Bulk Co3O4 Research Articles

Preparation of cobalt catalyst supported on perovskite-type oxide and application in liquid-phase selective oxidation reaction

Abstract Cobalt catalyst supported on the perovskite-type oxide sodium tantalate, NaTaO3 (NTO) was prepared by using the hydrothermal method and used in liquid-phase p-xylene oxidation, which led to p-methyl benzyl alcohol, p-tolualdehyde, and p-toluic acid. Investigation showed that the formation of alcohol and aldehyde was a competitive reaction. Further oxidation of the alcohol did not occur. On the other hand, the oxidation of p-tolualdehyde led to the formation of acid. Co-NTO catalyst showed higher selectivity toward the route of p-tolualdehyde than the p-methylbenzyl alcohol compared with the bulk Co3O4.

Cationic Disorder and Surface Effects on the Magnetic Properties of Co3O4$\left(\text{Co}\right)_{3} \left(\text{O}\right)_{4}$ Nanoparticles Synthesized by Co‐Precipitation with Addition of Sucrose

Herein, the effect of adding sucrose chelating agent on the structural and magnetic properties of single‐phase Co3O4 nanoparticles is examined. The samples are obtained using coprecipitation with varying concentrations of sucrose. The X‐ray diffraction data and the scanning electron microscopy and transmission electron microscopy images indicate that the average particle size, their shape, and size distribution depend on the sucrose concentration. The smallest size obtained is around 6 nm for the sample grown with 0.32 mol L−1 of sucrose. Magnetic measurements as a function of magnetic field and temperature indicate that the samples exhibit superparamagnetic behavior below 10 K, and the peak in susceptibility decreases with increasing sucrose concentration, reaching a minimum value of 4.5 K for the sample grown with 0.32 mol L−1 of sucrose. After subtracting the high‐field linear contribution, likely attributed to superparamagnetism, saturation in the M vs. H curves measured at T = 2 K is observed. The saturation is approximately 1.2 emu g−1 for all samples. Since bulk Co3O4 is expected to be antiferromagnetic at T = 40 K, this value of magnetization may be linked to the degree of cationic disorder in the occupation of and ions between A and B sites.

Low-Temperature Propane Activation and Mineralization over a Co3O4 Sub-nanometer Porous Sheet: Atomic-Level Insights.

Light alkanes make up a class of widespread volatile organic compounds (VOCs), bringing great environmental hazards and health concerns. However, the low-temperature catalytic destruction of light alkanes is still a great challenge to settle due to their high reaction inertness and weak polarity. Herein, a Co3O4 sub-nanometer porous sheet (Co3O4-SPS) was fabricated and comprehensively compared with its bulk counterparts in the catalytic oxidation of C3H8. Results demonstrated that abundant low-coordinated Co atoms on the Co3O4-SPS surface boost the activation of adsorbed oxygen and enhance the catalytic activity. Moreover, Co3O4-SPS has better surface metal properties, which is beneficial to electron transfer between the catalyst surface and the reactant molecules, promoting the interaction between C3H8 molecules and dissociated O atoms and facilitating the activation of C-H bonds. Due to these, Co3O4-SPS harvests a prominent performance for C3H8 destruction, 100% of which decomposed at 165 °C (apparent activation energy of 49.4 kJ mol-1), much better than the bulk Co3O4 (450 °C and 126.9 kJ mol-1) and typical noble metal catalysts. Moreover, Co3O4-SPS also has excellent thermal stability and water resistance. This study deepens the atomic-level insights into the catalytic capacity of Co3O4-SPS in light alkane purification and provides references for designing efficacious catalysts for thermocatalytic oxidation reactions.

Co3O4 nanosheets modified by Ni@C nanoparticles as effective flow-through electrode for electro-activation of PMS: Ni@C as electron shuttle for accelerated Co3+/Co2+ cycle in bulk Co3O4

Electro-assisted activation of peroxymonosulfate (EA-PMS) by transition metals oxides (TMOs) has been extensively studied for the removal of organic pollutants. Despite TMOs possess considerable activity and affinity to PMS, their poor bulk conductivity still limits the electron exchange during the TMδ/δ+1 redox cycle, especially the efficient reduction of TMδ+1 via cathodic process. In this study, carbon felt loaded with modified Co3O4 nanosheets (Co@FCF) was fabricated and applied as the flow-through electrode of EA-PMS process, where the Co3O4 nanosheets were embedded with numerous metallic Ni particles encapsulated within carbon layers (Ni@C). Driven by weak electric current, continuous electrons can be supplied to the bulk Co3O4 from the electron-rich Ni@C nanoparticles, resulting in accelerated Co3+/Co2+ cycle, enhanced production of SO4·− and improved energy utilization efficiency. Electrochemical tests along with density functional theory calculations indicate that the unique structure of Co@FCF played essential role in the enhanced performance.

