Dual Behavior of Dispersed Ni Nanoparticles for Hydrogen Evolution Reaction at the Interface of Ni/Alkaline Solution

The electrode kinetic parameters, that is, the interaction parameter (ɡ), fractional coverage (θ), and equilibrium constant (K), for the Frumkin adsorption isotherm in the Volmer step cannot be readily determined using conventional methods. These parameters for the Frumkin isotherm of H for the hydrogen evolution reaction (HER) in the Ni/0.1 M KOH (H2O and H2O + dispersed Ni nanoparticles) solutions were determined using the phase-shift method. The Frumkin isotherms of H are K = 9.8 × 10-4 exp(−5.7θ) mol−1 for the 0.1 M KOH (H2O) solution and KNPs = 1.2 × 10-4 exp(−3.5θ) mol−1 for the 0.1 M KOH (H2O + dispersed Ni NPs) solution. The dispersed Ni NPs behave as electrostatic shielding for the H adsorption in the Volmer step and as an electrocatalyst for the H2 evolution in the Tafel and/or Heyrovsky steps. The dual behavior of the dispersed Ni NPs in the HER was similar regardless of the weight of the dispersed Ni NPs. The electrostatic shielding behavior of the dispersed Ni NPs in the HER has been previously overlooked or missed. We hope that the dual behavior of dispersed NPs at the interfaces of electrocatalysts/solutions will be studied in more detail for their potential applications.