Rowley-Neale, Samuel J.; Foster, Christopher W.; Smith, Graham C.; Brownson, Dale A. C.; Banks, Craig E. (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.
Reid, David G.; Smith, Graham C. (Taylor & Francis, 2014-01)
The surfaces of ISO 2160 copper strips tested in iso-octane with elemental sulfur, aliphatic, cyclic and aromatic thiols, diphenyl sulfide, and diphenyl disulfide individually or in combination were studied using XPS. Aliphatic thiols bonded through the sulfur, whereas elemental sulfur formed a cuprous sulfide layer. Aromatics bonded partially through the sulfur with the rings oriented horizontally due to π orbital interactions, accounting in part for their inhibitory effects in the test. The test rating was not directly related to the sulfur concentration in solution or on the surface, and certain combinations of species resulted in higher levels of sulfur at the surface than found individually.
Chan, Chi-Wai; Smith, Graham C. (Elsevier, 2016-04-29)
Laser transmission joining (LTJ) is growing in importance, and has the potential to become a niche technique for the fabrication of hybrid plastic-metal joints for medical device applications. The possibility of directly joining plastics to metals by LTJ has been demonstrated by a number of recent studies. However, a reliable and quantitative method for defining the contact area between the plastic and metal, facilitating calculation of the mechanical shear stress of the hybrid joints, is still lacking. A new method, based on image analysis using ImageJ, is proposed here to quantify the contact area at the joint interface. The effect of discolouration on the mechanical performance of the hybrid joints is also reported for the first time. Biocompatible polyethylene terephthalate (PET) and commercially pure titanium (Ti) were selected as materials for laser joining using a 200 W CW fibre laser system. The effect of laser power, scanning speed and stand-off distance between the nozzle tip and top surface of the plastic were studied and analysed by Taguchi L9 orthogonal array and ANOVA respectively. The surface morphology, structure and elemental composition on the PET and Ti surfaces after shearing/peeling apart were characterized by SEM, EDX, XRD and XPS.
Kumar, Dinesh; Stoichkov, Vasil; Brousseau, Emmanuel; Smith, Graham C.; Kettle, Jeff (Royal Society of Chemistry, 2019-02-12)
The report of transparent and conducting silver nanowires (AgNWs) that produce remarkable electrical performance, surface planarity and environmental stability is given. This research presents an innovative process that relies on three sequential steps, which are roll-to-roll (R2R) compatible; thermal embossing, infrared sintering and plasma treatment. This process leads to the demonstration of a conductive film with a sheet resistance of 2.5Ω/sq and high transmittance, thus demonstrating the highest reported figure-of-merit in AgNWs to date (FoM = 933). A further benefit of the process is that the surface roughness is substantially reduced compared to traditional AgNW processing techniques. Finally, consideration of the long-term stability is given by developing an accelerated life test process that simultaneously stresses the applied bias and temperature. Regression line fitting shows that a ∼150-times improvement in stability is achieved at ‘normal operational conditions’ when compared to traditionally deposited AgNW films. X-ray photoelectron spectroscopy (XPS) is used to understand the root cause of the improvement in long-term stability, which is related to reduced chemcial changes in the AgNWs.
