UWCScholar :: Browsing by Author "Pasupathi, Sivakumar"

Browsing by Author "Pasupathi, Sivakumar"

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The effect of flow field design on the degradation mechanisms and long term stability of HT-PEM fuel cell
(University of the Western Cape, 2018) Bandlamudi, Vamsikrishna; Pasupathi, Sivakumar; Bujlo, Piotr
Fuel cells are long term solution for global energy needs. In current fuel cell technologies, Proton Exchange Membrane (PEM) fuel cells are known for quick start-up and ease of operation compared to other types of fuel cells. Operating PEM fuel cells at high temperature show promising applications for stationary combined heat and power application (CHP). The high operating temperature up to 160°C allows waste heat to be recovered for co-generation or tri-generation purposes. The commercially available PEM fuel cells operating at 160⁰C can tolerate up to 3% CO without significant loss of performance, making HT-PEM fuel cell viable choice when reformate is used. In reality these advantages convert to very little balance-of-plant compared to Nafion® based fuel cells operating at 60°C. However, there are some problems that prevent high temperature fuel cells from large scale commercialization. The cathode is said to have sluggish reaction kinetics and high cell potentials and operating temperature during fuel cell start-up may cause severe degradation. The formation of liquid water during the shut-down can cause the phosphoric acid to leach from the cell during operation. Efforts are being made to reduce the cost and increase the durability of fuel cell components (such as catalyst and membrane) at high temperatures. Apart from degradation issues, the problems are related to cost and performance. The performance of the PEM fuel cells depends on a lot of factors such as fuel cell design and assembly, operating conditions and the flow field design used on the cathode and anode plates. The flow field geometry is one important factor influencing the performance of fuel cells. The flow fields have significant effect on pressure and flow distribution inside the fuel cell. A homogeneous distribution of the reactant gases over the active catalyst surface leads to improved electrochemical reactions and thus enhances the performance of the fuel cell. So, the design of flow fields is one of the important issues for performance improvement of PEM fuel cell in terms of power density and efficiency. There are different types of flow fields available for PEM fuel cells such as serpentine, pin, interdigitated and straight flow fields but the most obvious choice is multiple serpentine. The same can be used for high temperature PEM fuel cell (HT-PEMFC) application with ease because of absence of liquid water during the high temperature operation and no need for complex water management.
Effect of synthetic methods on the characteristics and performance of IrO2 catalysts
(University of the Western Cape, 2022) Karels, Simoné; Pasupathi, Sivakumar
For many years fossil fuel has been the primary source of energy worldwide though, the environment is negatively affected because of the high carbon dioxide (CO2) emissions associated with the use of fossil fuels. Hydrogen (H2) is known for its ecological cleanliness and high energy efficiency. More consumers are considering H2 as an energy carrier for different stationery and transportation applications. The most sustainable way to synthesize H2 is by using the water electrolysis method with renewable energy sources like solar, wind, etc. Currently, the proton exchange membrane water electrolyzer (PEMWE), coupled with renewable energy sources, is the most efficient water electrolyzer technology to produce very pure H2 with no CO2 emissions.
Effects of heat treatment on the catalytic activity and methanol tolerance of carbon-supported platinum alloys
(Springer, 2012) Valisi, Andiswa; Maiyalagan, Thandavarayan; Khotseng, Lindiwe; Linkov, Vladimir; Pasupathi, Sivakumar
This work studies the effect of heat treatment of carbon-dispersed platinum and platinum alloys on its methanol tolerance and catalytic activity as gas diffusion electrodes for oxygen reduction reaction (ORR) in acid medium. The catalyst powders were subjected to heat treatments at three different temperatures for a fixed period at controlled atmospheres. Differences in catalyst morphology were characterized using X-ray diffraction, energy dispersive X-ray analysis and transmission electron microscope techniques. The electrochemical characteristics and activity of the electro-catalysts were evaluated for ORR and methanol tolerance using cyclic voltammetry, in the form of gas diffusion electrodes. The optimum heat-treatment temperature is found to be strongly dependent on the individual catalyst. The maximum ORR activity and better methanol tolerance for the oxygen reduction reaction (ORR) was observed in Pt-Fe/C and Pt-Cu/C catalysts subjected to heat treatment at 350 °C.A trend of catalytic activity for oxygen reduction reaction (ORR) was obtained: Pt-Cu/C (350°C)>Pt-Fe/C (350°C) > Pt-Ni/C (350°C) > Pt-Co/C (250°C) > Pt/C (350°C), showing that Pt-Cu/C-type catalysts had a higher catalytic activity with reasonable methanol tolerance.
