This study aims to identify the optimal Co–Ni composition for ethanol electrooxidation reaction by investigating the structural

morphological

and electrochemical properties of electrodeposited CoNi electrocatalysts. CoNi electrocatalysts with varying cobalt-to-nickel ratios were synthesized via electrodeposition and characterized using field-emission scanning electron microscopy (FESEM)

energy-dispersive X-ray spectroscopy

X-ray diffraction (XRD)

and Raman spectroscopy. Their electrocatalytic performance was evaluated using cyclic voltammetry and electrochemical impedance spectroscopy. FESEM observations revealed a clear morphological evolution from spherical particles to a compact mixed spherical–pebbly structure with increasing cobalt content. XRD analysis indicated a phase transition from a face-centred cubic structure to a dual-phase hexagonal close-packed/face-centred cubic structure

while Raman spectroscopy confirmed the formation of CoNi phases. Among the investigated compositions

the Co-rich catalyst exhibited the highest electrocatalytic activity towards ethanol oxidation

delivering a peak current density of 12.72 mA cm−2

the lowest onset potential

a low charge-transfer resistance of 5.70 Ω

and a reduced Tafel slope of 146 mV dec−1. The superior performance is attributed to the higher cobalt content

smaller crystallite size

increased defect density

and enhanced lattice strain

which collectively improve the density of active sites

optimize the electronic structure

and accelerate reaction kinetics. These findings demonstrate that precise control of CoNi composition is an effective strategy for developing efficient and stable non-noble metal electrocatalysts for ethanol electrooxidation applications.