Cactus-like NiCo₂S₄@NiFe LDH hollow spheres as an effective oxygen bifunctional electrocatalyst in alkaline solution

The high-performance non-precious electrocatalysts for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are crucial to the practical application of fuel cells and metal-air batteries. Herein, a novel cactus-like NiCo₂S₄@NiFe LDH hollow sphere assembled by one-dimensional (1D) NiFe LDH nanowires and two-dimensional (2D) NiFe LDH nanosheets on the NiCo₂S₄ hollow spheres is prepared by a facile hydrothermal method. The outer NiFe LDH nanowires and NiFe LDH nanosheets can effectively suppress the collapse and corrosion of inner NiCo₂S₄ hollow structure during long-term stability tests. The integration of the effective OER electrocatalyst NiFe LDH into NiCo₂S₄ to form heterostructures, as well as the strong electronic interaction between NiCo₂S₄ and NiFe LDH, can greatly boost both ORR and OER activities. Due to the above merits, the NiCo₂S₄@NiFe LDH achieves remarkably a small potential gap (ΔE = Ej=10-E_1/2) of only 0.667 V. This work offers a facile strategy to design efficient catalysts with heterostructures.