Synergistically promoted proton conduction of proton exchange membrane by phosphoric acid functionalized carbon nanotubes and graphene oxide

Abstract

One dimensional (1D) and two dimensional (2D) nanomaterials with suitable functional groups possess great potential as proton conduction accelerators due to their long-range proton conductive feature. Herein, two outstanding proton conduction accelerators, phosphoric acid functionalized 1D carbon nanotubes and 2D graphene oxide (PCNT and PGO) were prepared, and then incorporated into Nafion matrix to obtain the codoped proton exchange membrane (PEM). Compared with common sulfonation, phosphorylation exhibits the prospect of more efficient proton conduction due to the amphoteric characteristic, large hydration energy and polarizability of phosphoric acid group (–PO3H2). Introduction of PCNT and PGO provided extra excellent proton conductive sites and improved water retention capacity. More importantly, codoping of PCNT and PGO made their 1D and 2D proton conduction pathways combine as hierarchical proton conduction pathways for better interconnecting ionic clusters, which further generated synergistic effect to form more consecutive proton transfer channels in the codoped PEM, whose proton conductivity climbed to 0.282 S/cm under 90 °C, 95% RH, distinctly greater than that of the recast Nafion (0.130 S/cm). Meanwhile, the codoped PEM attained a peak power density of 493.8 mW/cm2, which was approximately 72% larger than that of the recast Nafion (286.8 mW/cm2).