Well-defined hierarchical teddy bear sunflower-like NiCo ₂O ₄ electrocatalyst for superior water oxidation

Abstract

Transition metal oxides were fabricated by a facile solvothermal route. The hierarchical NiCo ₂O ₄ electrocatalyst exhibited enhanced water oxidation performance due to the unique teddy bear sunflower-like morphology.

Abstract

The development of a robust and efficient electrocatalyst for water oxidation is challenging due to the large overpotential requirement to transfer four electrons. Herein, a novel spinel-type hierarchical teddy bear sunflower-like NiCo ₂O ₄ electrocatalyst was synthesized through the facile solvothermal process and evaluated for the challenging and demanding oxygen evolution reaction (OER) in the water electrolysis process. The teddy bear sunflower-like NiCo ₂O ₄ supported on nickel foam (NF) delivers a current density of 50 mA cm ⁻² at a small water oxidation overpotential ( η ₅₀ = 319 mV) which is significantly lower than that of the corresponding spherical NiO/NF ( η ₅₀ = 338 mV), and sea-urchin like Co ₃O ₄/NF ( η ₅₀ = 357 mV). A large specific and electroactive surface area, as well as a high TOF value exhibited by the hierarchical teddy bear sunflower-like NiCo ₂O ₄ electrocatalyst, demonstrates the potential of NiCo ₂O ₄ to catalyze the water oxidation reaction efficiently. The impact of the near-Fermi-level d-orbital states in NiCo ₂O ₄ electrocatalyst for boosting OER activity was unveiled by the density functional theory calculation. The stable performance even after 16 h and high catalyst utilization of the hierarchical teddy bear sunflower-like NiCo ₂O ₄ through the OER indicates that the catalyst is highly suitable for the large-scale water oxidation process.