Carbon Dots Decorated Hierarchical NiCo₂S₄/Ni₃S₂ Composite for Efficient\nWater Splitting

Abstract

The\ndecomposition of water into hydrogen and oxygen is an effective\nmethod to generate new energy. How to develop highly efficient catalysts\nwith low cost for the hydrolysis of water is a huge challenge. Herein,\nheterogeneous CDs/NiCo₂S₄/Ni₃S₂ nanorods were constructed on nickel foam (CDs/NiCo₂S₄/Ni₃S₂/NF) by Co ion exchange\non carbon dots (CDs) and sulfur codoped nickel foam (NF). The designed\nCDs/NiCo₂S₄/Ni₃S₂/NF as\na self-standing electrocatalyst shows excellent electrocatalytic properties.\nIn the hydrogen evolution reaction process, the current density can\nreach 10 mA cm^–2 only with the overpotential of\n0.127 V. During the oxygen evolution reaction process, overpotential\nof 0.116 V is enough to achieve the same current density. Meanwhile,\nthe CDs/NiCo₂S₄/Ni₃S₂/NF\nelectrode can serve as both anode and cathode in alkaline electrolyte,\nand overpotential of 1.50 V can drive the overall water splitting\nwith superior durability. Such excellent properties are mainly due\nto (1) a large number of exposed active sites provided by carbon dots\nmodified transition metal chalcogenide (NiCo₂S₄ and Ni₃S₂), (2) the changed electronic structure\ncaused by the incorporation of carbon dots and Co ions and the synergistic\neffect between NiCo₂S₄ and Ni₃S₂, (3) the accelerated electron transfer and mass transfer\nprocesses owing to the hierarchical structure formed by 3D nickel\nfoam and one-dimensional CDs/NiCo₂S₄/Ni₃S₂/NF nanorods. This study can facilitate with\nthe production of efficient and non-noble metal catalysts for overall\nwater splitting.