Effect of the matrix on proton conductivity in electrolyte membranes containing deoxyribonucleic acids

Organic–inorganic hybrid electrolyte membranes were prepared with a sol–gel reaction of 3-glycidoxypropyltrimethoxysilane (GPTMS) and tetraethoxysilane (TEOS) in the presence of different amounts of deoxyribonucleic acid (DNA), and compared with DNA/poly(ethylene imine) (PEI) and DNA/poly(ethylene oxide) (PEO) blend membranes with the aim of understanding the matrix effect on the electrolyte membrane properties. DNA, comprising of phosphates along a rod-like polymer of heteroatomic rings, was used as a facilitate proton transport channel in electrolyte membranes under low humidity conditions and was dispersed inside of the inorganic matrix created with the TEOS/GPTMS solution, which produced an amorphous electrolyte membrane. The proton conductivity of the DNA/TEOS/GPTMS electrolyte membranes increased with DNA loading and temperature. The proton conductivity of 30 wt% of DNA in an amorphous inorganic matrix at 120 °C under an N2 environment was measured at 4.9 × 10−4 S/cm, which is an order of magnitude higher than that of DNA in a crystalline PEO matrix and is lower than that in a more basic PEI matrix. This result implies that the main requirements for high proton transport under low humidity are the homogeneity of the membrane along with the dissociation of the proton from its ionic sites in the matrix.