Self-Template Synthesis of Hybrid Porous Co3 O4 -CeO2 Hollow Polyhedrons for High-Performance Supercapacitors (original) (raw)
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SSRN Electronic Journal, 2021
Bimetal oxides are promising materials in the field of energy storage due to their various oxidation states, synergistic interactions among multiple metal species, and stability. In this work, Co 3 V 2 O 8 hollow spheres are synthesized by a two-step hydrothermal method: (i) synthesis of V 2 O 5 spheres and (ii) partial replacement of V by Co through the Kirkendall effect. As an electrode, it shows an extrinsic pseudocapacitive charge-storage mechanism due to different oxidation states of V and Co ions. Because of the low crystallinity degree of the mesoporous wall and high accessible surface area of hollow spheres, the optimum Co 3 V 2 O 8 electrode reaches a high specific capacitance of 2376F g − 1 at a current density of 2 A g − 1 , which is more than two times higher than the top reported values, and a rate capability retention of ~80% at 20 A g − 1. Using Co 3 V 2 O 8 , activated carbon, and KOH as positive, negative electrodes, and electrolyte, respectively, a hybrid supercapacitor device presents maximum energy and power densities of 59.2 Wh kg − 1 and 36.6 kW kg − 1 , respectively. Further, the aqueous supercapacitor device shows superior structural and electrochemical stabilities after 10,000 galvanostatic charge-discharge cycles because of the arrays of voids in the orthorhombic crystal structure of Co 3 V 2 O 8 that can decrease the volume expansion/shrinkage during the intercalation/deintercalation processes. Our results provide a platform for exploring bimetallic Co and V-based oxides, hydroxides, and sulfides nanostructures as promising energy storage materials in the future.
Porous Thin-Wall Hollow Co3O4 Spheres for Supercapacitors with High Rate Capability
Applied Sciences
In this study, a zeolitic imidazolate framework-67 (ZIF-67) was prepared as a precursor using a facile hydrothermal method. After a calcination reaction in the air, the as-prepared precursor was converted to porous thin-wall hollow Co3O4 with its original frame structure almost preserved. The physical and chemical characterizations of the nanomaterial were analyzed systemically. The electrochemical tests indicate that the obtained Co3O4 possesses large specific capacitances of 988 and 925 F/g at 1 and 20 A/g accompanying an outstanding rate capability (a 93.6% capacitance retention) and retains 96.6% of the specific capacitance, even after 6000 continuous charge/discharge cycles. These excellent properties mark the Co3O4 a promising electrode material for high performance supercapacitors.
ACS omega, 2022
Electrochemical energy storage relies essentially on the development of innovative electrode materials with enhanced kinetics of ion transport. Pseudocapacitors are excellent candidates to bridge the performance gap between supercapacitors and batteries. Highly porous, anhydrous Ni 0.5 Co 0.5 C 2 O 4 is envisaged here as a potential electrode for pseudocapacitor applications, mainly because of its open pore framework structure, which poses inherent structural stability due to the presence of planar oxalate anions (C 2 O 4 2−), and active participation of Ni 2+/3+ and Co 2+/3+ results in high intercalative charge storage capacity in the aqueous KOH electrolyte. The Ni 0.5 Co 0.5 C 2 O 4 electrode shows specific capacitance equivalent to 2396 F/g at 1 A/g in the potential window of 0.6 V in the aqueous 2 M KOH electrolyte by galvanostatic charge/discharge experiments. Predominant pseudocapacitive mechanism seems to operative behind high charge storage due to active participation of Ni 2+/3+ and Co 2+/3+ redox couple as intercalative (inner) and surface (outer) charges stored by porous anhydrous Co 0.5 Ni 0.5 C 2 O 4 were close to high 38 and 62% respectively. Further, in full cell asymmetric supercapacitors (ASCs) in which porous anhydrous Co 0.5 Ni 0.5 C 2 O 4 was used as the positive electrode and activated carbon (AC) was utilized as the negative electrode, in the operating potential window 1.6 V, the highest specific energy of 283 W h/kg and specific power of ∼817 W/kg were achieved at 1 A/g current rates. Even at a very high power density of 7981 W/kg, the hybrid supercapacitor still attains an energy density of ∼75 W h/kg with high cyclic stability at a 10 A/g current rate. The detailed electrochemical studies confirm higher cyclic stability and a superior electrochemical energy storage property of porous anhydrous Co 0.5 Ni 0.5 C 2 O 4 , making it a potential pseudocapacitive electrode for large energy storage applications.
