This study has focused on solid oxide electrolyser cells for high temperature steam electrolysis. Solid oxide electrolysis is the reverse operation of solid oxide fuel cells (SOFC), so many of the same component materials may be used. However, other electrode materials are of interest to improve performance and efficiency. In this work anode materials were investigated for use in solid oxide electrolysers. Perovskite materials of the form L₁₋ｘSrｘMO₃ , where M is Mn, Co, or Fe. LSM is a well understood electrode material for the SOFC. Under electrolysis operation LSM performed well and no interface reactions were observed between the anode and YSZ electrolyte. LSM has a relatively low conductivity and the electrode reaction is limited to the triple phase boundary regions. Mixed ionic-electronic conductors of LSCo and LSF were investigated, with these materials the anode reaction is not limited to triple phase boundaries. The LSCo anode had adherence problems in the electrolysis cells due to the thermal expansion coefficient mismatch with the YSZ electrolyte. The LSCo reacted with the YSZ at the anode/electrolyte interface forming insulating zirconate phases. Due to these issues the LSCo anode cells performed the poorest of the three. The performance of electrolysis cells with LSF anode exceeded both LSM and LSCo, particularly under steam operation, although an interface reaction between the LSF anode and YSZ electrolyte was observed. In addition to the anode material studies this work included the development of solid oxide electrolyser tubes from tape cast precursor materials. Tape casting is a cheap processing method, which allows for co-firing of all ceramic components. The design development resulted in a solid design, which can be fabricated reliably, and balances strength with performance. The design used LSM anode, YSZ electrolyte, and Ni-YSZ cathode materials but could easily be adapted for the use of other component materials. Proper sintering rates, cathode tape formulation, tube length, tape thickness, and electrolyte thickness were factors explored in this work to improve the electrolyser tubes.

Os ésteres de ácido ftálico são utilizados como aditivos na manufatura de plásticos e a contaminação do meio ambiente por esses compostos pode ocorrer por diferentes mecanismos. Dado o efeito destes no sistema endócrino de animais e seres humanos, efluentes contendo esses compostos sintéticos devem ser adequadamente tratados antes de qualquer descarte. Os tratamentos convencionais são ineficientes para tratar efluentes aquosos contendo esses ésteres e a oxidação eletroquímica tem sido utilizada como uma opção viável. Assim, neste trabalho foi estudada a degradação eletroquímica de dimetil ftalato (DMFt) utilizando três tipos de ânodos: Ti/Ru0.3Ti0.7O2, F-β-PbO2 e diamante dopado com boro (DDB). Os experimentos foram conduzidos em condições galvanostáticas em células de compartimento do tipo filtro-prensa e vários parâmetros, tais como, eletrólito suporte e a densidade de corrente, foram avaliados. Durante as eletro-oxidações, alíquotas das soluções foram analisadas cromatograficamente e por determinações de carbono orgânico total (COT) e demanda química de oxigênio (DQO). Quando utilizado o ânodo de Ti/Ru0.3Ti0.7O2, foram observados níveis de combustão próximos a 100% em baixos valores de carga elétrica aplicada, indicando um possível processo de incineração direta. Com a incidência de radiação UV incidindo diretamente na superfície do eletrodo, foi obtida a completa remoção de DMFt e 98 % de mineralização em meio ácido, elevadas concentração de cloreto e temperatura. A limitação de ambos os processos foi o transporte de massa e assim, os melhores resultados foram obtidos a baixas densidades de corrente. Com o uso do ânodo de β-PbO2 a remoção de DMFt foi superior na presença de Na2SO4 e em baixas densidades de corrente, com 40 % de mineralização. Com o ânodo de DDB foram realizadas eletro-oxidações na ausência e na presença de radiação UV e ultrassônica. Foi obtida a completa remoção de DMFt, COT e DQO em todas as condições estudadas, com maior eficiência a baixas densidades de corrente, devido a menor limitação por transferência de massa. Ocorreu um efeito positivo na eletrooxidação com aplicação conjunta das duas radiações, no entanto, menor do que o obtido com a aplicação destes processos separadamente. O mecanismo de degradação proposto apresenta a oxidação de DMFt seguida da remoção de grupos metil éster e a quebra do anel aromático para formar ácidos carboxílicos, os quais são mineralizados a dióxido de carbono. Na presença de cloreto, a produção de clorofenóis e ácido tartárico e o aumento na concentração dos intermediários formados são as principais diferenças observadas. / The phthalic acid esters are used as additives in plastics manufacturing and the environmental contamination by these compounds may occur by different mechanisms. Considering its effect on the endocrine system of animals and humans beings, effluents containing these synthetic compounds must be properly treated before any disposal. Traditional methods present limited efficiency for treating wastewater containing these esters and electrochemical oxidation has been proposed as a viable option. In this work, the electrochemical degradation of dimethyl phthalate (DMFt) using three types of anodes: Ti/Ru0.3Ti0.7O2, β-PbO2,F and boron-doped diamond (BDD) was studied. The experiments were performed under galvanostatic conditions using a one compartment filter-press cell and different parameters, such as, electrolyte and current density, were analyzed. During the electro-oxidations, aliquots of the solutions extracted at diffent times were analyzed by liquid chromatography and by variations of total organic carbon (TOC) and chemical oxygen demand (COD). Using Ti/Ru0.3Ti0.7O2 anode, the combustion levels were almost 100% when low values of electrical charge were applied, indicating a possible direct incineration process. Applying UV radiation to the electrode surface, the complete removal of DMFt and 98% mineralization were obtained in acid medium with relative high chloride concentration. Both processes were limited by mass transport and therefore, the best results were obtained at low current densities. Using β-PbO2 anode, the removal of DMFt was higher with 40% of mineralization in the presence of Na2SO4 and at low current densities. Using DDB anode, the electrooxidations were performed in the absence and presence of UV and ultrasonic radiations. The complete removal of DMFT, TOC and COD was obtained for all conditions studied with greater efficiency at low current densities because the smallest mass transfer limitation. A positive effect on the electro-oxidation was observed when UV and ultrasound radiation were applied simultaneously however, lower than that obtained with the application of the processes separately. The degradation mechanism proposed presents the oxidation of DMFt followed by removal of methyl ester groups and breakage of the aromatic ring to form carboxylic acids, which are mineralized to carbon dioxide. In the presence of chloride, the production of chlorophenol and tartaric acid and the increased concentration of the intermediates formed are the majors differences observed.

