A catalyst layer optimisation approach using electrochemical impedance spectroscopy for PEM fuel cells operated with pyrolysed transition metal-N-C catalysts

AbstractThe effect of the ionomer to carbon (I/C) ratio on the performance of single cell polymer electrolyte fuel cells is investigated for three different types of non-precious metal cathodic catalysts. Polarisation curves as well as impedance spectra are recorded at different potentials in the presence of argon or oxygen at the cathode and hydrogen at the anode. It is found that a optimised ionomer content is a key factor for improving the performance of the catalyst. Non-optimal ionomer loading can be assessed by two different factors from the impedance spectra. Hence this observation could be used as a diagnostic element to determine the ideal ionomer content and distribution in newly developed catalyst-electrodes. An electrode morphology based on the presence of inhomogeneous resistance distribution within the porous structure is suggested to explain the observed phenomena. The back-pressure and relative humidity effect on this feature is also investigated and supports the above hypothesis. We give a simple flowchart to aid optimisation of electrodes with the minimum number of trials

Advances in solid polymer electrolyte fuel cell technology with low-platinum-loading electrodes

The Gemini Space program demonstrated the first major application of fuel cell systems. Solid polymer electrolyte fuel cells were used as auxiliary power sources in the spacecraft. There has been considerable progress in this technology since then, particularly with the substitution of Nafion for the polystyrene sulfonate membrane as the electrolyte. Until recently the performance was good only with high platinum loading (4 mg/sq cm) electrodes. Methods are presented to advance the technology by (1) use of low platinum loading (0.35 mg/sq cm) electrodes; (2) optimization of anode/membrane/cathode interfaces by hot pressing; (3) pressurization of reactant gases, which is most important when air is used as cathodic reactant; and (4) adequate humidification of reactant gases to overcome the water management problem. The high performance of the fuel cell with the low loading of platinum appears to be due to the extension of the three dimensional reaction zone by introduction of a proton conductor, Nafion. This was confirmed by cyclic voltammetry

Um estudo sobre a gestão de riscos na implantação de shortlines integradas à malha ferroviária brasileira

TCC (graduação) - Universidade Federal de Santa Catarina, Centro Tecnológico, Engenharia Civil.O Brasil é um país continental exportador de commodities que enfrenta desafios no desenvolvimento de suas ferrovias. Embora tenha iniciado investimentos em ferrovias no mesmo período que as grandes potências (final do século XIX) e estabelecido corredores de exportação que continuam a ser fundamentais para o transporte de grãos e minérios, que representam uma parte significativa do PIB do país, atualmente a malha ferroviária brasileira permanece praticamente inalterada (em termos de extensão) em relação ao início do século XX, sendo que metade da malha encontra-se subutilizada ou abandonada. Sabendo disto, recentemente houveram mudanças na legislação ferroviária brasileira, instituindo o novo marco regulatório e o regime de autorizações, que atraiu novos investimentos para o setor, abrindo caminho para possibilidade de implantação de shortlines, um modelo de negócio popular nos Estados Unidos, especialmente após a aprovação da lei Staggers Act em 1980, que destravou toda potencialidade do setor. As shortlines são caracterizadas por trechos de curta extensão operados independentemente das grandes empresas, não exigindo a necessidade de material rodante sofisticado ou um grande número de funcionários. Essas linhas desempenham um papel fundamental na integração da malha ferroviária e no aumento da densidade de vias, elementos essenciais para equilibrar a matriz de transportes e reduzir o chamado "custo Brasil". Com o objetivo de compreender melhor os riscos envolvidos nessa nova modalidade de exploração, realizou-se uma pesquisa na literatura e aplicou-se a metodologia de gerenciamento de riscos. Esse processo permitiu determinar quais riscos devem ser mitigados e priorizados, além de identificar as partes interessadas no processo. Como resultado da identificação, análise, avaliação, tratamento e monitoramento dos riscos, obteve-se uma matriz de priorização que estabelece critérios de avaliação e oferece um diagnóstico de como lidar com os riscos de forma mais eficiente, levando em consideração a gravidade, a probabilidade, a urgência e o custo.Brazil is a continental country that exports commodities and faces challenges in the development of its railways. Despite initiating investments in railroads during the same period as major powers (late 19th century) and establishing export corridors that continue to be essential for transporting grains and minerals, which represent a significant portion of the country's GDP, the Brazilian railway network remains largely unchanged (in terms of extent) since the early 20th century, with half of the network being underutilized or abandoned. Recognizing this, recent changes in Brazilian railway legislation have introduced a new regulatory framework and an authorization regime that has attracted new investments to the sector, paving the way for the possibility of implementing shortlines, a business model popular in the United States, particularly after the approval of the Staggers Act in 1980, which unlocked the full potential of the industry. Shortlines are characterized by short sections operated independently of large companies, without the need for sophisticated rolling stock or a large number of employees. These lines play a fundamental role in integrating the railway network and increasing track density, which are essential elements for balancing the transportation matrix and reducing the so-called "Brazil cost." In order to better understand the risks involved in this new mode of operation, a literature review was conducted, and a risk management methodology was applied. This process enabled the determination of risks that need to be mitigated and prioritized, as well as the identification of stakeholders in the process. As a result of the identification, analysis, evaluation, treatment, and monitoring of risks, a prioritization matrix was created that establishes evaluation criteria and provides a diagnosis of how to handle risks more efficiently, taking into consideration severity, probability, urgency, and cost

