A facile and efficient method to improve the proton conductivity of open-framework metal phosphates under aqueous condition

Abstract Herein, the K+ ions were doped into the inorganic layer of two 2D layer metal phosphates (C2H10N2)[Mn2(PO4)2].2H2O (1) and (C2H10N2)[Mn2(HPO4)3](H2O) (2), respectively, via ion exchange method. The resultant compounds maintained the original structures of 1 and 2, but significantly improved their proton conductivity, for example, the proton conductivity of 1 increased from 1.14×10-5 S.cm-1 to 3.39×10-2 S.cm-1 at 99% RH and 293K after doped 0.55 K+ ions; the proton conductivity of 2 is 0.70×10-2 S.cm-1 at 99% RH and 293K after doped 0.32 K+ ions, and is 4.3 times that of the orginal sample. Such a substantial increase in proton conductivity could be attributable to that the K+ ions in aqueous solutions create stronger electrostatic fields to accommodate water, and thus make a more dense and extensive hydrogen-bonding network to enhance the transport of protons.