Browsing by Author "Felix, Cecil"

Now showing 1 - 6 of 6
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    Ex-situ electrochemical characterization of iro2 synthesized by a modified Adams fusion method for the oxygen evolution reaction
    (MDPI, 2019) Felix, Cecil; Bladergroen, Bernard J.; Linkov, Vladimir
    The development of highly stable and active electrocatalysts for the oxygen evolution reaction (OER) has attracted significant research interest. IrO2 is known to show good stability during the OER however it is not known to be the most active. Thus, significant research has been dedicated to enhance the activity of IrO2 toward the OER. In this study, IrO2 catalysts were synthesized using a modified Adams fusion method. The Adams fusion method is simple and is shown to directly produce nano-sized metal oxides. The effect of the Ir precursor salt to the NaNO3 ratio and the fusion temperature on the OER activity of the synthesized IrO2 electrocatalysts, was investigated. The OER activity and durability of the IrO2 electrocatalysts were evaluated ex-situ via cyclic voltammetry (CV), chronopotentiometry (CP), electrochemical impedance spectroscopy (EIS) and linear sweep voltammetry (LSV).
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    Iridium based mixed oxides as efficient anode catalysts for Solid Polymer Electrolyte (SPE) electrolysers
    (2010) Felix, Cecil; Linkov, Vladimir M.; Pasupathi, Sivakumar
    The objective of the thesis is to develop highly efficient catalysts for solid polymer electrolyte (SPE) electrolyser anodes.The anode is the primary cause of the large overpotential of SPE electrolysers and also adds significantly to the cost of the electrolysers. Currently, unsupported IrO2 is a widely used anode catalyst as it exhibits the best stability during the oxygen evolution reaction. The activity of IrO2 needs to be improved significantly to address the high cost and efficiency issues of the SPE electrolyser. Developments aimed at improving the activity of unsupported IrO2 are however limited due to the limitations of the wellknown supports under the operating conditions of electrolysers, leading to their oxidation.In this study binary metal oxides based on IrO2 were developed and optimized as anode catalysts for the SPE electrolyser and compared to the ‘state-of-art’ commercial IrO2 catalyst. The Adams fusion method was adapted and used to synthesize the catalysts.The activities of the catalysts were determined using half-cell studies. Optimum conditions for the preparation of unsupported IrO2 catalysts were found to be 350 oC and 2 hours. The resulting catalysts had twice the activity of the ‘state-of-art’ commercial IrO2 catalyst. Secondary metals were carefully selected, after carrying out both a literature study and an experimental study. Binary metal oxides were then developed using the optimum synthesis conditions. Four binary metal oxides were studied to identify the best/most efficient catalyst for electrolysis. The catalysts were characterized using XRD, TEM, SEM and EDS analyses, in efforts to understand and correlate the activity of the catalysts to its physical properties and obtain information that could be useful for the further development of efficient catalysts.Although all the binary metal oxides studied showed improved activity compared to IrO2, the catalytic activity of Ir0.7Ru0.3O2 was found to be significantly better than the commercial catalyst: it was over 5 times more active than the ‘state-of-art’ commercial IrO2 catalyst. Ir-Pd mixed oxides also proved to be highly efficient as anode catalysts for SPE electrolysers.
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    Optimisation of electrophoretic deposition parameters for gas diffusion electrodes in high temperature polymer electrolyte membrane fuel cells
    (Elsevier, 2013) Felix, Cecil; Jao, Ting-Chu; Pasupathi, Sivakumar; Pollet, Bruno G.
    Electrophoretic deposition (EPD) method was used to fabricate gas diffusion electrodes (GDEs) for high temperature polymer electrolyte membrane fuel cells (HT PEMFC). Parameters related to the catalyst suspension and the EPD process were studied. Optimum suspension conditions are obtained when the catalyst particles are coated with Nafion® ionomer and the pH is adjusted to an alkaline range of about 8 e10. These suspensions yield good stability with sufficient conductivity to form highly porous catalyst layers on top of the gas diffusion layers (GDLs). GDEs were fabricated by applying various electric field strengths of which 100 V cm-1 yields the best membrane electrode assembly (MEA) performance. Compared to an MEA fabricated by the traditional hand sprayed (HS) method, the EPD MEA shows superior performance with a peak power increase of about 73% at similar platinum (Pt) loadings. Electrochemical Impedance Spectroscopy (EIS) analysis shows lower charge transfer resistance for the MEA fabricated via the EPD method compared to the HS MEA. The EPD GDE exhibits a greater total pore area (22.46 m2 g-1) compared to the HS GDE (13.43 m2 g-1) as well as better dispersion of the Pt particles within the catalyst layer (CL).
