Reduced graphene oxide@Co3O4 (rGO@Co3O4) composites are widely developed as promising electrode ma-terials; however, their practical applications are restricted owing to their complex synthesis process. In the current work, we developed a rapid, efficient, and facile method for the one-step synthesis of rGO@Co3O4 composites via assisted liquid-phase plasma electrolysis. During the plasma electrolysis process, uniform and ultrafine Co3O4 particles are grown in-situ on rGO. The rGO@Co3O4 composites present a specific capacitance as high as 1249.0F/g at 1 A/g and a capacitance retention of 89.7 % over 10,000 cycles in a three-electrode system. The superior electrochemical performance is ascribed to the synergistic effect of the high specific capacitance Co3O4 and highly conductive rGO, which is conducive to promoting the transportation efficiency of ions/elec-trons and reducing the volume change of Co3O4 in the charge-discharge cycle. Asymmetric supercapacitors are also assembled using rGO@Co3O4 composites as the positive electrode and rGO as the negative electrode. The asymmetric supercapacitors achieve a specific capacitance of 72.3F/g at 1 A/g, display an energy density of 23.6 Wh/kg at a power density of 0.4 kW/kg, and exhibit superior cycle stability with a capacitance retention of 88.2 % over 10,000 cycles at 5 A/g. The current work provides a rapid, efficient, and facile method for the one-step synthesis of rGO-transition metal oxide electrodes as advanced energy storage devices.

Effective adjustment of structure and morphology is considered to be an available strategy to improve the energy storage performance of supercapacitor electrode materials. Herein, a series of hierarchical NiS/carbon hexahedrons consist of self-assembling nanoplates or nanorods were synthesized via nitrilotriacetic acid (NTA)-assisted hydrothermal strategy. This study demonstrates that the micro-morphology of the unit structure constituting the hexahedrons can be controlled by adjusting the concentration of NTA. Benefiting from synergetic effect of high void space, hierarchical assembly mode and integrated composite structure, NiS/carbon hexahedrons promote adequate exposure of abundant active sites and enhance the structural stability, donating superior energy storage performance. As expected, the optimized NiS/carbon electrode (NiS/NTA-2) exhibits superb capacitive performance, including excellent specific capacitance of 1530.4 F g(-1) at 1.0 A g(-1) and remarkable cycle stability with 85.6% after 5000 cycles. Employing the as-prepared NiS/NTA-2 composites as positive electrode, the hybrid supercapacitor device with spectacular capacity of maximum energy density and power density up to 35.1 Wh kg(-1) and 4509.3 W kg(-1) and impressive long-term stability of 87.2% retention after 5000 cycles is assembled. Moreover, a light-emitting diode (LED) is successfully illuminated for up to 12 min by two devices connected in series. Based on this strategy, high-performance energy storage devices can be further developed through utilizing the modulation effect of metal complexes to design morphology controlled electrode materials.

The biomass derived carbon/Co3O4 composites are developed widely as promising electrode material; yet, the practical applications are restrained due to the complex synthesis process. Herein the current work develops a facile and environmentally-friendly method to realize one-step synthesis of peanut shell derived porous activated carbon/Co3O4 (P-AC/Co3O4) composite by the low-temperature calcination. The results of X-ray diffraction (XRD), Raman and Fourier transform infrared spectroscopy (FTIR) show that Co3O4 particles are synthesized on the P-AC surface. The asymmetric supercapacitors of P-AC/Co3O4 composites achieve a high specific capacitance of 58.2 F/g at 1 A/g, and a superior cycle stability with the capacitance retention of 93.1% over 5000 cycles in the two-electrode system. An energy density as high as 22.7 Wh/kg is exhibited at 400 W/kg, and the energy density of 12.7 Wh/kg is still kept at 8964.7 W/kg. The simple, environmentally-friendly and one-step synthesis method provides a path for the mass production of C/Co3O4 composites as supercapacitor electrode materials.

