Browsing by Author "Wijayantha, K. G. Upul"

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    A very simple flexible tandem dye-sensitized solar cell
    (Springer, 2024-12-01) Alessa, Hussain; Wijayantha, K. G. Upul
    Dye-sensitized solar cells (DSSCs) have been proposed as the most important third generation photovoltaic devices owing to their low fabrication cost, design flexibility, having low hazard to the environment and ease of construction. Tandem DSSCs (T-DSSC) were said to possess properties of its sensitized photoanode and sensitized photocathode in terms of the power conversion efficiency (PCE) parameters. With less studies on the fabrication of simple a flexible tandem DSSC, this work aims at filling this gap as well as showing the influence of one of the main factors that affect the performance of such a device. In this paper, TiO2 and NiO layers were prepared by blading method, sensitized separately, then sandwiched together. The fabricated device produced short circuit current, open circuit voltage and power conversion efficiency of 0.138 mA.cm−2, 0.942 V and 0.063%, respectively. This simple T-DSSC produced a high photovoltage and showed that the photocurrent produced by each photoelectrode should be identical. This match is to overcome the possible hump in the device performance.
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    Direct monitoring of the potassium charge carrier in Prussian blue cathodes using potassium K-edge X-ray absorption spectroscopy
    (Royal Society of Chemistry (RSC), 2023-10-07) Mayer, Alexander J.; Beynon, Owain T.; Logsdail, Andrew J.; Wijayantha, K. G. Upul; Dann, Sandra E.; Marco, José F.; Elliott, Joshua D.; Aramini, Matteo; Cibin, Giannantonio; Kondrat, Simon A.
    Prussian blue is widely utilized as a cathode material in batteries, due to its ability to intercalate alkaline metal ions, including potassium. However, the exact location of potassium or other cations within the complex structure, and how it changes as a function of cycling, is unclear. Herein, we report direct insight into the nature of potassium speciation within Prussian blue during cyclic voltammetry, via operando potassium K-edge X-ray Absorption Near Edge Structure (XANES) analysis. Clear and identifiable spectra are experimentally differentiated for the fully intercalated (fully reduced Fe2+FeII Prussian white), partially intercalated (Prussian blue; Fe3+FeII), and free KNO3(aq) electrolyte. Comparison of the experiment with simulated XANES of theoretical structures indicates that potassium lies within the channels of the Prussian blue structure, but is displaced towards the periphery of the channels by occluded water and/or structural water present resulting from [Fe(CN)6]4− vacancies. The structural composition from the charge carrier perspective was monitored for two samples of differing crystallite size and electrochemical stability. Reproducible potassium XANES spectral sequences were observed for large crystallites (ca. 100 nm) of Prussian blue, in agreement with retention of capacity; in contrast, the capacity of a sample with small crystallites (ca. 14 nm) declined as the potassium became trapped within the partially intercalated Prussian blue. The cause of degradation could be attributed to a significant loss of [Fe(CN)6]–[Fe(NC)6] ordering and the formation of a potassium-free non-conducting ferrihydrite phase. These findings demonstrate the potential of XANES to directly study the nature and evolution of potassium species during an electrochemical process.
