Deciphering the Stability of NiOOH Active Phase in Oxygen Evolution Reaction Using Ab Initio Molecular Dynamics Simulations

Abstract

The stability of the electrochemically active nickel oxyhydroxide (NiOOH) phase under oxygen evolution reaction (OER) conditions has been investigated using ab initio molecular dynamics simulations combined with the metadynamics sampling technique. Two potential nickel atom detachment pathways involving a plausible set of 11 elementary steps, specifically, at the edge surface and the corner position of the pristine NiOOH phase, were explored. Two-dimensional free energy landscapes for both OER and nickel atom detachment processes were constructed, revealing that the nickel atom preferentially detaches from the corner position rather than the edge surface. The stability number of the active NiOOH phase that derived from the ratio of the oxygen formation rate to the nickel detachment rate was determined to be 1.4 × 106, which is consistent with experimental observation. The present study offers valuable insights into the performance-stability relationship for nickel-based electrocatalysts in aqueous OER conditions, paving the way for designing more stable and efficient electrolysis catalysts.