Binder-free Co3O4 sheet-like morphology on 3D nickel foam for efficient alkaline water electrolysis

Abstract

This study presents an eco-friendly and efficient strategy for designing electrocatalysts for water electrolysis, particularly targeting the oxygen evolution reaction (OER). The electrocatalyst was developed from ligand-free cobalt oxide (Co₃O₄) nanoparticles grown directly on three-dimensional Nickel foam using a green sol-gel method followed by a closed low-temperature process and annealing. Uniquely, the synthesis used agar-agar (a natural polysaccharide from red algae) as a low-cost, biodegradable polymerizing agent. The resulting Co₃O₄/Ni foam electrodes showcased excellent structural integrity, with well-distributed nanoparticles forming a porous, sheet-like morphology. Compared to commercial Co₃O₄ catalysts, the grown electrodes displayed significantly better electrochemical performance — including a lower overpotential (η₃₀ = 332 mV), a favorable Tafel slope (70 mV dec⁻¹), and greater electrochemically active surface area (ECSA). The improved kinetics were associated with increased in-situ growth, thus increasing the active surface area, and efficient charge transfer dynamics, confirmed by impedance spectroscopy. Importantly, the electrode maintained long-term stability over 15 h of continuous operation, making it a promising, sustainable candidate for noble-metal-free alkaline water splitting. This work paves the way for future development of eco-conscious and scalable electrocatalyst technologies.