Highly transparent mixed electron and proton conducting polymer membranes

Abstract

The exploration of transparent electron and proton transport polymer membranes can lead to novel technological advances. We demonstrate the development of highly transparent proton and electron conducting polymer composites of poly(3,4-ethylenedioxythiophene)/sulfonated poly(2,6-dimethyl 1,4-phenylene oxide) (PEDOT:sPPO). The conductivity, optical, and mechanical properties of PEDOT:sPPO can be easily tuned by varying the ratio of the two polymeric components and by solvent treatment with dimethylsulfoxide (DMSO). 100 nm thick films of PEDOT:sPPO with a ratio of 1 : 2 exhibit transparency above 92%, with 97% transmittance at 550 nm, high protonic conductivity up to 20 mS cm⁻¹ and lithium ion conductivity of 1 mS cm⁻¹. Interestingly, after DMSO treatment, polymer electrical conductivity dramatically increased to 10 S cm⁻¹ without jeopardizing the protonic conductivity. We further investigated the proton transport mechanism of PEDOT:sPPO. These polymer materials are suitable for membrane applications for solar water splitting, battery electrode applications, and photovoltaic devices, as well as other potential electrochemical devices.