Carbon Dots Decorated Hierarchical NiCo₂S₄/Ni₃S₂ Composite for Efficient Water Splitting

Abstract

The decomposition of water into hydrogen and oxygen is an effective method to generate new energy. How to develop highly efficient catalysts with low cost for the hydrolysis of water is a huge challenge. Herein, heterogeneous CDs/NiCo2S4/Ni3S2 nanorods were constructed on nickel foam (CDs/NiCo2S4/Ni3S2/NF) by Co ion exchange on carbon dots (CDs) and sulfur codoped nickel foam (NF). The designed CDs/NiCo2S4/Ni3S2/NF as a self-standing electrocatalyst shows excellent electrocatalytic properties. In the hydrogen evolution reaction process, the current density can reach 10 mA cm–2 only with the overpotential of 0.127 V. During the oxygen evolution reaction process, overpotential of 0.116 V is enough to achieve the same current density. Meanwhile, the CDs/NiCo2S4/Ni3S2/NF electrode can serve as both anode and cathode in alkaline electrolyte, and overpotential of 1.50 V can drive the overall water splitting with superior durability. Such excellent properties are mainly due to (1) a large number of exposed active sites provided by carbon dots modified transition metal chalcogenide (NiCo2S4 and Ni3S2), (2) the changed electronic structure caused by the incorporation of carbon dots and Co ions and the synergistic effect between NiCo2S4 and Ni3S2, (3) the accelerated electron transfer and mass transfer processes owing to the hierarchical structure formed by 3D nickel foam and one-dimensional CDs/NiCo2S4/Ni3S2/NF nanorods. This study can facilitate with the production of efficient and non-noble metal catalysts for overall water splitting.