V.S. Silva

Membranes for direct methanol fuel cell based on modified heteropolyacids

Organic-inorganic membranes for direct methanol fuel cell (DMFC) application were prepared from sulfonated polyether ether ketone (SPEEK), containing heteropolyacids and an oxide phase either generated by hydrolysis ofamino-modified silanes or by dispersion of a surface-modified fumed silica. The heteropolyacid was based on lacunary divacant [γ-SiW10O36]−8 and contained epoxy groups which reacted with the ammo-groups in the oxide phase. The reaction provides a covalent bond between the heteropolyacid to the insoluble oxide phase, resulting in its fixation in the membrane. The organic-inorganic composites prepared in this way were more stable than the plain membrane, had lower methanol crossover and proton-conductivity in the same order of magnitude.

Zirconium Oxide Modified Sulfonated Poly (Ether Ether Ketone) Membranes for Direct Methanol Fuel Cell Applications

In order to perform a critical analysis of the zirconium oxide effects in sulfonated poly(ether ether ketone) (SPEEK) membranes with two sulfonation degrees (SD), 71 and 87%, the characterization of composite membranes prepared with a systematic variation of the inorganic content is proposed. The method involves preparation of inorganic composite membranes with a wide range of properties which concern water swelling, chemical and thermal stability, methanol and water permeations and, finally, proton conductivity. A good balance between high proton conductivity, good chemical stability and low methanol permeability is reached for the SPEEK polymer with a 7.5% (w/w) ZrO2 content and SD=87%. Compared to NAFION ® 112, this membrane is 3-times more selective towards water/methanol permeation and has a similar proton conductivity (81 compared to 88 mS/cm).

Pre‐treatment Effect on the Sulfonated Poly(ether ether ketone) Membrane Transport Properties and Direct Methanol Fuel Cell Performance

Abstract In this paper a critical study is presented on how the direct methanol fuel cell (DMFC) membrane properties are affected by a pre‐treatment. Membranes based on sulfonated poly(ether ether ketone) (sPEEK) with sulfonation degree (SD) of 42% were used, plain and modified inorganically with 1 wt.% of zirconium oxide. Nafion® 1135 was used as reference. The results obtained show that the sPEEK polymer (SD=42%) enables the preparation of proton exchange membranes with improved properties compared to Nafion® and to the ZrO2‐modified sPEEK membrane, mainly due to its improved relation between proton conductivity and methanol permeation. After the pre‐treatment, the plain sPEEK membrane had a performance 6.4 times higher in terms of maximum power output when used in the DMFC.

An Impedance Study on the sPEEK/ZrO2 Membranes for Direct Methanol Fuel Cell Applications

Electrochemical impedance experiments were carried out in order to study the influence of the ZrO2 inorganic incorporation on the proton conductivity of sulfonated poly(ether ether ketone) (sPEEK) membranes. The impedance data was fitted to an extension of Randles’ circuit, within the inorganic content and temperature ranges considered. The model fits quite well for ZrO2 loads up to 10 wt.%. Such a model allows for characterizing the diffusion phenomena (Warburg) of the membrane electrode assembly (MEA), membrane and electrodes resistances, capacitive and inductive behavior. Proton conductivity was obtained from the impedance spectra and it was observed that it increases with temperature and decreases with the inorganic content. As a general trend, the Warburg parameter decreases slightly with the temperature, except for the 5 wt. % ZrO2 membrane that suffers a more pronounced influence. The Warburg parameter also decreases with the ZrO2 content.