Solvent‐Induced Rearrangement of Ion‐Transport Channels: A Way to Create Advanced Porous Membranes for Vanadium Flow Batteries

Abstract

Porous membranes with critically hydrophobic/hydrophilic phase‐separated‐like structures for use in vanadium flow battery application are first realized by solvent‐induced reassembly of a polymer blend system. Porous poly(ether sulfone) (PES)/sufonated poly(ether ether ketone) (SPEEK) blend membranes with tunable pore size are prepared via the phase inversion method. After solidification, isopropanol (IPA) is introduced to induce the reassembly of sulfonated groups and further form ion‐transport channels by using the interaction between IPA and functional groups in SPEEK. As a result, a highly phase separated membrane structure is created, composed of a highly stable hydrophobic porous PES matrix and hydrophilic interconnected small pores. The charged pore walls are highly beneficial to improving proton conductivity, while pores are simultaneously shrunk during the IPA treatment. Therefore, the resultant membranes show an excellent battery performance with a coulombic efficiency exceeding 99%, along with an energy efficiency over 91%, which is among the highest values ever reported. This article supplies an ease‐to‐operate and efficient method to create membranes with controlled ion‐transport channels.

Hybrid Membranes Dispersed with Superhydrophilic TiO2 Nanotubes Toward Ultra‐Stable and High‐Performance Vanadium Redox Flow Batteries

“…An ideal membrane generally bears high chemical and mechanical stability, high proton conductivity, low vanadium ion permeability, and low cost. [ 1d,3 ] To date, the Nafion (DuPont) membrane has been widely employed, in light of its prominent proton conductivity and excellent chemical stability. [ 4 ] However, the VRFB cells with Nafion membranes suffer from severe self‐discharge, large capacity loss, and low energy efficiency, [ 5 ] because of the low ion selectivity caused by the large intrinsic channels (2–4 nm).…”

Advanced porous polyphenylsulfone membrane with ultrahigh chemical stability and selectivity for vanadium flow batteries

“…After the membrane was detached from the glass plate, the membrane was kept in deionized water before the isopropanol (IPA) treatment. The IPA treatment step consisted of immersing the membrane into IPA for 12 h, and then, the IPA was evaporated from the membrane at room temperature over 24 h to shrink the pores . Finally, the membrane was washed in a 3% hydrogen peroxide solution for 1 h and washed in boiling water for 1 h before further use.…”

“…A new idea based on pore size exclusion to block large vanadium ions in porous membranes has been proposed . However, it is difficult to control the pore size accurately since the Stokes radii of hydrated vanadium ions (>0.6 nm) and protons (<0.24 nm) to be separated are extremely small, the pores size of currently explored membranes are generally cannot meet the requirements . So far, various nonperfluorinated membranes have been studied such as poly(vinylidene fluoride), polyacrylonitrile, polybenzimidazole, polyethersulfone, and sulfonated polysulfone .…”

Porous Polyelectrolytes: The Interplay of Charge and Pores for New Functionalities

“…This resulted in the membrane surface being conferred with hydrophilicity and high ion conductivity, while the polyelectrolytes on the pore walls reduced the pore size of the substrate for higher ion selectivity. Similar porous polyelectrolyte membranes based on poly(ether sulfone)/sufonated poly(ether ether ketone) blends and cross‐linked networks on the pore walls of polysulfone were also realized and applied in vanadium flow batteries. Enhanced proton conducitivity, stability, and ion selectivity were achieved.…”