Proton electrolyte membrane properties and direct methanol fuel cell performance II. Fuel cell performance and membrane properties effects

In order to study the relationship between the properties of proton electrolyte membranes (PEMs), obtained through standard characterization methods, and the direct methanol fuel cell (DMFC) performance, inorganic-organic hybrid membranes, modified via in situ hydrolysis, were used in a membrane electrolyte assembly (MEA) for DMFC application. The membranes, the characterization of which was performed in the previous paper of this series, were based on sulfonated poly(ether ether ketone) (sPEEK) with a sulfonation degree (SD) of 87% and were loaded with different amounts of zirconium oxide (5.0, 7.5, 10.0, 12.5wt.%). The standard characterization methods applied were impedance spectroscopy (proton conductivity), water uptake, and pervaporation (permeability to methanol). The MEAs were characterized investigating the DMFC current-voltage polarization curves, constant voltage current (CV, 35mV), and open circuit voltage (OCV). The fuel cell ohmic resistance (null phase angle impedance, NPAI) and CO2 concentration in the cathode outlet were also measured. The characterization results show that the incorporation of the inorganic oxide in the polymer network decreases the DMFC current density for CV experiments, the CO2 concentration in the cathode outlet for both OCV and CV experiments and, finally, the maximum power density output. The opposite effect was verified in terms of the NPAI (ohmic resistance) for both OCV and CV experiments. A good agreement was found between the studied DMFC performance parameters and the characterization results evaluated by impedance spectroscopy, water uptake and pervaporation experiments

Performance and efficiency of a DMFC using non-fluorinated composite membranes operating at low/medium temperatures

In order to increase the chemical/thermal stability of the sulfonated poly(ether ether ketone) (sPEEK) polymer for direct methanol fuel cell (DMFC) applications at medium temperatures (up to 130ºC), novel inorganic-organic composite membranes were prepared using sPEEK polymer as organic matrix (sulfonation degree, SD, of 42 and 68%) modified with zirconium phosphate (ZrPh) pre-treated with n-propylamine and polybenzimidazole (PBI). The analyzed compositions were: 10wt.% ZrPh and 5.6wt.% PBI; 20wt.% ZrPh and 11.2wt.% PBI. These composite membranes were tested in DMFC at several temperatures by evaluating the current-voltage polarization curve, open circuit voltage (OCV) and constant voltage current (CV, 35mV). The fuel cell ohmic resistance (null phase angle impedance, NPAI) and CO2 concentration in the cathode outlet were also measured. A method is also proposed to evaluate the fuel cell Faraday and global efficiency considering the CH3OH, CO2, H2O, O2 and N2 permeation through the proton exchange membrane (PEM) and parasitic oxidation of the crossover methanol in the cathode. In order to improve the analysis of the composite membrane properties, selected characterization results presented in [V.S. Silva, B. Ruff,ann, S. Vetter, A. Mendes, L.M. Madeira, S.P. Nunes, Catal. Todaym in press] were also used in the present study. The unmodified sPEEK membrane with SD=42% (S42) was used as the reference material. In the present study, the composite membrane prepared with sPEEK SD=68% and inorganic composition of 20.0wt.%ZrPh and 11.2wt.%PBI proved to have a good relationship between proton conductivity, aqueous methanol swelling and permeability. DMFC tests results for this membrane showed similar current density output and higher open circuit voltage compared to that of sPEEK with SD=42%, but with much lower CO2 concentration in the cathode outlet (thus higher global efficiency) and higher thermal/chemical stability. This membrane was also tested at 130ºC with pure oxygen (cathode inlet) and achieved a maximum power density of 50.1 mW cm-2 at 250 mA cm-2

Sistema com aeração, decantação e filtragem para a melhoria da qualidade de água em irrigação localizada System with aeration, sedimentation and filtering for the improving of water quality in drip irrigation

A qualidade da água é muito importante para irrigação por gotejamento, pois ela escoa por pequenos bocais dos emissores, podendo ocorrer obstrução devido à deposição dos sólidos em suspensão. Portanto, antes da instalação do projeto, devem-se avaliar parâmetros de qualidade da água, para adotar medidas preventivas, evitando o risco de entupimento do sistema. Este trabalho teve como objetivo avaliar um sistema composto por aeradores com aspersores, sobre leito de pedra, para a precipitação dos íons Fe+2e Mn+2 em tanque de decantação, e um conjunto de filtragem composto por três filtros de areia e um de disco, em sistema de irrigação localizada. O trabalho foi realizado na Fazenda Alvorada, no município de Nova Granada - SP, no período de março a outubro de 2008. Foram realizadas determinações de variáveis físicas e químicas da água, ao longo do sistema de aeração, decantação e filtragem, o qual foi eficiente para a melhoria da qualidade de água, reduzindo os níveis de risco de entupimento de severo para médio e de médio para baixo. Oxigênio dissolvido, condutividade elétrica, pH, Fe+2e Fe+3 não diferenciaram a qualidade de água entre os pontos do sistema de tratamento, porém a turbidez, sólidos dissolvidos, sólidos em suspensão, ferro total e manganês total reduziram-se significativamente pelo uso do sistema proposto, melhorando a qualidade da água.<br>Water quality is very important to drip irrigation, as it flows in small diameter holes, and may cause obstruction due to deposition of solid matter. Whence the water must be evaluated before installation of the project. Parameters related to water quality are essential to define conducting measures to avoid the risk of clogging the system. This study aimed to evaluate a system with sprinklers aeration on bedrock, for Fe+2and Mn total precipitation in sedimentation tank and a set of filtering consisting of three sand filters and a disk, installed in drip irrigation system. The study was conducted at Alvorada Farm, in the municipality of Nova Granada - SP, Brazil, from March to October of 2008, when the physical and chemical water analyses were made. It was concluded that: the aeration system, sedimentation and filtration were efficient for improving water quality, reducing the levels of risk of severe to medium obstruction and medium to low obstruction. The variables, dissolved oxygen, electrical conductivity; pH, Fe+2and Fe+3 were not significant to indicate differences of water quality among the points of the water treatment. However, the variables such as: turbidity, dissolved solids, suspended solids, total iron and Mn+2 were statistically significant for the differentiation of the water quality