Mechanical Strength Of Nafion®/ZrO2 Nano-Composite Membrane

Mechanical Strength Of Nafion®/ZrO2 Nano-Composite Membrane

Rudzani Sigwadi (Department of Chemical Engineering, University of South Africa, Florida, South Africa), Fulufhelo Ṋemavhola (Department of Mechanical Engineering, University of South Africa, Florida, South Africa), Simon Dhlamini (Department of Physics, University of South Africa, Florida, South Africa) and Touhani Mokrani (Department of Chemical Engineering, University of South Africa, Florida, South Africa)
DOI: 10.4018/IJMMME.2018010104
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Abstract

The mechanical stability of modified membranes has become a priority for fuel cell applications as the membranes must endure all the fuel cell operations (to prevent crossover of the fuel while still conducting). Their mechanical stress and yielding stress in the recast and impregnation methods compared with the commercial Nafion® membrane were observed under tensile tests. The modulus of elasticity of wet commercial Nafion117 membrane, Nafion®/ Zr-0, Nafion®/Zr-50 and Nafion®/ Zr-80 membranes and Nafion®/ Zr-100 nano-composite membrane using impregnation methods in the region between 0 and 0.23 strain were determined to be 4817.5 kPa, 2434.7 kPa, 1872.4 kPa, 2092.1 kPa and 2661.4 kPa respectively. The tensile strength of the dry nano-composite membrane prepared using the recast method is higher than the wet nano-composite membrane prepared using the recast methods. It was found that the impregnation method plays an important role in strengthening the nan-composite membranes.
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1. Introduction

Proton exchange membrane fuel cells (PEMFCs) are considered as the future alternatives or replacement of combustion fossil fuels for power generation due to their high energy-efficient and environmentally-friendly characteristics. The proton exchange membranes (PEMs) such as Nafion® membranes have high proton conductivity, high mechanical, chemical and thermal stability at temperatures below the boiling point of water (Bauer & Willert-Porada, 2005; Dimitrova, Friedrich, Vogt, & Stimming, 2002). However, this Nafion® membrane must exhibit high mechanical properties in order to perform on the methanol or hydrogen fuel cell without mechanical failure, as tough membranes improve fuel cell longevity (Dimitrova et al., 2002; Hector, Lai, Tong, & Lukitsch, 2007; Huang et al., 2006). But the Nafion® membrane faces some challenges as the conductivity depends on the bound water within the membrane that hinders the operation in high temperatures and low relative humidity (Choi, Jalani, Thampan, & Datta, 2006). Moreover, its hydrophobic states can have effects on the mechanical properties of the membrane as it becomes swollen when in contact with water (Bauer, Denneler, & Willert‐Porada, 2005; Satterfield, Majsztrik, Ota, Benziger, & Bocarsly, 2006), and also reduces the mechanical stability at elevated temperatures (Zhang, Xu, Hou, Tang, & Deng, 2007). This due to the diminished stability of the polymer chains at high temperatures as a result of the relatively low glass transition temperature of Nafion (Aksoy, Akata, Bac, & Hasirci, 2007; Savadogo, 2004). Many researchers have enhanced the mechanical properties of commercial Nafion® membrane with inorganic materials such as zirconia, silica, titanium and clay that retain water in the Nafion® matrix and enhance thermal stability over 100 °C in order to function at high temperatures and low relative humidity (Adjemian, Srinivasan, Benziger, & Bocarsly, 2002; Sacca et al., 2005). By operating at high temperatures above 100 °C the PEMFC performance is improved. It increases the water and thermal management of the fuel cell system and there is an oxygen reduction reaction (ORR)) and carbon monoxide (CO) tolerance (Arico et al., 2003; Li, He, Jensen, & Bjerrum, 2003; Licoccia & Traversa, 2006), (Licoccia & Traversa, 2006). Furthermore, the mechanical failure of the membrane such as cracks, pinholes and tensile strength can limit its operation at fuel cell level (Adjemian et al., 2002; Chalkova, Pague, Fedkin, Wesolowski, & Lvov, 2005; Liu, Ruth, & Rusch, 2001; Sacca et al., 2005). Using the inorganic material as a nanofiller shows an improvement of the elastic modulus on the nano-composite membrane when compared with the commercial membrane (Kumar & Fellner, 2003). This may be due to the water retention of inorganic material within the membrane (Brown & Hargreaves, 1999; Lu et al., 2001), as incorporation of inorganic material within the Nafion® matrix increases the interaction between polymer matrix and filler materials (Wang et al., 2012). The inorganic incorporation in organic materials improves the thermal and mechanical stability while reducing the swelling of the membrane (Zulfikar, Mohammad, & Hilal, 2006). In this work, the incorporation of zirconium oxide nanoparticles within Nafion membrane was prepared by the recast and impregnation method to enhance the mechanical strength of the electrolytes for the PEM fuel cell applications. Mechanical stress-strain properties of all prepared nanocomposite membrane were measured under tensile stress-strain tests at wet and dry conditions and compared to the commercial Nafion 117 and plain recast membrane.

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