Ionomer thin-films by electrochemical synthesis: bipolar and ampholytic membranes

Thin-films of cation-conducting poly(styrene sulfonate) (PSS) and anion-conducting poly(N-vinyl-N-benzyl-N,N,N-trimethylammonium chloride) (PVBTMA) were electrochemically deposited. A low film thickness can be obtained, because the electrodeposition is a self-limiting process. Various cases were explored: i) the deposition of a single ionomer layer on various substrates, ii) the sequential deposition of the ionomers giving a bipolar membrane, and iii) the co-deposition of the ionomers giving an ampholytic membrane. The structure and microstructure of the thin films were investigated by NMR spectroscopy and optical and scanning electron microscopy (SEM). Impedance spectroscopy in through-plane configuration revealed a large resistance of the bipolar membrane, due to the ionic blocking interface between the ionomers. The ampholytic membrane also showed a low conductivity, probably due to the loss of ionic carrier pairs that can leave the ionomer without break of electroneutrality.