Mitigation of chemical degradation in perfluorosulfonic acid proton exchange membrane using regenerable hindered amine functionalized carbon quantum dots

Abstract

The chemical stability of perfluorosulfonic acid (PFSA) has a significant impact on the lifetime of a proton exchange membrane (PEM). Herein, we describe the design and fabrication of a novel PEM containing hindered amine functionalized carbon quantum dots (HA-CQDs) to improve the PEM's chemical stability. The novel CQDs are prepared by a hydrothermal reaction using citric acid as the carbon source, while groups of the free radical scavenger 4-amino-2, 2,6,6-tetramethylpiperidine are used to modify the oxygen-containing groups on the CQDs' surface. Benefiting from the introduction of the radical-scavenging groups, the HA-CQDs effectively eliminate active free radicals, thereby improving the PEM's chemical stability. Mass loss, FTIR, SEM, and SAXS are used to evaluate the PEM's chemical stability, surface morphology, and proton conduction by side-chain functional groups via free radicals. The electrochemical performance of the oxidized PEM is evaluated from proton conductivity and single-cell performance, and the free radical scavenging capability is characterized using the 1,1-diphenyl-2-picrylhydrazyl radical (DPPH) radical method. Our work reveals that introducing hindered amines can eliminate the free radicals generated by electrochemical reactions and effectively mitigate the chemical degradation of a PEM. This paper provides a promising way to improve the chemical stability of PFSA and enhance the lifetime of PEMs.