HER activity of nickel molybdenum sulfide electrocatalyst as function of the ionomer in the ink formulation

Transition metal sulfides (NiSx, MoSx and Ni0·5Mo0.5Sx) are synthesized and have their HER performance evaluated in three-electrode cell setup by applying LSV analyzes in 1 M KOH. XRD, Raman, TEM and XPS characterizations are applied aiming to correlate physicochemical properties/electrocatalytic activity. It is evidenced a synergistic effect in which nickel oxide, present in the surface of Ni0·5Mo0.5Sx, accelerates the water dissociation, while molybdenum sulfide catalyzes the reduction of adsorbed hydrogen species. When physically mixed with Carbon Vulcan, Ni0·5Mo0.5Sx only needs 60 mV higher overpotential to achieve −200 mA cm−2 than 40% Pt/C. Furthermore, Ni0·5Mo0.5Sx activity is assessed in interaction with different ionomers (Nafion® or Sustainion® XB-7). It is shown by an exploratory study that, when Nafion® is replaced by XB-7, the amount of ionomer and water to isopropanol volume ratio must be diminished in the ink formulation to, at least, maintain a comparable activity of the electrode material.