Hierarchical NiCo2O4@nickel-sulfide nanoplate arrays for high-performance supercapacitors
Graphical abstract
Nickel sulfide on NiCo2O4 core–shell nanoplate arrays are fabricated and show good energy density and cycling stability for supercapacitors.
Introduction
The environmental issues have pushed human being to find novel energy sources instead of fossil fuels to meet the increasing demands of energy consumptions. Currently, it is deeply urgent to develop reliable green energy storage technologies to achieve a secured and reliable energy supply. The high power performance of supercapacitors has made them important complement power sources of batteries to meet the increasing demands of energy storage and conversion [1], [2], [3]. In the two categories of supercapacitors (electrochemical double layer capacitor - EDLC and pseudocapacitor) with different charge storage mechanisms, the EDLC with traditional carbon materials has very limited specific energy. Researchers are trying to develop pseudocapacitive materials based on faradaic reactions with the specific capacitance an order of magnitude higher than that of carbon [4], [5]. To this end, metal oxides have been extensively studied as pseudocapacitor electrode materials, and it has been shown that the architecture design is very important to improve their supercapacitor performance [5], [6]. In particular, 3D array electrodes have drawn much attention because of their facile preparation and excellent performance [7], [8], [9]. On the other hand, recent research results show that metal sulfides can also be used as good active materials for pseudocapacitor applications [10], [11], [12], and especially, core–shell arrays of metal oxide and sulfide have shown excellent performance [12], [13], [14]. However, the syntheses of sulfides usually involve toxic gases as reactant or product, and therefore it is very urgent to develop a green strategy to construct the core–shell oxide-sulfide array architectures.
Nickel sulfides with various compositions, such as NiS, NiS2, Ni3S2, Ni6S5, Ni7S6, and Ni3S4 [15], are an important class of semiconductor materials with great potential multifunctional applications in high-performance supercapacitors, lithium ion batteries, and the photocatalysis production of hydrogen [15], [16], [17], [18], [19], [20]. In particular, Ni3S2 is of interest because of its good performance as electrode materials for supercapacitors and lithium ion batteries [15], [21], [22], [23]. A number of Ni3S2 composites, such as one-dimensional hierarchical structures of Ni3S2 nanosheets grown on carbon nanotube backbone [15], Ni3S2/graphene [24], and Ni3S2 nanoflakes on a 3D porous nickel foam [25], have been prepared for enhanced performance. Recently, NiCo2O4 has drawn intensive attention because of its low cost, environmental friendliness, natural abundance and importantly, a high theoretical capacitance. In addition, the NiCo2O4 array electrodes can be facilely synthesized on various substrate with excellent cycling stability, making it a good substrate to grow other pseudocapacitive materials [26]. In this paper, we demonstrate the electrodeposition of Ni–S on NiCo2O4 arrays supported by nickel foam. The NiCo2O4@Ni–S arrays were further tested as an electrode material for supercapacitors and found to exhibit a high specific capacitance of 1.85 F cm−2 at a current density of 8 mA cm−2, good rate capability and cycling stability.
Section snippets
Reagents and materials
NiCl2·6H2O, urea, Co(NO3)2•6H2O and the other chemicals were purchased from Aladdin Ltd. (Shanghai, China) and used as received without further purification. The water used throughout all experiments was purified through a Millipore system.
Growing NiCo2O4 array on nickel foam
In a typical synthesis, 1 mmol of Ni(NO3)2•6H2O, 2 mmol of Co(NO3)2•6H2O, 6 mmol of NH4F and 15 mmol of urea were dissolved in 80 mL of deionized water under magnetic stirring for 30 min in air to form a clear pink solution. 12 mL of the above solution was
Results and discussion
The NiCo2O4@Ni–S nanoplate arrays were synthesized by a two-step process, as illustrated in Scheme 1. Firstly, NiCo2O4 nanoplate arrays were grown on nickel foam by a hydrothermal process in an 80 mL solution containing 1 mmol of Ni(NO3)2, 2 mmol of Co(NO3)2, 6 mmol of NH4F and 15 mmol of urea [27]. Secondly, Ni–S nanostructures were electrodeposited on the pre-grown NiCo2O4 nanoplate arrays by CV in 10 mL solution containing 50 mM NiCl2·6H2O and 1 M thiourea [25]. The weak-crystalline nature
Conclusions
In conclusion, NiCo2O4@Ni–S hierarchical core–shell nanoplate arrays have been successfully fabricated by a two-step process combining hydrothermal synthesis and electrodeposition. Such NiCo2O4@Ni–S arrays can deliver high specific capacitances of 1.85 F cm−2 and 1.15 F cm−2 at current rates of 8 mA cm−2 and 40 mA cm−2, respectively, and also exhibit good cycling stability. The good stability of NiCo2O4 arrays, the good contact between nickel sulfides and NiCo2O4 arrays, and the pores present
Acknowledgments
X. Liu would like to acknwoledge the support from the National Natural Science Foundation of China (no. 21271082), and J. Chen AFOSR (no. FA9550-11-1-0135).
References (34)
J. Power Sources
(2000)- et al.
J. Power Sources
(2014) - et al.
Nano Energy
(2014) - et al.
Electrochem. Comm.
(2013) - et al.
J. Power Sources
(2014) - et al.
J. Power Sources
(2015) - et al.
Chem. Rev.
(2004) - et al.
Nat. Mater.
(2008) - et al.
Nanoscale
(2013) - et al.
Adv. Mater.
(2012)
Chem. Comm.
Chem. Comm.
Chem. Comm.
Nano Lett.
Chem. Comm.
J. Mater. Chem.
Nano Lett.
Cited by (97)
Comparative studies on the structural, optical and electrochemical properties of Gd, Nd and In-doped CeO<inf>2</inf> nanostructured thin films
2024, Materials Science in Semiconductor ProcessingN-doped bimetallic sulfides hollow spheres derived from MOF as battery-type electrode for asymmetric supercapacitors
2023, Journal of Energy StorageSpinel NiCo<inf>2</inf>O<inf>4</inf> based hybrid materials for supercapacitors: Recent developments and future perspectives
2023, Journal of Energy Storage