Denghua Zhang,Xihao Zhang,Chao Luan,Biao Tang,Zhongyu Zhang,Nianwen Pu,Kaiyue Zhang,Jianguo Liu,Chuanwei Yan
Thin membranes with high conductivity are of great importance for high power density vanadium flow batteries (VFBs), however, the trade-off between conductivity and ion selectivity limits their further development. Herein, an ultrathin composite membrane (∼10 μm) enabled by a zwitterionic interface between conductive polybenzimidazole (PBI) and porous polyethylene (PE) substrate is proposed to break the trade-off, and greatly enhance the power density of a VFB. The zwitterionic interface is engineered by the covalent reaction between polydopamine and zwitterionic sulfonated 3-dimethylaminopropylamine (DMAPAPS). The as-fabricated composite membrane features excellent mechanical properties and high dimensional stability. Furthermore, the zwitterionic interface facilitates proton transportation while blocking vanadium-ion permeation . More importantly, the ion selectivity of the ultrathin membrane is nearly three times higher than the pure PBI membrane (i.e., 2.71 × 10 4 vs. 1.09 × 10 4 S min cm −3 ). As a result, a VFB assembled with the ultrathin membrane demonstrates a superior energy efficiency of 78.7% at 300 mA cm −2 , and achieves an excellent cycle stability over 500 cycles at 300 mA cm −2 . Therefore, the engineering of zwitterionic interface provides a promising strategy in the development of ultrathin composite membrane for high power density VFBs.
Kai Cheng,Na Zhang,Na Yang,Shuai Hou,Jiahui Ma,Luhong Zhang,Yongli Sun,Bin Jiang
Zwitterionic materials are well known to possess extraordinary water affinity. However, micromolecular zwitterions have rarely been exploited for membrane hydrophilic modification. Herein, novel antifouling and antibacterial polyvinylidene fluoride (PVDF) ultrafiltration membranes with enhanced permselectivity were facilely fabricated through one-step co-deposition of dopamine and a newly synthesized micromolecular zwitterion (DMAPAPS). With the assistance of CuSO 4 /H 2 O 2 -triggered oxidation, a uniform and hydrophilic coating (water contact angle = 33°) was constructed on membrane surface in only 40 min. The impacts of the DMAPAPS concentration and coating time on membrane performance were investigated. Results showed that our strategy endowed the optimized membrane with high pure water flux of 364 L/m 2 ∙ h and BSA rejection of 98.6%. The flux recovery ratios of membrane were as high as 96.3% for bovine serum albumin, 98.1% for humic acid and 95.1% for sodium alginate after 3-cycle filtration, respectively. Moreover, the membrane displayed superior antibacterial activity towards E. coli and S. aureus as well as excellent chemical and mechanical stability. This work provides a versatile platform for the robust, time-saving and cost-effective fabrication of antifouling and antibacterial membranes.
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