Oxide versus oxynitride cobalt and nickel thin-film electrocatalysts prepared by reactive sputtering for alkaline oxygen reduction reaction

Abstract

Transition-metal oxynitrides are promising earth-abundant oxygen reduction reaction (ORR) catalysts, but conventional nitridation routes often limit control of nitrogen incorporation. Here, cobalt (Co)- and nickel (Ni)-based oxide and oxynitride were synthesized by reactive magnetron sputtering, producing uniform and adherent thin-film coatings on conductive substrates (Ti disk), and the ORR performance in alkaline O₂-saturated 0.1M KOH aqueous solution was evaluated. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) of CoO_1.6N_0.12 and NiO_1.14N_0.18 indicate amorphous films, while X-ray photoelectron spectroscopy (XPS) confirms the oxygen and nitrogen incorporation, and X-ray absorption near edge structure (XANES) Ni and Co K-edge shows a small positive edge shift upon nitridation. Relative to the corresponding oxides, the oxynitrides samples exhibited enhanced ORR activity and higher reaction electron number, with CoO_1.6N_0.12 showing consistently better performance (onset potential, E_onset = 0.82 V vs. RHE, reaction electron number, n ≈ 4.0) compared to the other samples. To demonstrate transferability to porous supports, CoO_xN_y was sputtered onto single-walled carbon nanotubes (SWCNTs) achieving E_onset = 0.83 V and half-wave potential, E_1/2 = 0.71 V vs. RHE with n ≈ 3.75 and ∼15% H₂O₂ yield. These results highlight reactive sputtering as a controllable route to fabricate oxide/oxynitride ORR electrodes and to upgrade carbon nanotubes-based cathode materials.