Solid Oxide Fuel Cells (SOFC) are electrochemical energy conversion devices which allow fuel gases, e.g. hydrogen or natural gas, to be converted to electricity and heat at much high efficiencies than combustion-based energy conversion technologies. SOFC are particularly suited to employment in stationary energy conversion applications, e.g. micro-combined heat and power (μ-CHP) and base load, which are certain to play a large role in worldwide decentralisation of power distribution and supply over the coming decades. Use of high-temperature SOFC technology within these systems is also a vital requirement in order to utilise fuel gases which are readily available in different areas of the world. Unfortunately, the limiting factor to the long-term commercialisation of SOFC systems is the redox instability, coking intolerance and sulphur poisoning of the state-of-the-art Ni-based cermet composite anode material. This research explores the ‘powder to power' development of alternative SOFC anode catalyst systems by impregnation of an A-site deficient La0.20Sr0.25Ca0.45TiO3 (LSCT[sub](A-)) anode ‘backbone' microstructure with coatings of ceria-based oxide ion conductors and metallic electrocatalyst particles, in order to create a SOFC anode which exhibits high redox stability, tolerance to sulphur poisoning and low voltage degradation rates under operating conditions. A 75 weight percent (wt. %) solids loading LSCT[sub](A-) ink, exhibiting ideal properties for screen printing of thick-film SOFC anode layers, was screen printed with 325 and 230 mesh counts (per inch) screens onto electrolyte supports. Sintering of anode layers between 1250 °C and 1350 °C for 1 to 2 hours indicated that microstructures printed with the 230 mesh screen provided a higher porosity and improved grain connectivity than those printed with the 325 mesh screen. Sintering anode layers at 1350 °C for 2 hours provided an anode microstructure with an advantageous combination of lateral grain connectivity and porosity, giving rise to an ‘effective' electrical conductivity of 17.5 S cm−1 at 850 °C. Impregnation of this optimised LSCT[sub](A-) anode scaffold with 13-16 wt. % (of the anode mass) Ce0.80Gd0.20O1.90 (CGO) and either Ni (5 wt. %), Pd, Pt, Rh or Ru (2-3 wt. %) and integration into SOFC resulted in achievement of Area Specific Resistances (ASR) of as low as 0.39 Ω cm−2, using thick (160 μm) 6ScSZ electrolytes. Durability testing of SOFC with Ni/CGO, Ni/CeO2, Pt/CGO and Rh/CGO impregnated LSCT[sub](A-) anodes was subsequently carried out in industrial button cell test rigs at HEXIS AG, Winterthur, Switzerland. Both Ni/CGO and Pt/CGO cells showed unacceptable levels of degradation (14.9% and 13.4%, respectively) during a ~960 hour period of operation, including redox/thermo/thermoredox cycling treatments. Significantly, by exchanging the CGO component for the CeO2 component in the SOFC containing Ni, the degradation over the same time period was almost halved. Most importantly, galvanostatic operation of the SOFC with a Rh/CGO impregnated anode for >3000 hours (without cycling treatments) resulted in an average voltage degradation rate of < 1.9% kh−1 which, to the author's knowledge, has not previously been reported for an alternative, SrTiO3-based anode material. Finally, transfer of the Rh/CGO impregnated LSCT[sub](A-) anode to industrial short stack (5 cells) scale at HEXIS AG revealed that operation in relevant conditions, with low gas flow rates, resulted in accelerated degradation of the Rh/CGO anode. During a 1451 hour period of galvanostatic operation, with redox cycles and overload treatments, a voltage degradation of 19.2% was observed. Redox cycling was noted to briefly recover performance of the stack before rapidly degrading back to the pre-redox cycling performance, though redox cycling does not affect this anode detrimentally. Instead, a more severe, underlying degradation mechanism, most likely caused by instability and agglomeration of Rh nanoparticles under operating conditions, is responsible for this observed degradation. Furthermore, exposure of the SOFC to fuel utilisations of >100% (overloading) had little effect on the Rh/CGO co-impregnated LSCT[sub](A-) anodes, giving a direct advantage over the standard HEXIS SOFC. Finally, elevated ohmic resistances caused by imperfect contacting with the Ni-based current collector materials highlighted that a new method of current collection must be developed for use with these anode materials.

