Experimental and Theoretical Assessment of Ni-Based Binary Compounds for the Hydrogen Evolution Reaction

Metallic binary compounds have emerged in recent years as highly active and stable electrocatalysts toward the hydrogen evolution reaction. In this work, the origin of their high activity from a theoretical and experimental point of view is elucidated. Here, different metallic ceramics as Ni₃S₂, Ni₃N, or Ni₅P₄ are grown directly on Ni support in order to avoid any contaminations. The correlation of theoretical calculations with detailed material characterization and electrochemical testing paves the way to a deeper understanding of possible active adsorption sites for each material and the observed catalytic activity. It is shown that heteroatoms as P, S, and N actively take part in the reaction and do not act as simple spectator. Due to the anisotropic nature of the materials, a variety of adsorption sites with highly coverage-dependent properties exists, leading to a general shift in hydrogen adsorption free energies ΔG_H close to zero. Extending the knowledge gained about the here described materials, a new catalyst is prepared by modifying a high surface Ni foam, for which current densities up to 100 mA cm⁻² at around 0.15 V (for Ni₃N) are obtained.