mass-produce SPEs/surfaces with unique electrochemical properties whilst providing substantial stability improvements over the traditionally utilised technique of drop-casting.
  • Mass-Producible 2D-MoS2‑Impregnated Screen-Printed Electrodes

    Rowley-Neale, Samuel J.; Smith, Graham C.; Banks, Craig E.; Manchester Metropolitan University; University of Chester; (American Chemical Society, 2017-06-02)
    Two-dimensional molybdenum disulfide (2D-MoS2) screen-printed electrodes (2D-MoS2-SPEs) have been designed, fabricated, and evaluated toward the electrochemical oxygen reduction reaction (ORR) within acidic aqueous media. A screen-printable ink has been developed that allows for the tailoring of the 2D-MoS2 content/mass used in the fabrication of the 2D-MoS2-SPEs, which critically affects the observed ORR performance. In comparison to the graphite SPEs (G-SPEs), the 2D-MoS2-SPEs are shown to exhibit an electrocatalytic behavior toward the ORR which is found, critically, to be reliant upon the percentage mass incorporation of 2D-MoS2 in the 2D-MoS2-SPEs; a greater percentage mass of 2D-MoS2 incorporated into the 2D-MoS2-SPEs results in a significantly less electronegative ORR onset potential and a greater signal output (current density). Using optimally fabricated 2D-MoS2-SPEs, an ORR onset and a peak current of approximately +0.16 V [vs saturated calomel electrode (SCE)] and −1.62 mA cm–2, respectively, are observed, which exceeds the −0.53 V (vs SCE) and −635 μA cm–2 performance of unmodified G-SPEs, indicating an electrocatalytic response toward the ORR utilizing the 2D-MoS2-SPEs. An investigation of the underlying electrochemical reaction mechanism of the ORR within acidic aqueous solutions reveals that the reaction proceeds via a direct four-electron process for all of the 2D-MoS2-SPE variants studied herein, where oxygen is electrochemically favorably reduced to water. The fabricated 2D-MoS2-SPEs are found to exhibit no degradation in the observed achievable current over the course of 1000 repeat scans. The production of such inks and the resultant mass-producible 2D-MoS2-SPEs mitigates the need to modify post hoc an electrode via the drop-casting technique that has been previously shown to result in a loss of achievable current over the course of 1000 repeat scans. The 2D-MoS2-SPEs designed, fabricated, and tested herein could have commercial viability as electrocatalytic fuel cell electrodes because of being economical as a result of their scales of economy and inherent tailorability. The technique utilized herein to produce the 2D-MoS2-SPEs could be adapted for the incorporation of different 2D nanomaterials, resulting in SPEs with the inherent advantages identified above.
  • A Silanol-Functionalized Polyoxometalate with Excellent Electron Transfer Mediating Behavior to ZnO and TiO 2 Cathode Interlayers for Highly Efficient and Extremely Stable Polymer Solar Cells

    Tountas, Marinos; Topal, Yasemin; Verykios, Apostolos; Soultati, Anastasia; Kaltzoglou, Andreas; Papadopoulos, Theodoros A.; Auras, Florian; Seintis, Kostas; Fakis, Mihalis; Palilis, Leonidas C.; Tsikritzis, Dimitris; Kennou, Stella; Fakharuddin, Azhar; Schmidt-Mende, Lukas; Gardelis, Spyros; Kus, Mahmut; Falaras, Polycarpos; Davazoglou, Dimitris; Argitis, Panagiotis; Vasilopoulou, Maria; National Centre for Scientific Research “Demokritos"; University of Athens; Pamukkale University Cal Vocational High School; University of Patras; University of Chester; University of Cambridge; University of Konstanz; Selcuk University (Royal Society of Chemistry, 2017-12-21)
    Combining high efficiency and long lifetime under ambient conditions still poses a major challenge towards commercialization of polymer solar cells. Here we report a facile strategy that can simultaneously enhance the efficiency and temporal stability of inverted photovoltaic architectures. Inclusion of a silanol-functionalized organic–inorganic hybrid polyoxometalate derived from a PW9O34 lacunary phosphotungstate anion, namely (nBu4N)3[PW9O34(tBuSiOH)3], significantly increases the effectiveness of the electron collecting interface, which consists of a metal oxide such as titanium dioxide or zinc oxide, and leads to a high efficiency of 6.51% for single-junction structures based on poly(3-hexylthiophene):indene-C60 bisadduct (P3HT:IC60BA) blends. The above favourable outcome stems from a large decrease in the work function, an effective surface passivation and a decrease in the surface energy of metal oxides which synergistically result in the outstanding electron transfer mediating capability of the functionalized polyoxometalate. In addition, the insertion of a silanol-functionalized polyoxometalate layer significantly enhances the ambient stability of unencapsulated devices which retain nearly 90% of their original efficiencies (T90) after 1000 hours.
  • Mixed dimension silver nanowires for solution processed, flexible, transparent and conducting electrodes with improved optical and physical properties