Carbon fibers consistently suffer from low specific capacitance due to underutilized structure, severely hindering their application in high-performance supercapacitors. In this work, a novel and scalable “inner-outer synergistic strategy” is developed for superior electrode materials via embedding NiS nanoflakes in electrospun carbon fibers encapsulated with NiS nanoparticles (NiS NF /CF@NiS NP ). Uniformly sized NiS nanoparticles are encapsulated in the inner region of the carbon fibers as redox active agent, which impart additional faraday capacitance to the electrode while efficiently avoiding the aggregation of the nanoparticles. Simultaneously, the ultra-thin NiS nanoflakes firmly immobilized on the outer surface of the carbon fibers by the impregnating-sulfurization procedure significantly expand the accessible area of ions. Profiting from the felicitous designed architecture, the NiS NF /CF@NiS NP -3 electrode delivers a reversible specific capacitance of 1691.1 F g -1 at 1 A g -1 and remarkable coulombic efficiency of 98.5 %. Furthermore, the hybrid supercapacitor demonstrates a maximum energy density of 31.2 Wh kg -1 and power density of 4004.3 W kg -1 along with impressive cycling durability of 87.8 % retention for up to 5000 cycles. This demonstrated “inner-outer simultaneous exploitation” engineering provides an appealing and instructive insight for enhanced electrochemical performance of fibrous materials, and can be extended to a variety of energy material systems.

N-doped celery-based biomass carbon with tunable Co3O4 loading is prepared and shows enhanced specific capacitance.

Constructing functionalized carbons decorated with transition metal oxide is an efficient way to combine the cycling stability and high specific capacitance of electrodes for electric double layer capacitors and pseudocapacitors, and the morphology is undoubtedly a key factor for the electrochemical performance. Here, three activated carbons derived from biomass with different morphologies are obtained by carbonizing rosewood (R), corncob (C) and lotus seedpod (L) waste plant body, and then the bio-activated carbons decorated with Co3O4 are prepared by simple oxidation-precipitation and crystallization method. Among the R, C, L carbons, Co3O4, R-Co3O4, C-Co3O4 and L-Co3O4 composites, the L-Co3O4 composite shows best electrochemical performance. At a scan rate of 5 mV s(-1), its specific capacitance reaches 1405.3 F g(-1) (975 C g(-1) at 1 A g(-1)). Furthermore, a hybrid capacitor is fabricated using L-Co3O4 as the positive electrode and activated carbon as the negative electrode, resulting in energy density of 23.1 W h kg(-1), tremendous power density of 3990.6 W kg(-1) and high cycling stability (80.2% retention and coulombic efficiency of 98.8% after 5000 cycles). The equipped hybrid supercapacitor device can work for more than 10 min by lighting a red bulb. Thus, this unique L-Co3O4 composite with simple fabrication method can be considered to be a promising candidate for the electrochemical energy conversion and storage. (C) 2021 Elsevier B.V. All rights reserved.

Biomass-based carbon is gaining increasing attention because it presents a promising prospect for economic growth and social sustainable development. Moreover, it is an excellent medium for application in electromagnetic and electronic devices. Here, puffed-rice-based carbon is obtained at various activating temperatures, and when the hollow bulges on the carbon disappear, the morphology of the carbon changes into sheet-like structures. The R-800 sample displays the highest ID/IG value and demonstrates the best performance when used as both a microwave absorber and an electrode material. The minimum reflection loss (RL) and bandwidth for RL < -10 dB of the R-800 sample reach -72.1 dB and 13.2 GHz, respectively, and the bandwidth for RL < -20 dB is as large as 7.0 GHz, illustrating the widest bandwidth among the five carbon specimens. The multiple reflection effects and scattering, good impedance matching, and interfacial polarization synergistically enhance the microwave absorption performances of the sample. At 1 A g-1, the specific capacitance of the R-800 sample reaches 117.2 F g-1 and the capacitance retention remains at 85.3%. Moreover, a hybrid supercapacitor R-800//R-800 demonstrates an outstanding energy density of 15.23 Wh kg-1, power density of 5739.43 W kg-1, and high cycle stability (94.5% after 5000 cycles). This functionalized biomass carbon provides a promising media for constructing a bridge between sustainable development and biomass materials. (c) 2021 Elsevier Inc. All rights reserved.