Exceptionally stable CePO4 and RuO2 contributing to catalytic oxidation of 1,2-dichloroethane on Co3O4 catalysts: Complete inhibition of chlorinated byproducts

Highly toxic, reactive and refractory chlorinated VOCs (Cl-VOCs) is urgent for purification by the most favoured catalytic oxidation technique, however, the formation of polychlorinated byproducts is huge obstacle for most catalysts. Here, nanorods assembled monoclinic CePO4 microspheres were synthesized and used as the support of highly active but low-selective Co3O4 for catalytic oxidation of Cl-VOCs. The prepared Co3O4/CePO4 using ascorbic acid (AA) as a chelating agent presented a high activity and low selectivity of vinyl chloride (VC) for catalytic oxidation of 1,2-dichloroethane (DCE) due to the high dispersion of Co3O4, compared with bulk Co3O4 and Co3O4/SiO2, possible polychlorinated byproducts were completely inhibited in the presence of CePO4 support. The co-introduction of RuO2 further suppressed the formation of VC as a representative dechlorinated byproduct owing to the enhanced redox ability and migration of surface lattice oxygen, below 0.5% VC selectivity was detected on the optimized RuCoOx/CePO4 and completely disappeared above 275 °C. Moreover, RuCoOx/CePO4 also revealed the superior versatility, durability and thermal stability as well as the outstanding resistance to CO2, H2O and sulfur. The restraint of polychlorinated byproducts also can be achieved by other phosphates besides CePO4 and attributed to the strong coordination effect and electron-withdrawing function of PO43-. This work was contributed to further understand the inhibition of chlorinated byproducts for catalytic oxidation of Cl-VOCs and rationally design full-featured catalysts.

A Friendly Environmental Route for the Fabrication of Spinel Co3O4 Nanorods, Using Inorganic Precursor Salt and Aqueous Extracts of Moringa oleifera Leaves

Nowadays many researchers are focused on the sytnhesis of nanoscale tricobalt tetraoxide (Co3O4) particles, owing to their unique properties. These particles have indeed many potential technological applications. The present investigation deals with the fabrication of this spinel oxide: it was successfully synthesized through a friendly environmental method, using cobalt (II) chloride as cobalt precursor and aqueous extract of Moringa oleifera leaves. The latter contains alkaloids as a base source while flavonoids present in the leaves acted as capping agent to prevent the particles agglomeration. Alkaloids present in the leaves were hydrolyzed in water and consequently, hydroxilated Co2+ leads to the formation of Co3O4 powder via calcination. The electronic transmission microscopy has revealed the single crystalline nanorods morphology of the synthetised materials. These nanorods are about several hundred nanometers long and several tens of nanometers in diameter. The bulk Co3O4 is known to be antiferromagnetic, the vibrating sample magnetometer data (at room temperature) of the prepared powder exhibited the lower coercivity and remanence, signaling that the produced spinel was pure and was constituted of superparamagnetic particles made of Co3O4. The UV–visible spectrum exhibited a photoluminescence peak in the visible light range positioned at about 538nm, suggesting this spinel as a visible light emitting material and as photocatalyst under visible light.

Interfacial synthesis of Co-based ultrathin nanosheets with NaF crystal as template and inducer: fluorine doped Co(OH)2, porous fluorine doped Co3O4, and porous Co3O4

NaF crystals were used as the template and inducer, and fluorine doped cobalt hydroxy ultrathin nanosheets (F-Co(OH)2) were synthesized at room temperature. F-Co(OH)2 exhibits a petal-like morphology with a thickness of ∼1.7 nm. Porous fluorine doped Co3O4 ultrathin nanosheets (pF-Co3O4) and porous Co3O4 ultrathin nanosheets (p-Co3O4) were synthesized through the calcinations of F-Co(OH)2 at 230 °C and 330 °C, respectively. They exhibit a petal-like morphology with a thickness of ∼1.6 nm. pF-Co3O4 and p-Co3O4 have been applied for the catalytic oxidation benzyl alcohol. At the identical conditions, pF-Co3O4 achieved 100% benzyl alcohol conversion and 100% yield of benzaldehyde, and p-Co3O4 achieved 100% benzyl alcohol with 69.8% yield of benzaldehyde and 30.2% yield of benzoic acid. For the oxidation benzyl alcohol, both pF-Co3O4 and p-Co3O4 have exhibited much higher catalytic efficiencies than bulk Co3O4.