    Kumar, D.; Ghosh, S.; Stoichkov, V.; Smith, Graham C.; Kettle, Jeff; University of Chester; Bangor University (IOP Publishing, 2017-03-20)
    In this work, we present an alternative method for the spray coating of silver nanowires contact electrodes by employing a mixture of short and long nanowires. Mixed silver nanowires are found to give improve optical properties with 2-5% higher transparency for the same sheet resistance of 25 Ωsq-1, when compared to silver nanowires prepared with a single geometry nanowire. The figure of merit (FoM) for the 25 Ωsq-1 sheet resistance electrode was found to be highest for the mixed composition AgNWs-M1 based electrodes. Furthermore, the average root mean square surface roughness (Rq) parameter by WLI measurement are found to be lower for the mixed composition silver nanowires electrodes (Rq= 3-4 nm) when compare to the individual parent fixed dimension type silver nanowire electrodes (Rq = 6-8 nm).
  • Using sub-micron silver-nanoparticle based films to counter biofilm formation by Gram-negative bacteria

    Gillett, Alice R.; Baxter, S. N.; Hodgson, Simon D.; Smith, Graham C.; Thomas, P. J.; University of Chester; Bangor University (Elsevier, 2018-02-16)
    Composite films comprised of silver nanoparticles (AgNPs) grown using a low-cost straightforward chemical bath based method have been deposited on glass microscope slides to investigate their potential as a sacrificial antibacterial coating. The as-deposited films have been characterised using scanning electron microscopy (SEM) and optical profilometry. These suggested that the films were relatively uniform in coverage. Chemical composition of the AgNP films has been studied by using x-ray photoelectron spectroscopy (XPS). The XPS analysis indicated that the Ag was in a metallic form able to sustain plasmon behaviour, and that low levels of residual nanoparticle precursors were present. Particle size was characterised using transmission electron microscopy (TEM) which showed an average particle size of 10.6 nm. The effectiveness of the films as an antibacterial coating was tested against Escherichia coli. The AgNP film was determined to be effective in the killing of E.coli cells over a 24 hour period when compared to equivalent samples that contained no silver. Of particular note was that only minimal bacterial growth was detected over the first 12 hours of testing, up to 78.6 times less than the control samples, suggesting the film is very efficient at slowing initial biofilm formation. The use of AgNP based films that have been synthesised using a novel low-cost, low-temperature and highly upscalable method is demonstrated as a promising solution for the deployment of silver as an effective sacrificial antimicrobial coating to counter the formation of potentially hazardous Gram negative biofilms.
  • A preliminary study to enhance the tribological performance of CoCrMo alloy by laser remelting for articular joint implant applications

    Chan, Chi-Wai; Smith, Graham C.; Lee, Seunghwan; Queens University Belfast; University of Chester; Technical University Denmark (MDPI, 2018-03-02)
    CoCrMo alloy has long been used as a pairing femoral head material for articular joint implant applications because of its biocompatibility and reliable tribological performance. However, friction and wear issues are still present for CoCrMo (metal)/CoCrMo (metal) or CoCrMo (metal)/ultrahigh molecular weight polyethylene (UHMWPE) (plastic) pairs in clinical observations. The particulate wear debris generated from the worn surfaces of CoCrMo or UHMWPE can pose a severe threat to human tissues, eventually resulting in the failure of implants and the need for revision surgeries. As a result, a further improvement in tribological properties of this alloy is still needed, and it is of great interest to both the implant manufacturers and clinical surgeons. In this study, the surface of CoCrMo alloy was laser-treated by a fibre laser system in an open-air condition (i.e., no gas chamber required). The CoCrMo surfaces before and after laser remelting were analysed and characterised by a range of mechanical tests (i.e., surface roughness measurement and Vickers micro-hardness test) and microstructural analysis (i.e., XRD phase detection). The tribological properties were assessed by pin-on-disk tribometry and dynamic light scattering (DLS). Our results indicate that the laser-treated surfaces demonstrated a friction-reducing effect for all the tribopairs (i.e., CoCrMo against CoCrMo and CoCrMo against UHHMWPE) and enhanced wear resistance for the CoCrMo/CoCrMo pair. Such beneficial effects are chiefly attributable to the presence of the laser-formed hard coating on the surface. Laser remelting possesses several competitive advantages of being a clean, non-contact, fast, highly accurate and automated process compared to other surface coating methods. The promising results of this study point to the possibility that laser remelting can be a practical and effective surface modification technique to further improve the tribological performance of CoCr-based orthopaedic implants.
  • Graphene oxide electrochemistry: the electrochemistry of graphene oxide modified electrodes reveals coverage dependent beneficial electrocatalysis

