Temperature-dependent structural tuning of flower-like NiFe₂O₄ nanostructures as simplistic electrocatalyst for oxygen evolution reaction toward alkaline water splitting

Electrochemical water splitting is one of the best routes to produce highly demanding carbon-neutral green hydrogen using renewable energy sources. Therefore, oxygen evolution reaction (OER) which is bottleneck in electrocatalysis process due to its sluggish kinetics needs to be evaluated. In this work we fabricated flower like nickel ferrites with different annealing temperatures via chemical bath deposition technique and they are utilized for the OER properties. The nickel ferrite thin film annealed at 200 °C was found to be the most active OER electrocatalyst among the tested materials in 1 M KOH electrolyte. It exhibited an overpotential of 372 mV (vs RHE) at a current density of 20 mA cm⁻² and an ultralow Tafel slope of 42 mV dec⁻¹ revealing faster reaction kinetics of the catalyst. Moreover, the catalysts showed outstanding electrochemical stability tested for more than 10 h of continuous operation in alkaline electrolyte without deviation in its overpotentials. It has been evidenced that the OER enhancement is due to the increased number of active sites, faster reaction kinetics (Rct = 0.42 Ω), hydrophilic surface properties, and high electrochemical surface area of 222 cm². Thus, this work represents a simple and cost-effective way to develop catalyst materials for water splitting.