(248e) Activating Limiting Water Dissociation Kinetics for Neutral pH Water Reduction to Hydrogen through Surface Heterointerfaced Ni-Based Oxide/Nitride

Feed water quality is one of the primary causes for stack failure in commercial water splitting electrolyzers. To that end, benchmark cathodic Pt/C suffers from irreversible adsorption of chloride ions from minor upstream upsets in electrolyzer feed water quality, leading to near-immediate degradation in performance. Moreover, for both seawater and impaired water electrolysis operating in conventional alkaline environments, or locally near the cathodic surface, the presence of calcium and magnesium species form precipitates which passivate catalytically active sites and fouls membrane dividers. To avoid formation of these precipitates, neutral and near-neutral pH operation is desired. However, this mode of operation further hampers the hydrogen evolution reaction (HER) kinetics due to the requirement of an initial water dissociation step. Herein, we sought after tailoring a surface that features sites for promoting the kinetically hindered H₂O dissociation step and simultaneously lowering cathodic chloride deactivation through electrostatically shielding the catalyst from Cl^− in the electrolyte. A core-sheath design comprising of core metallic Ni/Ni₃N and surface sheathing of ETM-based oxynitrides including V or Cr, which have low electronegativities relative to anionic [O−N]^δ−, and higher d-band electronic states relative to Ni. The developed materials exhibit robust stability in neutral pH saline environments due to the enhanced divergence in electrostatic affinity between electroactive surface [ETM]^δ+−[O−N]^δ− allowing for docile H^δ+−OH^δ− dissociation, as shown by low Tafel slopes attained in near-neutral pH regimes, as well as electrostatic shielding from anionic Cl^− attack. The optimum NiVN@NF electrocatalyst yielded low overpotentials of -53 mV in neutral saline electrolyte, at −10 mA cm^−2 of current density. Unlike benchmark Pt/C, the developed NiVN@NF exhibited stable performance at the same −50 mA cm^-2 for 50 hours, followed by an additional 50 hours at −100 mA cm^-2 of current density. This work provides insight into future work tailored towards growing neutral pH electrochemical reactions.