In recent years an emphasis has been placed on the development of alternative and clean energy sources to reduce the global use of fossil fuels. One of these alternatives entails the use of H2 as an energy carrier, which can be obtained amongst others using thermochemical processes, for example the hybrid sulphur process (HyS). The HyS process is based on the thermal decomposition of sulphuric acid into water, sulphur dioxide and oxygen. The subsequent chemical conversion of the sulphur dioxide saturated water back to sulphuric acid and hydrogen is achieved in an electrolyser using a platinum coated proton exchange membrane. This depolarised electrolysis requires a theoretical voltage of only 0.158 V compared to water electrolysis requiring approximately 1.23 V. One of the steps in the development of this technology at the North-West University, entailed the establishment of the platinum coating technology which entailed two steps; firstly using newly obtained equipment to manufacture the membrane electro catalyst assemblies (MEA’s) and gas diffusion electrodes (GDE’s) and secondly to test these MEA’s and GDE’s using sulphur dioxide depolarized electrolysis by comparing the manufactured MEA’s and GDE’s to commercially available MEA’s and GDE’s. Different MEA’s and GDE’s were manufactured using both a screen printing (for the microporous layer deposition) and a spraying technique. The catalyst loadings were varied as well as the type and thickness of the proton exchange membranes used. The proton exchange membranes that were included in this study were Nafion 117®, sPSU-PBIOO and SfS-PBIOO membranes whereas the gas diffusion layer consisted of carbon paper with varying thicknesses (EC-TP01-030 – 0.11 mm and EC-TP01-060 – 0.19mm). MEA and GDE were prepared by first preparing an ink that was used both for MEA and GDE spraying. The MEA’s were prepared by spraying various catalyst coatings onto the proton exchange membranes containing 0.3, 0.6 and 0.9 mg/cm2 platinum respectively. The GDE’s were first coated by a micro porous carbon layer using the screen printing technique in order to attain a suitable surface for catalyst deposition. Using the spraying technique GDE’s containing 0.3, 0.6, 0.9 mg/cm2 platinum were prepared. After SEM analysis, the MEA’s and GDE’s performance was measured using SO2 depolarized electrolysis. From the electrolysis experiments, the voltage vs. current density generated during operation, the hydrogen production, the sulphuric acid generation and the hydrogen production efficiency was obtained. From the results it became clear that while the catalyst loading had little effect on performance there were a number of factors that did have a significant influence. These included the type of proton exchange membrane, the membrane thickness and whether the catalyst coating was applied to the proton exchange membrane (MEA) or to the gas diffusion layer (GDE). During SO2 depolarized electrolysis VI curves were generated which gave an indication of the performance of the GDE’s and MEA’s. The best preforming GDE was GDE-3 (0.46V @ 320 mA/cm2), which included a GDE EC-TP01-060, while the best preforming MEA’s were NAF-4 (0.69V @ 320mA/cm2) consisting of a Nafion117 based MEA and PBI-1 (0.43V @ 320mA/cm2) made from a sPSU-PBIOO blended membrane. During hydrogen production it became clear that the GDE’s produced the most hydrogen (best was GDE-02 a in house manufactured GDE yielding 67.3 mL/min @ 0.8V), followed by the Nafion® MEA’s (best was NAF-4 a commercial MEA yielding 57.61 mL/min @ 0.74V) and the PBI based MEA’s. , (best was PBI-2 with 67.11 mL/min @ 0.88V). Due to the small amounts of acid produced and the SO2 crossover, a significant error margin was observed when measuring the amount of sulphuric acid produced. Nonetheless, a direct correlation could still be seen between the acid and the hydrogen production as had been expected from literature. The highest sulphuric acid concentrations produced using the tested GDE’s and MEA’s from this study were the in-house manufactured GDE-01 (3.572mol/L @ 0.8V), the commercial NAF-4 (4.456mol/L @ 0.64V) and the in-house manufactured PBI-2 (3.344mol/L @ 0.8V). The overall efficiency of the GDE’s were similar, ranging from less than 10% at low voltages (± 0.6V) increasing to approximately 60% at ± 0.8V. For the