Xiaobing Zhu

Challenging reinforced composite polymer electrolyte membranes based on disulfonated poly(arylene ether sulfone)-impregnated expanded PTFE for fuel cell applications

An ultrathin, low cost and high performance reinforced composite membrane (20 μm, thick) based on disulfonated poly(arylene ether sulfone)-impregnated polytetrafluoroethylene (PTFE) for polymer electrolyte membrane (PEM) fuel cell application was investigated. For comparison, PTFE-reinforced Nafion® membrane (Nafion/PTFE), pristine disulfonated poly(arylene ether sulfone) membrane (SPSU) and recast Nafion112 membrane (rN112) membrane were employed. The peak power density of a single PEM fuel cell employing the composite membrane (SPSU/PTFE) reached 2.4 W cm−2, twice that of the rN112 membrane. The SPSU/PTFE membrane structure was characterized and confirmed by scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS), and Fourier transform infrared (FTIR) spectroscopy. The improved interface compatibilty of the two components in the SPSU/PTFE membrane, reflected by enhanced morphology/surface property, was ascribed to the surface pre-treatment of microporous expanded PTFE and the presence of the n-butanol auxiliary solvent in the membrane fabrication process. The excellent single cell performance employing our SPSU/PTFE membrane was attributed to the implementation of ultrathin PTFE-reinforced membrane with low areal resistance and utilization of a high proton conductive SPSU ionomer. Our SPSU/PTFE membrane might indicate or pave a way of fluorine-less or non-fluorinated ionomer membranes to replace Nafion® membranes for PEM fuel cell applications.

A Novel PTFE-Reinforced Multilayer Self-Humidifying Composite Membrane for PEM Fuel Cells

A novel polytetrafluoroethylene (PTFE)-reinforced multilayer self-humidifying composite membrane is developed. The membrane is composed of Nafion-impregnated porous PTFE composite as the central layer and nanosized SiO2 supported Pt catalyst imbedded into Nafion as the two side layers. The proton exchange membrane (PEM) fuel cells employing the self-humidifying membrane (20 mu m thick) under dry H-2/O-2 gave a peak power density of 0.95 W/cm(2) and an open-circuit voltage of 1.032 V. The good membrane performance is attributed to hygroscopic Pt-SiO2 catalyst at the two side layers, which results in enhanced anode side self-humidification function and decreased cathode polarization. (c) 2005 The Electrochemical Society.

A Low-Cost PTFE-Reinforced Integral Multilayered Self-Humidifying Membrane for PEM Fuel Cells

A low-cost polytetrafluoroethylene (PTFE)-reinforced integral multilayered self-humidifying membrane Pt-C/sulfonated poly (ether ether ketone) (SPEEK)/PTFE/Nafion was developed for proton exchange membrane (PEM) fuel cells. The membrane was based on a thin porous PTFE film, by which a Pt/C catalyst dispersed SPEEK resin (as the self-humdifying layer) and a small quantity of Nafion resin (as the antidegradation layer) on each side are bonded. The porous PTFE film tightly bonds with the SPEEK and Nafion resins to form an integral membrane and, accordingly, prevents delamination of the two different resins. Energy dispersive spectroscopy measurements were conducted to characterize the membrane structure. The single cell test of the self-humidifying membrane indicated its self-humidifying function. (c) 2006 The Electrochemical Society.

Blend Membranes of Highly Phosphonated Polysulfone and Polybenzimidazoles for High Temperature Proton Exchange Membrane Fuel Cells

Blend Membranes of Highly Phosphonated Polysulfone and Polybenzimidazoles for High Temperature Proton Exchange Membrane Fuel Cells R. A. Potrekar † , K. T. Clark †‡ , X. Zhu † , and J. B. Kerr †* Environmental Energy Technologies Division, Lawrence Berkeley National Laboratory, One Cyclotron Road, Berkeley, CA 94720 Department of Materials Science and Engineering, University of California Berkeley, Berkeley, CA 94720 The aim of the presented work is to develop a polymer electrolyte having the specific composition of polysulfone (PSU) with phosphonic acid groups in the tethered form and polybenzimidazoles, doped with phosphoric acid, which facilitates self-ion transfer. The blended membranes show high proton conductivity (3.8 x 10 -2 S/cm at 170°C at 25% RH) and have good thermal and mechanical properties. Introduction Proton conduction in polymer membranes in fuel cells is due to the vehicular, Grotthuss (hopping or structure diffusion), and segmented motion mechanisms. These mechanisms are dependent on the morphology of the polymers as well as the proton conducting functional groups. It is observed that polymers containing acid groups mainly facilitate structure diffusion and vehicular transport mechanisms for proton transport. However, the presence of these acid groups imposes a limitation on the operating temperature (<90°C) (1). For the vehicular proton transport mechanism, an aqueous media is essential to act as a mobile phase to facilitate the conduction of protons. Nevertheless, the presence of an aqueous media acts as a plasticizer and adversely affects the mechanical properties (swelling), increases the permeability of the fuel and oxidant, etc (2). On the other hand, the segmental proton transfer mechanism depends on the segmental motion of the polymer backbone, which requires a very low glass transition temperature that limits its mechanical properties, especially at high temperatures (3). In the Grotthuss mechanism, the proton, or protonic defects, diffuse through the hydrogen bond network by formation of cleavage of bonds and the proton is transferred through self or auto ionization (4). For example, at high temperatures in imidazole, protonic defects form and the proton is conducted through hydrogen bonding. Considering the limitations and advantages of all of the above three mechanisms, the transport phenomena involved, conformational, morphological contrast, mechanical strength, permeability of fuel/oxidant, and its temperature dependency etc., a polymer material needs to be designed and developed that can satisfy all the necessary properties and provide a robust material which can sustain the harsh oxidation/reduction environment.

Research and Development of Key Materials of PEMFC

In this paper, R & D on the electrocatalysts and the proton conductive membranes for proton exchange membrane fuel cells in our group is presented. It is shown that both the electrocatalysts and the proton conductive membranes have attained an enhanced performance.Copyright