Browsing by Author "Wijayantha, Upul K. G."
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Item Open Access Electrodeposited poly(phenylene oxide) suppresses anodic parasitic processes in carbon-based supercapacitor electrodes operating in an aqueous electrolyte(Elsevier, 2022-06-02) Baptista, J. M.; Gaspar, G.; Wijayantha, Upul K. G.; Lobato, K.Aqueous electrolytes, when compared to organic electrolytes, are safer, cheaper and usually enable a higher capacitance and lower internal resistance. However, their narrow operational voltage window (ca. 1.2 V) limits the device's energy density and, as such, their current commercial use is limited. Poly(phenylene oxide) was electrodeposited on the surface of activated carbon electrodes and has been shown to decrease the anodic parasitic current. The impact on the cathodic parasitic current was minimal. Comparison of the polarisation curves obtained in 1 M Na2SO4 (aq) for coated and uncoated electrodes between 0.5 V and 1.1 V vs Ag|AgCl demonstrated a >66% decrease in the exchange current density of anodic processes (from 10.1 μA/cm2 to 3.4 μA/cm2). Assuming supercapacitor degradation is proportional to the parasitic faradaic current, this change in the anodic parameters enables a 31% increase in the upper positive potential when a maximum parasitic current density of 29 μA/cm2 is considered acceptable. When these coated electrodes were mounted as symmetrical coin cells and operated at an increased voltage window of 1.5 V (up from 1.2 V), gains in energy and power densities were from 2.2 Wh/kg to 4.6 Wh/kg and 159 W/kg to 465 W/kg, respectively.Item Open Access Hydrogen technology adoption analysis in Africa using a Doughnut-PESTLE hydrogen model (DPHM)(Elsevier, 2022-09-14) Mukelabai, Mulako Dean; Wijayantha, Upul K. G.; Blanchard, Richard E.The hydrogen economy requires the right conditions to produce hydrogen by sustainable routes and provide it to local and international markets for suitable applications. This study evaluated the political, economic, social, technological, legal, and environmental (PESTLE) conditions that can be instrumental in adopting hydrogen technologies most effectively by encapsulating aspects relevant to key stakeholders from hydrogen technology developers through to end-users. For instance, the analysis has shown that countries within a government effectiveness index of 0.5 and −0.5 are leading the planning of hydrogen economies through strategic cooperation with hydrogen technology developers. Furthermore, the combination of a Doughnut and PESTLE analysis created a novel approach to assessing the adoption of hydrogen technologies while evaluating the impact of the hydrogen economy. For instance, the estimated ammonia demand in 2050 and subsequent anthropogenic nitrogen extraction rate will be about two and a half times more than the 2009 extraction rate.Item Open Access The impact of laser-scribing carbon-based supercapacitor electrodes(Elsevier, 2022-06-06) Baptista, M.; Gaspar, G.; Wijayantha, Upul K. G.; Lobato, K.In highly porous carbon electrodes, a large fraction of pores can be inaccessible to the electrolyte, which translates into lower specific capacitances. This is accentuated at high current densities. To circumvent this, channels can be opened to enhance ionic diffusion. In this work, ionic channels were created using a pulsed laser. Nine sets of laser-scribing parameters (pulse fluence and spot spacing) were applied on two sets of carbon-based supercapacitor electrodes: K-bar hand-coated electrodes (“K”) and screen-printed electrodes (“SP”). Profilometry and scanning electron microscopy revealed that, before laser-scribing, the latter already had several holes and trenches, whilst the former were compact films. Electrochemical measurements in Na2SO4 indicate improvements in the rate capability of the laser-scribed SP electrodes, namely an up to 50% reduction of the rate at which energy density decreases as power densities increase. For laser-scribed K electrodes, the slope of the Ragone plot only decreased by ca. 20% in the best set of conditions. However, for both sets of electrodes, a negative trade-off is observed: laser processed electrodes seem to have a lower specific capacitance. This might be caused by the entrapment of debris in the laser-drilled holes, which could lead to the overestimation of the active mass. Moreover, X-ray Photoelectron Spectroscopy analysis suggests that this may also be explained by the decrease in the oxygen functionalities and by its impact on the electrodes’ wettability. On the other hand, for electrodes tested in