MEA’s larger variation was observed with NAF-4 reaching efficiencies of nearly 80% at 0.7V. In terms of consistency of performance it was shown that the Nafion MEA’s preformed most consistently followed by the GDE’s and lastly the PBI based MEA’s which for the PBI based membranes can probably be ascribed to the significant difference in thickness of the thin PBI vs. the Nafion based membranes. In summary the study has shown the results between the commercially obtained and the in-house manufactured GDE’s and MEA’s were comparable confirming the suitability of the coating techniques evaluated in this study. / MSc (Chemistry), North-West University, Potchefstroom Campus, 2014

In recent years an emphasis has been placed on the development of alternative and clean energy sources to reduce the global use of fossil fuels. One of these alternatives entails the use of H2 as an energy carrier, which can be obtained amongst others using thermochemical processes, for example the hybrid sulphur process (HyS). The HyS process is based on the thermal decomposition of sulphuric acid into water, sulphur dioxide and oxygen. The subsequent chemical conversion of the sulphur dioxide saturated water back to sulphuric acid and hydrogen is achieved in an electrolyser using a platinum coated proton exchange membrane. This depolarised electrolysis requires a theoretical voltage of only 0.158 V compared to water electrolysis requiring approximately 1.23 V. One of the steps in the development of this technology at the North-West University, entailed the establishment of the platinum coating technology which entailed two steps; firstly using newly obtained equipment to manufacture the membrane electro catalyst assemblies (MEA’s) and gas diffusion electrodes (GDE’s) and secondly to test these MEA’s and GDE’s using sulphur dioxide depolarized electrolysis by comparing the manufactured MEA’s and GDE’s to commercially available MEA’s and GDE’s. Different MEA’s and GDE’s were manufactured using both a screen printing (for the microporous layer deposition) and a spraying technique. The catalyst loadings were varied as well as the type and thickness of the proton exchange membranes used. The proton exchange membranes that were included in this study were Nafion 117®, sPSU-PBIOO and SfS-PBIOO membranes whereas the gas diffusion layer consisted of carbon paper with varying thicknesses (EC-TP01-030 – 0.11 mm and EC-TP01-060 – 0.19mm). MEA and GDE were prepared by first preparing an ink that was used both for MEA and GDE spraying. The MEA’s were prepared by spraying various catalyst coatings onto the proton exchange membranes containing 0.3, 0.6 and 0.9 mg/cm2 platinum respectively. The GDE’s were first coated by a micro porous carbon layer using the screen printing technique in order to attain a suitable surface for catalyst deposition. Using the spraying technique GDE’s containing 0.3, 0.6, 0.9 mg/cm2 platinum were prepared. After SEM analysis, the MEA’s and GDE’s performance was measured using SO2 depolarized electrolysis. From the electrolysis experiments, the voltage vs. current density generated during operation, the hydrogen production, the sulphuric acid generation and the hydrogen production efficiency was obtained. From the results it became clear that while the catalyst loading had little effect on performance there were a number of factors that did have a significant influence. These included the type of proton exchange membrane, the membrane thickness and whether the catalyst coating was applied to the proton exchange membrane (MEA) or to the gas diffusion layer (GDE). During SO2 depolarized electrolysis VI curves were generated which gave an indication of the performance of the GDE’s and MEA’s. The best preforming GDE was GDE-3 (0.46V @ 320 mA/cm2), which included a GDE EC-TP01-060, while the best preforming MEA’s were NAF-4 (0.69V @ 320mA/cm2) consisting of a Nafion117 based MEA and PBI-1 (0.43V @ 320mA/cm2) made from a sPSU-PBIOO blended membrane. During hydrogen production it became clear that the GDE’s produced the most hydrogen (best was GDE-02 a in house manufactured GDE yielding 67.3 mL/min @ 0.8V), followed by the Nafion® MEA’s (best was NAF-4 a commercial MEA yielding 57.61 mL/min @ 0.74V) and the PBI based MEA’s. , (best was PBI-2 with 67.11 mL/min @ 0.88V). Due to the small