Various loadings (0, 5, 10, 20 wt%) of wet-mechanochemically prepared CsHSO4-H-4-SiW12O40 (CHS-WSiA) composite were incorporated into polymer electrolyte membranes (PEM) based on commercial polybenzimidazole (PBI) and synthesized fluorine-containing PBI (F6PBI). The membranes thus obtained were evaluated by thermal analysis, Fenton's test, acid leaching test, proton conductivity and fuel cell performance. The addition of CHS-WSiA inorganic composite improved acid retention ability and proton conductivity. F6PBI composite membrane exhibited enhanced chemical stability against hydroxyl radical attack, while improving acid doping characteristics and acid retention ability significantly. With 8 mol phosphoric acid doping level (PADL) (173 wt% phosphoric acid uptake), F6PBI with 10 wt% CHS-WSiA, namely F6PBI(10), exhibited the highest conductivity of 2.14 mScm(-1) at 150 degrees C under dry conditions. Under similar conditions as for fuel cell performance, F6PBI(10) achieved a maximum power density of 498 mWcm(-2) with a stable voltage of 0.614 V under a constant current 0.2 Acm(-2) durability test over 24 h. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.