Research Articles (SAIAMC)

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Components for PEM fuel cells: An overview
(Trans Tech Publications, 2010) Sivakumar, Pasupathi; Maiyalagan, Thandavarayan
Fuel cells, as devices for direct conversion of the chemical energy of a fuel into electricity by electrochemical reactions, are among the key enabling technologies for the transition to a hydrogen-based economy. Among the various types of fuel cells, polymer electrolyte membrane fuel cells (PEMFCs) are considered to be at the forefront for commercialization for portable and transportation applications because of their high energy conversion efficiency and low pollutant emission. Cost and durability of PEMFCs are the two major challenges that need to be addressed to facilitate their commercialization. The properties of the membrane electrode assembly (MEA) have a direct impact on both cost and durability of a PEMFC. An overview is presented on the key components of the PEMFC MEA. The success of the MEA and thereby PEMFC technology is believed to depend largely on two key materials: the membrane and the electro-catalyst. These two key materials are directly linked to the major challenges faced in PEMFC, namely, the performance, and cost. Concerted efforts are conducted globally for the past couple of decades to address these challenges. This chapter aims to provide the reader an overview of the major research findings to date on the key components of a PEMFC MEA.
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:
Pt decorated amorphous RuIr alloys as high efficiency electrocatalyst for methanol oxidation
(The Electrochemical Society, 2012) Ma, Y.J.; Wang, H.; Ji, Shan; Pollet, Bruno G.; Wang, R.F.
This study focuses primarily on improving the utilization and activity of anodic catalysts for methanol electro-oxidation. The Direct Methanol Fuel Cell (DMFC) anodic catalyst, a carbon supported Pt decorated amorphous RuIr nanoparticles catalyst (Pt@RuIr/C) was prepared by a two-step reduction method. The structure of Pt@RuIr/C nanoparticles was confirmed by Transmission Electron Microscopy (TEM) and X-ray Diffraction (XRD). The Pt@RuIr electrocatalysts exhibited good uniformity in distribution. Cyclic Voltammetry experiments showed that under the same quality of noble-metal, the Pt@RuIr/C catalyst had higher activity than the PtRuIr/C catalyst for methanol oxidation. It was also shown that the as-prepared structure of the Pt decorated amorphous RuIr alloys could obviously decrease the usage of noble-metal and enhance its catalytic activity at the same time.
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.
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.
Characterization and activity test of commercial Ni/Al2O3, Cu/ZnO/Al2O3 and prepared NieCu/Al2O3 catalysts for hydrogen production from methane and methanol fuels
(Elsevier, 2013) Khzouz, Martin; Wood, Joe; Pollet, Bruno G.; Bujalski, Waldemar
In this study, methane and methanol steam reforming reactions over commercial Ni/Al2O3, commercial Cu/ZnO/Al2O3 and prepared NieCu/Al2O3 catalysts were investigated. Methane and methanol steam reforming reactions catalysts were characterized using various techniques. The results of characterization showed that Cu particles increase the active particle size of Ni (19.3 nm) in NieCu/Al2O3 catalyst with respect to the commercial Ni/ Al2O3 (17.9). On the other hand, Ni improves Cu dispersion in the same catalyst (1.74%) in comparison with commercial Cu/ZnO/Al2O3 (0.21%). A comprehensive comparison between these two fuels is established in terms of reaction conditions, fuel conversion, H2 selectivity, CO2 and CO selectivity. The prepared catalyst showed low selectivity for CO in both fuels and it was more selective to H2, with H2 selectivities of 99% in methane and 89% in methanol reforming reactions. A significant objective is to develop catalysts which can operate at lower temperatures and resist deactivation. Methanol steam reforming is carried out at a much lower temperature than methane steam reforming in prepared and commercial catalyst (275-325 o C). However, methane steam reforming can be carried out at a relatively low temperature on NieCu catalyst (600-650 o C) and at higher temperature in commercial methane reforming catalyst (700-800 o C). Commercial Ni/Al2O3 catalyst resulted in high coke formation (28.3% loss in mass) compared to prepared NieCu/Al2O3 (8.9%) and commercial Cu/ZnO/Al2O3 catalysts (3.5%).
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.
