Dimethylamine-tuned guanidinium arylphosphonate iHOFs and superprotonic conduction Nafion hybrid membranes for DMFCs

The fabrication of proton exchange membranes (PEMs) with excellent conductivity and low methanol permeability is critical but challenging for the further development of high-performance direct methanol fuel cells (DMFCs). In this work, two ionic hydrogen -bonded organic frameworks ( iHOF-14 and iHOF-15 ) are obtained from 1,3,5-tris(4-phosphonophenyl)benzene and guanidine hydrochloride under the control of dimethylamine cations. Due to the abundant hydrogen bonding network, iHOF-14 and iHOF-15 exhibit good proton conductivity of over 10 -2 S cm -1 . In addition, we dope the iHOFs into Nafion matrix to get the PEMs with richer proton transport pathways and good methanol barrier properties. At 100 degrees C and 98 % RH, the conductivity of 9 %-iHOF-14/Nafion and 9 %-iHOF-15/Nafion reaches up to 1.53 x 10 -1 and 1.78 x 10 -1 S cm -1 , respectively. The 72 h permeation experiment results show that the methanol permeability of the composite membranes is 73.7 % lower than that of the recast Nafion. The maximum power densities of hybrid membranes for DMFCs reach about 80 mW cm -2 , which is 1.5 times higher compared to the recast Nafion. This work not only enriches the high proton conductivity of arylphosphonate iHOFs, but also expands iHOFs/Nafion PEMs materials for DMFCs.