Sandwiching h-BN Monolayer Films between Sulfonated Poly(ether ether ketone) and Nafion for Proton Exchange Membranes with Improved Ion Selectivity

Jiaman Liu; Liwei Yu; Xingke Cai; Usman Khan; Zhengyang Cai; Jingyu Xi; Bilu Liu; Feiyu Kang

doi:10.1021/acsnano.8b08680

Sandwiching h-BN Monolayer Films between Sulfonated Poly(ether ether ketone) and Nafion for Proton Exchange Membranes with Improved Ion Selectivity

ACS Nano. 2019 Feb 26;13(2):2094-2102. doi: 10.1021/acsnano.8b08680. Epub 2019 Feb 15.

Authors

Jiaman Liu¹, Liwei Yu², Xingke Cai¹, Usman Khan¹, Zhengyang Cai¹, Jingyu Xi², Bilu Liu¹, Feiyu Kang^{1

3

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Affiliations

¹ Shenzhen Environmental Science and New Energy Technology Engineering Laboratory, Shenzhen Geim Graphene Center (SGC), Tsinghua-Berkeley Shenzhen Institute (TBSI) , Tsinghua University , Shenzhen 518055 , China.
² Institute of Green Chemistry and Energy , Graduate School at Shenzhen, Tsinghua University , Shenzhen 518055 , China.
³ Shenzhen Key Laboratory for Graphene-based Materials and Engineering Laboratory for Functionalized Carbon Materials, Shenzhen Geim Graphene Center (SGC) , Graduate School at Shenzhen, Tsinghua University , Shenzhen 518055 , China.
⁴ Laboratory of Advanced Materials, School of Materials Science and Engineering , Tsinghua University , Beijing 100084 , China.

PMID: 30768234
DOI: 10.1021/acsnano.8b08680

Abstract

Two-dimensional (2D) hexagonal boron nitride (h-BN) has attracted great interest due to its excellent chemical and thermal stability, electrical insulating property, high proton conductivity, and good flexibility. Integration of 2D h-BN into commercial proton exchange membranes (PEMs) has the potential to improve ion selectivity while maintaining the proton conductivity of PEMs simultaneously, which has been a longstanding challenge in membrane separation technology. Until now, such attempts are only limited in mechanically exfoliated small area h-BN and in proof-of-concept devices, due to the difficulty of growing and transferring large area uniform h-BN monolayers. Here, we develop a space-confined chemical vapor deposition approach and achieve the growth of wafer-scale uniform h-BN monolayer films on Cu rolls. We further develop a Nafion functional layer assisted transfer method which effectively transfers as-grown h-BN monolayer films from the Cu roll to sulfonated poly(ether ether ketone) (SPEEK) membrane. The as-fabricated Nafion/h-BN/SPEEK sandwich structure is used as the membrane and compared with the pure SPEEK membrane for flow batteries. Results show that the sandwich membrane exhibits ion selectivity 3-fold greater than that of a pure SPEEK membrane ( i.e., 32.1 × 10⁴ vs 9.7 × 10⁴ S min cm^-3). In addition, we fabricate vanadium flow batteries using the Nafion/h-BN/SPEEK sandwich membrane and find that the sandwich structure does not affect the proton transport but inhibits vanadium crossover at low current density (<120 mA cm^-2) due to the selective blocking of vanadium ions by 2D h-BN. As a result, the sandwich membrane exhibits a significantly improved Coulombic efficiency and energy efficiency, ∼95% and ∼91%, respectively. Our results suggest that a functional layer/2D film/target substrate-based sandwich structure shows clear potential for future 2D material-based membranes in separation technologies.

Keywords: 2D materials; Cu roll; Knudsen diffusion; hexagonal boron nitride; proton transport; space-confined chemical vapor deposition; transfer; wafer-scale.