Synthesis of carbon-supported PdSn–SnO2 nanoparticles with different degrees of interfacial contact and enhanced catalytic activities for formic acid oxidation
(Royal Society of Chemistry, 2013) Wang, Hui; Liu, Ziyue; Ma, Yanjiao; Julian, Key; Ji, Shan; Linkov, Vladimir; Wang, Rongfang
The conjunction of the PdSn alloy and SnO2 is of interest for improving catalytic activity in formic acid oxidation (FAO). Here, we report the synthesis of PdSn–SnO2 nanoparticles and a study of their catalytic FAO activity. Different degrees of interfacial contact between SnO2 and PdSn were obtained using two different stabilizers (sodium citrate and EDTA) during the reduction process in catalyst preparation. Compared to the PdSn alloy, PdSn–SnO2 supported on carbon black showed enhanced FAO catalytic activity due to the presence of SnO2 species. It was also found that interfacial contact between the PdSn alloy and the SnO2 phase has an impact on the activity towards CO oxidation and FAO.
Membrane electrode assemblies with low noble metal loadings for hydrogen production from solid polymer electrolyte water electrolysis
(Elsevier, 2013) Su, Huaneng; Linkov, Vladimir; Bladergroen, Bernard Jan
High performance membrane electrode assemblies (MEAs) with low noble metal loadings (NMLs) were developed for solid polymer electrolyte (SPE) water electrolysis. The electro- chemical and physical characterization of the MEAs was performed by IeV curves, elec- trochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM). Even though the total NML was lowered to 0.38 mg cm-2, it still reached a high performance of 1.633 V at 2 A cm-2 and 80 o C, with IrO2 as anode catalyst. The influences of the ionomer content in the anode catalyst layer (CL) and the cell temperature were investigated with the purpose of optimizing the performance. SEM and EIS measurements revealed that the MEA with low NML has very thin porous cathode and anode CLs that get intimate contact with the electrolyte membrane, which makes a reduced mass transport limitation and lower ohmic resistance of the MEA. A short-term water electrolysis operation at 1 A cm-2 showed that the MEA has good stability: the cell voltage maintained at ~1.60 V without distinct degradation after 122 h operation at 80 o C and atmospheric pressure.
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
Palygorskite hybridized carbon nanocomposite as a high-performance electrocatalyst support for formic acid oxidation
(South African Chemical Institute (SACI), 2013) Linkov, Vladimir; Ji, Shan; Wang, Keliang; Wang, Hui; Wang, Rongfang; Key, Julian
A nanocomposite, in which acid-treated palygorskite was hybridized with carbon, was prepared and designed as an efficient support for electrocatatlysts. Pd nanoparticles were deposited on the hybrid support as an electrocatalyst for formic acid oxidation. The hybrid supports and electrocatalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS).TEMandXRDresults showed that acid treatment had an effective impact on the morphology of palygorskite, but did not destroy its architecture. XPS results indicated that the introduction of palygorskite resulted in a negative shift of binding energy of Pd deposited on it. The electrochemical results showed that the addition of palygorskite into the carbon facilitated the formation ofOHads orOads on the surface of Pd/C-PLS, and further improved the formic acid electrooxidation activity. Therefore, considerable improvements in electrocatalytic activity toward formic acid oxidation was achieved by using this hybrid support when compared with conventional carbon support, suggesting that the introduction of SiO2-based porous palygoriskite was an excellent and cost-efficient way to improve the electrocatalytic performance of carbon support.
Magnesium–carbon hydrogen storage hybrid materials produced by reactive ball milling in hydrogen
(Elsevier, 2013) Lototskyy, Mykhaylo; Sibanyoni, J.M.; Denys, R.V.; Williams, M.; Pollet, Bruno G.; Yartys, V.A.
