Investigation on proton conductivity behavior of sulfuric acid crosslinked chitosan membrane

The sulfuric acid crosslinked chitosan membrane was prepared for fuel cells. The proton conductivity, mechanical performance, infrared spectroscopy and elemental analysis were investigated. The interaction between sulfuric acid and the chitosan membrane was analyzed. Proton conductivity and mechanical performance were clearly enhanced by interaction, reaching a steady level after 6 h crosslinking. The 6 h crosslinked chitosan membrane showed the high proton conductivity of 0.0472 S·cm^-1 at room temperature under fully hydrated conditions, a 5-fold increase compared to the non-crosslinked chitosan membrane. And the mechanism for the proton conductivity of the crosslinked chitosan membrane was proposed. The relationship between conductivity and temperature accords with the law of Arrhenius and the activation energy of the proton conductivity in the crosslinked chitosan membranes is 18 kJ/mol corresponding to Grotthus mechanism. The contribution of the sulfuric acid to the proton conductivity improvement in the crosslinked chitosan membranes is as follows: the amino groups in the chitosan were protonated efficiently by sulfuric acid; SO₄^2- located between the amino groups, and acted as the ionic bridge in the process of the proton conduction.