an organic electrolyte (tetrabutylammonium perchlorate in acetonitrile), the specific capacitance at 2 A/g was up to 66% higher for laser-scribed electrodes and an energy density of 13 Wh/kg was achieved even at 2.8 kW/kg.Item Open Access Renewable hydrogen economy outlook in Africa(Elsevier, 2022-06-28) Mukelabai, Mulako Dean; Wijayantha, Upul K. G.; Blanchard, Richard E.Hydrogen presents an opportunity for Africa to not only decarbonise its own energy use and enable clean energy access for all, but also to export renewable energy. This paper developed a framework for assessing renewable resources for hydrogen production and provides a new critical analysis as to how and what role hydrogen can play in the complex African energy landscape. The regional solar, wind, CSP, and bio hydrogen potential ranges from 366 to 1311 Gt/year, 162 to 1782 Gt/year, 463 to 2738 Gt/year, and 0.03 to 0.06 Gt/year respectively. The water availability and sensitivity results showed that the water shortages in some countries can be abated by importing water from regions with high renewable water resources. A techno-economic comparative analysis indicated that a high voltage direct current (HVDC) system presents the most cost-effective transportation system with overall costs per kg hydrogen of 0.038 $/kg, followed by water pipeline with 0.084 $/kg, seawater desalination 0.1 $/kg, liquified hydrogen tank truck 0.12 $/kg, compressed hydrogen pipeline 0.16 $/kg, liquefied ammonia pipeline 0.38 $/kg, liquefied ammonia tank truck 0.60 $/kg, and compressed hydrogen tank truck with 0.77 $/kg. The results quantified the significance of economies of scale due to cost effectiveness of systems such as compressed hydrogen pipeline and liquefied hydrogen tank truck systems when hydrogen production is scaled up. Decentralization is favorable under some constraints, e.g., compressed hydrogen and liquefied ammonia tank truck systems will be more cost effective below 800 km and 1400 km due to lower investment and operation costs.Item Open Access Review of the production of turquoise hydrogen from methane catalytic decomposition: Optimising reactors for Sustainable Hydrogen production(Elsevier, 2024-05-31) Sanyal, Aryamman; Malalasekera, Weeratunge; Bandulasena, Hemaka; Wijayantha, Upul K. G.Hydrogen is gaining prominence in global efforts to combat greenhouse gas emissions and climate change. While steam methane reforming remains the predominant method of hydrogen production, alternative approaches such as water electrolysis and methane cracking are gaining attention. The bridging technology – methane cracking – has piqued scientific interest with its lower energy requirement (74.8 kJ/mol compared to steam methane reforming 206.278 kJ/mol) and valuable by-product of filamentous carbon. Nevertheless, challenges, including coke formation and catalyst deactivation, persist. This review focuses on two main reactor types for catalytic methane decomposition – fixed-bed and fluidised bed. Fixed-bed reactors excel in experimental studies due to their operational simplicity and catalyst characterisation capabilities. In contrast, fluidised-bed reactors are more suited for industrial applications, where efforts are focused on optimising the temperature, gas flow rate, and particle characterisation. Furthermore, investigations into various fluidised bed regimes aim to identify the most suitable for potential industrial deployment, providing insights into the sustainable future of hydrogen production. While the bubbling regime shows promise for upscaling fluidised bed reactors, experimental studies on turbulent fluidised-bed reactors, especially in achieving high hydrogen yield from methane cracking, are limited, highlighting the technology's current status not yet reaching commercialisation.Item Open Access Superior rate capability of high mass loading supercapacitors fabricated with carbon recovered from methane cracking(MDPI, 2023-07-27) Baptista, Joana; Shacklock, Jack; Shaban, Muhammad; Alkayal, Anas; Lobato, Killian; Wijayantha, Upul K. G.High mass loading (ca. 30 mg/cm2) electrodes were prepared with carbon recovered from catalytic methane cracking (MC). As-fabricated supercapacitors displayed 74% of capacitance retention from 6 mA/cm2 to 60 mA/cm2 and a Ragone plot’s slope of −7 Wh/kW (compared to 42% and −31 Wh/kW, respectively, for high mass loading devices fabricated with commercial carbon). The high-rate capability of the MC-recovered carbon is attributed to the presence of carbon black and carbon nanotubes produced during the reaction, which likely increased the electronic and