Enhanced performance of polybenzimidazole-based high temperature proton exchange membrane fuel cell with gas diffusion electrodes prepared by automatic catalyst spraying under irradiation technique
(Elsevier, 2013) Su, Huaneng; Pasupathi, Sivakumar; Bladergroen, Bernard Jan; Linkov, Vladimir; Pollet, Bruno G.
Gas diffusion electrodes (GDEs) prepared by a novel automatic catalyst spraying under irradiation (ACSUI) technique are investigated for improving the performance of phosphoric acid (PA)-doped polybenzimidazole (PBI) high temperature proton exchange membrane fuel cell (PEMFC). The physical properties of the GDEs are characterized by pore size distribution and scanning electron microscopy (SEM). The electrochemical properties of the membrane electrode assembly (MEA) with the GDEs are evaluated and analyzed by polarization curve, cyclic voltammetry (CV) and electrochemistry impedance spectroscopy (EIS). Effects of PTFE binder content, PA impregnation and heat treatment on the GDEs are investigated to determine the optimum performance of the single cell. At ambient pressure and 160 o C, the maximum power density can reach 0.61 W cm-2, and the current density at 0.6 V is up to 0.38 A cm-2, with H /air and a platinum loading of 0.5 mg cm-2 on both electrodes. The MEA with the GDEs shows good stability for fuel cell operating in a short term durability test.
Factors influencing fuel cell life and a method of assessment for state of health
(University of the Western Cape, 2018) Dyantyi, Noluntu; Pasupathi, Sivakumar
Proton exchange membrane fuel cells (PEMFC) converts chemical energy from the electrochemical reaction of oxygen and hydrogen into electrical while emitting heat, oxygen depleted air (ODA) and water as by-products. The by-products have useful functions in aircrafts, such as heat that can be used for ice prevention, deoxygenated air for fire retardation and drinkable water for use on board. Consequently, the PEMFC is also studied to optimize recovery of the useful products. Despite the progress made, durability and reliability remain key challenges to the fuel cell technology. One of the reasons for this is the limited understanding of PEMFC behaviour in the aeronautic environment. The aim of this thesis was to define a comprehensive non-intrusive diagnostic technique that provides real time diagnostics on the PEMFC State of Health (SoH). The framework of the study involved determining factors that have direct influence on fuel cell life in aeronautic environment through a literature survey, examining the effects of the factors by subjecting the PEMFC to simulated conditions, establishing measurable parameters reflective of the factors and defining the diagnostic tool based on literature review and this thesis finding.
Fuel cell-battery hybrid powered light electric vehicle (golf cart): Influence of fuel cell on the driving performance
(Elsevier, 2013) Tolj, Ivan; Lototskyy, Mykhaylo; Davids, Moegamat Wafeeq; Pasupathi, Sivakumar; Swart, Gerhard; Pollet, Bruno G.
A light electric vehicle (golf cart, 5 kW nominal motor power) was integrated with a commercial 1.2 kW PEM fuel cell system, and fuelled by compressed hydrogen (two composite cylinders, 6.8 L/300 bar each). Comparative driving tests in the battery and hybrid (battery þ fuel cell) powering modes were performed. The introduction of the fuel cell was shown to result in extending the driving range by 63-110%, when the amount of the stored H2 fuel varied within 55-100% of the maximum capacity. The operation in the hybrid mode resulted in more stable driving performances, as well as in the increase of the total energy both withdrawn by the vehicle and returned to the vehicle battery during the driving. Statistical analysis of the power patterns taken during the driving in the battery and hybrid-powering modes showed that the latter provided stable operation in a wider power range, including higher frequency and higher average values of the peak power.