Particularly, in lithium (Li)-ion battery (LIB) and supercapacitor (SC) applications, surface area and porosity properties of MOFs boost electrolyte uptake capability and shorten diffusion length. [4] Furthermore, the nanoscale voids in the MOF matrix alleviate severe volume fluctuations while performing electrochemical reactions. [5] Owing to these properties, the research community has been focused on the development of MOF-based/derived active materials to explore their applicability in the energy storage field. For instance, Shuai Nan Guo et al. prepared MOF-polyaniline sandwich-like composite using a successive oil bath method and carbonization, followed by polymerization. The as-prepared material demonstrated a maximum specific capacitance of 477 F g −1 at a current density of 1 A g −1. [6] Recently, Xueying Cao et al. synthesized the cobaltdoped Cu-MOF/Cu 2+1 O material, and investigated its SC performance. At a current density of 2 mA cm −2 , the prepared hybrid material delivered a superior specific capacitance of 518.50 F g −1. [7] In another report, Danni Shao et al. achieved a maximum specific capacitance of 414.50 F g −1 at 0.50 A g −1 from the high nitrogen (N)-contained Co-MOF nanorods. [8] Very recently, Zhuo Li et al. fabricated a 3D interconnected architecture with MOF-derived metal oxides (Fe 2 O 3 , ZnO) and N-doped carbon nanofibers. The prepared composite material was explored as an anode in LIB. At 50 mA g −1 , the composite material delivered a high initial specific capacity of 1571.40 mAh g −1. [9] In the other literature, Shiji Hao et al. employed a zeolitic imidazolate framework-67 as a template to synthesize the Co 3 S 2 nanoparticles-incorporated N-doped carbon particles for use as an anode material in LIB. The resulted material demonstrated a superior specific capacity of 950 mAh g −1 at 0.20 C. [10] Therefore, designing the MOFbased/derived electrode materials would be an inciting strategy to achieve exalted energy storage performance. On the other hand, electrode materials are the key components of energy storage systems and are predominantly responsible for energy storage performance. To date, several transition metal oxides have been synthesized and their electrochemical behavior was investigated in LIB and SC studies. [11] Compared Metal-organic frameworks (MOFs) are promising materials in diverse fields because of their constructive traits of varied structural topologies, high porosity, and high surface area. MOFs are also an ideal precursor/template to derive porous and functional morphologies. Herein, Co 3 V 2 O 8 nanohexagonal prisms are grafted on CuV 2 O 6 nanorod arrays (CuV-CoV)-grown copper foam (CF) using solution-processing methods, followed by thermal treatment. Direct preparation of active material on CF can potentially eliminate electrochemically inactive and non-conductive binders, leading to improved charge-transfer rate. Furthermore, solution-processing methods are simple and cost-effective. Owing to versatile valence states and good redox activity, the vanadium-incorporated mixed metal oxides (CuV-CoV) exhibited superior electrochemical performance in lithium (Li)-ion battery and supercapacitor (SC) studies. Furthermore, hollow carbon particles (HCPs) derived from MOF particles (MOF-HCPs) are used as the anode material in SCs. A hybrid SC (HSC) fabricated with CuV-CoV and MOF-HCP materials exhibited noteworthy electrochemical properties. Moreover, a solid-state HSC (SSHSC) is constructed and its real-time feasibility is investigated by harvesting the dynamic energy of a bicycle with the help of a direct current generator. The charged SSHSCs potentially powered various electronic components.
Carbon, 2019
Low-cost multi-heteroatom doped porous carbons derived from agricultural waste were prepared as the base material. Then, the cobalt oxides nanosheets were anchored to the surface of the carbon material to obtain the composites. It was found that the adoption of porous carbon is of great significance for the improvement of materials properties. The presence of porous structure derived from carbon materials not only increases the stability of the material, but also facilitates the diffusion and transfer of electrolyte ions. Meanwhile, the flaky Co 3 O 4 endows the material with high energy density and high charge transport efficiency. The resulted composite materials exhibit high specific surface area with low electrochemical impedance. Both aqueous and solid-state SCs were assembled separately. The energy density of aqueous SC can reach up to 42.5 Wh kg À1 at a power density of 746 W kg À1 and even with power density up to 30 kW kg À1 as the energy density still maintained 25 Wh kg À1. As for solid-state SC, the energy density can reach 40.6 mWh cm À2. The retention of solid-state SC can maintain at 87.1% even after 3000 cycle numbers. The excellent performance of composites enables them to be promising electrode materials for energy storage.
