Co-precipitation synthesis of CuCo2O4 nanoparticles for supercapacitor electrodes with large specific capacity and high rate capability

Multifunctional sulfur doping in cobalt-based materials for high-energy density supercapacitors

In this study, S-CCO@Co(OH)2('CCO' representing CuCo2O4/Cu2O; 'S-'representing sulfur doping) was synthesized by hydrothermal method followed by electrodeposition. The multiple effects of S doping were studied by S doping and constructing 3D core-shell structure. S doping induced the reduction of Cu2+and Co3+to Cu+and Co2+, respectively. Also, S partially replaces O and creates oxygen vacancies, which increases a number of active sites for the redox reaction enhancing the redox reaction activity. After the electrodeposition, S-Co bond is formed between the Co(OH)2shell and the S-CCO core, which suggests a synergistic effect between S doping and core-shell structure. The formation of S-Co bond is conducive to electron and ion transport, thus improving electrochemical performance. After modification, the specific capacitance of S-CCO@Co(OH)2is 4.28 times higher than CCO, up to 1730 Fg-1. Furthermore, the assembled S-CCO@Co(OH)2//activated carbon supercapacitor exhibits an energy density of 83.89 Whkg-1at 848.81 Wkg-1and a retention rate of 98.48% after 5000 charge and discharge cycles. Therefore, S doping and its mutual effect with the utilization of the core-shell structure considerably enhanced the electrochemical performance of the CCO-based electrodes, endowing its potential in further application.

Nitrogen-doped graphene quantum dots embedding CuCo-LDH hierarchical hollow structure for boosted charge storage capability in supercapacitor

The nanostructure optimization of layered double hydroxide (LDH) can effectively alleviate fragile agglomerated problems. Herein, nitrogen-doped graphene quantum dots (NGQDs) embedded in CuCo-LDH hierarchical hollow structure is synthesized by hydrothermal and impregnation methods. The electrochemical results show that the ordered multi-component structure could effectively inhibit the aggregation and layer stacking. At the same time, the hierarchical structure establishes new electron and ion transfer channels, greatly reducing the resistance of interlayer transport and accelerating the diffusion rate of electrolyte ions. Besides, NGQDs have both good electrical conductivity and abundant active sites, which can further improve the electron transmission rate and effectively strengthen the energy storage capacity of the material. Therefore, the large specific capacity of 1009 F g-1 can be displayed at 1 A g-1. The energy density of the assembled carbon cloth (CC)@CuCo-LDH/NGQDs//activated carbon (AC) device can reach 58.6 Wh kg-1 at 850 W kg-1. Above test results indicate that CC@CuCo-LDH/NGQDs//AC devices exhibit stable multi-component hierarchical structure and excellent electrical conductivity, which provides an effective strategy for enhancing the electrochemical characteristics of asymmetric supercapacitors.

Nanostructured mixed transition metal oxide spinels for supercapacitor applications

There have been numerous applications of supercapacitors in day-to-day life. Along with batteries and fuel cells, supercapacitors play an essential role in supplementary electrochemical energy storage technologies. They are used as power sources in portable electronics, automobiles, power backup, medical equipment, etc. Among various working electrode materials explored for supercapacitors, nanostructured transition metal oxides containing mixed metals are highly specific and special, because of their stability, variable oxidation states of the constituted metal ions, possibility to tune the mixed metal combinations, and existence of new battery types and extrinsic pseudocapacitance. This review presents the key features and recent developments in the direction of synthesis and electrochemical energy storage behavior of some of the recent morphology-oriented transition metal oxide and mixed transition metal oxide nanoparticles. We also targeted the studies on a few of the recently developed flexible and bendable supercapacitor devices based on these mixed transition metal oxides.

Hierarchically nanostructured Zn0.76C0.24S@Co(OH)2 for high-performance hybrid supercapacitor

It is a great challenge to achieve both high specific capacity and high energy density of supercapacitors by designing and constructing hybrid electrode materials through a simple but effective process. In this paper, we proposed a hierarchically nanostructured hybrid material combining Zn_0.76Co_0.24S (ZCS) nanoparticles and Co(OH)₂ (CH) nanosheets using a two-step hydrothermal synthesis strategy. Synergistic effects between ZCS nanoparticles and CH nanosheets result in efficient ion transports during the charge-discharge process, thus achieving a good electrochemical performance of the supercapacitor. The synthesized ZCS@CH hybrid exhibits a high specific capacity of 1152.0 C g^-1 at a current density of 0.5 A g^-1 in 2 M KOH electrolyte. Its capacity retention rate is maintained at ∼ 70.0% when the current density is changed from 1 A g^-1 to 10 A g^-1. A hybrid supercapacitor (HSC) assembled from ZCS@CH as the cathode and active carbon (AC) as the anode displays a capacitance of 155.7 F g^-1 at 0.5 A g^-1, with a remarkable cycling stability of 91.3% after 12,000cycles. Meanwhile, this HSC shows a high energy density of 62.5 Wh kg^-1 at a power density of 425.0 W kg^-1, proving that the developed ZCS@CH is a promising electrode material for energy storage applications.

MnCo2O4/Ni3S4 nanocomposite for hybrid supercapacitor with superior energy density and long-term cycling stability

MnCo₂O₄ is regarded as a good electrode material for supercapacitor due to its high specific capacity and good structural stability. However, its poor electrical conductivity limits its wide-range applications. To solve this issue, we integrated the MnCo₂O₄ with Ni₃S₄, which has a good electrical conductivity, and synthesized a MnCo₂O₄/Ni₃S₄ nanocomposite using a two-step hydrothermal process. Comparing with individual MnCo₂O₄ and Ni₃S₄, the MnCo₂O₄/Ni₃S₄ nanocomposite showed a higher specific capacity and a better cycling stability as the electrode for the supercapacitor. The specific capacity value of the MnCo₂O₄/Ni₃S₄ electrode was 904.7 C g^-1 at 1 A g^-1 with a potential window of 0-0.55 V. A hybrid supercapacitor (HSC), assembled using MnCo₂O₄/Ni₃S₄ and active carbon as the cathode and anode, respectively, showed a capacitance of 116.4 F g^-1 at 1 A g^-1, and a high energy density of 50.7 Wh kg^-1 at 405.8 W kg^-1. Long-term electrochemical stability tests showed an obvious increase of the HSC's capacitance after 5500 charge/discharge cycles, reached a maximum value of ∼162.7% of its initial value after 25,000 cycles, and then remained a stable value up to 64,000 cycles. Simultaneously, its energy density was increased to 54.2 Wh kg^-1 at 380.3 W kg^-1 after 64,000 cycles.