Bulk Co3O4 for Methane Oxidation: Effect of the Synthesis Route on Physico-Chemical Properties and Catalytic Performance

The synthesis of bulk pure Co3O4 catalysts by different routes has been examined in order to obtain highly active catalysts for lean methane combustion. Thus, eight synthesis methodologies, which were selected based on their relatively low complexity and easiness for scale-up, were evaluated. The investigated procedures were direct calcination of two different cobalt precursors (cobalt nitrate and cobalt hydroxycarbonate), basic grinding route, two basic precipitation routes with ammonium carbonate and sodium carbonate, precipitation-oxidation, solution combustion synthesis and sol-gel complexation. A commercial Co3O4 was also used as a reference. Among the several examined methodologies, direct calcination of cobalt hydroxycarbonate (HC sample), basic grinding (GB sample) and basic precipitation employing sodium carbonate as the precipitating agent (CC sample) produced bulk catalysts with fairly good textural and structural properties, and remarkable redox properties, which were found to be crucial for their good performance in the oxidation of methane. All catalysts attained full conversion and 100% selectivity towards CO2 formation at a temperature of 600 °C while operating at 60,000 h−1. Among these, the CC catalyst was the only one that achieved a specific reaction rate higher than that of the reference commercial Co3O4 catalyst.

Triggering anomalous capacity by nanoengineered ordered mesoporous structure for Co3O4 anode material in Li-ion rechargeable batteries

Nanostructured engineering is one of the strategies for optimizing transition metal oxides as anode materials in lithium-ion batteries. Among them, mesoporous structures have received significant attention due to their intrinsic properties which are related to porous structure. This structure provides short Li-ion diffusion pathways and acts as a buffer for volume changes during electrochemical reactions, affecting various electrochemical properties and performances. One of the intriguing aspects of the mesoporous structure effect is that it sometimes triggers a negative fading. Herein, we observed that ordered mesoporous Co3O4 exhibits a higher reversible capacity and anomalous cycle behavior that capacity increases during cycling, known as a negative fading, compared to bulk Co3O4. Moreover, the observed capacity is even higher than its theoretical capacity. Mesoporous Co3O4 exhibits stable and more reversible conversion reactions, and even gradually activated electrolyte-derived surface layer formation/decomposition during cycling. Based on combined synchrotron-based X-ray analyses and electrochemical tests, we found the weaker Co-O and Co-Co bond strength in mesoporous material than those in the bulk material, gives rise to a more reversible conversion reaction during cycling. In addition, the distinctive structural properties of mesoporous leads to the further formation/decomposition of electrolyte-derived surface layer, resulting in the negative fading.

Spinel Co3O4 oxides-support synergistic effect on catalytic oxidation of toluene

Bulk spinel Co3O4 oxide and supported Co3O4 catalysts (Co3O4/YSZ and Co3O4/TiO2) were synthesized by one-step hydrothermal method. Their physicochemical properties were characterized by inductively coupled plasma optical emission spectroscopy, N2-sorption, powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy, hydrogen-temperature programmed reduction and X-ray photoelectron spectroscopy.These characterization strategies were applied to corroborate and better understand the interaction between Co3O4 and the supports induced by the synergistic effect of support and the subsequent catalytic performance in toluene oxidation. The catalytic stability was evaluated by three consecutive runs and a long-term test. A highest toluene catalytic activity was achieved over Co3O4/YSZ supported catalyst comparing to that of the bulk Co3O4 and Co3O4/TiO2 catalysts, which could be attributed to its better low-temperature reducibility, oxygen activation and mobility induced by the intrinsic support properties. Thus, the positive interaction between spinel Co3O4 phase and YSZ support promoted the intrinsic catalytic properties for toluene oxidation, which was verify by testing a dual catalyst bed system consisting of bulk Co3O4 catalyst and YSZ support beds. These results were further confirmed by temperature-programmed oxygen isotopic exchange experiments, which indicated that the activation and diffusion of oxygen species on the YSZ oxygen vacancy sites were promoted by Co3O4, resulting in a significant increase of the reaction rate for toluene oxidation.

