In this work we presented a general strategy for the fabrication of membranes with well-defined ions transport channels through solvent-responsive layer-by-layer assembly (SR-LBL). Multilayered poly (diallyldimethylammonium chloride) (PDDA) and poly (acrylic acid) (PAA) complexes were first introduced on the inner pore wall and the surface of sulfonated poly (ether ether ketone)/poly (ether sulfone) (PES/SPEEK) nanofiltration membranes to form ions transport channels with tuned radius. This type of membranes are highly efficient for the separators of batteries especially vanadium flow batteries (VFBs): the VFBs assembled with prepared membranes exhibit an outstanding performance in a wide current density range, which is much higher than that assembled with commercial Nafion 115 membranes. This idea could inspire the development of membranes for other flow battery systems, as well as create further progress in similar areas such as fuel cells, electro-dialysis, chlor-alkali cells, water electrolysis and so on.
The sulfonated spindle-like carbon derived from metal-organic framework, MOF- C -SO 3 H, has been employed as a filler for the SPEEK membrane. The obtained MOF- C -SO 3 H@SPEEK membrane shows improved properties as a PEM for DMFCs . In particular, with the presence of 3.0 wt% of MOF- C -SO 3 H, the MOF- C -SO 3 H@SPEEK membrane can exhibit higher proton conductivity and much lower methanol permeability than Nafion 115. The specific porous and sulfonated carbon structure is believed to play an important role in the high performance of the MOF- C -SO 3 H@SPEEK membrane. It helps the good dispersion of MOF- C -SO 3 H in the SPEEK matrix, decreasing the swelling ratio and methanol permeability of the membrane, and promotes the transport of protons through the membrane, improving the proton conductivity of the membrane. More interestingly, when used in the DMFCs , it can give maximum power density of 83.91 mW cm −2 , which is ~50% higher than that of Nafion 115. This, together with its higher stability of the DMFC with the MOF- C -SO 3 H@SPEEK membrane than that with Nafion 115, suggests that the MOF- C -SO 3 H@SPEEK membrane is a promising proton exchange membrane for fuel cells.
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