A novel approach to in-situ synthesize and encapsulate phosphotungstic acid into the cavity of MIL-101 (Cr) using Na2WO4 center dot 2H(2)O and Na2HPO4 as precursors is presented to increase the acid loading content (31.4 wt.%). The phosphotungstic acid-encapsulating MIL-101(Cr) (HPW@MIL101) is introduced in sulfonated poly(ether ether ketone) (SPEEK) to prepare SPEEK/HPW@MIL101 nanohybrid membranes for PEMFC applications. Due to the introduction of HPW@MIL101, proton-conducting nanochannels are constructed both in the, cavity of MIL101 and at the interface between HPW@MIL101 and SPEEK. Meanwhile, due to the hygroscopicity of phosphotungstic acid, the membrane dehydration at elevated temperatures is alleviated. The proton conductivity at low relative humidity is remarkably enhanced. The nanohybrid membrane with 9 wt.% HPW@MIL101 exhibits proton conductivity of 272 mS cm(-1) at 65 degrees C, 100% RH and 6.51 mS cm-1 at 60 degrees C, 40% RH, which are 45.5% and 7.25 times higher than those of pristine SPEEK membrane (187 mS cm(-1) and 0.898 mS cm(-1)), respectively. The single H-2/O-2 fuel cell with SPEEK/HPW@MIL-9 membrane acquires the power density of 383 mW cm(-2) at 100% RH, which is 27.2% higher than that of pristine SPEEK membrane. The peak power density of SPEEK/HPW@MIL-9 membrane at 55% RH is 2.97 times higher than that of pristine SPEEK membrane (79 mW/cm(2)). (C) 2017 Elsevier Ltd. All rights reserved.