    Brownson, Dale A. C.; Smith, Graham C.; Banks, Craig E.; University of Chester; Manchester Metropolitan University (The Royal Society, 2017-11-15)
    The modification of electrode surfaces is widely implemented in order to try and improve electron transfer kinetics and surface interactions, most recently using graphene related materials. Currently, the use of ‘as is’ graphene oxide (GO) has been largely overlooked, with the vast majority of researchers choosing to reduce GO to graphene or use it as part of a composite electrode. In this paper, ‘as is’ GO is explored and electrochemically characterized using a range of electrochemical redox probes, namely potassium ferrocyanide(II), N,N,N ,N -tetramethyl-p-phenylenediamine (TMPD), dopamine hydrochloride and epinephrine. Furthermore, the electroanalytical efficacy of GO is explored towards the sensing of dopamine hydrochloride and epinephrine via cyclic voltammetry. The electrochemical response of GO is benchmarked against pristine graphene and edge plane-/basal plane pyrolytic graphite (EPPG and BPPG respectively) alternatives, where the GO shows an enhanced electrochemical/electroanalytical response. When using GO as an electrode material, the electrochemical response of the analytes studied herein deviate from that expected and exhibit altered electrochemical responses. The oxygenated species encompassing GO strongly influence and dominate the observed voltammetry, which is crucially coverage dependent. GO electrocatalysis is observed, which is attributed to the presence of beneficial oxygenated species dictating the response in specific cases, demonstrating potential for advantageous electroanalysis to be realized. Note however, that crucial coverage based regions are observed at GO modified electrodes, owing to the synergy of edge plane sites and oxygenated species. We report the true beneficial electrochemistry of GO, which has enormous potential to be beneficially used in various electrochemical applications ‘as is’ rather than be simply used as a precursor to making graphene and is truly a fascinating member of the graphene family
  • Performance Comparison of Protonic and Sodium Phosphomolybdovanadate Polyoxoanion Catholytes Within a Chemically Regenerative Redox Cathode Polymer Electrolyte Fuel Cell

    Ward, David B.; Gunn, Natasha L.O.; Uwigena, Nadine; Davies, Trevor J.; University of Chester (Elsevier, 2017-11-23)
    The direct reduction of oxygen in conventional polymer electrolyte fuel cells (PEFCs) is seen by many researchers as a key challenge in PEFC development. Chemically regenerative redox cathode (CRRC) polymer electrolyte fuel cells offer an alternative approach via the indirect reduction of oxygen, improving durability and reducing cost. These systems substitute gaseous oxygen for a liquid catalyst that is reduced at the cathode then oxidised in a regeneration vessel via air bubbling. A key component of a CRRC system is the liquid catalyst or catholyte. To date, phosphomolybdovanadium polyoxometalates with empirical formula H3+nPVnMo12-nO40 have shown the most promise for CRRC PEFC systems. In this work, four catholyte formulations are studied and compared against each other. The catholytes vary in vanadium content, pH and counter ion, with empirical formulas H6PV3Mo9O40, H7PV4Mo8O40, Na3H3PV3Mo9O40 and Na4H3PV4Mo8O40. Thermodynamic properties, cell performance and regeneration rates are measured, generating new insights into how formulation chemistry affects the components of a CRRC system. The results include the best CRRC PEFC performance reported to date, with noticeable advantages over conventional PEFCs. The optimum catholyte formulation is then determined via steady state tests, the results of which will guide further optimization of the catholyte formulation.
  • Reverse microemulsion synthesis of layered gadolinium hydroxide

