Novel composite polymer electrolyte membrane using solid superacidic sulfated zirconia - Functionalized carbon nanotube modified chitosan

Utilization of proton conductor functionalized carbon nanotube (CNT) as an additive is an effective way to simultaneously improve the mechanic strength and proton conductivity of polymer electrolyte membranes (PEMs). Herein, superacidic sulfated zirconia coated carbon nanotube (SZr@CNT), a combination of excellent proton conductor and effective reinforcements, was fabricated via a facile surface-deposition method. And then, SZr@CNT was used as a functional additive in chitosan (CS) to prepare PEMs. Owing to the SZr coating, the SZr@CNT possesses desirable dispersibility and compatibility with the polymer matrix. Therefore, the obtained CS/SZr@CNT composite membranes exhibit better mechanical properties than that of pure CS membrane. Meanwhile, the proton conductor on the surface of CNT could afford the opportunity to build new long-range proton conducting pathways along the interfaces between CS and SZr@CNT, thus enhancing the proton conductivity of the composites. Satisfactorily, incorporation of 0.5% SZr@CNT shows a 1.3-fold increase of proton conductivity when compared with pure CS membrane. As a consequence, such superior proton transport ability guarantees outstanding fuel cell performances of the composite membranes. The maximum power density of the CS/SZr@CNT-0.5 composite membrane is 64.6 mWcm−2 at 70 °C, which is nearly the double of that of pure CS membrane (only 36.3 mWcm−2). Furthermore, the durability test confirms that the CS/SZr@CNT-0.5 composite membrane still possesses satisfactory stability even after continuous operation at 70 °C for 100 h.