ionic conductivity within the electrode. These results suggest that the by-product of this hydrogen generation route might be a suitable active material for supercapacitors.Item Open Access Surfactant control of coffee ring formation in carbon nanotube suspensions(American Chemical Society, 2023-01-06) Howard, Naomi S.; Archer, Andrew J.; Sibley, D. N.; Southee, Darren; Wijayantha, Upul K. G.The coffee ring effect regularly occurs during the evaporation of colloidal droplets and is often undesirable. Here we show that adding a specific concentration of a surfactant can mitigate this effect. We have conducted experiments on aqueous suspensions of carbon nanotubes that were prepared with cationic surfactant dodecyltrimethylammonium bromide added at 0.2, 0.5, 1, 2, 5, and 10 times the critical micelle concentration. Colloidal droplets were deposited on candidate substrates for printed electronics with varying wetting characteristics: glass, polyethylene terephthalate, fluoroethylene propylene copolymer, and polydimethylsiloxane. Following drying, four pattern types were observed in the final deposits: dot-like, uniform, coffee ring deposits, and combined patterns (coffee ring with a dot-like central deposit). Evaporation occurred predominantly in constant contact radius mode for most pattern types, except for some cases that led to uniform deposits in which early stage receding of the contact line occurred. Image analysis and profilometry yielded deposit thicknesses, allowing us to identify a coffee ring subfeature in all uniform deposits and to infer the percentage coverage in all cases. Importantly, a critical surfactant concentration was identified for the generation of highly uniform deposits across all substrates. This concentration resulted in visually uniform deposits consisting of a coffee ring subfeature with a densely packed center, generated from two distinct evaporative phases.Item Open Access Techno-economic analysis of low carbon hydrogen production from offshore wind using battolyser technology(MDPI, 2022-08-10) Jenkins, Brian; Squires, David; Barton, John; Strickland, Dani; Wijayantha, Upul K. G.; Carroll, James; Wilson, Jonathan; Brenton, Matthew; Thomson, MurrayA battolyser is a combined battery electrolyser in one unit. It is based on flow battery technology and can be adapted to produce hydrogen at a lower efficiency than an electrolyser but without the need for rare and expensive materials. This paper presents a method of determining if a battolyser connected to a wind farm makes economic sense based on stochastic modelling. A range of cost data and operational scenarios are used to establish the impact on the NPV and LCOE of adding a battolyser to a wind farm. The results are compared to adding a battery or an electrolyser to a wind farm. Indications are that it makes economic sense to add a battolyser or battery to a wind farm to use any curtailed wind with calculated LCOE at £56/MWh to £58/MWh and positive NPV over a range of cost scenarios. However, electrolysers, are still too expensive to make economic sense.Item Open Access Using machine learning to expound energy poverty in the global south: understanding and predicting access to cooking with clean energy(Elsevier, 2023-08-03) Mukelabai, M. D.; Wijayantha, Upul K. G.; Blanchard, R. E.Efforts towards achieving high access to cooking with clean energy have not been transformative due to a limited understanding of the clean-energy drivers and a lack of evidence-based clean-energy policy recommendations. This study addresses this gap by building a high-performing machine learning model to predict and understand the mechanisms driving energy poverty - specifically access to cooking with clean energy. In a first-of-a-kind, the estimated cost of US14.5 to enable universal access to cooking with clean energy encompasses all the intermediate inputs required to build self-sufficient ecosystems by creating value-addition sectors. Unlike previous studies, the data-driven clean-cooking transition pathways provide foundations for shaping policy that can transform the energy and cooking landscape. Developing these pathways is necessary to increase people's financial resilience to tackle energy poverty. The findings also show the absence of a linear relationship between electricity access and clean cooking - evidencing the need for a rapid paradigm shift to address energy poverty. A new fundamental approach that focuses on improving and sustaining the financial capacity of households through a systems approach is required so that they can afford electricity or fuels for cooking.