Functionalized Co3O4 graphitic nanoparticles: A high performance electrocatalyst for the oxygen evolution reaction

We describe a novel synthesis technique for the production of graphitic carbon functionalized Co3O4 (G/Co3O4), which involves the rapid decomposition of cobalt nitrate in the presence of citric acid. Upon immobilization of the G/Co3O4 upon Screen-Printed macroElectrodes (G/Co3O4-SPEs) the G/Co3O4-SPEs were found to exhibit remarkable electrocatalytic properties towards the Oxygen Reduction Reaction (OER). A detailed investigation has been carried out on the influence that the graphitization of the citric acid has, during the course of preparation of Co3O4, upon the ability of the G/Co3O4 to catalyse the OER within alkaline conditions (1.0 M KOH). The graphitization of citric acid ensures the uniform distribution of Co3O4 and enhanced conductivity with maximal exposure of active sites, which are the key parameters to delivering enhanced electrochemical activity. The G/Co3O4-SPEs exhibits an overpotential of 304 mV (recorded at 10 mA cm−2), a Tafel slope of 110 mV dec−1 and remain stable in its signal output (achievable current density) at varying temperatures (5–50 °C), and after 10 h of chronoamperometry in 1.0 M KOH. The G/Co3O4-SPE's OER activity was found to be superior to that of bulk and nano Co3O4. The results exhibited within this study will enable production of high-performance and environmentally benign electrocatalysts towards the OER for use within water splitting devices.

Synthesizing Co3O4-BiVO4/g-C3N4 heterojunction composites for superior photocatalytic redox activity

In this study, a novel coral-like Co3O4-BiVO4/g-C3N4 ternary composite catalyst was successfully synthesized via high temperature polymerization and controlled hydrothermal reaction. In the Co3O4-BiVO4/g-C3N4 ternary hybrid system, the bulk Co3O4 particles were uniformly dispersed on the coral-like BiVO4 nanosheet, which not only enhanced to increase the response range and absorption to visible light, also contributed to suppress the recombination of photogenerated electron holes. The introduction of flocculent g-C3N4 increased the specific surface area of the catalytic system while accelerating the transmission efficiency of photogenerated carriers. After being illuminated for 90 min under the visible light, the degradation efficiency of pure BiVO4 and g-C3N4 catalysts were 81% and 80.2%, respectively. And the two binary catalysts, Co3O4-BiVO4 and BiVO4/g-C3N4 composite catalyst, performed the higher photocatalytic activity, which reached 94.8% and 96.8%, while ternary catalyst Co3O4-BiVO4/g-C3N4 composite catalyst showed the highest photocatalytic activity, the removal rate of KN-R was up to 99.6% after being irradiated for only 30 min with visible-light. Even more, its optical and electrochemical properties were greatly improved, making it as a forceful candidate for practical photocatalysts under visible light. In summary, this work not only provided a highly efficient heterojunction-structured visible-light photocatalyst, but also supplied a novel method to diminish the photo-carriers recombination.

Modernization of the bulk Co3O4 to produce meso-porous Co3O4 nano-particles with enhanced structural and morphological characteristics

Ordered meso-porous Co3O4 (meso-Co3O4) was prepared via the nano-casting route using three-dimensionally (3D) ordered meso-porous silica (KIT-6) as a hard template, whereas the bulk Co3O4 was prepared by the precipitation method for comparison. The prepared meso- and bulk Co3O4 were used as supports to prepare V2O5 (6 wt%) loaded catalysts by conventional wetness impregnation technique. The structural and morphological characterizations of the prepared samples were investigated by XRD, N2-physisorption, TEM–EDX, H2-TPR, and FT-IR analyses. The result informed that the meso-Co3O4 retains small particle size, high surface area, rich surface adsorbed oxygen species, and low temperature reducibility as compared with the bulk one. These characters are responsible for the better dispersion of vanadium onto the meso-Co3O4 support.

