Selective Growth of MoS₂ for Proton Exchange Membranes with Extremely High Selectivity

Abstract

Proton conductivity and methanol permeability are the most important transport properties of proton exchange membranes (PEMs). The ratio of proton conductivity to methanol permeability is usually called selectivity. Herein, a novel strategy of <i>in situ</i> growth of MoS₂ is employed to prepare MoS₂/Nafion composite membranes for highly selective PEM. The strong interactions between the Mo precursor ((NH₄)₂MoS₄) and Nafion’s sulfonic groups in a suitable solvent environment (DMF) probably lead to a selective growth of MoS₂ flakes mainly around the ionic clusters of the resultant MoS₂/Nafion composite membrane. Therefore, it would significantly promote the aggregation and hence lead to a better connectivity of these ionic clusters, which favors the increase in proton conductivity. Meanwhile, the existence of MoS₂ in the ionic channels effectively prevents methanol transporting through the PEM, contributing to the dramatic decrease in the methanol permeability. Consequently, the MoS₂/Nafion composite membranes exhibit greatly increased selectivity. Under some severe conditions, such as 50 °C with 80 v/v% of methanol concentration, an increase in the membrane selectivity by nearly 2 orders of magnitude compared with that of the recast Nafion membrane could be achieved here, proving our method as a very promising way to prepare high-performance PEMs. All these conclusions are confirmed by various characterizations, such as (FE-) SEM, TEM, AFM, IR, Raman, TGA, XRD, <i>etc.</i