In the past decade, fossil fuel resources have been exploited and utilized extensively, which could lead to increasing environmental crises, like greenhouse effect, water pollution, etc. Accordingly, many coping strategies have been put forward, such as water electrolysis, metal-air batteries, fuel cell, etc. Among the strategies mentioned above, water electrolysis is one of the most promising. Water splitting, which can achieve sustainable hydrogen production, is a favorable strategy due to the abundance of water resources. Splitting of water includes two half reactions integral to its operation: hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). However, its practical application is mainly impeded by the sluggish anode reaction. Simultaneously, noble metal oxides (IrO2 and RuO2) and Pt-based catalysts have been recognized as typical OER catalysts; however, the scarcity of noble metals greatly limits their development. Hence, designing an alternative electrocatalyst plays a vital role in the development of OER. However, exploring a highly active electrocatalyst for OER is still difficult. Herein, a miraculous construction of a tree-like array of NiS/Ni3S2 heterostructure, which is directly grown on Ni foam substrate, is synthesized via one-step hydrothermal process. Since NiS and Ni3S2 have shown great OER performance in previous investigations, this novel NiS-Ni3S2/Nikel foam (NF) heterostructure array has tremendous potential as a practical OER catalyst. Upon application in OER, the NiS-Ni3S2/NF heterostructure array catalyst exhibits excellent activity and stability. More specifically, this novel tree-like NiS-Ni3S2 heterostructure array shows extremely low overpotential (269 mV to achieve a current density of 10 mA·cm-2) and small Tafel slope for OER. It also shows extraordinary stability in alkaline electrolytes. Compared with the Ni3S2 nanorods array, the NiS-Ni3S2 heterostructure array has a synergistic effect that can improve the OER performance. Due to the secondary structure (Ni3S2 nanosheets), the tree-like NiS-Ni3S2 array provides more active sites could have higher specific surface area. The greater activity of the NiS/Ni3S2 heterostructure may also stem from the tight conjunction between tree-like NiS/Ni3S2 and the Ni foam substrate, which is beneficial for electronic transmission. Hydroxy groups can accumulate in large amounts on the surface of the tree-like array, and it also generates some Ni-based oxides that are favorable to OER. Moreover, the synergistic effect of such heterostructure can intrinsically improve the OER activity. The unique tree-like NiS-Ni3S2 heterostructure array has great potential as an alternative OER electrocatalyst.
Fund: the Fundamental Research Funds for the Central Universities, China(0301005202017);the Thousand Young Talents Program of the Chinese Central Government(0220002102003);the National Natural Science Foundation of China(21373280);the National Natural Science Foundation of China(21403019);the Beijing National Laboratory for Molecular Sciences, China;the Hundred Talents Program at Chongqing University, China(0903005203205);the State Key Laboratory of Mechanical Transmissions Project, China(SKLMT-ZZKT-2017M11)
Huijuan ZHANG,Yu WANG