Reasonable construction of low migration energy barrier and continuous proton transfer channels via bimetallic MOFs nanofibers (MIL-(Cr Al)–NH2) for its composite proton exchange membrane

Abstract

Reasonable construction of low migration energy barrier and continuous proton transfer channel is the key to improving the performance of composite proton exchange membranes. In this paper, we prepared a novel bimetallic MOFs (MIL-(Cr Al)–NH2) nanofibers (MCANs) consisting of Cr and Al elements by electro-blown spinning method (EBS) and hydrothermal synthesis, and subsequently introduced them into non-fluorinated sulfonic acid polymer sulfonated polysulfone (SPSF) matrix to obtain composite proton exchange membranes (MCANs@SPSF). Importantly, MCANs successfully constructed relatively long-range continuous unsaturated metal site proton transfer channels provided by the Cr-based MOFs, thereby reducing the proton migration energy barrier in the MCANs@SPSF, which confirmed by the density functional theory (DFT) calculation. In detail, DFT studies indicated that the migration energy barrier between H+ and MCANs was 1.677 eV, while that of single Al-based MOF (MAN) and single Cr-based MOF (MCN) were 1.879 eV and 1.762 eV respectively. The existence of efficient low migration energy barrier and continuous proton transfer channels made the proton conduction efficiency of MCANs@SPSF greatly improved, that was under the condition of 80 °C and 100 % RH, the proton conductivity of MCANs@SPSF reached the maximum value of 0.358 S cm−1 and the power density reached 104 mW cm−2. Moreover, MCANs@SPSF-5 displayed best DMFC durability performance with only 14.65 % voltage loss under 24h test. In addition, due to the acid-base pair interaction between MCANs and SPSF enhanced the interface binding force between the two phases, meanwhile, the pore structure of MOFs also had a certain adsorption effect on methanol, thus reducing the methanol permeability, and the addition of 5 wt% MCANs in SPSF was tested to reduce the methanol permeability to 5.53 × 10-7 cm2 s−1. Overall, this work provided a new strategy for construction of low migration energy barrier and continuous proton transfer channels, which was beneficial for the development of high performance proton exchange membranes.