Electrochemical and structural evaluation of CoFeNiOx-based catalysts for water splitting applications

We report trimetallic cobalt-iron-nickel oxide (CoFeNiOx) electrocatalysts prepared by a hydrothermal route followed by thermal annealing and post-synthesis alkaline activation (sodium hydroxide [NaOH]/potassium hydroxide [KOH]/urea). By tuning the Co:Fe:Ni molar ratio (1:1:1, 1:3:1, and 3:1:1), we correlate phase composition and morphology with electrocatalytic water splitting performance. X-ray powder detraction indicates the coexistence of layered double hydroxide–derived motifs with spinel-type oxides, while scanning and transmission electron microscopy reveal increased roughness and porosity in Co-rich samples after KOH/urea treatment. In 1 M KOH, the CoFeNiOx (1:1:1) electrocatalyst exhibits the most favorable oxygen evolution reaction activity (η10 = 264 mV; Tafel slope = 84.4 mV dec⁻1), stable chronopotentiometry at 10 mA cm⁻2 for 24 h with a ~40 mV increase in overpotential, and low charge transfer resistance based on electrochemical impedance spectroscopy. The CoFeNiOx (3:1:1) electrocatalyst delivers the best hydrogen evolution reaction response among the tested electrocatalysts. X-ray photoelectron spectroscopy confirms mixed valence states with enrichment of trivalent species (Co³⁺/Co²⁺, Ni³⁺/Ni²⁺, Fe³⁺/Fe²⁺) on the surface, consistent with the formation of catalytically active oxyhydroxide layers under alkaline conditions. Overall, controlled composition coupled with urea‑assisted alkaline activation enhances the exposure of active sites exposure and charge transport, enabling the production of bifunctional CoFeNiOx electrocatalysts that are suitable for integrated water‑splitting systems.