No description available.

In this paper, we report that various kinds of active sites on graphite surface including active hydrophilic sites markedly affect the electrochemical performance of graphite anodes for lithium ion batteries under different humidity conditions. After depositing metals such as Ag and Cu by immersing and heat-treating, these active sites on the graphite surface were removed or covered and its electrochemical performance under the high humidity conditions was markedly improved. This suggests that lithium ion batteries can be assembled under less strict conditions and that it provides a valuable direction to lower the manufacturing cost for lithium ion batteries.

The surface of a dense Ni-YSZ anode was modified with a thin-film coating of niobium oxide (Nb2O5) in order to understand the mechanism of sulfur tolerance and the behavior of carbon deposition. Results suggest that the niobium oxide was reduced to NbO2 under operating conditions, which has high electrical conductivity. The NbOx coated dense Ni-YSZ showed sulfur tolerance when exposed to 50 ppm H2S at 700°C over 12 h. Raman spectroscopy and XRD analysis suggest that different phases of NbSx formed on the surface. Further, the DOS (density of state) analysis of NbO2, NbS, and NbS2 indicates that niobium sulfides can be considered as active surface phases in the H2S containing fuels. It was demonstrated that carbon formation was also suppressed with niobium oxide coating on dense Ni-YSZ in humidified CH4 (3% H2O) at 850ºC. In particular, under active operating conditions, there was no observable surface carbon as revealed using Raman spectroscopy due probably to electrochemical oxidation of carbon. Stable performances of functional cells consisting of Pt/YSZ/Nb2O5 coated dense Ni-YSZ in the fuel were achieved; there was no observable degradation in performance due to carbon formation. The results suggest that a niobium oxide coating has prevented carbon from formation on the surface probably by electrochemically oxidation of carbon on niobium oxide coated Ni-YSZ. On the other hand, computational results suggest that, among the metals studied, Mo seems to be a good candidate for Ni surface modification. Ni-based anodes were modified with Mo using wet-impregnation techniques, and tested in 50 ppm H2S-contaminated fuels. It was found that the Ni-Mo/CeO2 anodes have better sulfur tolerance than Ni, showing a current transient with slow recovery rather than slow degradation in 50 ppm H2S balanced with H2 at 700°C.

