Properties of Composite Membranes of SPEEK and Nanodiamond
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Properties of Composite Membranes of SPEEK and Nanodiamond
Hongying Hou1, Brunella Maranesi1,2, Mustapha Khadhraoui 1, Philippe Knauth1, Riccardo Polini2, M. Luisa Di Vona2 1 LCP-MADIREL, Aix-Marseille Univ - CNRS, 13397 Marseille, France; 2 Dip.Scienze Tecnologie Chimiche, Univ Roma Tor Vergata, 00133 Roma, Italy. Abstract The manufacture of composite materials can improve the properties of proton-conducting polymers as membranes in PEM fuel cells. We have investigated composite membranes obtained by dispersion of nanodiamond particles in a sulfonated PolyEtherEtherKetone (SPEEK) matrix. SPEEK is a major proton-conducting aromatic polymer. Nanodiamond has been studied for various applications and can be functionalized with different surface groups. For use in proton-conducting membranes, surface functionalization with proton-donating groups is a promising approach. In this preliminary work, we have studied the properties of membranes made using pristine nanodiamond from diverse origins for a first assessment of the potential properties. The composites were analysed by various techniques, including Thermogravimetric Analysis, water vapor uptake and mechanical tensile tests. Introduction As one of the key components, proton exchange membranes play an important role in the performance of proton exchange membrane fuel cells (PEMFCs) and their cost accounts for a large proportion of total material cost of PEMFCs. Although Nafion has been used as standard polymer membrane in PEMFCs, high cost may be one of bottle-necks in terms of large scale civil application besides high fuel permeability and rapid loss of proton conductivity above 100oC[1]. Therefore, inexpensive sulfonated aromatic polymers (SAP) were expected to be promising alternative materials. Sulfonated polyetheretherketone (SPEEK) is known as a major SAP and has been extensively investigated [2-3]. However, in water-rich environment, poor mechanical stability is still a big challenge [4]. If excessive swelling of SPEEK with high degree of sulfonation can be suppressed and the mechanical properties can be improved, the cost of SPEEK-based PEMFCs can be significantly reduced compared with Nafion-based PEMFCs. Various strategies were resorted to improve thermal and mechanical stability: Besides pure SPEEK [5-7] and its composites with other polymer materials [8-10], some desirable promotion effects of inorganics on SPEEK membranes also triggered great interest in inorganic/organic composite membranes. For example, the proton conductivity can be improved by introducing heteropolyacids and boron phosphate into a SPEEK matrix [11-15]. As solid acids, ZrP and sulfated zirconia (SO42--ZrO2) were introduced into a SPEEK matrix in order to improve its ability of self-humidifying under high RH [16-17]. Some ceramic materials, such as TiO2, SiO2 and ZrO2,
were also introduced into SPEEK in order to modify mechanical properties owing to interactions between inorganic and polymer matrix [18-19]. It is known that diamond has the highest hardness among all materials, which
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