Ultrathin mesoporous NiO nanosheet-anchored 3D nickel foam as an advanced electrode for supercapacitors

Abstract

As promising electrode materials for electrochemical supercapacitors, pseudocapacitive transition metal oxides such as NiO possess high theoretical specific capacitance, environmental benignity and well abundance. However their areal capacitance and cycling stability are greatly restricted by poor electronic conductivity (NiO, 10 −2~1 0 -3 S cm -1 ). Here we propose an in-situ growth strategy in combination with nanoscale design to construct ultrathin mesoporous NiO nanosheets on 3D network of nickel foam. The hybrid structures show well enhanced conductivity and ion transfer, giving rise to ultrahigh specific capacitance of 2504.3 F g -1 which is close to the theoretical value of NiO. The electrodes also exhibit remarkable cycling 2 stability (no degradation of the overall capacitance after 45000 cycles). The amazing electrochemical performance of such hybrid structures makes them potential electrodes in supercapacitors. The present strategy could be popularized in other transition metal oxides like Co 3 O 4 , MnO 2 , etc, to create electrodes with desirable nanostructures. IntroductionDue to the development of portable systems and hybrid electric vehicles (HEVs), the demand for high power in short-term pulses is increasing greatly. Among energy storage devices, supercapacitors have attracted considerable interests recently owing to their high power density, long lifespan and good pulse charge-discharge characteristics. 1-3 Since practical applications of supercapacitors highly depend on the performance of electrodes, how to design and obtain high-capacity, low-cost and safe electrode materials turns to be a great challenge. As is well known, conventional carbon-based materials suffer from really low specific capacitance (100-120 F g -1 ) and energy density (~4-5 Wh kg -1 ). 4 Transition metal oxides are considered as promising alternative electrode materials for high pseudocapacitance owing to their multiple accessible valence states for efficient reversible redox reactions. 5,6 Pseudocapacitive transition metal oxides, hydroxides and oxalates (such as RuO 2 , MnO 2 , NiO, Co 3 O 4 , Ni(OH) 2 , Co(OH) 2 , NiC 2 O 4 etc.) and their composites could produce a much higher 3 capacitance than carbonaceous electrode materials. For example, RuO 2 demonstrates high specific capacitance (more than 600 F g -1 ) and excellent reversibility. 4, 7 Yang et al.have reported that Co 3 O 4 demonstrated superior capacitance (~1782 F g -1 ) and long-term stability (>90% of capacitance after 2000 cycles). 8 NiC 2 O 4 electrodes have been developed to show high specific capacitance of 813.5 F g -1 and excellent cycling performance with 92.5 % retention after 10000 cycles and excellent capability as asymmetric supercpacitors. 9 Nevertheless, the semiconductor or insulator nature of transition metal oxides largely restricts their performances in supercapacitors. Among the pseudocapacitive materials, NiO is considered to be particularly potential for applications in supercapacitors, owing to its low cost, environmental friendliness an...

Boosting the cycling stability of transition metal compounds-based supercapacitors

“…The electroactive materials in the array structure can be nanoparticles, [196] nanowires, [197] nanotubes [153,173] and nanosheets. [121] The higher anisotropic shapes of nanowires, nanotubes and nanosheets can avoid the aggregation issues of nanoparticles effectively. In particular, material structure based on nanotube arrays provides a higher specific surface area with more electroactive sites than nanowires while the interconnected network of nanosheet array benefits better structural stability.…”

In Situ Growth of Hierarchical Ni‐Mn‐O Solid Solution on a Flexible and Porous Ni Electrode for High‐Performance All‐Solid‐State Asymmetric Supercapacitors

“…[26][27][28][29] Another solution is to utilize the synergistic effect of several metal elements. [30][31][32] The battery-type pseudocapacitance materials, such as Co 3 O 4 , [33] NiO, [34] and RuO 2 , [35] show great charge storage abilities duet ot heir high electronic conductivity,r apid redox activity,a nd high theoretical capacity. Though NiO has ah ight heoretical specific capacitance of 2573 Fg À1 within 0.5 V, easy availability and fast faradaic reactions, the real performances of NiO-based electrodes are far below their theoretical values and their cycle performances are not satisfactory.…”

Pollen-inspired synthesis of porous and hollow NiO elliptical microstructures assembled from nanosheets for high-performance electrochemical energy storage

“…Interestingly, recent studies demonstrate that the electrochemical performance of NiO-based supercapacitors could be improved by tailoring multifunctional nano-architecture engineering (nanowires, [19] nanosheets, [20] nanodots, [21] nanoflake, [22] hierarchical nanostructures, [23] hollow structures, [24] etc.). Among them, porous/ hollow morphology is an effective approach to enhance the electrochemical properties of NiO.…”