amounts of acid produced and the SO2 crossover, a significant error margin was observed when measuring the amount of sulphuric acid produced. Nonetheless, a direct correlation could still be seen between the acid and the hydrogen production as had been expected from literature. The highest sulphuric acid concentrations produced using the tested GDE’s and MEA’s from this study were the in-house manufactured GDE-01 (3.572mol/L @ 0.8V), the commercial NAF-4 (4.456mol/L @ 0.64V) and the in-house manufactured PBI-2 (3.344mol/L @ 0.8V). The overall efficiency of the GDE’s were similar, ranging from less than 10% at low voltages (± 0.6V) increasing to approximately 60% at ± 0.8V. For the MEA’s larger variation was observed with NAF-4 reaching efficiencies of nearly 80% at 0.7V. In terms of consistency of performance it was shown that the Nafion MEA’s preformed most consistently followed by the GDE’s and lastly the PBI based MEA’s which for the PBI based membranes can probably be ascribed to the significant difference in thickness of the thin PBI vs. the Nafion based membranes. In summary the study has shown the results between the commercially obtained and the in-house manufactured GDE’s and MEA’s were comparable confirming the suitability of the coating techniques evaluated in this study. / MSc (Chemistry), North-West University, Potchefstroom Campus, 2014

Fármacos tem sido foco de diversas estudos e pesquisas devido à constatação de sua ocorrência em diversos compartimentos ambientais. Esses compostos, com destaque para os antibióticos, apresentam biodegradação limitada e contínua introdução nos sistemas hídricos devido ao descarte incorreto, eliminação por excreção de parte da dose ingerida e, principalmente, pelo processo de fabricação nas indústrias farmacêuticas. Como as formas convencionais de tratamento têm se mostrado pouco efetivas, a tecnologia eletroquímica associada aos processos oxidativos avançados (POA) têm se mostrado uma maneira eficiente na degradação desses compostos. Em diversos estudos, os eletrodos de difusão gasosa (EDG) são apresentados como uma opção promissora no que diz respeito à eletrogeração de peróxido de hidrogênio, uma das principais fontes de radical hidroxila utilizado nos POA. Nesse aspecto, surgem estudos sobre modificadores que podem atuar como catalisadores nesse processo. Neste trabalho estudou-se o comportamento eletroquímico de dois modificares orgânicos suportados em matriz condutora de carbono Printex 6L. Os compostos orgânicos escolhidos, pertencentes a classe das quinonas, foram a 2-terc-butil-9,10-antraquinona (TBA) e a 9,10 fenantraquinona (FQA). Os estudos foram realizados em um eletrodo de disco/anel rotatório (RRDE), depositando-se uma microcamada porosa, contendo ou não o modificador, sobre o carbono vítreo deste eletrodo. Através dos resultados de voltametria cíclica e linear pode-se avaliar a geração de peróxido de hidrogênio, que foi superior para as microcamadas com adição dos modificadores. O material com 0,5% (m/m) de FQA mostrou-se o mais eficiente entre todos, com 30% de rendimento a mais quando comparado à matriz Printex e 6% maior quando comparada a mesma quantidade de TBA na produção do peróxido. Estudou-se também a eficiência da FQA para a produção de peróxido de hidrogênio (H2O2) a partir da reação de redução do oxigênio gasoso (O2), em eletrodos de difusão gasosa (EDG). Considerando os cinco eletrodos estudados (Printex não modificado e modificado com 0,1, 0,5, 1,0 e 2,0% de FQA) foi realizada uma avaliação sobre qual eletrodo seria o mais apto a ser utilizado nos trabalhos de degradação dos fármacos. Para isso fez-se a análise da concentração de peróxido de hidrogênio eletrogerada, o consumo energético e a cinética envolvida no processo. Os resultados mostraram um aumento significativo na produção de peróxido para os eletrodos modificados com 0,5 e 1,0% de FQA. Sendo que o eletrodo sem modificação atingiu um máximo de 215 ppm de H2O2 em um potencial de -1,4 V com um consumo energético de 29 kWh kg-1 de H2O2. O eletrodo modificado com 0,5% de FQA alcançou 566 pmm de H2O2 em um potencial de -1,4 V com um consumo energético de 14 kWh kg-1 de H2O2. Estudou-se também a degradação dos antibióticos amoxicilina e ampicilina (AMX e AMP) com anodos condutores comerciais de diamante dopados com boro. A influência da