Researchers in China have developed a hybrid membrane based on two-dimensional nanohybrid materials to improve the performance of vanadium redox flow batteries (VRFBs).
The team from the Shenzhen Institute of Advanced Technology of the Chinese Academy of Sciences embedded graphene oxide (GO) nanosheets in the perfluorinated sulfonic acid (PFSA) matrix to act as a ‘barrier’ to reduce vanadium ion permeation.
Tungsten trioxide (WO3) nanoparticles were grown on the surface of the GO nanosheets to overcome the electrostatic effect and enhance the hydrophilicity and dispersibility of the GO nanosheets.
Severe vanadium ion permeation of the PFSA ion-exchange membrane (IEM) used in most VRFBs will shorten the life of the cell and cause unsatisfactory cell performance.
The team was led by professor Huiyun Li, professor Shuhui Yu and doctor Jiaye Ye.
The study was published in the journal Advanced Functional Materials in November.
Doctor Ye, the first author of the study, said: "These hydrophilic tungsten trioxide nanoparticles on GO nanosheet surfaces serve as proton active sites to facilitate proton transportation."
The sheets were embedded into a novel PFSA membrane with a sandwich structure, that had also been reinforced for stability, with a thin layer of polytetrafluoroethylene (PTFE). This enabled the graphene oxide sheets to act as a barrier, reducing the permeation of vanadium ions.
The nanoparticles also served as active sites to promote the transport of protons, making for a high coulombic efficiency (>98.1%) and high energy efficiency (>88.9%).
The authors say this exceeds the efficiencies of commercially available membranes, while also addressing the stability issue. The team says the experiments indicate the hybrid membrane is highly suited to vanadium redox flow batteries.
In a previous study, published in Chemical Engineering Journal, the research team developed a sandwich structure composite membrane based on one-dimensional functionalised silicon carbide nanowires.
The researchers introduced functionalised silicon carbide nanowires in a PFSA matrix and sandwiched an ultrathin porous PTFE layer.
This hybrid membrane not only maintains good proton conductivity but also effectively reduces the penetration of vanadium ions, thus improving the performance of the VRFB cell.
These studies provide a preparation strategy for designing high-performance IEMs for VRFBs based on one-dimensional and two-dimensional modified materials, which can be extended to other fields including water treatment and fuel cells.