Time-resolved studies uncovered kinetics and mechanism of Mg–hydrogen interactions during High energy reactive ball milling in hydrogen (HRBM) in presence of various types of carbon, including graphite (G), activated carbon (AC), multi-wall carbon nanotubes (MWCNT), expandable (EG) and thermally-expanded (TEG) graphite. Introduction of carbon significantly changes the hydrogenation behaviour, which becomes strongly dependent on the nature and amount of carbon additive. For the materials containing 1 wt.% AC or TEG, and 5 wt.% MWCNT, the hydrogenation becomes superior to that for the individual magnesium and finishes within 1 h. Analysis of the data indicates that carbon acts as a carrier of the ‘‘activated’’ hydrogen by a mechanism of spill-over. For Mg–G the hydrogenation starts from an incubation period and proceeds slower. An increase in the content of EG and TEG above 1 wt.% results in the deterioration of the hydrogenation kinetics. The effect of carbon additives has roots in their destruction during the HRBM to form graphene layers encapsulating the MgH2 nanoparticles and preventing the grain growth. This results in an increase of absorption–desorption cycle stability and a decrease of the MgH2 crystallite size in the re-hydrogenated Mg–C hybrid materials (40–125 nm) as compared to Mg alone (180 nm).
Biomass-derived activated carbon as high-performance non-precious electrocatalyst for oxygen reduction
(Royal Society of Chemistry, 2013) Wang, Keliang; Wang, Hui; Ji, Shan; Feng, Hanqing; Linkov, Vladimir; Wang, Rongfang
A new type of Fe and N doped carbon material is synthesized by pyrolyzing ferric chloride doped egg white (EW) and the proposed synthetic route is easy, green, and low-cost. In addition, the as-prepared sample exhibits a feasible magnetism and comparable oxygen reduction reaction (ORR) activity to commercial Pt/C.
A new route to control texture of materials: Nanostructured ZnFe2O4 photoelectrodes
(2013) Tahir, Asif Ali; Burch, Henry A.; Wijayantha, K.G. Upul; Pollet, Bruno G.
Studies were conducted to investigate the influence of deposition solution composition (methanol ≤ the deposition solvent ≤ ethanol) on their physical and chemical properties that matters in the aerosol formation and subsequent decomposition during the aerosol assisted chemical vapour deposition (AACVD) of ZnFe2O4 electrodes. The FEGSEM studies found that the change of composition of deposition solution produced a dramatic change in the ZnFe2O4 electrode texture. The ZnFe2O4 electrodes deposited from methanol as well as predominately methanolic solvents had a relatively compact morphology. In contrast, the electrodes deposited from ethanol as well as predominately ethanolic solvents showed highly textured rod-like structure at nanoscale. The change in electrode texture is explained in terms of changes occurred in precursor decomposition pathways from heterogeneous and homogeneous when the composition of deposition solution is systematically varied. The photoelectrochemical (PEC) properties of all ZnFe2O4 electrodes were studied by recording JeV characteristics under AM1.5 illumination and the photocurrent spectra. The textured electrodes exhibited a significantly higher photocurrent compared to their compact counterparts. This is attributed to the improved photogenerated minority carrier collection at the ZnFe2O4/electrolyte interface as the average feature size gradually decreased. The photocurrent density (at 0.25 V vs. Ag/AgCl/3M KCl) increases rapidly when the electrode is deposited from the solvent containing 60% ethanol and above, which is in close agreement with the textural changes taken place in ZnFe2O4 electrodes.
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.
Effect of the structure of Ni nanoparticles on the electrocatalytic activity of Ni@Pd/C for formic acid oxidation
(Elsevier, 2013) Wang, Rongfang; Wang, Hui; Wang, Xingli; Liao, Shijun; Linkov, Vladimir; Ji, Shan
Ni@Pd/C catalysts were synthesized, using Ni/C with different crystalline structures prepared with various ligands. A series of characterizations were performed by transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy. The results indicated the electrocatalysts with amorphous/crystalline (denoted as Nia and Nic) Ni structures decorated with Pd. The formic acid electrocatalytic oxidation results showed that the peak current of Nia@Pd/C was about 1.2 times higher than that of Nic@Pd/C. The good electrochemical performance and stability of Pd-modified amorphous Ni substrate reveals that the core structure plays an important role in the electrocatalytic activity and the change of the structure can improve the activity and stability of electrocatalysts.
Selenium-functionalized carbon as a support for platinum nanoparticles with improved electrochemical properties for the oxygen reduction reaction and CO tolerance
(Electrochemical Society, 2013) Wang, Hui; Da, Huahua; Ji, Shan; Liao, Shijun; Wang, Rongfang
Using selenium-functionalized carbon as supports, platinum nanoparticles were uniformly dispersed on the carbon surface, and showed improved electrochemical properties for the oxygen reduction reaction. At the same time the CO tolerance is improved. The method provides a new route for functionalization of the carbon surface on which to disperse noble metal nanoparticles for use as electrocatalysts in the oxygen reduction reaction.
