High Temperature Membrane Reactor System for Hydrogen Permeation Measurements and Validation with Pd Based Membranes

Abstract: Hydrogen separation membranes are under development for integration with a coal gasifier or natural gas reformer for pre-combustion separation of hydrogen and carbon dioxide. Because of the high operating temperatures and pressures, a robust reactor and associated control systems are required for fast screening of membrane materials with a strong emphasis on operator and plant safety. In this paper, the design, construction and commissioning of a reliable membrane reactor and a versatile test station for evaluation of hydrogen permeation membrane materials (metals, ceramics or cermets) at high temperatures and high differential pressures has been described. The membrane reactor system has been designed to operate at temperatures up to 800 o C and pressure differentials across the membrane to 1.0MPa. The system has multiple levels of safety redundancy built-in which include a range of controls and monitors for both operator and system safety. A number of Pd and Pd-Ag alloys of nominal thicknesses in the 20 and 140 m range were sourced and alumina based porous ceramic support structure were fabricated for evaluation of metal membranes. The test station has been validated with Pd and Pd-Ag alloys of different thicknesses. The data obtained from the reactor for various membrane types and thicknesses are in agreement with those reported in the literature

Investigation of the stability of ceria-gadolinia electrolytes in solid oxide fuel cell environments

Doped ceria-based materials are potential electrolytes for use in lower operating temperature (500-700 degrees C) solid oxide fuel cells because of their high ionic conductivity. In this study, impedance behaviour and microstructure of the (Ce0.8Gd0.2)O-1.9 exposed to mild fuel environments (H-2-N-2 mixtures) have been investigated. The exposure of specimens to H-2-N-2 mixtures at 1000 degrees C resulted in a substantial expansion of the lattice as a consequence of the reduction of Ce4+ to Ce3+, which in turn led to the development of microcracks and loss of continuity at the grain boundary region and increase in both the grain boundary (major effect) and the lattice (minor effect) resistivity. The behaviour for the grain boundary resistivity after the 800 degrees C exposure was somewhat similar although expansion of the lattice at 800 degrees C (or lower temperatures) was considerably less conspicuous. After exposure to H-2-N-2 atmosphere at lower temperatures (650 and 500 degrees C), although no significant increase in the grain boundary resistivity for exposures up to 1000 h was observed, the shape of the grain boundary are was clearly affected. The large increase in the grain boundary resistivity in reduced specimens has been attributed to the observed microcracking, loss of continuity between grains and possibly the formation of new phase regions with extremely poor oxygen-ion conductivity along grain boundaries during the reduction. The disruption to the microstructure is not recovered on subsequent oxidation in air. (C) 1999 Elsevier Science B.V. All rights reserved

An investigation of conductivity, microstructure and stability of electrolyte compositions in the system 9 mol% (Sc2O3-Y2O3)-ZrO2(Al 2O3)

In search for better ionically conducting ceramics for oxygen separators, fuel cells and sensors, the electrical conductivity and micro structure of the 9 mol% (ScO-YO)-ZrO system with varying ScO/YO ratios has been investigated in detail with XRD, SEM, TEM and conductivity measurements as a function of temperature. The stability of electrolyte compositions was studied by continuously monitoring conductivity as a function of time at 850 and 1000°C. Impedance spectroscopy was employed for determining the contribution of the grain boundary resistivity. The role of alumina additions to selected ScO-YO-ZrO compositions was studied as alumina is known to reduce the grain boundary resistivity by scavenging silica impurities and enhance mechanical properties in zirconia-based systems. AlO-containing compositions show much higher conductivity degradation compared with alumina-free materials. This behaviour has been investigated in more detail with XRD and TEM analysis

Investigations on fabrication and lifetime performance of self-air breathing direct hydrogen micro fuel cells

There is an ever - increasing demand for more powerful, compact and longer - life power modules for portable electronic devices for leisure, communication and computing. Micro fuel cells have the potential to replace battery packs for portable electronic appliances because of their high power density, longer operating and standby times, and substantially shorter recharging times. However, fuel cells have stringent operating requirements, including no fuel leakage, water formed in the electrochemical reactions, heat dissipation, robustness, easy and safe use, and reliability. Due to the large market potential, several companies are currently involved in the development of micro fuel cells. For application of fuel cells as a battery charger or in a battery replacement market, the cells require simplification in terms of their construction and operation and must have volumetric power densities equivalent to or better than those of existing battery power packs. This paper discusses results of investigation on methods and materials for direct hydrogen micro fuel cells as well as the lifetime performance of single cells and 2 We arrays. The paper also reviews the global technology development status for the direct hydrogen micro fuel cell and compares its salient features with other types of micro fuel cells

Direct coupling of an electrolyser to a solar PV system for generating hydrogen

Hydrogen as an energy currency, carrier and storage medium may be a key component of the solution to problems of global warming, poor air quality and dwindling reserves of liquid hydrocarbon fuels. Hydrogen is a flexible storage medium and can be generated by the electrolysis of water. It is particularly advantageous if an electrolyser may be simply and efficiently coupled to a source of renewable electrical energy. This paper examines direct coupling of a polymer electrolyte membrane (PEM) electrolyser to a matched solar photovoltaic (PV) source for hydrogen generation and storage. Such direct coupling with minimum interfacing electronics would lead to substantial cost reduction and thereby enhance the economic viability of solar-hydrogen systems. The electrolyser is designed for fail-safe operation with multiple levels of safety and operational redundancy. A control system in the electrolyser unit provides for disconnection when required and for auto-start in the morning and auto shut-down at night, simultaneously addressing the goals of minimum energy loss and maximum safety. The PV system is a 2.4 kW array (20.4 m2 total area) comprising 30, 12 V, 80 W, Solarex polycrystalline modules in a series-parallel configuration. The integrated system has been operated for approximately 60 days over a 4-month period from September 2007 to January 2008 with many periods of unattended operation for multiple days, experiencing weather ranging from hot and sunny (above 40 ºC) to cool and cloudy. The principle and practicality of direct coupling of a suitably matched PV array and PEM electrolyser have been successfully demonstrated. Details of electrolyser operation coupled to a PV array along with modelling work to match current-voltage characteristics of the electrolyser and PV system are described