    Xu, Yadong; Suthar, Jugal; Egbu, Raphael; Weston, Andrew J.; Fogg, Andrew M.; Williams, Gareth R.; University College London; University of Chester (Elsevier, 2017-11-05)
    A reverse microemulsion approach has been explored for the synthesis of layered gadolinium hydroxide (LGdH) nanoparticles in this work. This method uses oleylamine as a multifunctional agent, acting as surfactant, oil phase and base. 1-butanol is additionally used as a co-surfactant. A systematic study of the key reaction parameters was undertaken, including the volume ratio of surfactant (oleylamine) to water, the reaction time, synthesis temperature, and the amount of co-surfactant (1-butanol) added. It proved possible to obtain pristine LGdH materials at temperatures of 120 °C or below with an oleylamine: water ratio of 1:4. Using larger amounts of surfactant or higher temperatures caused the formation of Gd(OH)3, either as the sole product or as a major impurity phase. The LGdH particles produced have sizes of ca. 200 nm, with this size being largely independent of temperature or reaction time. Adjusting the amount of 1-butanol co-surfactant added permits the size to be varied between 200 and 300 nm.
  • Energetic fluctuations in amorphous semiconducting polymers: Impact on charge-carrier mobility

    Manjoj Gali, Sai; D'Avino, Gabriele; Aurel, Philippe; Han, Guangchao; Yi, Yuanping; Papadopoulos, Theodoros A.; Coropceanu, Veaceslav; Bredas, Jean-Luc; Hadziiannou, Georges; Muccioli, Luca; University of Bologna; University of Chester; Georgia Institute of Technology (American Institute of Physics, 2017-10-03)
    We present a computational approach to model hole transport in an amorphous semiconducting fluorene-triphenylamine copolymer (TFB), which is based on the combination of molecular dynamics to predict the morphology of the oligomeric system and Kinetic Monte Carlo (KMC), parameterized with quantum chemistry calculations, to simulate hole transport. Carrying out a systematic comparison with available experimental results, we discuss the role that different transport parameters play in the KMC simulation and in particular the dynamic nature of positional and energetic disorder on the temperature and electric field dependence of charge mobility. It emerges that a semi-quantitative agreement with experiments is found only when the dynamic nature of the disorder is taken into account. This study establishes a clear link between microscopic quantities and macroscopic hole mobility for TFB and provides substantial evidence of the importance of incorporating fluctuations, at the molecular level, to obtain results that are in good agreement with temperature and electric field-dependent experimental mobilities. Our work makes a step forward towards the application of nanoscale theoretical schemes as a tool for predictive material screening.
  • Improved Stability of Polymer Solar Cells in Ambient Air via Atomic Layer Deposition of Ultra-Thin Dielectric Layers

    Polydorou, Ermioni; Botzakaki, Martha A.; Sakellis, Ilias; Soultati, Anastasia; Kaltzoglou, Andreas; Papadopoulos, Theodoros A.; Briscoe, Joe; Drivas, Charalabos; Seintis, Kostas; Fakis, Mihalis; Palilis, Leonidas C.; Georga, Stavroula N.; Krontiras, Christoforos A.; Kennou, Stella; Falaras, Polycarpos; Boukos, Nikos; Davazoglou, Dimitris; Argitis, Panagiotis; Vasilopoulou, Maria; National Center for Scientific Research Demokritos; University of Patras; University of Chester; Queen Mary University of London; (Wiley, 2017-07-12)
    Polymer solar cells have attracted tremendous interest in the highly competitive solar energy sector, due to the practical advantages they exhibit, such as being lightweight, flexible, and low cost, in stark contrast to traditional photovoltaic technologies. However, their successful commercialization is still hindered by issues related to device instability. Here, atomic layer deposition (ALD) is employed to deposit conformal ultrathin dielectrics, such as alumina (Al2O3) and zirconia (ZrO2), on top of ZnO electron extraction layers to address problems that arise from the defect-rich nature of these layers. The deposition of dielectrics on ZnO significantly improves its interfacial electronic properties, manifested primarily with the decrease in the work function of ZnO and the concomitant reduction of the electron extraction barrier as well as the reduced recombination losses. Significant efficiency enhancement is obtained with the incorporation of six ALD cycles of Al2O3 into inverted devices, using photoactive layers, that consist of poly(3-hexylthiophene):indene-C60-bisadduct or poly({4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl}{3-fluoro-2-[(2-ethylhexyl)carbonyl] thieno[3,4-b] thiophenediyl}):[6,6]-phenyl-C70-butyric acid methyl ester. More importantly, upon performing lifetime studies (over a period of 350 h), a strong improvement in polymer solar cell stability is observed when using the ALD-modified ZnO films.
  • Surfactant-exfoliated 2D hexagonal boron nitride (2D-hBN): role of surfactant upon the electrochemical reduction of oxygen and capacitance applications

