Ionomer Thin‐Films by Electrochemical Synthesis: Bipolar and Ampholytic Membranes

Abstract

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 micro-structure 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.

Electrodeposited Ionomer Protection Layer for Negative Electrodes in Zinc–Air Batteries

“…Before the electrodeposition of PVBTMA on Zn, R1 corresponds to the resistance of the monomer solution in DMSO; the small increase after electropolymerization can be attributed to the PVBTMA coating. From the average resistance increase of 3 Ω and the coating thickness of 28 μm estimated from the cyclovoltammogram ( Figure 1 ), the ionic conductivity of PVBTMA in a ClO 4 − form (anion of the supporting electrolyte) can be calculated; the value (0.5 mS/cm) is consistent with data previously reported in the literature [ 30 , 31 ]. The resistance R2 increases strongly after electropolymerization.…”

“…The decrease in the current with the cycle number can be attributed to the increase in the ionomer thickness and the related increase in sample and interfacial resistances (see the discussion of impedance spectra). The electropolymerization mechanism [ 30 , 31 ] involves a one-electron reduction with the cleavage of the vinylic double bond and formation of a radical anion, which forms a secondary radical by reaction with a proton (from residual water in hygroscopic DMSO). The secondary radical is the initiator of radical polymerization giving the polymer ( Scheme 1 ).…”

“…𝐹 𝜌. 𝐴 F is the Faraday constant (F = 96,485 C/mol), M is the molar mass of the PVBTMA repeat unit (211.6 g/mol), ρ is the PVBTMA density (1.3 g/cm 3 [31]), and A is the Zn electrode area (1.7 cm 2 ). From the experiment shown in Figure 1, the integrated charge is 2.8 C, and an ionomer film thickness d = 28 µm is obtained from Equation ( 3).…”

“…In this work, we explore an advanced coating of the zinc anode by anion-conducting poly(N-vinylbenzyl N,N,N-trimethylammonium) chloride (PVBTMA, Scheme 1 ) that is electropolymerized [ 30 , 31 ] directly on the zinc metal. The major advances foreseen by this approach are the excellent quality of the metal/ionomer interface, due to the in situ electropolymerization process, which should improve the corrosion protection and the selective anion permeability of the coating, allowing the transport of small hydroxide ions but restricting the diffusion of larger zincate ions.…”

Communication—Electropolymerization of Anion-Conducting Polymer Films

“…42 Later on, the same group electropolymerized both cationic-conducting and anion-conducting monomers to form bipolar and ampholytic membranes. 50 In this work, we performed cathodic EP to synthesize anionconducting solid polymer films started from the monomers vinylbenzyltrimethylammonium chloride (VBTMA) and divinylbenzene (DVB). These monomers were chosen because their vinyl double bonds can be opened to form a radical anion by electroreduction.…”