densidade de corrente aplicada (15, 30 e 60 mA cm-2) para o mesmo eletrólito de suporte (3 g / L de Na2SO4) e a mesma concentração inicial de antibióticos (100 mg dm-3 cada) foi avaliada. A mineralização total dos antibióticos foi atingida. Além disso, o processo foi encontrado para ser mais eficiente na densidade de corrente de 30 mA cm-2. Os resultados demonstram a importância dos processos eletroquímicos mediados na degradação de AMX e AMP. Esta influência foi confirmada por alguns testes em que a eletrólise foi acoplada à radiação UV ou à radiação ultrassônica. O uso de radiação UV resulta em uma degradação menos eficiente, enquanto que o ultrassom melhora um pouco a taxa de mineralização quando comparado ao processo eletrolítico simples. / Drugs have been the focus of several studies and researches due to the finding of their occurrence in several environmental compartments. These compounds, especially antibiotics, present limited biodegradation and continuous introduction into water systems because of incorrect disposal, elimination by excretion of part of the ingested dose and, mainly, by the manufacturing process in the pharmaceutical industries. As conventional mode of treatment have been shown to be ineffective, electrochemical technology associated with advanced oxidative processes (POA) has been shown to be an efficient way of degradation of these compounds. In several studies, gas diffusion electrodes (EDG) are presented as a promising option with respect to hydrogen peroxide electrogeneration, one of the main sources of hydroxyl radical used in POAs. In this aspect, studies on modifiers appear that can act as catalysts in this process. In this work the electrochemical behavior of two organic modifiers supported in Printex 6L carbon matrix was studied. The organic compounds chosen, belonging to the class of quinones, were 2-tert-butyl-9,10-anthraquinone (TBA) and 9,10-phenanthraquinone (FQA). The studies were performed on a rotating disk / ring electrode (RRDE), depositing a porous micro-layer, containing or not the modifier, on the glassy carbon of this electrode. Through the results of cyclic and linear voltammetry the generation of hydrogen peroxide can be evaluated, which was superior to the micro-layers with addition of the modifiers. The material with 0.5% (w / w) of FQA was the most efficient of all, with 30% more yield when compared to the Printex matrix and 6% higher when compared to the same amount of TBA in peroxide production . It was also studied the efficiency of the FQA for the production of hydrogen peroxide (H2O2) from the reduction reaction of gaseous oxygen (O2) in gaseous diffusion electrodes (EDG). Considering the five electrodes studied (Printex not modified and modified with 0.1, 0.5, 1.0 and 2.0% of FQA) an evaluation was made on which electrode would be the most suitable to be used in the degradation works of the drugs. For that, the analysis of the hydrogen peroxide concentration, the energy consumption and the kinetics involved in the process were analyzed. The results showed a significant increase in peroxide production for electrodes modified with 0.5 and 1.0% of FQA. Since the unmodified electrode reached a maximum of 215 ppm of H2O2 at a potential of -1.4 V with an energy consumption of 29 kWh kg-1 of H2O2. The electrode modified with 0.5% of FQA reached 566 pmm of H2O2 at a potential of -1.4 V with an energetic consumption of 14 kWh kg-1 of H2O2. The degradation of antibiotics amoxicillin and ampicillin (AMX and AMP) with commercial boron-doped diamond conducting anodes was also studied. The influence of the applied current density (15, 30 and 60 mA cm-2) for the same support electrolyte (3 g / L Na2SO4) and the same initial concentration of antibiotics (100 mg dm-3 each) was evaluated. Total mineralization of antibiotics was achieved. In addition, the process was found to be more efficient at current density of 30 mA cm-2. The results demonstrate the importance of the electrochemical processes mediated in the degradation of AMX and AMP. This influence was confirmed by some tests in which the electrolysis was coupled to UV radiation or to ultrasonic radiation. The use of UV radiation results in less efficient degradation, while ultrasound improves the rate of mineralization somewhat compared to the simple electrolyte process.

