Construction of hierarchical proton sieving-conductive channels in sulfated UIO-66 grafted polybenzimidazole ion conductive membrane for vanadium redox flow battery

Sieving of H+/VII + ions is essential to vanadium redox flow battery (VRFB). Herein, the interconnected hierarchical proton sieving-conductive channels are constructed through the graft of sulfated UIO-66 (UIO-66OSO3) along the polybenimidazole (PBI) backbone with the highly reactive and acidic sulfate ester functional group. Highly porous UIO-660SO3 provides numerous angstrom scale sieving channels (about 5 angstrom) to transport proton and repel vanadium ion, and the sulfated groups ended flexible side chains are densely bonded to UIO-66 and aggregate into broad nanoscale ionic clusters (similar to 8 nm) for fast proton conduction between UIO-660SO3 nanoparticles. The as-prepared membrane exhibits low vanadium permeability (7.88 x 10(-9) cm(2)s(-1)) and area resistance (0.23 Omega cm(-2), lower than that of Nafion 212). High energy efficiency (86.1%) and low discharge capacity decay (0.15% per cycle) are achieved even after 100 charge-discharge cycles at 100 mA cm(-2), and the battery keeps running for 2000 cycles without morphological and chemical changes. The VRFB proprieties are far superior to Nafion 212 membrane VRFB proprieties (energy efficiency 74.9%, decay rate 0.71% per cycle), and also surpasses most recently reported porous, dense and hybrid ion conductive membranes.

Automated summary

In this study, interconnected hierarchical proton sieving-conductive channels were constructed to design an efficient vanadium redox flow battery membrane. The membrane exhibited high proton sieving capability and fast proton conduction, effectively preventing vanadium ion permeation. After 100 charge-discharge cycles, the battery performance remained stable and showed high energy efficiency and low discharge capacity decay rate.