Sulfonated reduced graphene oxide as a conductive layer in sulfonated poly(ether ether ketone) nanocomposite membranes

- SRGO was prepared by an arylation of RGO with diazonium salt.
- SRGO/SPEEK composite membrane exhibited excellent mechanical strength and dimensional stability.
- Extra proton transfer channel contributed to the enhanced conductivity and fuel cell performance.

In this work, sulfonated reduced graphene oxide (SRGO) has been synthesized and incorporated into conventional random sulfonated poly(ether ether ketone) (SPEEK) in order to decrease the proton conduction barrier between isolated sulfonic acid groups in SPEEK and improve its conduction properties. SRGO was prepared by a facile arylation of reduced graphene oxide (RGO) with diazonium salt, which allowed the benzene sulfonate groups to be covalently bonded to the RGO layer. By a physical blending approach, the SRGO/SPEEK composite membranes were obtained in a homogenous state, and exhibited considerably improved thermal stability, mechanical strength and dimensional stability. Since the sulfonic acid groups presented in SRGO promote ion conduction through both Vehicle and Grotthuss mechanisms, the composite membranes exhibited better proton conductivities (σ), particularly at low relative humidity (RH) conditions. Taking SPEEK/SRGO-1.0 membrane as an example, its σ was as high as 8.6 mS cm-1 at 80 °C/50% RH, which is three times greater than that of the blank. Moreover, the H2/air single cell test further confirmed the superior performance of the SPEEK/SRGO-1.0 membrane. A higher power output of 705 mW cm-2 was generated with this composite membrane under the testing conditions, whereas only 636 mW cm-2 for the pristine SPEEK membrane.

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