A novel electrode material of alpha-NiS, beta-NiS and Ni3S4 particles co-decorated rGO is obtained by co-reduction of Ni2+ and GO with thiourea. The multiple nickel sulfide phases and rGO synergistically improve the electrochemical performance of the supercapacitor electrode, which shows high specific capacity of 609.4C g(-1) at current density of 1 A g(-1). The electrode can keep a good stability with coulombic efficiency of as high as 99.5% after 1000 cycles. The small solution and charge transfer resistances of 0.42 and 0.24 0 indicate the positive synergistic effects of the multiple phases of NiS and graphene on the electrochemical performance.

Designing a battery-type electrode material with high electrochemical performance based on eco-friendly and sustainable strategy has great significance for the development of supercapacitors. Herein, NiS nanoparticles are deposited on the surface of the porous hollow carbon spheres (PHCSs) derived from inexpensive and pollution-free yeast cells wall by an in situ hydrothermal process, forming a litchi shell-like three-dimensional (3D) double-shell structure. The PHCSs as a carbon substrate can effectively suppress the aggregation of NiS nanoparticles and ensure more ground storage sites to enhance the performance of the electrode material. More notably, the reaction concentration of nickel ion has a remarkable effect on the electrochemical performance of composites. The optimized sample shows a high specific capacity of 531.5 C g−1 at 1 A g−1, excellent rate capability of 412.1 C g−1 at 10 A g−1 and outstanding cycling life span of 83.3% after 5000 cycles. Furthermore, the assembled hybrid device delivers a high energy density of 24.4 Wh kg−1 at a power density of 767 W kg−1 and an excellent cycle stability by delivering 89.3% capacitance retention after 5000 ultralong cycles. This work offers a feasible strategy to synthesize economical and efficient electrode materials and demonstrates its enormous potential in energy storage. A novel NiS/porous hollow carbon sphere composite with double-shell structure was synthesized by a green and available self-template method, which exhibits superior supercapacitor performance.

CoNi alloy is an important absorber and it can combine characteristics of transition metals Co and Ni with various advantages of strong magnetic loss, low cost and easy morphology control. The microporous CoNi@(CoO-NiO) nanoparticles (NPs) of about 45 nm are obtained by using hydrogen plasma metal reaction (HPMR) and dealloying methods. The Al element in Al9Co2, Al70Co15Ni15 and Al14Co3Ni3 phases can be dealloyed by NaOH at 323 K. The CoNi surface would oxidize to CoO and NiO, leading to the core@shell structure. The CoNi@(CoO-NiO)-paraffin wax composite displays high microwave absorption performance with minimum reflection loss (RL) of -38.1 dB at matching thickness of 5.0 mm. The effective absorption bandwidth (RL < -10 dB, at thickness of 2.0 mm) is 5.9 GHz. The RL values below -10 dB cover frequencies of 4.6-18.0 GHz with thickness ranging from 2.0 to 5.0 mm. The effective permittivity modification for a mixture of air and microporous CoNi host, and the large interfacial polarization relaxation of the CoNi@(CoO-NiO) structure contribute much to the enhanced microwave absorption performances.

It very important to be able to efficiently detect hydrazine hydrate in an aqueous medium due to its high toxicity. Here, we have proposed a new idea: to construct a sensor for the rapid determination of hydrazine hydrate based on the nano-CuO derived by controlled pyrolysis of HKUST-1 [Cu3(BTC)2(H2O)3]. The as-prepared CuO at 400 °C possesses a uniform appearance with nano-structure via SEM images, and the nano-CuO-400 has exhibited excellent electrocatalytic activity towards hydrazine oxidation. Amperometric i-t curves shows the peak current as linearly proportional to the hydrazine concentration within 1.98–169.3 μmol L−1 and 232–2096 μmol L−1 with the detection limit of 2.55 × 10−8 mol L−1 and 7.01 × 10−8 mol L−1, respectively. Moreover, the sensor constructed in the experiment shows good selectivities, and it is feasible to determining actual water samples.