Neste trabalho foi estudado o comportamento eletroquímico de materiais à base de carbono Printex 6L, sem e com a adição de compostos orgânicos da classe das quinonas (2-terc-butil-9,10-antraquinona (TBA) e 2-etil-9,10-antraquinona (EA)) para a produção de peróxido de hidrogênio (H2O2) a partir da reação de redução do oxigênio gasoso (O2). Na primeira etapa, foi utilizada a técnica de microcamada porosa depositada sobre um eletrodo de disco/anel rotatório, sendo que a partir dos resultados obtidos foram confeccionados eletrodos de difusão gasosa (EDG) para a eletrogeração de H2O2. Os melhores resultados utilizando a microcamada porosa foram para os materiais com a adição dos modificadores, sendo que o material com 1,0% (m/m) de TBA na demonstrou ser o mais eficiente na geração de peróxido de hidrogênio, apresentando eficiência 20% maior comparado ao Printex 6L sem modificador. Com o eletrodo de difusão gasosa confeccionado com o composto orgânico escolhido, na melhor porcentagem de adição mássica de modificador, obteve-se a concentração de 301 mg L-1, sendo que com o eletrodo confeccionado com Printex 6L sem modificador obteve-se a concentração de 175 mg L-1, sob as mesmas condições experimentais. A eficiência cinética também apresentou os mesmos resultados quanto à eficiência dos materiais escolhidos, sendo de 5,94 mg L-1 min-1 para o material com 1,0% de TBA, no potencial de -1,0 V (vs. ECS), e de 3,05 mg L-1 min-1 para o eletrodo de difusão gasosa sem modificador, no potencial de -0,8 V (vs. ECS). / In this work, the electrochemistry behavior of the materials prepared with Printex 6L, with and without addition of organic compounds of the class of quinones, being the compounds: 2-tert-butyl-9,10-anthraquinone (TBA) and 2-ethyl-9,10-anthraquinone (EA). These materials were used to promote the electrogeneration of hydrogen peroxide through the oxygen reduction reaction. In the first phase, it was used the technique of porous microlayer deposited on the rotating ring/disk electrode, and after has been confectioned gas diffusion electrodes (GDE). The best results using the porous microlayer were for the materials with addition of modifiers, and the material with 1.0% (m/m) of 2-terc-butyl-9,10-anthraquinone was demonstrated to be the most efficient in generating hydrogen peroxide, presenting an efficiency 20% higher when compared to Printex 6L without the modifier. The gas diffusion electrode made with the chosen organic compound, in the best massic percentage of modifier, obtained the concentration of 301 mg L-1, and the electrode made with Printex 6L without the modifier obtained the maximum concentration of 175 mg L-1, under the same experimental conditions. The kinect efficiency also demonstrated the same results regarding the efficiency of the chosen materials, which means 5.94 mg L-1 min-1 for the material with 1.0% of 2-terc-butyl-9,10-anthraquinone, in the potential of -1.0 V(vs. SCE), and 3.05 mg L-1 min-1 for the gas diffusion electrode without the modifier, in the potential of -0.8 V (vs. SCE).

Fármacos tem sido foco de diversas estudos e pesquisas devido à constatação de sua ocorrência em diversos compartimentos ambientais. Esses compostos, com destaque para os antibióticos, apresentam biodegradação limitada e contínua introdução nos sistemas hídricos devido ao descarte incorreto, eliminação por excreção de parte da dose ingerida e, principalmente, pelo processo de fabricação nas indústrias farmacêuticas. Como as formas convencionais de tratamento têm se mostrado pouco efetivas, a tecnologia eletroquímica associada aos processos oxidativos avançados (POA) têm se mostrado uma maneira eficiente na degradação desses compostos. Em diversos estudos, os eletrodos de difusão gasosa (EDG) são apresentados como uma opção promissora no que diz respeito à eletrogeração de peróxido de hidrogênio, uma das principais fontes de radical hidroxila utilizado nos POA. Nesse aspecto, surgem estudos sobre modificadores que podem atuar como catalisadores nesse processo. Neste trabalho estudou-se o comportamento eletroquímico de dois modificares orgânicos suportados em matriz condutora de carbono Printex 6L. Os compostos orgânicos escolhidos, pertencentes a classe das quinonas, foram a 2-terc-butil-9,10-antraquinona (TBA) e a 9,10 fenantraquinona (FQA). Os estudos foram realizados em um eletrodo de disco/anel rotatório (RRDE), depositando-se uma microcamada porosa, contendo ou não o modificador, sobre o carbono vítreo deste eletrodo. Através dos resultados de voltametria cíclica e linear pode-se avaliar a geração de peróxido de hidrogênio, que foi superior para as microcamadas com adição dos modificadores. O material com 0,5% (m/m) de FQA mostrou-se o mais eficiente entre todos, com 30% de rendimento a mais quando comparado à matriz Printex e 6% maior quando comparada a mesma quantidade de TBA na produção do peróxido. Estudou-se também a eficiência da FQA para a produção de peróxido de hidrogênio (H2O2) a partir da reação de redução do oxigênio gasoso (O2), em eletrodos de difusão gasosa (EDG). Considerando os cinco eletrodos estudados (Printex não modificado e modificado com 0,1, 0,5, 1,0 e 2,0% de FQA) foi