Highly Water Dispersible Polymer Acid-Doped Polyanilines as Low-Cost, Nafion-Free Ionomers for Hydrogen Evolution Reaction

While research efforts are devoted toward exploring low-cost electrocatalysts for hydrogen evolution reaction (HER), little attention is paid to another expensive component of the catalyst layer—ionomers. Both the electrocatalyst and a proportionately large amount of ionomer are required for a large-scale production of hydrogen. Presently, commercially available expensive Nafion is the state-of-the-art ionomer for proton conduction in the electrocatalyst layer. Interpolymer composites such as polymer acid-doped polyanilines (PANI) could be low-cost alternatives to Nafion. Highly water-dispersible PANI polymers doped with poly(2-acryl-amido-2-methyl-1-propanesulfonic acid) (PAAMPSA)—the polymer backbone of which is similar to that of Nafion—have been explored as cheaper alternatives to Nafion in acid medium. PANI-PAAMPSA, poly(ortho-toluidine)-PAAMPSA, and poly(meta-toluidine)-PAAMPSA have been used as ionomers in MoS2 and CoSe2 electrocatalysts. Electrocatalysts with PANI-PAAMPSA ionomers have achieved the highest HER activities and the lowest Tafel slopes in comparison to that with Nafion. Specifically, poly(meta-toluidine)-PAAMPSA has been found as a promising alternative to Nafion ionomer. Replacing expensive Nafion in the electrocatalyst layer with PANI-PAAMPSA-based ionomers would further reduce the cost of hydrogen in a large-scale production.