To make use of two waste natural corncob and rosewood, activated carbons are obtained through KOH activation at 1073 K. The two samples show sheet like morphology with some swells on the surface of the corncob activated carbon and pores in the rosewood activated carbon. The higherI(D)/I(G)value of rosewood activated carbon for the Raman spectrum measurement indicates its lower graphitization degree than corncob activated carbon, which is proved by X-ray diffraction patterns. The higher real and imaginary parts of the complex permittivity for the rosewood activated carbon are benefited from the differences of morphology and graphitization degree of the two samples. Apart from the dipole polarization, the charge polarization and interfacial polarization also contribute to the dielectric loss for the porous rosewood activated carbon.

As an emerging energy storage device, the supercapacitor with high energy density, fast charging/discharging, and good cycle stability has aroused great interest. The performance of supercapacitors mainly depend on the electrode material. Manganese dioxide (MnO2) has emerged as one of the most promising electrode materials for high theoretical specific capacitance, wide potential range, high electrochemical activity, and environmental friendliness. However, its deteriorated volume expansion and inherently low conductivity limit its development and application in supercapacitors. To circumvent the mentioned issues, the porous, thin film, or layered composite materials were prepared to enhance the electrical conductivity and specific surface area of MnO2. Carbon materials are the ideal choice to compound with MnO2 owing to their low electrical resistance, significant thermal stability, large specific surface area, and porosity. Up to now, several kinds of MnO2/carbon composites as supercapacitor electrodes have been designed and fabricated. Herein, we give a concise review of the latest researches on MnO2/carbon supercapacitor electrodes, focusing on the fabrication strategies and analyzing the influencing factors of electrochemical performance of MnO2/carbon materials. An outlook on the possible development directions in future of designing high-performance MnO2/carbon materials for the current challenges is also provided.

Novel dual phased CoO/Co3O4 particles with Co3O4 nanoneedles on surface are obtained by annealing dual-phased Co (hexagonal and cubic phases) particles. Their phase and morphology evolution are clarified by XRD, SEM and TEM measurements. The early formed CoO and Co3O4 on surface from dual-phased Co promote the outdiffusion process of inside Co with kirkendall effect and restrict the growth of Co3O4 with a specific orientation, leading to the formation of Co3O4 nanoneedles on the surface. The microwave absorption measurement shows that the CoO/Co3O4 particles with annealing time of 1 h possess higher permittivity and better performances than pure Co and Co3O4 particles. An enhanced reflection loss (RL) value of - 38.8 dB is obtained for the CoO/Co3O4-paraffin wax (PW) composite with a thickness of 2.8 mm. The absorption bandwidth for RL below -10 dB reaches 8.7 GHz. The Co3O4 nanoneedles on surface, porous structure and inner dual phased CoO/Co3O4 bring increased multiple reflection, interface/dipolar polarizations, conductive loss and better impedance matching. This clarification of phase and morphology evolution and novel CoO/Co3O4 material with nanoneedles on surface may provide new routes for designing high performance Co-based microwave absorbers with unique structures.

Polyaniline has been widely used in high-performance pseudocapacitors, due to its low cost, easy synthesis, and high theoretical specific capacitance. However, the poor mechanical properties of polyaniline restrict its further development. Compared with polyaniline, functionalized carbon materials have excellent physical and chemical properties, such as porous structures, excellent specific surface area, good conductivity, and accessibility to active sites. However, it should not be neglected that the specific capacity of carbon materials is usually unsatisfactory. There is an effective strategy to combine carbon materials with polyaniline by a hybridization approach to achieve a positive synergistic effect. After that, the energy storage performance of carbon/polyaniline hybridization material has been significantly improved, making it a promising and important electrode material for supercapacitors. To date, significant progress has been made in the synthesis of various carbon/polyaniline binary composite electrode materials. In this review, the corresponding properties and applications of polyaniline and carbon hybrid materials in the energy storage field are briefly reviewed. According to the classification of different types of functionalized carbon materials, this article focuses on the recent progress in carbon/polyaniline hybrid materials, and further analyzes their corresponding properties to provide guidance for the design, synthesis, and component optimization for high-performance supercapacitors.

