Synthesis and characterization of TEMPO- and viologen-polymers for water-based redox-flow batteries†
Redox-flow batteries that employ redox-active polymers (pRFB) represent a novel energy storage technology requiring innovative materials. Polymers bearing a viologen unit (N,N′-dialkyl-4,4′-bipyridines) or a TEMPO radical are synthesized. Acrylamide, poly(ethyleneglycol) methyl acrylates, di(ethylene glycol) methacrylate and 2-(methacryloyloxy)-N,N,N-trimethylethane ammonium chloride are studied as water-solubility-enhancing comonomers. The rheological and electrochemical properties of these polymers in aqueous solutions are evaluated, revealing poly(1-methyl-1′-(4-vinylbenzyl)-[4,4′-bipyridine]-1,1′-diium dichloride) (P2a) and poly(4-methacryloyloxy-2,2,6,6-tetramethylpiperidine-1-oxyl-co-2-(methacryloyloxy)-N,N,N-trimethylethane ammonium chloride) (P4e) to be most suited as anode and cathode materials, respectively, for a pRFB.