Proton conductive composite electrolytes in the KH2PO4–H3PW12O40 system for H2/O2 fuel cell operation

Potassium dihydrogen phosphate (KH2PO4, PDP) 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 °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 H2/O2 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 (1H 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.