realizada uma avaliação sobre qual eletrodo seria o mais apto a ser utilizado nos trabalhos de degradação dos fármacos. Para isso fez-se a análise da concentração de peróxido de hidrogênio eletrogerada, o consumo energético e a cinética envolvida no processo. Os resultados mostraram um aumento significativo na produção de peróxido para os eletrodos modificados com 0,5 e 1,0% de FQA. Sendo que o eletrodo sem modificação atingiu um máximo de 215 ppm de H2O2 em um potencial de -1,4 V com um consumo energético de 29 kWh kg-1 de H2O2. O eletrodo modificado com 0,5% de FQA alcançou 566 pmm de H2O2 em um potencial de -1,4 V com um consumo energético de 14 kWh kg-1 de H2O2. Estudou-se também a degradação dos antibióticos amoxicilina e ampicilina (AMX e AMP) com anodos condutores comerciais de diamante dopados com boro. A influência da densidade de corrente aplicada (15, 30 e 60 mA cm-2) para o mesmo eletrólito de suporte (3 g / L de Na2SO4) e a mesma concentração inicial de antibióticos (100 mg dm-3 cada) foi avaliada. A mineralização total dos antibióticos foi atingida. Além disso, o processo foi encontrado para ser mais eficiente na densidade de corrente de 30 mA cm-2. Os resultados demonstram a importância dos processos eletroquímicos mediados na degradação de AMX e AMP. Esta influência foi confirmada por alguns testes em que a eletrólise foi acoplada à radiação UV ou à radiação ultrassônica. O uso de radiação UV resulta em uma degradação menos eficiente, enquanto que o ultrassom melhora um pouco a taxa de mineralização quando comparado ao processo eletrolítico simples. / Drugs have been the focus of several studies and researches due to the finding of their occurrence in several environmental compartments. These compounds, especially antibiotics, present limited biodegradation and continuous introduction into water systems because of incorrect disposal, elimination by excretion of part of the ingested dose and, mainly, by the manufacturing process in the pharmaceutical industries. As conventional mode of treatment have been shown to be ineffective, electrochemical technology associated with advanced oxidative processes (POA) has been shown to be an efficient way of degradation of these compounds. In several studies, gas diffusion electrodes (EDG) are presented as a promising option with respect to hydrogen peroxide electrogeneration, one of the main sources of hydroxyl radical used in POAs. In this aspect, studies on modifiers appear that can act as catalysts in this process. In this work the electrochemical behavior of two organic modifiers supported in Printex 6L carbon matrix was studied. The organic compounds chosen, belonging to the class of quinones, were 2-tert-butyl-9,10-anthraquinone (TBA) and 9,10-phenanthraquinone (FQA). The studies were performed on a rotating disk / ring electrode (RRDE), depositing a porous micro-layer, containing or not the modifier, on the glassy carbon of this electrode. Through the results of cyclic and linear voltammetry the generation of hydrogen peroxide can be evaluated, which was superior to the micro-layers with addition of the modifiers. The material with 0.5% (w / w) of FQA was the most efficient of all, with 30% more yield when compared to the Printex matrix and 6% higher when compared to the same amount of TBA in peroxide production . It was also studied the efficiency of the FQA for the production of hydrogen peroxide (H2O2) from the reduction reaction of gaseous oxygen (O2) in gaseous diffusion electrodes (EDG). Considering the five electrodes studied (Printex not modified and modified with 0.1, 0.5, 1.0 and 2.0% of FQA) an evaluation was made on which electrode would be the most suitable to be used in the degradation works of the drugs. For that, the analysis of the hydrogen peroxide concentration, the energy consumption and the kinetics involved in the process were analyzed. The results showed a significant increase in peroxide production for electrodes modified with 0.5 and 1.0% of FQA. Since the unmodified electrode reached a maximum of 215 ppm of H2O2 at a potential of -1.4 V with an energy consumption of 29 kWh kg-1 of H2O2. The electrode modified with 0.5% of FQA reached 566 pmm of H2O2 at a potential of -1.4 V with an energetic consumption of 14 kWh kg-1 of H2O2. The degradation of antibiotics amoxicillin and ampicillin (AMX and AMP) with commercial boron-doped diamond conducting anodes was also studied. The influence of the applied current density (15, 30 and 60 mA cm-2) for the same support electrolyte (3 g / L Na2SO4) and the same initial concentration of antibiotics (100 mg dm-3 each) was evaluated. Total mineralization of antibiotics was achieved. In addition, the process was found to be more efficient at current density of 30 mA cm-2. The results demonstrate the importance of the electrochemical processes mediated in the degradation of AMX and AMP. This influence was confirmed by some tests in which the electrolysis was coupled to UV radiation or to ultrasonic radiation. The use of UV radiation results in less efficient degradation, while ultrasound improves the rate of mineralization somewhat compared to the simple electrolyte process.

