Study on the Application Performance of Polymer Electrolyte Membrane Functionalized with Triethyl Phosphite-Modified Graphene Oxide in Fuel Cells

In this paper, we successfully synthesize phosphoric acid functionalized graphene oxide (PGO) based on acid modification of graphene oxide. The composite membrane is further prepared by adding PGO into sulfonated poly(aryl ether ketone sulfone) containing carboxyl groups matrix (C-SPAEKS). The PGO as well as the composite membranes were characterized by a series of tests. The prepared composite proton exchange membranes (PEMs) have good mechanical and electrochemical properties. Compared to the C-SPAEKS membrane, the best composite membrane has a tensile strength of 40.7 MPa while exhibiting superior proton conductivity (110.17 mS cm-1 at 80 °C). In addition, the open-circuit voltage and power density of C-SPAEKS@1% PGO are 0.918 V and 792.17 mW cm-2, respectively. Compared with C-SPAEKS (0.867 V and 166 mW cm-2), it can be seen that our work has a certain effect on the improvement of the single cell performance. The above results demonstrate that the functionalized graphene oxide has greatly improved the electrochemical performance and even the overall performance of PEMs.

Carboxyl-functionalized nanocellulose/sulfonated poly(aryl ether ether ketone ketone) composites for proton exchange membrane by electrospinning

A novel nanocomposite proton-exchange membrane (PEM) was obtained by combined electrospinning and solution casting of a composite solution of sulfophenylated poly(ether ether ketone ketone) (SP-PEEKK) and maleic anhydride modified nanocellulose (MN). SP-PEEKK was prepared by polymerization between phenyl hydroquinone and 1,4-bis(4-fluorobenzoyl)benzene followed by post-sulfonation. Nanocellulose (NCC) was prepared by the acid treatment of MCC with sulfuric acid, and MN with carboxyl group was obtained by modifying NCC with maleic anhydride. PEMs with 2% MN (MN2) showed a water uptake of 28% at 100°C, which was higher than that of MN0 (with 0% MN content). MN2 possessed a high tensile strength of 48.7 MPa, Young’s modulus of 1.3 GPa, and elongation at break of 34%, which was 54%, 21%, and 16% higher than those of MN0, respectively. Thus, the ordered distributed of MN was illustrated to be the effective reinforcing material for SP-PEEKK membranes because of the strong interface between the hydroxyl group of rigid MN and the sulfonic acid group of SP-PEEKK. MN2 also had a substantially higher proton conductivity of 0.09 S cm−1 at 90°C than MN0 (0.037 S cm−1). Therefore, combined electrospinning and solution casting was found to be a promising choice to improve the proton conductivity of nanocomposite PEMs, as promoted by the three-dimensional hydrogen bond-proton-transport network formed by the well-oriented MN in SPEEKK produced by the electrospinning.

Cross-Linked Sulfonated Poly(arylene ether sulfone) Membrane Using Polymeric Cross-Linkers for Polymer Electrolyte Membrane Fuel Cell Applications

Cross-linked membranes for polymer electrolyte membrane fuel cell application are prepared using highly sulfonated poly(arylene ether sulfone) (SPAES) and polymeric cross-linkers having different hydrophilicities by facile in-situ casting and heating processes. From the advantage of the cross-linked structures made with the use of polymeric cross-linkers, a stable membrane can be obtained even though the polymer matrix with a very high degree of sulfonation was used. In particular, hydrophilic cross-linker is found to be effective in improving physicochemical properties of the cross-linked membranes and at the same time showing reasonable proton conductivity. Accordingly, membrane electrode assembly made from the cross-linked membrane prepared by using hydrophilic polymeric cross-linker exhibits outstanding cell performance under high temperature and low relative humidity conditions (e.g., maximum power density of 176.4 mW cm^-2 at 120 °C and 40% RH).