High performance acid-base composite membranes from sulfonated polysulfone containing graphitic carbon nitride nanosheets for vanadium redox flow battery

Abstract In this paper, a series of proton exchange membranes are fabricated with graphitic carbon nitride (g-C3N4) nanosheets as nanofillers and sulfonated polysulfone (SPSF) as membrane matrix via a simple solution-casting method. The structure, physicochemical properties and single-cell energy efficiency of SPSF/g-C3N4 composite membranes are detailed investigated. The introduced g-C3N4 nanosheets greatly optimize the ion selectivity of SPSF membrane, and SPSF/g-C3N4-1 shows the higher ion selectivity (21.8 × 103 S min cm−3) than Nafion 117 (4.0 × 103 S min cm−3) and pristine SPSF (4.6 × 103 S min cm−3). For the vanadium redox flow battery (VRFB) single-cell performance, SPSF/g-C3N4-1 further demonstrates its higher coulombic efficiency (CE, 95.5% and 98%) and energy efficiency (EE, 90.4% and 87.3%) than that of Nafion 117 membrane (CE, 91.3% and 96.5%; EE, 81.7% and 75.7%) at 50 and 100 mA cm−2, respectively. Besides, a good structure stability and durability of SPSF/g-C3N4-1 is proved after 100 charge-discharge cycles, and its chemical stability shows an obvious enhancement under strong acidic and oxidizing condition. Such a contribution from the acid-base interfacial interaction from g-C3N4 and SPSF indicates an effective method to improve the performance of proton exchange membrane. Therefore, SPSF/g-C3N4 composite membranes are applicable as proton exchange membrane for VRFB system.