Neste trabalho foi estudado o comportamento eletroquímico de materiais à base de carbono Printex 6L, sem e com a adição de compostos orgânicos da classe das quinonas (2-terc-butil-9,10-antraquinona (TBA) e 2-etil-9,10-antraquinona (EA)) para a produção de peróxido de hidrogênio (H2O2) a partir da reação de redução do oxigênio gasoso (O2). Na primeira etapa, foi utilizada a técnica de microcamada porosa depositada sobre um eletrodo de disco/anel rotatório, sendo que a partir dos resultados obtidos foram confeccionados eletrodos de difusão gasosa (EDG) para a eletrogeração de H2O2. Os melhores resultados utilizando a microcamada porosa foram para os materiais com a adição dos modificadores, sendo que o material com 1,0% (m/m) de TBA na demonstrou ser o mais eficiente na geração de peróxido de hidrogênio, apresentando eficiência 20% maior comparado ao Printex 6L sem modificador. Com o eletrodo de difusão gasosa confeccionado com o composto orgânico escolhido, na melhor porcentagem de adição mássica de modificador, obteve-se a concentração de 301 mg L-1, sendo que com o eletrodo confeccionado com Printex 6L sem modificador obteve-se a concentração de 175 mg L-1, sob as mesmas condições experimentais. A eficiência cinética também apresentou os mesmos resultados quanto à eficiência dos materiais escolhidos, sendo de 5,94 mg L-1 min-1 para o material com 1,0% de TBA, no potencial de -1,0 V (vs. ECS), e de 3,05 mg L-1 min-1 para o eletrodo de difusão gasosa sem modificador, no potencial de -0,8 V (vs. ECS). / In this work, the electrochemistry behavior of the materials prepared with Printex 6L, with and without addition of organic compounds of the class of quinones, being the compounds: 2-tert-butyl-9,10-anthraquinone (TBA) and 2-ethyl-9,10-anthraquinone (EA). These materials were used to promote the electrogeneration of hydrogen peroxide through the oxygen reduction reaction. In the first phase, it was used the technique of porous microlayer deposited on the rotating ring/disk electrode, and after has been confectioned gas diffusion electrodes (GDE). The best results using the porous microlayer were for the materials with addition of modifiers, and the material with 1.0% (m/m) of 2-terc-butyl-9,10-anthraquinone was demonstrated to be the most efficient in generating hydrogen peroxide, presenting an efficiency 20% higher when compared to Printex 6L without the modifier. The gas diffusion electrode made with the chosen organic compound, in the best massic percentage of modifier, obtained the concentration of 301 mg L-1, and the electrode made with Printex 6L without the modifier obtained the maximum concentration of 175 mg L-1, under the same experimental conditions. The kinect efficiency also demonstrated the same results regarding the efficiency of the chosen materials, which means 5.94 mg L-1 min-1 for the material with 1.0% of 2-terc-butyl-9,10-anthraquinone, in the potential of -1.0 V(vs. SCE), and 3.05 mg L-1 min-1 for the gas diffusion electrode without the modifier, in the potential of -0.8 V (vs. SCE).