Oxygen Reduction on Platinum Surfaces in Acid Media: Experimental Evidence of a CECE/DISP Initial Reaction Path

In this work, a detailed kinetic analysis of the oxygen reduction reaction (ORR) on platinum is performed by applying steady and non-steady-state methodologies at stationary and rotating disk electrodes and by comparing experimental results to calculated curves via digital simulations. Results reveal the existence of a complex chemical–electrochemical–chemical–electrochemical initial reaction sequence, a CECE-mechanism, and the possible contribution of a parallel disproportionation process in acid media during the reaction. Under convection-controlled circumstances, the first charge-transfer step would be the rate-determining step (RDS) on bulk electrodes, in agreement with early reports, but at different working conditions other initial steps can become the RDS. Additionally, contrary to the current accepted view, results support the formation of a soluble intermediate in the initial, and fast, chemical reaction, with a short lifetime, compatible with the formation of either the hydroperoxyl radical, HO2*, or superoxide anion, O2–, followed by a fast protonation. In light of present results, possible mechanisms, including the oxidation of H2O2 that could be produced either by disproportionation or by reduction of HO2*, and/or O2–, radicals, are discussed. This interrelated reaction scheme would be the principal cause of large ORR overpotentials, but at the same time, it would open the opportunity for designing alternative catalysts beyond fundamental limits imposed by the apparent scaling relations between reaction intermediates, such as OHads, Oads, and HO2,ads adsorbates.The authors thank the Fundação de Amparo a Pesquisa do Estado de São Paulo, Brazil (FAPESP), through projects 2013/16930-7 and 2014/23486-9 (A.M.G-M. and E.T.), the Spanish MINECO through project CTQ2016-76221-P (FEDER), and GV through PROMETEOII/2014/013 (FEDER) (J.F.), for financial support

Carbon monoxide oxidation on Pt-Ru electrocatalysts supported on high surface area carbon

This find is registered at Portable Antiquities of the Netherlands with number PAN-0000787

DO CONTEXTO JURÍDICO-POLÍTICO DA ADOÇÃO DE BIOCOMBUSTÍVEIS NO BRASIL: UMA ANÁLISE SOBRE SEGURANÇA ALIMENTAR E DESENVOLVIMENTO SUSTENTÁVEL

O presente artigo busca analisar a relação do meio ambiente com o desenvolvimento e a globalização. Propõe a análise de documentos internacionais que versam sobre questões ambientais, sociais e econômicas. Procura identificar se o Estado Brasileiro tem respondido às demandas ambientais, especialmente nas duas últimas décadas do século XX, quando a tutela ambiental passou a ser discutida internacionalmente, destacando alguns importantes princípios ambientais que foram constitucionalizados. Analisa questões nucleares que fundamentam a produção e uso de formas de energias limpas e renováveis, tais como mudanças climáticas, dependência e crises do setor petrolífero e um potencial mercado interno e internacional. Aborda a produção de etanol e biodiesel no Brasil, alguns marcos regulatórios específicos,bem como os impactos ambientais e sociais dessa atividade. Ressalta a necessidade da discussão sobre as externalidades decorrentes da produção de biocombustíveis, com ênfase na segurança alimentar.

Performance Characteristics of a PEM Fuel Cell with Parallel Flow Channels at Different Cathode Relative Humidity Levels

In fuel cells flow configuration and operating conditions such as cell temperature, humidity at each electrode and stoichiometric number are very crucial for improving performance. Too many flow channels could enhance the performance but result in high parasite loss. Therefore a trade-off between pressure drop and efficiency of a fuel cell should be considered for optimum design. This work focused on numerical simulation of the effects of operating conditions, especially cathode humidity, with simple micro parallel flow channels. It is known that the humidity at the cathode flow channel becomes very important for enhancing the ion conductivity of polymer membrane because fully humidified condition was normally set at anode. To investigate the effect of humidity on the performance of a fuel cell, in this study humidification was set to 100% at the anode flow channel and was changed by 0–100% at the cathode flow channel. Results showed that the maximum power density could be obtained under 60% humidified condition at the cathode where oxygen concentration was moderately high while maintaining high ion conductivity at a membrane