Two novel lithium host materials were investigated using structural and electrochemical analysis; the cathode material Li₂CoSiO₄ and the LiMO₂ class of anodes (where M is a transition metal ion). Li₂CoSiO₄ materials were produced utilising a combination of solid state and hydrothermal synthesis conditions. Three Li₂CoSiO₄ polymorphs were synthesised; β[subscript(I)], β[subscript(II)] and γ₀. The Li₂CoSiO₄ polymorphs formed structures based around a distorted Li₃PO₄ structure. The β[subscript(II)] material was indexed to a Pmn2₁ space group, the β[subscript(I)] polymorph to Pbn2₁ and the γ₀ material was indexed to the P2₁/n space group. A varying degree of cation mixing between lithium and cobalt sites was observed across the polymorphs. The β[subscript(II)] polymorph produced 210mAh/g of capacity on first charge, with a first discharge capacity of 67mAh/g. It was found that the β[subscript(I)] material converted to the β[subscript(II)] polymorph during first charge. The γ₀ polymorph showed almost negligible electrochemical performance. Capacity retention of all polymorphs was poor, diminishing significantly by the tenth cycle. The effect of mechanical milling and carbon coating upon β[subscript(II)], β[subscript(I)] and γ₀ materials was also investigated. Various Li[subscript(1+x)]V[subscript(1-x)]O₂ materials (where 0≤X≤0.2) were produced through solid state synthesis. LiVO₂ was found to convert to Li₂VO₂ on discharge, this process was found to be strongly dependent on the amount of excess lithium in the system. The Li₁.₀₈V₀.₉₂O₂ material had the highest first discharge capacity at 310mAh/g. It was found that the initial discharge consisted of several distinct electrochemical processes, connected by a complicated relationship, with significant irreversible capacity on first discharge. Several other LiMO₂ systems were investigated for their ability to convert to layered Li₂MO₂ structures on low voltage discharge. While LiCoO₂ failed to convert to a Li₂CoO₂ structure, LiMn₀.₅Ni₀.₅O₂ underwent an addition type reaction to form Li₂Mn₀.₅Ni₀.₅O₂. A previously unknown Li₂Ni[subscript(X)]Co[subscript(1-X)]O₂ structure was observed, identified during the discharge of LiNi₀.₃₃Co₀.₆₆O₂.

Made available in DSpace on 2014-10-09T12:34:06Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:00:10Z (GMT). No. of bitstreams: 0 / Dissertação (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Submitted by Claudinei Pracidelli (cpracide@ipen.br) on 2014-11-10T12:31:52Z No. of bitstreams: 0 / Made available in DSpace on 2014-11-10T12:31:52Z (GMT). No. of bitstreams: 0 / Tese (Doutorado em Tecnologia Nuclear) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Made available in DSpace on 2014-10-09T12:34:06Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:00:10Z (GMT). No. of bitstreams: 0 / Diversos anodos para célula a combustível de óxido sólido (SOFC) têm sido estudados devido aos problemas de deterioração dos anodos tradicionalmente usados, os compósitos à base de zircônia estabilizada/Ni (YSZ/Ni). Estudos prévios evidenciaram que a perovskita La0,75Sr0,25Cr0,50Mn0,50O3 (LSCM) possui desempenho similar em SOFCs usando hidrogênio e metano como combustível, tornando essa cerâmica um possível substituto dos compósitos à base de níquel. No presente estudo, foram sintetizados compostos La0,75Sr0,25Cr0,50-xMn0,50- yRux,yO3 (LSCM-Ru) pelo método dos precursores poliméricos. Análises termogravimétrica e térmica diferencial (TG/ATD) simultâneas e difração de raios X (DRX) foram utilizadas para monitorar a evolução térmica das resinas precursoras e a formação de fase dos compostos. As propriedades elétricas de amostras sinterizadas foram estudadas pela técnica de 4 pontas de prova dc na faixa de temperatura entre 25 °C e 800 °C. Os resultados experimentais indicaram a formação de fase única dos compostos LSCM-Ru calcinados a ~1200 °C. Os parâmetros de rede, calculados a partir dos dados de DRX, revelaram que a substituição parcial dos íons Cr ou Mn pelo Ru não altera significativamente a estrutura cristalina do LSCM até x,y ~ 0,10; uma característica consistente com os raios iônicos similares dos cátions Cr, Mn e Ru com número de coordenação seis. Medidas de resistividade elétrica ao ar mostraram que o mecanismo de transporte não é alterado e que o efeito da substituição de Ru nas propriedades elétricas do composto depende do íon substituído (Cr ou Mn) de maneira consistente com suas substituições parciais. Os testes de SOFCs unitárias revelaram que células com os anodos constituídos por uma camada coletora de corrente do anodo cerâmico LSCM-Ru e uma camada funcional de YSZ/Ni têm desempenho superior a células contendo apenas o anodo cerâmico. As células contendo os anodos cerâmicos LSCM-Ru foram testadas em hidrogênio e etanol, entre 800 °C e 950 °C, e mostraram desempenho em etanol superior ao em hidrogênio; uma característica que foi associada às propriedades de transporte eletrônico dos compostos LSCM-Ru em atmosfera redutora. Os resultados sugerem que os compostos LSCM com substituição parcial de Ru são anodos promissores para SOFC operando com etanol. / Dissertação (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP