Crosslinking of polybenzimidazole membranes by divinylsulfone post‐treatment for high‐temperature proton exchange membrane fuel cell applications

Phosphoric acid‐doped polybenzimidazole (PBI) has been suggested as a promising electrolyte for proton exchange membrane fuel cells operating at temperatures up to 200 °C. This paper describes the development of a crosslinking procedure for PBI membranes by post‐treatment with divinylsulfone. The crosslinking chemistry was studied and optimized on a low‐molecular‐weight model system and the results were used to optimize the crosslinking conditions of PBI membranes. The crosslinked membranes were characterized with respect to chemical and physiochemical properties, showing improved mechanical strength and oxidative stability compared with their linear analogues. Fuel cell tests were further conducted in order to demonstrate the feasibility of the crosslinked membranes. Copyright © 2011 Society of Chemical Industry     

Preparation and operation of gas diffusion electrodes for high-temperature proton exchange membrane fuel cells

Gas diffusion electrodes for high-temperature PEMFC based on acid-doped polybenzimidazole membranes were prepared by a tape-casting method. The overall porosity of the electrodes was tailored in a range from 38% to 59% by introducing porogens into the supporting and/or catalyst layers. The investigated porogens include volatile ammonium oxalate, carbonate and acetate and acid-soluble zinc oxide, among which are ammonium oxalate and ZnO more effective in improving the overall electrode porosity. Effects of the electrode porosity on the fuel cell performance were investigated in terms of the cathodic limiting current density and minimum air stoichiometry, anodic limiting current and hydrogen utilization, as well as operations under different pressures and temperatures.     

Purification of Nickel Sulfate by Batch Cooling Crystallization

Cooling crystallization was successfully carried out in a batch cooling crystallizer from impure acidic solutions to recover nickel as nickel sulfate salt with three different cooling rates. The compositions of the solutions included impurities of sodium, magnesium, chloride, and sulfuric acid to mimic industrial nickel electrowinning process solutions. The results show that NiSO₄·6H₂O mainly crystallized, and its solubility and purity decreased with the increase in the mass ratio of chloride to sulfate. Cooling rates did not have a significant influence on crystal purity; however, it did affect the filter cake moisture; lower moisture can be obtained with a lower cooling rate. The sequence of impurity removal efficiency from high to low was Cl > Na > Mg.     

Indium doped niobium phosphates as intermediate temperature proton conductors

Indium doped niobium phosphates were prepared from precursors of trivalent indium oxide, pentavalent niobium oxide and phosphoric acid. The obtained materials were characterized by X-ray diffraction, impedance spectroscopy, FT-IR spectroscopy and scanning electron microscopy. It was found that the indium doping promoted formation of the cubic Nb₂P₄O₁₅ phase instead of the monoclinic Nb₅P₇O₃₀ phase in the pristine niobium phosphates and enhanced the preservation of OH functional groups in the phosphates. The preserved OH functionalities in the phosphates after the heat treatment at 650 °C contributed to the anhydrous proton conductivity. The Nb_0.9In_0.1 phosphate exhibited a proton conductivity of five times higher than that of the un-doped analog at 250 °C. The conductivity was stabilized at a level of above 0.02 S cm⁻¹ under dry atmosphere at 250 °C during the stability evaluation for 3 days.     

A spirit of urban capitalism: market cities,people cities,and cultural justifications

ABSTRACT

Diverse urban theories discuss how economic processes shape conceptions of a city, but less research focuses on how pragmatic situations of urban life contribute to the characterisation of cities. We argue that pragmatic justifications reify socially constructed meanings of cities by creating a ‘spirit of urban capitalism.’ This framework conceives of two spirits: the market city, which aligns with neoliberal assumptions, and the people city, which foregrounds a resident-focused model. Using case studies of Copenhagen and Houston, we showcase how these conceptions of cities are justified by elites and residents, and thereby build empirical scaffolding connecting urban economies and cultures.     

Effect of chloride impurities on the performance and durability of polybenzimidazole-based high temperature proton exchange membrane fuel cells

The effect of chloride as an air impurity and as a catalyst contaminant on the performance and durability of polybenzimidazole (PBI)-based high temperature proton exchange membrane fuel cell (HT-PEMFC) was studied. The ion chromatographic analysis reveals the existence of chloride contaminations in the Pt/C catalysts. Linear sweep voltammetry was employed to study the redox behavior of platinum in 85% phosphoric acid containing chloride ions, showing increase in oxidation and decrease in reduction current densities during the potential scans at room temperature. The potential scans at high temperatures in 85% phosphoric acid containing chloride ions showed both increase in oxidation and reduction current densities. The fuel cell performance, i.e. the current density at a constant voltage of 0.4 V and 0.5 V was found to be degraded as soon as HCl was introduced in the air humidifier. The performance loss was recovered when switching from the HCl solution back to pure water in the air humidifier. Under an accelerated aging performance test conducted through potential cycling between 0.9 V and 1.2 V, the PBI-based fuel cell initially containing 0.5 NaCl mg cm⁻² on the cathode catalyst layer exhibited a drastic degradation in the performance as compared to the chloride free MEAs. The mechanisms of the chloride effect on the fuel cell performance and durability were further discussed.     

SCI-LVDS 500 MHz differential pad drivers in a standard CMOS process

In this paper a set of high-speed differential pad cells are presented. The pad cells are designed to work with the IEEE Draft Standard for Low-Voltage Differential Signals for Scalable Coherent Interface (SCI-LVDS) [4]. The standard sets specifications for high-speed point to point communication between complex subcircuits in digital systems. The pad cells are in compliance with the draft, but are designed to operate up to at least 500 MHz instead of the 250 MHz proposed in the draft. The pad cells presented in this paper are designed in a standard 1µm CMOS process using standard DIL packaging. This has proved possible despite the electrical specifications being narrowed as a result of the doubling of the operating frequency. The circuit has ESD protection and utilizes internal termination with a single external impedance reference and thereby facilitates ease of use and higher package density.     

An integrated CMOS telephone line adapter

A novel fully CMOS circuit for electronic telephone line adaption is described. In the on-hook state the circuit operates in micropower condition, dissipates only 5 A, and is capable of generating the supply voltage required for retention of data stored on external RAM. In the off-hook state the circuit is boosted into the normal operation mode and is able to drive external bipolar transistors to synthesize the line impedance. The dc and the ac line impedances are set with external components, thus permitting the fulfillment of different PTT specifications. The circuit also performs line signal extraction and transmission, both for voice and DTMF. The dc line voltage is monitored, and a supervision block generates a precise reset signal when the line voltage drops out. The circuit has been integrated in a CMOS P-well 3-m double-poly single-metal technology; the silicon area is 6 mm².     

Self-Standing Nanofiber Electrodes with Pt–Co Derived from Electrospun Zeolitic Imidazolate Framework for High Temperature PEM Fuel Cells

Expedited conversion of O₂ to H₂O with minimal amounts of Pt is essential for wide applicability of PEM fuel cells (PEMFCs). Therefore, it is imperative to develop a process for catalyst management to circumvent unnecessary catalyst loss while improving the Pt utilization, catalytic activity, and durability. Here, the fabrication of a self-standing nanofiber electrode is demonstrated by employing electrospinning. This film-type catalyst simultaneously contains Pt–Co alloy nanoparticles and Co embedded in an N-doped graphitized carbon (Co–N_x) support derived from the electrospun zeolitic imidazolate frameworks. Notably, the flexible electrode is directly transferrable for the membrane-electrode assembly of high temperature PEMFC. In addition, the electrodes exhibit excellent performance, maybe owing to the synergistic interaction between the Pt–Co and Co–N_x as revealed by the computational modeling study. This method simplifies the fabrication and operation of cell device with negligible Pt loss, compared to ink-based conventional catalyst coating methods.     

Fertilizers, agronomy and N2O

N₂O is emitted from agricultural soils due to microbial transformation of N from fertilizers, manures and soil N reserves. N₂O also derives from N lost from agriculture to other ecosystems: as NH₃ or through NO ₃ ^- leaching. Increased efficiency in crop N uptake and reduction of N losses should in principle diminish the amount of N₂O from agricultural sources. Precision in crop nutrient management is developing rapidly and should increase this efficiency. It should be possible to design guidelines on good agricultural practices for low N₂O emissions in special situations, e.g. irrigated agriculture, and for special operations, e.g. deep placement of fertilizers and manures. However, current information is insufficient for such guidelines. Slow-release fertilizers and fertilizers with inhibitors of soil enzymatic processes show promise as products which give reduced N₂O emissions, but they are expensive and have had little market penetration. Benefits and possible problems with their use needs further clarification.