Stabilizing Electrochemical Interfaces With Multifunctional Cobalt Nitride Layers

ABSTRACT The oxygen evolution reaction remains a kinetic and stability bottleneck in different (photo)electrochemical energy conversion systems, motivating the development of novel, earth‐abundant catalyst coatings that simultaneously enhance surface activity and protect interface properties. Here, we synthesize cobalt nitride thin films via plasma‐enhanced atomic layer deposition and evaluate their application as multifunctional catalysts and protection layers under alkaline conditions. By varying the deposition temperature, we systematically tune the film composition and elucidate composition‐function relationships that govern catalytic performance and durability. Films deposited at ≤150°C exhibit incomplete precursor conversion and substantial carbon impurity incorporation, resulting in poor catalytic activity and rapid mechanical failure. In contrast, depositions at 200°C and 250°C form cobalt nitride films with lower N/Co ratios, reduced oxygen and carbon impurity concentrations, yielding catalytically active coatings with operational stability. Post‐operando analysis reveals surface oxidation, suggesting that oxygen evolution activity may be governed by an oxide‐derived layer rather than the nitride phase. Importantly, compared to cobalt oxide, cobalt nitrides can suppress substrate surface oxidation by using ammonia plasma as an oxygen‐free co‐reactant, thereby enabling favorable interface properties for hole extraction. Taken together, cobalt nitride layers are highly promising for engineering stable, high‐performance catalytic interfaces in energy conversion systems.