RSC Advances, 2021
To overcome the environmental challenges caused by utilization of fossil fuel based energy technologies and to utilize the full potential of renewable energy sources such as solar, wind and tidal, high power and high energy density containing large scale electrochemical energy storage devices are a matter of concern and a need of the hour. Pseudocapacitors with accessibility to multiple oxidation states for redox charge transfer can achieve a higher degree of energy storage density compared to electric double layer capacitors (EDLC) and the hybrid supercapacitor is one of the prominent electrochemical capacitors that can resolve the low energy density issues associated with EDLCs. Due to its open pore framework structure with superior structural stability and accessibility of Co 2+/3+/4 redox states, porous anhydrous CoC 2 O 4 nanorods are envisaged here as a potential energy storage electrode in a pseudocapacitive mode. Superior specific capacitance equivalent to 2116 F g À1 at 1 A g À1 in the potential window of 0.3 V was observed for anhydrous CoC 2 O 4 nanorods in aqueous 2 M KOH electrolyte. A predominant pseudo-capacitive mechanism seems to be operative behind the high charge storage at electrodes as intercalative (Inner) and surface (outer) charge storage contributions were found to be 75% and 25% respectively. Further, in full cell asymmetric supercapacitor (ASC) mode in which porous anhydrous CoC 2 O 4 nanorods were used as positive electrodes and activated carbon (AC) was utilised as negative electrodes within an operating potential window of 1.3 V, a highest specific energy of W h kg À1 and specific power of $647 W kg À1 at 0.5 A g À1 current density were obtained with superior cycling stability. High cycling stability coupled with superior electrochemical storage properties make anhydrous CoC 2 O 4 nanorods potential pseudo-capacitive electrodes for large scale energy storage applications.
Tunable Synthesis of Hollow Co3O4 Nanoboxes and Their Application in Supercapacitors
Applied Sciences
Hollow Co3O4 nanoboxes constructed by numerous nanoparticles were prepared by using a facile method consisting of precipitation, solvothermal and annealing reactions. The desirable hollow structure as well as a highly porous morphology led to synergistically determined and enhanced supercapacitor performances. In particular, the hollow Co3O4 nanoboxes were comprehensively investigated to achieve further optimization by tuning the sizes of the nanoboxes, which were well controlled by initial precipitation reaction. The systematical electrochemical measurements show that the optimized Co3O4 electrode delivers large specific capacitances of 1832.7 and 1324.5 F/g at current densities of 1 and 20 A/g, and only 14.1% capacitance decay after 5000 cycles. The tunable synthesis paves a new pathway to get the utmost out of Co3O4 with a hollow architecture for supercapacitors application.
Energy Storage Materials, 2019
This study reports the design and fabrication of ultrathin zinc-cobalt oxide nanoflakes@N-doped carbon hollow nanowall arrays (ZnCo 2 O 4 @NC NWAs) from vertically aligned 2D Co-MOF solid nanowall arrays by controllable cation ion-exchange and post annealing strategies. The unique 3D self-branched nanostructure anchored on flexible carbon textiles (CTs) can offer short ion diffusion length, fast and continuous electron transport pathway, and abundant reaction active sites. More importantly, the rational incorporation of Zn 2+ generates hollow structure as well as reduces the intrinsic band gap, which further enhance the ion transportation efficiency and electronic conductivity. The above superiorities endow the 3D self-branched ZnCo 2 O 4 @NC/CTs electrodes with remarkable performances in terms of flexible asymmetric supercapacitor and oxygen electrocatalysis. When evaluated as a flexible cathode for asymmetric supercapacitor, the as-fabricated ZnCo 2 O 4 @NC/CTs electrode exhibits outstanding electrochemical performance with a wide work voltage up to 2.0 V, high areal energy density of 0.278 mWh cm-2 (or volumetric energy density of 2.32 mWh cm-3) and long-term cycling stability (~85.89% capacitance retention over 6000 cycles). Additionally, the ZnCo 2 O 4 @NC/CTs electrode shows excellent oxygen evolution reaction (OER) performance with a small overpotential of 196.4 mV at 10 mA cm-2 and long-term durability (over 45 h). This work provides a rational design strategy for controllable synthesis of 3D self-branched hollow nanostructure on flexible substrate for energy storage and conversion applications.
Nanomaterials, 2020
The demand for eco-friendly renewable energy resources as energy storage and management devices is increased due to their high-power density and fast charge/discharge capacity. Recently, supercapacitors have fascinated due to their fast charge–discharge capability and high-power density along with safety. Herein, the authors present the synthesis of 3D-hierarchical peony-like ZnCo2O4 structures with 2D-nanoflakes by a hydrothermal method using polyvinylpyrrolidone. The reaction time was modified to obtain two samples (ZCO-6h and ZCO-12h) and the rest of the synthesis conditions were the same. The synthesized structures were systematically studied through various techniques: their crystalline characteristics were studied through XRD analysis, their morphologies were inspected through SEM and TEM, and the elemental distribution and oxidation states were studied by X-ray photoelectron spectroscopy (XPS). ZCO-12h sample has a larger surface area (55.40 m2·g−1) and pore size (24.69 nm) t...