It is needed to speed up the development of a sensitive detection platform for simultaneous determination of dihydroxybenzene isomers with harmful properties. Here, two isomorphic Metal–organic frameworks (MOFs) [Zn(Trz)(R-BDC)1/2] (FJU-40-R, R = H or NH2; Trz = 1,2,4-Triazole; H-BDC = terephthalic acid) were selected to derive two N-doping porous carbon (NPC) materials. Further, a strategy for constructing electrochemical sensors for simultaneous determination of hydroquinone (HQ) and catechol (CT) was proposed by the MOF-derived NPC modifying glass carbon electrode (GCE). It was found that HQ and CT had good responses on NPC-FJU-40-H/GCE, but had no obvious responses on NPC-FJU-40-NH2/GCE. NPC-FJU-40-H/GCE displayed excellent reproducibility, stability, and anti-interference. Under the optimal conditions, the linear ranges of HQ and CT on NPC-FJU-40-H/GCE were 1 ~ 70 µmol L−1 and 1 ~ 100 µmol L−1 with the detection limits of 0.18 µmol L−1 for HQ and 0.31 µmol L−1 for CT, respectively. Although the porous carbon (PC) derived from MOFs has been applied in electrochemical sensing, the effect of the ligand functional groups of isomorphic MOFs on the electrochemical properties of the derived PC materials is still lack of relevant research. Our research provided an idea that the electrocatalysis properties of MOF-derived porous carbon materials could be tuned by changing the functional groups in ligands of isomorphic MOFs in electrochemical sensing field.

Soybean straw (SS)-based activated carbon was employed as a precursor to prepare carbon molecular sieves (CMSs) via chemical vapor deposition (CVD) technique using methane as carbon source. Prior to the CVD process, SS was activated by 0.5 wt% ZnCl2, followed by a carbonization at 500 degrees C for 1 h in N-2 atmosphere. N-2 (77 K) adsorption-desorption and CO2 (273 K) adsorption tests were carried out to analyze the pore structure of the prepared CMSs. The results show that increasing the deposition temperature, time or methane flow rate leads the decrease in N-2 adsorption capacity, micropore volume and average pore diameter of CMSs. The adsorption selectivity coefficient of CO2/CH4 achieves as high as 20.8 over CMSs obtained under the methane flow rate of 30 mL min(-1) at 800 degrees C for 70 min. The study demonstrates the prepared CMSs are a candidate adsorbent for CO2/CH4 separation.

Here we propose a new strategy in which two isomorphic metal-organic frameworks (MOFs) [FJU-40-H (a) and FJU-40-NH2 (b)] are used to construct the core-shell material MOF@MOF. This strategy based on nitrogen doping and specific surface has resulted in an N-doped porous carbon (NPC) material in a one-step thermal treatment in N2 atmosphere; this material displays high catalytic activity for the oxygen reduction reaction (ORR). The materials were analyzed by SEM, XPS, Raman, specific surface area, pore size distribution and electrochemical measurements. It was found that NPC derived from the core-shell MOF@MOF can provide excellent catalytic ORR performance exceeding that of the single MOF. The onset potential is NPC-b@a-4h (-0.068 V)>NPC-a@b-4h (-0.075 V)>NPC-a-4h (-0.109 V)>NPC-b-4h (-0.113 V). Moreover, the results also show that the performance of NPC-b@a (n=4.15) is better than that of NPC-a@b (n=3.32), which means the different nitrogen content of ligands inside and outside of the core affects the ORR properties.