Yuxiang Wen

Facile synthesis of ultrathin NiCo2S4 nano-petals inspired by blooming buds for high-performance supercapacitors

3D petal-like NiCo2S4 nanostructures have been fabricated via a simple, mild and efficient hydrothermal strategy and the growth mechanism of NiCo2S4 nano-petals has been investigated. Such NiCo2S4 nano-petal electrodes can deliver an ultrahigh specific capacitance of 2036.5 F g−1 at a current density of 1 A g−1, superior rate capability and remarkable cycle stability (94.3% of capacitance retention after 5000 cycles). The as-fabricated asymmetric supercapacitors based on NiCo2S4 nano-petals//active carbon electrodes demonstrate a high energy density of 35.6 W h kg−1 at a power density of 819.5 W kg−1, with both long-term cycling and high rate stabilities. Such supercapacitors have been tested to power ten LEDs (2.03 V, 20 mA) in series for around 60 minutes, indicating their great potential for practical application.

Freestanding flexible graphene foams@polypyrrole@MnO2 electrodes for high-performance supercapacitors

A new composite electrode design was successfully fabricated based on 3D flexible graphene foams (GF) with interconnected macropores as the freestanding substrate and a composite of MnO2 nanoparticles and polypyrrole (PPy) as an integrated electrode. Under assistance of PPy, the microscopic morphology of MnO2 changed from flower-like to nanoparticles, and correspondingly, a high specific capacity of 600 F g−1 at a current density of 1 A g−1 was obtained from the GF@PPy@MnO2 nanoparticles composite electrode. Moreover, over 92% of the initial capacity was retained after 5000 cycles at 30 A g−1. Also, the role of PPy in improving the electrochemical performance of the composite electrode was investigated. We also tested a full symmetric supercapacitor of GF@PPy@MnO2//GF@PPy@MnO2 obtaining the maximum energy density of 28 W h kg−1 at 508 W kg−1 and the maximum power density of 13 kW kg−1 at 14 W h kg−1. This well-designed nanostructured composite electrode could be a promising electrode material for high-performance supercapacitors.

Fabrication of hybrid Co 3 O 4 /NiCo 2 O 4 nanosheets sandwiched by nanoneedles for high-performance supercapacitors using a novel electrochemical ion exchange

Electrochemical ion exchange has been used to tailor the composition of transition metal oxides (Co3O4) electrode with enhanced capacity while maintaining its crystal structure and morphology. Specifically, Ni ions were incorporated to Co3O4 nanosheets sandwiched by nanoneedles to form Co3O4/NiCo2O4 composite. As positive electrode for supercapacitors, the Co3O4/NiCo2O4 composite presents a high areal capacitance of 3.2 F cm−2(1060 F g−1) at a current density of 5 mA cm−2 and outstanding rate capability as well as long cycle stability. Moreover, the assembled aqueous asymmetric supercapacitor based on Co3O4/NiCo2O4//carbon cloth electrodes delivers a considerable energy density of 3.0 mW h cm−3 at power density of 136 mW cm−3, and high rate capability (85% retention at a current density of 30 mA cm−2). A safety light composed of ten green LEDs in parallel was lit for ∼360 s using two identical supercapacitors in series, indicating a promising practical application.摘要离子交换技术被广泛用于调节过渡金属氧化物的成分, 采用该技术制备的超级电容器电极材料, 在保持其形貌的同时能增加其比容量. 本文报道了一种新颖的电化学方法辅助制备复合Co3O4/NiCo2O4纳米材料. 通过电化学离子交换, 可以将Ni2+快速引入并部分替换Co3O4纳米材料中的Co2+, 从而得到Co3O4和NiCo2O4的复合纳米材料.将其用作超级电容器正极材料, 在5 mA cm−2的电流密度下, 其面电容达到了3.2 F cm−2, 并展现出了良好的倍率性能及优异的循环稳定性. 此外, 两个串联的非对称器件(Co3O4/NiCo2O4//碳布)在充电3min后可以将10个并联的绿色LED点亮大约6 min, 展现出良好的实用性.

A low crystallinity oxygen-vacancy-rich Co3O4 cathode for high-performance flexible asymmetric supercapacitors

Co3O4 has received ever-growing interest as an electro-active material for supercapacitors due to its high theoretical specific capacitance (3560 F g−1) and simple synthesis process. However, the intrinsically poor conductivity and sluggish reaction kinetics lead to a low practical capacity. In this work, a type of low crystallinity oxygen-vacancy-rich Co3O4 cathode has been fabricated through the introduction of Pd2+ during the hydrothermal process. The results indicate that the introduction of Pd can cause a disordered lattice orientation of Co3O4 nanoparticles and lead to reduced crystallinity. Numerous lattice boundaries caused by the poor crystallinity can facilitate the infiltration of electrolyte and contribute to the generation of oxygen vacancies, resulting in enhanced redox reaction and improved conductivity. The Pd–Co3O4 electrode delivers a high specific capacitance of 1353 F g−1 (4.6 F cm−2, about 2 times the capacitance of pristine Co3O4) at a current density of 7 mA cm−2 and presents 95% capacitance retention after 5000 charge/discharge cycles. The aqueous flexible asymmetric supercapacitor (Pd–Co3O4//carbon cloth) exhibits an energy density of 4.7 mW h cm−3 at the power density of 7 mW cm−3. This study underscores the potential importance of incorporating low crystallinity and oxygen vacancies into transition metal oxides as a strategy for increasing the charge storage ability of redox-active electrode materials.

Flexible All-solid-state Ultrahigh-energy Asymmetric Supercapacitors Based on Tailored Morphology of NiCoO2/Ni(OH)2/Co(OH)2 Electrodes

One of the important requirements of energy storage devices is to store more energy per unit area. In this paper a novel strategy is explored to design and fabricate high-energy supercapacitors by enhancing the areal capacity of electrodes based on the tailored morphology. The morphology of the fabricated samples changed from 3D dense bulk and 2D agglomerated thick sheets to interconnected thin nanosheet networks with ordered nano-holes, and a new phase of NiCoO2 was simultaneously produced. A 3D interconnected NiCoO2/Ni(OH)2/Co(OH)2 nanosheet network was used as an electrode; a high volumetric capacity of 420 C cm−3 was obtained at a current density of 14.7 mA cm−2 and 294 C cm−3 of capacity was retained at a current density of 100 mA cm−2. The reason for the improvement of the electrochemical properties has also been discussed. Besides, an energy density of 37.41 mW h cm−3 and a power density of 155 mW cm−3 in an aqueous asymmetric supercapacitor have been achieved; an energy density of 11.98 mW h cm−3 and a power density of 77 mW cm−3 have also been demonstrated in an all-solid-state asymmetric supercapacitor, with excellent cycling stability and outstanding flexibility. The fabricated all-solid-state supercapacitors were further tested in a heart-shaped logo to supply power for ∼1 hour, indicating the promising applications of these supercapacitors. This strategy provides new opportunities for the fabrication of electrodes and devices with high energy and power density.