Materials with high proton conductivity above 200 °C based on a nanoporous metal–organic framework and non-aqueous ionic media

Abstract

Fuel cell devices working above 200 °C provide a number of advantages such as low poisoning of the catalyst, high energy output and efficient heat recovery. However, new materials for proton exchange membranes (PEM) must be developed to operate at such conditions. Here we demonstrate that by mixing nanoporous coordination polymer MIL-101 and (benz)imidazolium triflate salts at high pressure with subsequent annealing a hybrid material with superior proton conducting properties approaching 0.1 S cm⁻¹ at temperatures above 200 °C and in a dry atmosphere could be obtained. The ionic components completely fill the nanopores of the MIL-101 coordination polymer as well as the intercrystallite space, forming a continuous anhydrous proton conducting media. The MIL-101 microcrystalline framework improves the mechanical properties of the material and provides a number of other advantages, such as an increase of the ion conductivity at lower temperatures and a facilitation of the proton transfer by lowering of the activation energy. The present study contains spectroscopic, texture and calorimetric analyses of the reported compounds as well as the investigation of nanoscopic composite effects which affect the phase transition parameters of the ionic components.