Electrochemical Cycling‐Induced Amorphization of Cobalt(II,III) Oxide for Stable High Surface Area Oxygen Evolution Electrocatalysts

AbstractThe activity of electrocatalysts critically depends on the chemical coordination around the active sites. Amorphous materials have short‐range atomic ordering while their crystalline counterparts have both short and long‐range ordering. Traditional synthesis of amorphous materials, involving quenching from high temperatures is unsuitable as it results in less porosity and surface area. In this context, room‐temperature syntheses of high surface area amorphous materials with high activity are desirable. Here, we contrast two electrochemical synthesis procedures for generating high surface area amorphous Co3O4 at room temperature via electrochemical ion intercalation/deintercalation and surface oxidation/reduction cycles and evaluate their performance for electrocatalytic oxygen evolution reaction (OER). In the first approach, Li‐ion is used for the intercalation/deintercalation (Li/D−Li) cycles in Co3O4, which leads to expansion and contraction of structure, inducing amorphization of Co3O4 by the pulverization of crystal structure in non‐aqueous medium. In the second approach, rapid electrochemical surface oxidation/reduction (Ox/Red) of Co3O4 in the aqueous medium leads to the formation of a metastable amorphous structure. The OER specific activity (activity per unit electrochemical surface area) for Li/D−Li−Co3O4 is ∼3.5 times and Ox/Red‐ Co3O4 induced amorphization is ∼2.5 times higher than their crystalline Co3O4. The superior OER metrics of both the room‐temperature amorphization techniques are rationalized via the increase in the ratio of Co2+/Co3+ obtained from the Co‐2p XPS spectra. Further, the decrease in overall polarization resistance per site for the OER reaction for both amorphous samples were analyzed from the Tafel plot and electrochemical impedance spectroscopy (EIS). In Li/D−Li−Co3O4, the Li‐ion intercalation in bulk Co3O4 structure generates higher bulk‐oxygen vacancies leading to higher conductivity and reduction in overall charge‐transport resistance for electrocatalyst. On the other hand, Ox/Red‐ induced amorphization is restricted to the surface or near‐surface only with the formation of a small amount of metallic Co which hampers the OER.

Effect of Metal‐Support Interactions in Mixed Co/Al Catalysts for Dry Reforming of Methane

AbstractComposite Co/Al oxide materials were prepared via flame spray pyrolysis and examined as catalysts for the dry reforming of methane. The interaction between the metal (Co) and the support (Al‐oxide) was regulated by varying the Co : Al ratio and its influence on catalyst performance studied. The synthesis of materials with a Co content of 30 mol % (Co3Al7) promoted the formation of readily reduced and highly‐dispersed Co particles. This, in combination with a high relative surface basicity, contributed to Co3Al7 delivering a high and stable activity towards the dry reforming reaction. The formation of bulk Co3O4 particles, which exhibit weak interactions with the support material, in samples with a Co content of 50 (Co5Al5) and 70 mol % (Co7Al3) caused rapid catalyst deactivation via coking. The findings demonstrate the importance of metal‐support interactions between the Co catalyst and Al‐oxide support for the activity and selectivity in the dry reforming of methane. Highly dispersed Co deposits and high support basicity, induced by an ideal FSP Co : Al synthesis ratio, are key to delivering an active and stable catalyst for the dry reforming of methane.

One-dimensional mesoporous Co3O4 tubules for enhanced performance supercapacitor and enzymeless glucose sensing

One-dimensional hollow Co3O4 tubules have been synthesized by using a template method followed by a simple thermal annealing treatment. The obtained hollow Co3O4 nanomaterial displays one-dimensional architecture with a highly mesoporous nature and hollow interiors, leading to better electrolyte/electrode contact and more efficient transport pathways. Our experimental results demonstrate that the hollow Co3O4 nanostructures exhibit enhanced electrochemical performance for charge storage and enzymeless glucose sensing applications. Supercapacitor electrodes employing mesoporous hollow Co3O4 tubules exhibit specific capacitance of 326 F g−1 at a current density of 1 A g−1, a high capacity retention of 73.6% at 10 A g−1, and a long stable cycling performance of retaining ~ 91.6% after 5000 cycles. Compared with the bulk Co3O4, it also has good sensing ability for glucose with high sensitivity of 994.6 μA mM−1 cm−2 and 369.7 μA mM−1 cm−2 for the lower and higher concentration of glucose, fast response time of 5 s, detection limit as low as 0.84 μM, good selectivity, stability, and reproducibility. These results show that the hollow Co3O4 tubules is a versatile material for various applications.