Gas diffusion electrodes for high temperature polymer electrolyte membrane fuel cells membrane electrode assemblies
(University of the Western Cape, 2014) Barron, Olivia; Pasupathi, Sivakumar
The need for simplified polymer electrolyte membrane fuel cell (PEMFCs) systems, which do not require extensive fuel processing, has led to increased study in the field of high temperature polymer electrolyte membrane fuel cells (HT-PEMFCs) applications. Although these HT-PEMFCs can operate with less complex systems, they are not without their own challenges; challenges which are introduced due to their higher operation temperature. This study aims to address two of the main challenges associated with HT-PEMFCs; the need for alternative catalyst layer (CL) ionomers and the prevention of excess phosphoric acid (PA) leaching into the CL. The first part of the study involves the evaluation of suitable proton conducting materials for use in the CL of high temperature membrane electrode assemblies (HT-MEAs), with the final part of the study focusing on development of a novel MEA architecture comprising an acid controlling region. The feasibility of the materials in HT-MEAs was evaluated by comparison to standard MEA configurations.
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.
A modified Adams fusion method for the synthesis of binary metal oxide catalysts for the oxygen evolution reaction
(University of Western Cape, 2020) Soudens, Franschke A; Pasupathi, Sivakumar
The majority of the global energy is sourced from conventional fossil fuels. The high demand for energy is accelerating along with the depletion of these fossil fuels. Hence, the shift to renewable energy sources and technology becomes indispensable. Hydrogen is considered a promising alternative to fossil fuels. Polymer electrolyte membrane water electrolysers offer an environmentally friendly technique for the production of hydrogen from renewable energy sources. However, the high overpotential and acidic environment at the anode is one of the challenges faced by polymer electrolyte membrane water electrolysers. This harsh environment requires distinct electrocatalysts which currently consist of expensive precious metals such as Ir, Ru and their oxides.
Multi-objective optimization of a metal hydride reactor coupled with phase change materials for fast hydrogen sorption time
(Journal of Energy Storage, 2023) Pasupathi, Sivakumar; Nyamsi, Serge Nyallang; Tolj, Ivan
Recently, the utilization of phase change materials (PCM) for the heat storage/recovery of the metal hydride's reaction heat has received increasing attention. However, the poor heat management process makes hydrogen sorption very slow during heat recycling. In this work, the H2 charging/discharging performance of a metal hydride tank (MHT) filled with LaNi5 and equipped with a paraffin-based (RT35) PCM finned jacket as a passive heat management medium is numerically investigated. Using a two-dimensional mathematical model validated with our in-house experiments, the effects of design parameters such as PCM thermophysical properties and the fin size on hydrogen charging/discharging times of the MHT are investigated systematically. The results showed that the PCM's melting point and apparent heat capacity have a conflicting impact on the hydrogen sorption times, i.e., the low melting point and high specific heat capacity reduce the H2 charging time
Nafion-stabilised platinum nanoparticles supported on titanium nitride: An efficient and durable electrocatalyst for phosphoric acid based polymer electrolyte fuel cells
(Elsevier, 2013) Kumar, Ravi; Pasupathi, Sivakumar; Pollet, Bruno G.; Scott, Keith
Nafion derived platinum nanoparticles were produced and successfully anchored on titanium nitride (TiN) support (Pt/TiN) and its suitability for phosphoric acid based polymer electrolyte membrane fuel cells is reported. Electrochemical cycling of Nafion stabilised Pt/TiN electrocatalyst exhibits good stability, durability and better electrocatalytic activity than the traditionally employed carbon supported Pt (Pt/C). Platinum supported on TiN exhibits better oxygen reduction reaction (ORR) activity as compared to carbon black (Vulcan XC 72). Nafion stabilised Pt/TiN shows a positive shift of 20 mV in half-wave potential measured from ORR polarisation curve in relation to Pt/C. Nafion stabilised Pt/TiN shows approximately two-fold increase in mass and specific activities than the Pt/C calculated from ORR data at 0.9 V. The improved durability of Pt/TiN catalyst arises from Nafion layer surrounding the Pt nanoparticles and corrosion resistant TiN support. Transition metal nitride based electrocatalysts are more active for cathode due to synergistic effect, which is observed in oxygen reduction reaction.