    Khan, Aamar F.; Down, Michael P.; Smith, Graham C.; Foster, Christopher W.; Banks, Craig E.; University of Chester; Manchester Metropolitan University (Royal Society of Chemistry, 2017-02-02)
    Surfactant-exfoliated 2D hexagonal boron nitride (2D-hBN) nanosheets are fabricated using the surfactant sodium cholate in aqueous media and are explored towards the electrochemical reduction of oxygen (oxygen reduction reaction) within acidic media for the first time. Large quantifiable voltammetric signatures are observed at significantly reduced potentials compared to traditional graphitic-based electrodes indicating 2D-hBN's possible electrocatalytic activity towards the oxygen reduction reaction, therefore having the potential as a useful electrode platform within fuel cell technology. We also demonstrate, for the first time, that surfactant-exfoliated 2D-hBN is an effective electrochemical supercapacitor material with a specific capacitance value of up to 1745 F g-1. A full analysis of the electrochemical properties of 2D-hBN is performed, including the application of a novel capacitive circuit applied to galvanostatic charge/discharge analysis, which provides an unambiguous analysis of the capacitance of the 2D-hBN. Furthermore, a diverse range of methods are introduced and utilised to calculate the specific capacitance, a substantially overlooked and misinterpreted parameter within the literature allowing standardisation in the academic literature to be achieved. In both examples, we demonstrate through control experiments in the form of surfactant modified graphite electrodes, sodium cholate is the major contributing factor to the aforementioned electrocatalytic and capacitive behaviour, which has yet to be reported.
  • Synthesis, characterisation and in-vitro cytotoxicity of mixed ligand Pt(II) oxadiazoline complexes with hexamethylenetetramine and 7-nitro-1,3,5-triazaadamantane.

    Sieste, Stefanie; Lifincev, Irina; Stein, Nina; Wagner, Gabriele; University of Ulm (Germany); University of Chester (UK) (Royal Society of Chemistry, 2017-08-21)
    Trans-platinum(II) oxadiazoline complexes with 7-nitro-1,3,5-triazaadamantane (NO2-TAA) or hexamethylenetetramine (hmta) ligands have been synthesised from trans-[PtCl2(PhCN)2] via cycloaddition of nitrones to one of the coordinated nitriles, followed by exchange of the other nitrile by NO2-TAA or hmta. Stoichiometric control allows for the selective synthesis of mono- and dinuclear complexes where 7-NO2TAA and hmta act as mono- and bidentate ligands, respectively. Precursors and the target complexes trans-[PtCl2(hmta)(oxadiazoline)], trans-[PtCl2(NO2-TAA)(oxadiazoline)] and trans-[{PtCl2(oxadiazoline)}2(hmta)] were characterised by elemental analysis, IR and multinuclear (1H, 13C, 195Pt) NMR spectroscopy. DFT (B3LYP/6-31G*/LANL08) and AIM calculations suggest a stronger bonding of hmta with the [PtCl2(oxadiazoline)] fragment, in agreement with the experimentally observed reactivity in the ligand exchange (hmta > 7-NO2TAA). Replacement of the nitrile by hmta is predicted more exothermic than that with 7-NO2-TAA, although the activation barriers are similar. Protonation of the non-coordinated N atoms is anticipated to weaken the Pt-N bond and lower the activation barrier for ligand exchange. This effect might help activate these compounds in a slightly acidic environment such as some tumour tissues. Ten of the new compounds were tested for their in vitro cytotoxicity in the human cancer cell lines HeLa and A549. Some of the mononuclear complexes are more potent than cisplatin, and their activity is still high in A549 where cisplatin shows little effect. The dinuclear complexes are inactive, presumably due to their lipophilicity and reduced solubility in water.

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