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(<i>ortho</i>-toluidine)-PAAMPSA, and poly­(<i>meta</i>-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(<i>meta</i>-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

Single-Step Electrodeposited Molybdenum Incorporated Nickel Sulfide Thin Films from Low-Cost Precursors as Highly Efficient Hydrogen Evolution Electrocatalysts in Acid Medium

Large-scale production of hydrogenthe energy carrier of the futureremains challenging on economy grounds. Low-cost synthetic designs are necessary to produce electrocatalysts for hydrogen evolution reaction (HER). Ternary nickel molybdenum sulfides Ni_1–<i>x</i>Mo_<i>x</i>S (<i>x</i> = 0, 0.04, 0.08, 0.16) have been electrochemically grown on fluorine-doped tin oxide substrate as highly active and stable HER electrocatalysts. The merits of this method are (1) the electrochemical method is energy efficient at ambient conditions and can be easily scaled up on large surface area substrates; (2) Ni, Mo, and S precursors used for the deposition are readily available and relatively cheaper compared to similar methods; and (3) the synthesis procedure is simple, one step, and requires no further heat treatments. The deposited thin films have been examined using regular physical characterization techniques, and their HER activity has been evaluated through electrochemical methods. Ni_0.96Mo_0.04S, especially, has exhibited a promising HER activity with a lowest Tafel slope of 46 mV/dec. The mechanistic aspects of HER on the thin films have been extensively studied by voltammetric and impedance methods. Tafel analysis and double-layer capacitance measurements have revealed that the high activity of Ni_0.96Mo_0.04S can be attributed to the larger electrochemical surface area and the faster discharge of protons in the initial Volmer step. Moreover, stability tests performed on various thin films have shown that Mo-doped thin films could retain more than 80% of the initial activity whereas NiS has lost more than 50% of the same