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).
Optimization of gas diffusion electrode for polybenzimidazole-based high temperature proton exchange membrane fuel cell: Evaluation of polymer binders in catalyst layer
(Elsevier, 2013) Su, Huaneng; Pasupathi, Sivakumar; Bladergroen, Bernard Jan; Linkov, Vladimir; Pollet, Bruno G.
Gas diffusion electrodes (GDEs) prepared with various polymer binders in their catalyst layers (CLs) were investigated to optimize the performance of phosphoric acid doped polybenzimidazole (PBI)-based high temperature proton exchange membrane fuel cells (HT-PEMFCs). The properties of these binders in the CLs were evaluated by structure characterization, electrochemical analysis, single cell polarization and durability test. The results showed that polytetrafluoroethylene (PTFE) and polyvinylidene difluoride (PVDF) are more attractive as CL binders than conventional PBI or Nafion binder. At ambient pressure and 160 o C, the maximum power density can reach w 0.61 W cm-2 (PTFE GDE), and the current density at 0.6 V is up to ca. 0.52 A cm-2 (PVDF GDE), with H2/air and a platinum loading of 0.5 mg cm-2 on these electrodes. Also, both GDEs showed good stability for fuel cell operation in a short term durability test.
Platinum based catalysts for the cathode of proton exchange membrane fuel cells
(University of the Western Cape, 2018) Ndzuzo, Linathi; Pasupathi, Sivakumar; Gómez, Juan Carlos Calderón
Oxygen reduction reaction (ORR) is carried out in the cathode of the proton exchange membrane fuel cell (PEMFC) and it is known for its sluggish kinetics and the existence of two-pathway mechanism, related with the production of water and hydrogen peroxide. Nowadays, the design of novel cathode catalysts that are able to generate both high oxygen reduction currents and water as main product is a challenge since it causes an enhancement in the performance of PEMFC. Generally, these catalysts are composed of platinum nanoparticles, bearing in mind its high activity towards the ORR. However, the use of platinum means an increase in the total cost of PEMFCs due to its scarcity and high cost. This topic has been the motivation for a wide research in the field of PEMFCs during the last several years, being the main goal to design efficient and low cost catalysts for the cathode of PEMFCs. In this Master thesis project, platinum-palladium (Pt-Pd) catalysts supported on carbon black (CB), carbon nanofibers (CNF) and carbon xerogels (CX) were synthesised using methanol (MeOH), formaldehyde (FMY), n-propanol (nPrOH), ethanol (EtOH) and ascorbic acid (AA). The as-prepared materials were physically characterised by energy dispersive X-ray (EDS), X-ray diffraction (XRD) and transmission electronic microscopy (TEM), in order to determine its composition and morphological characteristics. The catalytic activity towards ORR was assessed by means of electrochemical techniques as rotating disc electrode (RDE) and cyclic voltammetry (CV).
Pt-Sn/C as a possible methanol-tolerant cathode catalyst for DMFC
(Springer Verlag, 2013) Martin, Lynwill G.; Green, Ivan; Wang, X.; Pasupathi, Sivakumar; Pollet, Bruno G.
An effective method was developed for preparing highly dispersed nano-sized Pt–Sn/C electrocatalyst synthesised by a modified polyol reduction method. From XRD patterns, the Pt–Sn/C peaks shifted slightly to lower 2θ angles when compared with commercial Pt/C catalyst, suggesting that Sn formed alloy with Pt. Based on HR-TEM images, the Pt–Sn/C nanoparticles showed small particle sizes and well dispersed onto the carbon support with a narrow particle distribution. The methanol oxidation reaction on the as-prepared Pt–Sn/C catalyst appeared at lower currents (+7.08 mA at +480 mV vs. Ag/AgCl) compared to the commercial Pt/C (+8.25 mA at +480 mV vs. Ag/AgCl) suggesting that the Pt–Sn/C catalyst has ‘methanol tolerance capabilities’. Pt–Sn/C HA Slurry pH3 catalysts showed better activity towards the oxygen-reduction reaction (ORR) than commercial Pt/C which could be attributed to smaller particle sizes. In our study, the Pt–Sn/C catalyst appears to be a promising methanol-tolerant catalyst with activity towards the ORR in the DMFC.