Foster, Christopher W.; Down, Michael P.; Zhang, Yan; Ji, Xiaobo; Rowley-Neale, Samuel J.; Smith, Graham C.; Kelly, Peter J.; Banks, Craig E. (Springer Nature, 2017-03-03)
3D printing technology provides a unique platform for rapid prototyping of numerous applications due to its ability to produce low cost 3D printed platforms. Herein, a graphene-based polylactic acid filament (graphene/PLA) has been 3D printed to fabricate a range of 3D disc electrode (3DE) configurations using a conventional RepRap fused deposition moulding (FDM) 3D printer, which requires no further modification/ex-situ curing step. To provide proof-of-concept, these 3D printed electrode architectures are characterised both electrochemically and physicochemically and are advantageously applied as freestanding anodes within Li-ion batteries and as solid-state supercapacitors. These freestanding anodes neglect the requirement for a current collector, thus offering a simplistic and cheaper alternative to traditional Li-ion based setups. Additionally, the ability of these devices’ to electrochemically produce hydrogen via the hydrogen evolution reaction (HER) as an alternative to currently utilised platinum based electrodes (with in electrolysers) is also performed. The 3DE demonstrates an unexpectedly high catalytic activity towards the HER (−0.46 V vs. SCE) upon the 1000th cycle, such potential is the closest observed to the desired value of platinum at (−0.25 V vs. SCE). We subsequently suggest that 3D printing of graphene-based conductive filaments allows for the simple fabrication of energy storage devices with bespoke and conceptual designs to be realised.
Gillett, Alice R.; Baxter, S. N.; Hodgson, Simon D.; Smith, Graham C.; Thomas, P. J. (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.
Implant failure caused by bacterial infection is extremely difficult to treat and usually requires the removal of the infected components. Despite the severe consequence of bacterial infection, research into bacterial infection of orthopaedic implants is still at an early stage compared to the effort on enhancing osseointegration, wear and corrosion resistance of implant materials. In this study, the effects of laser surface treatment on enhancing the antibacterial properties of commercially pure (CP) Ti (Grade 2), Ti6Al4V (Grade 5) and CoCrMo alloy implant materials were studied and compared for the first time. Laser surface treatment was performed by a continuous wave (CW) fibre laser with a near-infrared wavelength of 1064 nm in a nitrogen-containing environment. Staphylococcus aureus, commonly implicated in infection associated with orthopaedic implants, was used to investigate the antibacterial properties of the laser-treated surfaces. The surface roughness and topography of the laser-treated materials were analysed by a 2D roughness testing and by AFM. The surface morphologies before and after 24 h of bacterial cell culture were captured by SEM, and bacterial viability was determined using live/dead staining. Surface chemistry was analysed by XPS and surface wettability was measured using the sessile drop method. The findings of this study indicated that the laser-treated CP Ti and Ti6Al4V surfaces exhibited a noticeable reduction in bacterial adhesion and possessed a bactericidal effect. Such properties were attributable to the combined effects of reduced hydrophobicity, thicker and stable oxide films and presence of laser-induced nano-features. No similar antibacterial effect was observed in the laser-treated CoCrMo.
Khan, Aamar F.; Down, Michael P.; Smith, Graham C.; Foster, Christopher W.; Banks, Craig E. (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.
Randviir, Edward P.; Kanou, Omar; Liauw, Christopher M.; Miller, Gary; Andrews, Hayley; Smith, Graham C. (Royal Society of Chemistry, 2019-04-10)
Textile waste is on the rise due to the expanding global population and the fast fashion market. Large volumes of textile waste are increasing the need for new methods for recycling mixed fabric materials. This paper employs a hydrothermal conversion route for a polyester/cotton mix in phosphoric acid to generate carbon materials (hydrochars) for electrochemical applications. A combination of characterization techniques revealed the reaction products were largely comprised of two major components. The ﬁrst is a granular material with a surface C : O ratio of 2 : 1 interspersed with phosphorous and titanium proved using energy dispersive X-ray spectroscopy, and the other is a crystalline material with a surface C : O ratio of 3 : 2 containing no phosphorous or titanium. The latter material was found via X-ray diﬀraction and diﬀerential scanning calorimetry to be terephthalic acid. Electrochemical experiments conducted using the hydrochar as a carbon paste electrode demonstrates an increase in current response compared to carbon reference materials. The improved current responses, intrinsically related to the surface area of the material, could be beneﬁcial for electrochemical sensor applications, meaning that this route holds promise for the development of a cheap recycled carbon material, using straightforward methods and simple laboratory reagents.
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