Proton conducting membranes based on impregnating cellulose acetate (CA) supports with mixtures of the organic ionic plastic crystal (OIPC) choline dihydrogen phosphate and various acids – 18mol% H3PO4, 4mol% HN(Tf)2 and 4, 8 and 12mol% TfOH are discussed. These membranes showed high thermal stability and high ionic conductivity especially in the temperature range of interest (around 110°C). The cyclic voltammetry (CV) results showed significant H+ reduction currents, particularly at temperatures above the plastic crystal phase transition. Fuel cell assemblies incorporating the membranes containing 18mol% H3PO4 and 4mol% HN(Tf)2/[Choline][DHP] were also tested. Although the efficiencies were not high, likely due to the cell configuration and the proton conducting material itself being far from optimized, the conductivity and electrochemical properties suggest that further developments of this type of membrane material would be promising.