RuxNb1-xO2 catalyst for the oxygen evolution reaction in proton exchange membrane water electrolysers
(Elsevier, 2013) Puthiyapura, Vinod Kumar; Pasupathi, Sivakumar; Basu, Suddhasatwa; Wu, Xu; Su, Huaneng; Varagunapandiyan, N.; Pollet, Bruno G.; Scott, Keith
Bimetallic catalyst system of ruthenium oxide (RuO2) and niobium oxide (Nb2O5) was prepared using the Adams method and the hydrolysis method. Physical and electrochemical characterizations of the catalysts were studied using X-ray diffraction (XRD), Scanning electron microscopy (SEM), cyclic voltammogram (CV) and polarization measurements. Nb2O5 addition to RuO2 was found to increase the stability of RuO2. In Adams method the sodium nitrate was found to be forming complex with Nb2O5 at high temperature reaction. This makes Adams method unsuitable for the synthesis of RuO2eNb2O5 bimetallic system. Hydrolysis method on other hand does not have this problem. But a proper mixture of two oxides was not obtained in hydrolysis method. A lower crystallite size for bimetallic system was obtained with Adams method compared to hydrolysis method. RuO2 prepared by Adams method had higher activity compared to the hydrolysis counterpart in electrolyzer operation with nafion membrane. A cell voltage of 1.62 V was obtained with RuO2 (A) at 1 A/cm2. A higher stability for Ru0.8Nb0.2O2(A) compared to RuO2
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:
Thermal conductivity and temperature profiles of the micro porous layers used for the polymer electrolyte membrane fuel cell
(Elsevier, 2013) Burheim, Odne S.; Su, Huaneng; Pasupathi, Sivakumar; Pharoah, Jon G.; Pollet, Bruno G.
The thermal conductivity and the thickness change with pressure of several different micro porous layers (MPL) used for the polymer electrolyte membrane fuel cell (PEMFC) were measured. The MPL were made with different compositions of carbon and polytetrafluoroethylene (PTFE). A one-dimensional thermal PEMFC model was used to estimate the impact that the MPL has on the temperature profiles though the PEMFC. The thermal conductivity was found to vary from as low as 0.05 up to as high as 0.12 W K 1 m 1 while the compaction pressure was varied from 4 bar and up to around 16 bar resulting in a decrease in thickness of approximately 40%. The PTFE content, which varied between 10 and 25%, did not result in any significant change in the compression or thermal conductivity. Both the thickness and the thermal conductivity changed irreversibly with compaction pressure. Considering a MPL thermal conductivity of 0.1 W K 1 m 1, a MPL thickness of 45 mm, a current density of 10 kAm 2 (1.0 A cm 2), liquid water (production and sorption), and a 30 mm membrane it was found that the MPL is responsible for a temperature increase of up to 2 C. This contribution can be lowered by integrating the MPL into the porous transport layer.
Validation of an externally oil-cooled 1 kWel HT-PEMFC stack operating at various experimental conditions
(Elsevier, 2013) Bujlo, P.; Pasupathi, Sivakumar; Ulleberg, Ø.; Scholta, J.; Nomnqa, M.V.; Rabiu, A.; Pollet, Bruno G.
The performance of 1 kWel 48-cell HT-PEMFC at various experimental conditions is presented, particularly at several CO concentrations (up to 1.0%). Polarization curves measured at various anode (1.0-2.5) and cathode (1.6-4.0) stoichiometries; stack operating temperatures (120-160 o C) and gas pressures (up to 0.5 barg) arereported and analysed. The minimum gas stoichiometries of 1.25 and 2.0 were determined for the anode and cathode, respectively. The highest stack power density of 225 mW cm-2 was measured at 160 o C and 0.4 A cm-2. Operation at COconcentrations up to 1% was achieved, although a loss of performance of about 4% was observed for low CO concentrations. The operating temperature enhanced fuel cell performance and tolerance to CO, even when supplied with higher CO concentration in the anode feed gas.

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