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    Synthesis and optimisation of IrO2 electrocatalysts by Adams fusion method for solid polymer electrolyte electrolysers
    (Bentham Science Publishers, 2012) Felix, Cecil; Maiyalagan, Thandavarayan; Sivakumar, Pasupathi; Linkov, Vladimir
    IrO2 as an anodic electrocatalyst for the oxygen evolution reaction (OER) in solid polymer electrolyte (SPE) electrolysers was synthesised by adapting the Adams fusion method. Optimisation of the IrO2 electrocatalyst was achieved by varying the synthesis duration (0.5 – 4 hours) and temperature (250 - 500°C). The physical properties of the electrocatalysts were characterised by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and x-ray diffraction (XRD). Electrochemical characterisation of the electrocatalysts toward the OER was evaluated by chronoamperometry (CA). CA analysis revealed the best electrocatalytic activity towards the OER for IrO2 synthesised for 2 hours at 350oC which displayed a better electrocatalytic activity than the commercial IrO2 electrocatalyst used in this study. XRD and TEM analyses revealed an increase in crystallinity and average particle size with increasing synthesis duration and temperature which accounted for the decreasing electrocatalytic activity. At 250°C the formation of an active IrO2 electrocatalyst was not favoured.
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    Synthesis, characterisation and evaluation of IrO2 based binary metal oxide electrocatalysts for oxygen evolution reaction
    (Electochemical Society Inc., 2012) Felix, Cecil; Maiyalagan, Thandavarayan; Pasupathi, Sivakumar; Bladergroen, Bernard Jan; Linkov, Vladimir
    IrO2, IrxRu1-xO2, IrxSnx-1O2 and IrxTax-1O2 (1 ≥ x ≥ 0.7) were synthesized, characterised and evaluated as electrocatalysts for the oxygen evolution reaction in solid polymer electrolyte electrolysers. The electrocatalysts were synthesised by adapting the Adams fusion method. The physical properties of the electrocatalysts were characterised by scanning electron microscopy, transmission electron microscopy and x-ray diffraction. Electrochemical activity of the electrocatalysts toward the oxygen evolution reaction was evaluated by cyclic voltammetry and chronoamperometry. X-ray diffraction revealed no phase separation when RuO2 or SnO2 was introduced into the IrO2 lattice suggesting that solid solutions were formed. Transmission electron microscope analysis revealed nanosize particles for all synthesised metal oxides. Crystallinity increased with the addition of RuO2 and SnO2 while a suppression of crystal growth was observed with the addition of Ta2O5 to IrO2. Chronoamperometry revealed that the addition of all the secondary metal oxides to IrO2 resulted in improved catalytic performance. Ir0.7Ru0.3O2 was identified as the most promising electrocatalyst for the oxygen evolution reaction. Keywords:
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    Towards the development of a novel bipolar-based battery in aqueous electrolyte: Evaluation of the electrochemical properties of NiCu based hydroxide electrodes fabricated on Ni–mesh and graphite composite current collectors
    (Journal of Energy Storage, 2022) Felix, Cecil
    The use of bipolar electrodes in rechargeable batteries can improve specific power, simplify cell design, and reduce manufacturing costs. However, bipolar-based batteries still suffer from many drawbacks. Therefore, developing high-performance active materials and developing improvement strategies encompassing the entire cell's design is essential. The current collector significantly impacts the viability of mass production; however, it is the most neglected feature of electrochemical energy storage devices. The current collector serves a dual purpose; it allows the movement of electrons among active electrode material and provides mechanical support. It can also act as transportation of current to terminals of the battery. This study constructed a novel bipolar battery cell utilizing graphite as a current collector, and its discharge capacities for Ni-Fe battery applications were evaluated. Monopolar NiFe cells, one using a graphite substrate current collector and the other using a Ni-mesh current collector, were used for comparison. The monopolar-based electrode coated onto a graphite substrate demonstrated a 29% (199 mAh/g) higher discharge capacity than the Ni-mesh-based electrode (142 mAh/g) after the 100th cycle. In contrast, the bipolar-based NiFe battery cell resulted in a discharge capacity of 158 mAh/g after the 100th cycle, corresponding to a coulombic efficiency of 72%.