Potassium dihydrogen phosphate (KH2PO4, POP) and phosphotungstic acid (H3PW12O40, PTA) were mechanochemically milled in dry nitrogen atmosphere to synthesize highly proton conductive composite electrolytes in the PDP-PTA system. Proton conductivity of these composites significantly depends on the molar ratio of PDP and PTA in the temperature range of room temperature (RT) to 180 degrees C under both anhydrous and hydrous conditions, and the composites exhibited proton conductivities more than 2 orders of magnitude higher than those of the raw substances. Furthermore, when the binders-free PDP-PTA composites in pellet form were used as an electrolyte in H-2/O-2 fuel cell systems, higher open circuit potential than 0.9 V and a maximum power density of 20 mW cm(-2) were achieved during the single cell test. The structural studies and solid-state proton-magic angle spinning-nuclear magnetic resonance (H-1 MAS-NMR) results showed new chemical interaction between dihydrogen phosphate anion and K-substituted PTA via ion-exchange and hydrogen bonds, which manifested the essential role of a newly developed hydrogen-bonding network to the improvement of protic conduction behavior, leading to the increase in the electrochemical performances of these composites. (C) 2013 Elsevier Ltd. All rights reserved.