Mixed Oxide Membranes Research Articles

Improvement of PEMFC performance with Nafion/inorganic nanocomposite membrane electrode assembly prepared by ultrasonic coating technique

Abstract Membrane electrode assemblies with Nafion/nanosize titanium silicon dioxide (TiSiO4) composite membranes were manufactured with a novel ultrasonic-spray technique and tested in proton exchange membrane fuel cell (PEMFC). Nafion/TiO2 and Nafion/SiO2 nanocomposite membranes were also fabricated by the same technique and their characteristics and performances in PEMFC were compared with Nafion/TiSiO4 mixed oxide membrane. The composite membranes have been characterized by thermogravimetric analysis, scanning electron microscopy, X-ray diffraction, water uptake, and proton conductivity. The composite membranes gained good thermal resistance with insertion of inorganic oxides. Uniform and homogeneous distribution of inorganic oxides enhanced crystalline character of these membranes. Gas diffusion electrodes (GDE) were fabricated by Ultrasonic Coating Technique. Catalyst loading was 0.4 mg Pt/cm2 for both anode and cathode sides. Fuel cell performances of Nafion/TiSiO4 composite membrane were better than that of other membranes. The power density obtained at 0.5 V at 75 °C was 0.456 W cm−2, 0.547 W cm−2, 0.477 W cm−2 and 0.803 W cm−2 for Nafion, Nafion/TiO2, Nafion/SiO2, and Nafion/TiSiO4 composite membranes, respectively.

Synthesis and characterization of microporous silica–alumina membranes

The development of microporous ceramic thin layers is of prime interest for sensors or gas separation membranes working at high temperature. Microporous silica membranes can be easily prepared by the sol–gel process. However the microporosity of pure silica is rapidly modified by steam at high temperature. One way to improve hydrothermal stability is to use mixed-oxide membranes. In this work, microporous silica–alumina membranes were prepared by a simple and robust sol–gel method. Tetraethoxysilane was mixed with an acidic alumina hydrosol. Urea was added for preparing the alumina hydrosol, for controlling the mixed-oxide network polycondensation and also as porogen agent. FTIR and 27Al NMR spectroscopic analyses showed that for Si/Al molar ratios up to 6/1, homogeneous mixed oxides were obtained with a random distribution of Al and Si atoms in the oxide lattice based on tetrahedral units. The derived supported layers were crack-free as demonstrated by scanning electron microscopy (SEM) observations. Their microporosity was investigated using ellipsoporosimetry (EP) with films supported on flat dense substrates. He, N2 and CO2 permeance measurements were performed for membranes deposited on porous tubular substrates. The measured values of He/N2 and He/CO2 ideal selectivities are in agreement with the microporous nature of the prepared layers.

Development of microporous ceramic membranes in the system TiO 2/ZrO 2

The aim of the investigations is the development of new nanoporous ceramic membranes (pore size <1 nm) for gas separation with a significantly higher chemical and hydrothermal resistance than the generally used silica membranes. In selecting mixed-oxide systems as well as suitable calcination conditions, the favoured microporous properties and the corrosion resistance should be obtained. An increase of the crystallization temperature is necessary to keep the nanoporosity up to higher temperatures. TiO 2–ZrO 2 mixed-oxide membranes with varying compositions were prepared via sol–gel technique. At first tubular α-alumina supports (pore size 60 nm) were coated with mixed-oxide (TiO 2–ZrO 2) intermediate layers using the colloidal sol–gel route. The formed UF-membranes are applied as supports for subsequent coating experiments. The nanoporous TiO 2–ZrO 2 mixed-oxide membranes were prepared via a polymeric sol–gel method. The composition of the membranes is already predefined during the preparation of the sols by using the corresponding quantities of the starting alkoxides. The influence of the chemical composition and sintering parameters onto crystalline phases, pore size and surface area of the systems was investigated. SEM, filtration and corrosion tests as well as structural investigations like 17O NMR spectroscopy were carried out and discussed.

Sol–Gel Route to Synthesis of Microporous Ceramic Membranes: Thermal Stability of TiO2–ZrO2Mixed Oxides

In this paper concerning the synthesis of microporous ceramic membranes, we focus on the preparation and ther‐ mal stability of unsupported microporous TiO2‐ZrO2, mixed‐oxide membranes. It has been observed that, by add‐ ing up to 20% ZrO2, into TiO2, or up to 10% TiO2, into ZrO2, these microporous membranes display improved thermal stability. They can be fired up to 500°C for 0.5 h without closing micropores. However, membranes containing almost equal percentages of each component have lost microporous features and have low surface areas and low porosities. A phase diagram of a two‐component TiO2‐ ZrO2, mixed‐oxide membrane has been prepared based on DTA and X‐ray diffraction data in order to better under‐ stand the microstructure changes upon firing.