Among the obstacles for the commercialization of the MoltenCarbonate Fuel Cell (MCFC), the dissolution of thestate-of-the-art lithiated NiO cathode is considered as aprimary lifetime limiting constraint. Development ofalternative cathode materials is considered as a main strategyfor solving the cathode dissolution problem. LiFeO2and LiCoO2had earlier been reported as the most promisingalternative materials; however, they could not satisfactorilysubstitute the lithiated NiO. On the other hand, ternarycompositions of LiFeO2, LiCoO2and NiO are expected to combine some desirableproperties of each component. The aim of this work was todevelop alternative cathode materials for MCFC in the LiFeO2-LiCoO2-NiO ternary system. It was carried out byinvestigating electronic conductivity of the materials, firstin the form of bulk pellets and then in ex-situ sinteredporous-gas-diffusion cathodes, and evaluating theirelectrochemical performance by short-time laboratory-scale celloperations. Materials in the LiFeO2-NiO binary system and five ternary sub-systems,each with a constant molar ratio of LiFeO2:NiO while varying LiCoO2content, were studied. Powders withcharacteristics appropriate for MCFC cathode fabrication couldbe obtained by the Pechini method. The particle size of LiFeO2-LiCoO2-NiO powders considerably depends on thecalcination temperature and the material composition. Theelectrical conductivity study reveals the ability of preparingLiFeO2-LiCoO2-NiO materials with adequate electricalconductivity for MCFC cathode application. A bimodal pore structure, appropriate for the MCFC cathode,could be achieved in sintered cathodes prepared usingporeformers and sub-micron size powder. Further, this studyindicates the nature of the compromise to be made between theelectrical conductivity, phase purity, pore structure andporosity in optimization of cathodes for MCFC application. Cellperformance comparable to that expected for the cathode in acommercial MCFC could be achieved with cathodes prepared from20 mole% LiFeO2- 20 mole% LiCoO2- 60 mole% NiO ternary composition. It shows aniR-corrected polarization of 62 mV and a iR-drop of 46 mV at acurrent density of 160 mAcm-2at 650 °C. Altogether, this study revealsthe possibility of preparing LiFeO2-LiCoO2-NiO cathode materials suitable for MCFCapplication. Keywords: molten carbonate fuel cell (MCFC), MCFC cathode,LiFeO2-LiCoO2-NiO ternary compositions, electrical conductivity,porous gas diffusion electrodes, polarization, electrochemicalperformance, post-cell characterization.

<p>Among the obstacles for the commercialization of the MoltenCarbonate Fuel Cell (MCFC), the dissolution of thestate-of-the-art lithiated NiO cathode is considered as aprimary lifetime limiting constraint. Development ofalternative cathode materials is considered as a main strategyfor solving the cathode dissolution problem. LiFeO₂and LiCoO₂had earlier been reported as the most promisingalternative materials; however, they could not satisfactorilysubstitute the lithiated NiO. On the other hand, ternarycompositions of LiFeO₂, LiCoO₂and NiO are expected to combine some desirableproperties of each component. The aim of this work was todevelop alternative cathode materials for MCFC in the LiFeO₂-LiCoO₂-NiO ternary system. It was carried out byinvestigating electronic conductivity of the materials, firstin the form of bulk pellets and then in ex-situ sinteredporous-gas-diffusion cathodes, and evaluating theirelectrochemical performance by short-time laboratory-scale celloperations.</p><p>Materials in the LiFeO₂-NiO binary system and five ternary sub-systems,each with a constant molar ratio of LiFeO₂:NiO while varying LiCoO₂content, were studied. Powders withcharacteristics appropriate for MCFC cathode fabrication couldbe obtained by the Pechini method. The particle size of LiFeO₂-LiCoO₂-NiO powders considerably depends on thecalcination temperature and the material composition. Theelectrical conductivity study reveals the ability of preparingLiFeO₂-LiCoO₂-NiO materials with adequate electricalconductivity for MCFC cathode application.</p><p>A bimodal pore structure, appropriate for the MCFC cathode,could be achieved in sintered cathodes prepared usingporeformers and sub-micron size powder. Further, this studyindicates the nature of the compromise to be made between theelectrical conductivity, phase purity, pore structure andporosity in optimization of cathodes for MCFC application. Cellperformance comparable to that expected for the cathode in acommercial MCFC could be achieved with cathodes prepared from20 mole% LiFeO₂- 20 mole% LiCoO₂- 60 mole% NiO ternary composition. It shows aniR-corrected polarization of 62 mV and a iR-drop of 46 mV at acurrent density of 160 mAcm^-2at 650 °C. Altogether, this study revealsthe possibility of preparing LiFeO₂-LiCoO₂-NiO cathode materials suitable for MCFCapplication.</p><p>Keywords: molten carbonate fuel cell (MCFC), MCFC cathode,LiFeO₂-LiCoO₂-NiO ternary compositions, electrical conductivity,porous gas diffusion electrodes, polarization, electrochemicalperformance, post-cell characterization.</p>