Anchoring Water Soluble Phosphotungstic Acid by Hybrid Fillers to Construct Three-Dimensional Proton Transport Networks

Phosphotungstic acid (HPW)-filled composite proton exchange membranes possess high proton conductivity under low relative humidity (RH). However, the leaching of HPW limits their wide application. Herein, we propose a novel approach for anchoring water soluble phosphotungstic acid (HPW) by polydopamine (PDA) coated graphene oxide and halloysite nanotubes (DGO and DHNTs) in order to construct hybrid three-dimensional proton transport networks in a sulfonated poly(ether ether ketone) (SPEEK) membrane. The introduction of PDA on the surfaces of the hybrid fillers could provide hydroxyl groups and secondary amine groups to anchor HPW, resulting in the uniform dispersion of HPW in the SPEEK matrix. The SPEEK/DGO/DHNTs/HPW (90/5/5/60) composite membrane exhibited higher water uptake and much better conductivity than the SPEEK membrane at low relative humidity. The best conductivity reached wass 0.062 S cm(−1) for the composite membrane, which is quite stable during the water immersion test.