Electrochemical behavior of polyaniline doped with dodecylbenzenesulfonic acid

Abstract

A zinc and a lithium as electrodes in rechargeable batteries are relatively electrochemically reversible in a weak acidic aqueous(pH$\sim$4) and propylene carbonate-based organic solutions, respectively. The electrochemical reversibility and redox mechanism of charge transfer for polyaniline (PAn) films doped with dodecylbenzenesulfonic acid (DBSA) were investigated in these solutions by means of cyclic voltammetry and energy dispersive X-ray spectroscopy (EDXS). The films were made by casting the PAn-DBSA solution. The DBSAs were incorporated to the polymer matrix to neutralize the positive charge produced by oxidation of the main backbone of PAn. In an aqueous electrolyte solution, the DBSAs were not removed out of the film due to their bulkiness and hydrophobicity. Meanwhile, in propylene carbonate-based organic electrolyte solutions, the DBSAs leaked out due to the swelling of polymer and aliphatic chain of DBSAs. The redox reaction of the PAn-DBSA film was predominantly controlled by proton transfer process in a strong acidic aqueous solution (pH~1) and by cation transfer process instead of the immobilized DBSAs through the polymer matrix in the weak acidic aqueous(pH~4). The PAn-DBSA film showed a good electrochemical reversibility and cyclability even in a acidic aqueous solution as well as a strong acidic aqueous pH solution, because the small size of cation instead of DBSA trapped and the fibrous structure enhanced the charge transfer through the film. The PAn-DBSA film showed a high discharge capacity in the PAn-DBSA/Zn cell containing the aqueous solution of $ZnCl_2$ and $NH_4Cl$. The PAn-DBSA film showed the electrochemical reversibility in the order of the mixture solution of propylene carbonate(PC)-1,2-dimethoxy ethane(DME, 50% vol)>PC-ethylene carbonate(EC, 50% mol) > PC containing 1 M $LiClO_4$. The viscosity and dielectric constant of the solvents appeared to be responsible for these different electrochemical reversibilities. The decrease ...