Synergistic effect of ZIF-8 and NiCo2O4 toward efficient performance for urea electrooxidation

Abstract

Efficient and stable electrocatalysts for urea electrooxidation are essential for sustainable energy generation and wastewater treatment. In this study, a hybrid nanocomposite of nickel cobaltite (NiCo₂O₄, NCO) and zeolitic imidazolate framework-8 (ZIF-8), denoted NCO-ZIF-8B, was synthesized using ZIF-8 prepared by a conventional hydrothermal method, followed by low-temperature annealing. Structural and morphological analyses using XRD, SEM, EDX, IR, UV-vis, and TGA confirmed the formation of a porous NCO-ZIF-8B architecture with uniform nanoparticle distribution. Electrochemical measurements in 1.0 M NaOH containing 1.0 M urea demonstrated superior performance of NCO-ZIF-8B compared to pristine NCO. Additionally, NCO-ZIF-8B achieved a peak current density of 38.3 mA cm⁻² at 0.558 V vs. Ag/AgCl, a lower onset potential of 0.35 V, and a Tafel slope of 47 mV dec⁻¹, outperforming pristine NCO (I_P = 21.8 mA cm⁻², onset potential = 0.41 V, Tafel slope = 69 mV dec⁻¹). The enhanced activity is attributed to increased surface area, improved conductivity, and a higher density of active redox sites. The results highlight NCO-ZIF-8B as a promising electrocatalyst for efficient urea electrooxidation.