Thermally induced top-down nanostructuring for the synthesis of a core/shell-structured CoO/CoSx electrocatalyst

A top-down nanostructuring approach based on sequential reduction and sulfurization reactions is devised to prepare a highly active Co-based electrocatalyst from bulk Co3O4.

Oxidation of residual methane from VNG vehicles over Co3O4-based catalysts: Comparison among bulk, Al2O3-supported and Ce-doped catalysts

Cobalt oxide based catalysts with three different active phase configurations, namely bulk, alumina supported and cerium-doped Co3O4 samples were examined for the complete oxidation of methane under conditions similar to those found in the exhaust of VNG engines. The structural and redox properties of the resulting catalysts were determined by N2 adsorption-desorption, WDXRF, ICP-AES, X-Ray diffraction, temperature-programmed reactions, UV–vis-NIR DRS, XPS and Raman spectroscopy. Alumina-supported catalysts (10–40%wt. Co) were found to be less active, since the strong interactions between the alumina and the Co3O4 active phase were highly detrimental for the redox properties of these catalysts. On the other hand, doping with cerium (10%wt.) led to an increased inherent activity of the Co3O4 phase by distorting the spinel lattice, which resulted in improved structural and redox properties and enhanced mobility of the oxygen species within the spinel lattice. These catalysts were also stable over a prolonged period of time under both dry and humid conditions (150 h).

Crystal Facet Effects on Nanomagnetism of Co3O4

The magnetic performance of nanomaterials depends on size, shape, and surface of the nanocrystals. Here, the exposed crystal planes of Co3O4 nanocrystals were analyzed to research the dependence of magnetic properties on the configuration environment of the ions exposed on different surfaces. The Co3O4 nanocrystals with exposed (1 0 0), (1 1 0), (1 1 1), and (1 1 2) planes were synthesized using a hydrothermal method in the shapes of nanocube, nanorod, hexagonal nanoplatelet, and nanolaminar, respectively. Ferromagnetic performance was detected in the (1 0 0) and (1 1 1) plane-exposed samples. First-principles calculation results indicate that unlike the nonmagnetic nature in the bulk, the Co3+ ions exposed on or close to the surface possess sizable magnetic moments because of the variation of coordination numbers and lattice distortion, which is responsible for the ferromagnetic-like behavior. The (1 1 0)-exposed sample keeps the natural antiferromagnetic behavior of bulk Co3O4 because either the surface Co3+ ions have no magnetic moments or their moments are in antiferromagnetic coupling. The (1 1 2)-exposed sample also displays antiferromagnetism because the interaction distances between the magnetized Co3+ ions are too long to form effective ferromagnetic coupling.

Synthesis of Self-Assembled rGO-Co3O4 Nanoparticles in Nanorods Structure for Supercapacitor Application

A simple hydrothermal process was used to design self-assembled Co3O4 nanoparticles in nanorod structure in the presence of graphene oxide as a template. The as-prepared Co3O4 sample in a loose powder form was calcined at 450 °C to get the well-crystalline phase of the same compound. The obtained Co3O4 powder sample was characterized by using the powder XRD and SEM. The XRD pattern shows totally nine distinct reflection peaks of (111), (220), (311), (222), (400), (422), (511), (440), and (533) planes. The most intense peaks were chosen to evaluate the structural parameters. The lattice parameters (a), volume (V), and density (ρ) of the samples are 8.09 A, 529.47 A3, 6.06 g/cc, which are comparable to the value of lattice parameter (a = 8.056 A), volume (V = 528.30 A3), and density (ρ = 6.055 gm/cc) for bulk Co3O4. The average size of the Co3O4 nanoparticles is 14 nm which is smaller than the SEM size of 50 nm corresponding to the agglomeration of tiny particles. Further, the formation of Co3O4 nanoparticles were also confirmed by obtaining the band at 569, 1334,1337, 1566, and 3397 cm−1 in FTIR spectrum. Totally five characteristics peaks from Co3O4 at 182.57, 456.49, 505.84, 605.80, and 618.02 cm−1 and peaks from GO-Co3O4 at 182.57, 483.44, 505.84, 605.80, and 618.02 cm−1 corresponding to F2g, Eg, F2g, F2g, and Ag modes of the crystalline Co3O4, respectively, in the Raman spectra. In the case of GO-Co3O4 composite, low-intensity peaks of D and G bands are observed. The specific capacitance in rGO-Co3O4 nanocomposite is about 65.15 Fg−1.