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    Improvements of electrochemical water splitting efficiency by using economically viable Co/CoPs/TiO₂/NiF electrocatalysts
    (Cranfield University, 2024-08) Kulathunga Mudiyansele, Soorya Dananjaya Bandara Kulathunga; Wijayantha, K. G. Upul; Jiang, Ying
    The drive for sustainable energy solutions has led to the search for efficient and cost-effective electrocatalysts for green hydrogen production via electrochemical water splitting (EWS). This study addresses the limitations of precious metal- based catalysts by investigating alternative, earth-abundant materials. This research introduces a novel Co/CoPs(240)/TiO₂/NiF electrocatalyst, synthesized using deep eutectic solvent (DES)-mediated electrodeposition of Co and cobalt phosphides (CoPs) on TiO₂-coated nickel foam (NiF) substrate. Electrophoretic deposition of TiO₂ nanoparticles was successfully applied to NiF, resulting in a smooth and even surface. On this TiO₂-coated substrate, subsequent Co/CoPs deposition produced unique hexagonal and cauliflower-like structures with a uniform distribution of Co and P. Energy dispersive X-ray spectroscopy (EDX), scanning electron microscopy (SEM), and X-ray diffraction (XRD) were used to confirm these features. Optimizing the Co/CoPs deposition times significantly reduced the hydrogen evolution reaction (HER) overpotential to 34.42 ± 4.2 mV at 10 mA cm⁻² in 1 M KOH. Remarkably, the Co/CoPs(240)/TiO2/NiF catalyst required only 27.43 mV with a Tafel slope of 48.35 mV dec⁻¹. Stability tests demonstrated minimal performance degradation after 5000 cycles and 40 hours of operation, demonstrating excellent durability. This optimized catalyst outperformed Co/CoPs(240)/NiF, commercial 10% Pt/C electrodes, and other reported catalysts. The oxygen evolution reaction (OER) performance also highlighted the catalyst's efficiency, with an overpotential of 331.70 mV at 10 mA cm⁻² in 1 M KOH and a Tafel slope of 73.96 mV dec⁻¹. Stability tests revealed minimal performance degradation after 1000 cycles. Furthermore, a full water electrolyser system using Co/CoP(240)/TiO2/NiF electrodes achieved a total voltage of 1.612 V at 10 mA cm⁻², indicating the practical viability of the optimized electrodes for water splitting applications. The remarkable performance of the Co/CoPs(240)/TiO₂/NiF electrode is primarily due to the presence of the TiO₂ layer, which enhances the surface area and acts as a catalyst promoter through synergistic effects and enhanced charge transfer kinetics. This research suggests that incorporating an intermediate TiO₂ layer can promote the catalytic activity of other catalysts as well. In conclusion, this study presents an effective and economical alternative to noble metal-based electrocatalysts for water splitting. By integrating TiO₂ with Co/CoPs on a NiF substrate, the research advances the development of high-performance, low-cost catalysts and contributes to the sustainable production of green hydrogen.
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    Temperature-dependent electrosynthesis of PEDOT:PSS: enhanced Na+ transfer targeting high-performance Na-ion batteries
    (Elsevier, 2025-04-01) Santos, Daniel R.; Zeferino, Jorge F.; Viana, Ana S.; Wijayantha, K. G. Upul; Lobato, Killian; Correia, Jorge P.
    Poly(3,4-ethylenedioxythiophene):Poly(sodium 4-styrenesulfonate) (PEDOT:PSS) is a versatile conducting polymer with physicochemical properties favourable for energy storage applications, such as chemical and mechanic stability and flexibility. However, the temperature at which the polymer is synthesised can significantly influence its properties. In this study, a detailed investigation of the effect of temperature on the electroactivity, morphology, optical properties, and ionic/solvent transport during the redox conversion of potentiostatically and galvanostatically synthesised films was conducted. Electrochemical data, supported by ellipsometry, atomic force microscopy, microgravimetry, and probe beam deflection measurements, revealed that films synthesised at lower temperatures (0 °C) were more compact compared to those synthesised at higher temperatures (40 °C). Films synthesised at 0 °C also exhibited near-ideal reversibility, with a QO/QR ratio of ca. 1. Importantly, the 0 °C films showed a strong pseudocationic doping behaviour, characterised by predominant sodium ion exchange during redox processes. In contrast, films synthesised at 40 °C exhibited mixed ion participation (both sodium and perchlorate), which could negatively impact the performance of electrode material in battery applications. This study demonstrates the potential of PEDOT:PSS as a versatile material for sodium ion cathodes, with properties that can be finely tuned through the synthesis temperature, yielding more compact ion-storage films at lower temperatures.