Poisoning-tolerant metal hydride materials and their application for hydrogen separation from CO2/CO containing gas mixtures
(Elsevier, 2013) Modibane, K.D.; Williams, M.; Lototskyy, Mykhaylo; Davids, M.W.; Klochko, Ye.; Pollet, Bruno G.
Metal hydride materials offer attractive solutions in addressing problems associated with hydrogen separation and purification from waste flue gases. However, a challenging problem is the deterioration of hydrogen charging performances resulting from the surface chemical action of electrophilic gases. In this work, the feasibility study of poisoning tolerance of surface modified AB5-type hydride forming materials and their application for hydrogen separation from process gases containing carbon dioxide and monoxide was carried out. Target composition of La(Ni,Co,Mn,Al)5 substrate was chosen to provide maximum reversible hydrogen capacity at the process conditions. The selected substrate alloy has been shown to be effectively surface-modified by fluorination followed by electroless deposition of palladium. The surface-modified material exhibited good coating quality, high cycle stability and minimal deterioration of kinetics of selective hydrogen absorption at room temperature, from gas mixtures containing 10% CO2 and up to 100 ppm CO. The experimental prototype of a hydrogen separation unit, based on the surface-modified metal hydride material, was tested and exhibited stable hydrogen separation and purification performances when exposed to feedstocks containing concentrations of CO2
Application of surface-modified metal hydrides for hydrogen separation from gas mixtures containing carbon dioxide and monoxide
(Elsevier, 2013) Lototskyy, Mykhaylo; Modibane, K.D.; Williams, M.; Klochko, Ye.; Linkov, Vladimir; Pollet, Bruno G.
Application of surface-modified MH material for H2 separation using temperature/pressure swing absorption–desorption was studied. The substrate alloy had the following composition LaNi3.55Co0.75Al0.4-Mn0.3, and the surface modification was carried out through fluorination followed by aminosilane functionalization and electroless deposition of Pd. The material was found to have good poisoning tolerance towards surface adsorbates, even for the large (rv1.5 kg) batches. Feasibility of its application for H2 separation from gas mixtures (up to 30% CO2 and 100 ppm CO) was demonstrated by testing of a prototype H2 separation system (rv280 g of MH in two reactors), and H2 separation reactor (0.75 kg of MH). The H2 separation was characterized by stable performances in the duration of 250 absorption/desorption cycles. However, the total process productivity was found to be limited by the sluggish H2 absorption (partial H2 pressure 62.5 bar, temperature below 100 °C). In the presence of CO2 and CO, additional deceleration of H2 absorption was observed at space velocities of the feed gas below 5000 h
Ethanol oxidation activity and structure of carbon-supported Pt-modified PdSn-SnO2 influenced by different stabilizers
(Elsevier, 2013) Wang, Hui; Liu, Ziyue; Ji, Shan; Wang, Keliang; Zhou, Tianbao; Wang, Rongfang
PdSn-SnO2 nanoparticles supported on Vulcan XC-72 carbon were synthesized by chemical reduction in the presence of three different stabilizing agents: ethylene diamine tetra-acetic acid (EDTA), sodium citrate (Nacitrate) and hexamethylenetetramine (HMTA). TEM analysis showed that PdSn-SnO2 /C catalyst made using the HMTA stabilizer produced the smallest particle size. XRD analysis detected the presence of PdSn alloy and the SnO2 phase in all three PdSn-SnO2 /C samples, and showed that PdSn-SnO2 (HMTA) had the smallest lattice parameter. After PdSn-SnO2 samples were modified by Pt, the particle size distribution and average size of nanoparticles of Pt-PdSn-SnO2 did not obviously change, and the fcc structure of PdSn in all three samples was retained. XPS measurement showed a higher upshift of Pt 4f binding energy occurred for Pt/PdSn-SnO2 /C (HMTA) compared to those of Pt/PdSn-SnO2 /C (EDTA) and Pt/PdSn-SnO2 /C (Nacitrate). Pt/PdSn-SnO2 /C (HMTA) was also found to have the highest CO and ethanol oxidation activity among the three catalysts.

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