Abstract: Membrane/solution interface consists of a neutral concentration polar layer(CPL) and a charge layer(CL) under external electrical field, and the neutral CPL can be neglected under high frequency AC electrical field. The relationship of CL thickness e with electrolyte concentration C and fixed ion exchange sites density σ in membrane surface layer can be expressed as e=σ/C. According to this model, the thickness of the CL on Nafion1135 membrane/solution interface(e_c) was calculated under different membrane surface charge quantity Q and variable electrolyte concentration C. The membrane/solution interface CL thickness(e_m) is obviously related with the membrane properties, and decreases dramatically in a higher electrolyte concentration. e_m values are 76.3 nm and 110.3 nm respectively for Nafion1135 and PE01 ion exchange membrane in 0.05 mol/L H₂SO₄ solution, and e_m values for both membrane tend to 2 nm in 2 mol/L H₂SO₄ solution. For Nafion1135 membrane, the comparison of e_c and e_m gives the result that CL thickness e_m obtained by resistance measurement fits well with the calculated CPL thickness e_c while proton in CL transferred to membrane surface is 14.56×10⁻¹⁰ mol, which corresponds to the fixed exchange group number in a surface layer with a thickness τ=2 nm for Nafion1135 membrane.

Key words: ion exchange membrane; AC electrical field; AC impedance; membrane/solution interface; structure; resistance