Achieving efficient proton conduction in a MOF-based proton exchange membrane through an encapsulation strategy

Abstract

Metal-organic frameworks (MOFs) have attracted immense attention in the field of proton-conducting materials due to their high tunability and designability. Although considerable advances have been achieved in the design and fabrication of MOF-based proton-conducting materials, the design of MOF-based proton exchange membranes (PEMs) with excellent conductivity and low methanol permeability for fuel cells remains a great challenge. MOF-polymer hybrids exhibit excellent performances hard to realize from the individual components so that they are known as potential candidates for PEMs. Encapsulation of polymer into nanoporous MOFs is an effective strategy for constructing long-range ordered and continuous nanochannels to achieve efficient ion transport. Herein, a simple and rapid encapsulation strategy is used to encapsulate poly(4-styrenesulfonate) (PSS) into the nanochannels of ZIF-8 to prepare the MOF-polymer hybrid membranes (PSS@ZIF-8). The PSS is threaded in ZIF-8 through a solid confinement conversion process, whereby fast proton transport occurs in the ionic nanochannels created in ZIF-8. Strikingly, the resulting membrane possesses superior proton conductivity (2.59 × 10-1 S cm-1 at 80 °C and 100% RH) and good methanol-barrier property (2.08 × 10-9 cm2 s-1), surpassing state-of-the-art Nafion membranes and most of the reported MOF-based proton-conducting materials.