Pristine NiCo2O4 Research Articles

Optimization of Al-doped NiCo2O4 hybrid nanostructures and their electrochemical activation feature in supercapacitors

The performance of supercapacitors majorly depends on electrode materials, while optimizing the composition and microstructure of materials is the key for boosting electrochemical activity. Herein, Al-doping and electrochemical activation strategy are combined to boost the electrochemical activity of NiCo2O4. The influence of Al dopant dosage on the performance is discussed firstly. With an increasing Al3+ dosage, Al-doped samples show a morphology transition from nanoneedles to hybrid structures of nanowire/nanosheet. Optimized Al1.0-NiCo2O4 sample with hybrid nanostructures delivers the highest areal capacitance of 8.22 F cm−2 at 1 mA cm−2, much higher than that of pristine NiCo2O4 and other Al-doped samples. Serving as a working electrode, the activation of Al1.0-NiCo2O4 is conducted to induce the reconstruction of microstructure and composition. When activated for 200 cycles, expansive rod structures consisted of vertical nanosheets are generated, which presents a high areal capacitance of 9.93 F cm−2. Under the same operating conditions, the activation is also proceeded on the Al0.5-NiCo2O4 sample with only nanowires. The maximum capacitance reaches 6.49 F cm−2, much lower than that of activated Al1.0-NiCo2O4, due to the absence of nanosheets in Al0.5-NiCo2O4. The activation process is confirmed as the structure transition from nanoparticles to thin nanosheets, with the composition transition from initial Al-doped NiCo2O4 to NiCoAl-OH/OOH. When applied in an asymmetric supercapacitor, the NF/Al1.0-NiCo2O4 electrode presents a superior electrochemical performance and a charge/discharge activation feature.

Synergistic effects of defects and surface engineering in Ni-Co metal oxides to improve the high performance of Zn-ion hybrid supercapacitors

NiCo2O4 (NCO) is an auspicious pseudocapacitor material for high energy density zinc-ion hybrid supercapacitors (ZHSCs), but its low intrinsic conductivity and significant volume expansion seriously hinder its electrochemical performance. Here, we develop a nitrogen (N) doped and oxygen-vacancy-rich (Ov) NiCo oxide nanolines grown in-situ on the carbon cloth (CC) named N-Ov-NCO@CC. The morphology and structure of N-Ov-NCO@CC were characterized by XRD, XPS, EPR, SEM and TEM. It can be clearly observed that N-Ov-NCO@CC nanowires are composed of many tiny nanoparticles, and this unique structure provides abundant gaps at the microscopic scale, providing ample sites for the attachment of electrolyte ions. Due to N-functionalization, synergistic effects of doping, defect and surface engineering are realized. As a result, N-Ov-NCO@CC exhibits significantly enhanced electrochemical performance. The N-Ov-NCO@CC single electrode exhibits a high capacitance of 993.0 F/g (496.5C/g) at 1 A/g and excellent cycle stability with a capacitance retention rate of 98 % after 5000 cycles. In addition, the assembled N-Ov-NCO@CC//Zn-ZHSC operates stably in the voltage range of 1.2–2.0 V. A high specific capacitance of 484.4 F/g is available at current densities of 1 A/g. In addition, it still has a high cycle life with a capacitance retention rate of 97.1 % after 10,000 cycles and a high specific energy/power (50.3 Wh/kg at 300.2 W/kg). Density function theory (DFT) verification shows that N-Ov-NCO has higher conductivity than Ov-NCO and pristine NCO, which is conducive to improving electrochemical performance. This work provides a new idea for developing stable electrode materials for new ZHSCs.

Urchin-like structure and nanowire arrays of NiCo2O4/NiCoSe2 as a binder-free electrode material for high-performance supercapacitor

Hybrid structures targeted at high-performance electrochemical applications circumvent great challenges. Nanostructures with high porosity facilitating electrolyte penetration and providing fast ion and electron transfer are suitable candidates for constructing hybrid structured electrode materials. Here in, an architecture composed of nanowires and urchin-like structures of NiCo2O4 covered by NiCoSe2 nanosheets is successfully constructed on Ni foam through hydrothermal treatment in association with electrodeposition. The fabricated NiCo2O4/NiCoSe2 hybrid electrode demonstrates areal capacitance of 12.09 F cm-2 at current density of 5 mA cm-2, surpassing that of pristine NiCo2O4. Furthermore, the electrode evidences cycling stability with 87.6% capacitance retention over 3000 cycles. An asymmetric hybrid supercapacitor, assembled by the NiCo2O4/NiCoSe2 as a positive electrode and activated carbon as a negative electrode, represents areal capacitance of 3.07 F cm-2 at 5 mA cm−2. The as-fabricated device with excellent cycling stability (90.9% capacitance retention over 2000 cycles) delivers an energy density of 66.13 Wh kg-1 at a power density of 233 W kg-1. Our results convey a promising synthesis method of the core-shell structure of NiCo2O4/NiCoSe2 nanowire arrays for application in supercapacitors.

Facet-specific NiCo2O4/Fe2O3 p-n heterojunction with promising triethylamine sensing properties

Semiconductor gas sensing materials with specific crystal facets exposure have attracted researchers’ attention recently. However, related research mainly focuses on single metal oxide semiconductor. The research on crystal facets designing of semiconductor p-n heterojunction is still highly challenging. Herein, based on NiCo2O4 octahedral nanocrystals with high-energy {111} crystal facets as substrate, Fe2O3 nanorods with {001} crystal facets were decorated to obtain a facet-specific NiCo2O4/Fe2O3 p-n heterojunction. The p-n heterojunction showed promising triethylamine sensing properties with a high response of 70 (Ra/Rg, 100 ppm) at 300 °C, which was about 57 and 10 times higher than that of pristine NiCo2O4 and Fe2O3, respectively. Theoretical calculation suggested that the electronic coupling effect formed by d-orbitals of Co-Fe in heterojunction strengthened the influence on the orbitals of N site in triethylamine, which improved the triethylamine adsorption and interface charge transfer. The results indicate that crystal facets designing of NiCo2O4 and Fe2O3 can achieve synergistic optimization of surface/interface characteristics of p-n heterojunction, thereby achieving a comprehensive improvement in gas sensing performance. This study not only provides a high performance triethylamine sensing material, but also greatly enriches the gas sensing mechanism of p-n heterojunction at the atomic and electronic levels.

Nickel–cobalt oxides decorated Chitosan electrocatalyst for ethylene glycol oxidation

A composite of NiCo2O4 modified electrocatalyst is prepared to enhance the ethylene glycol electrooxidation. Chitosan matrix is used to improve the activity and adsorption ability of the surface to enhance ethylene glycol conversion. A Comparative study is investigated between pristine NiCo2O4 and Chitosan-modified spinel oxide to evaluate the synergistic effect between spinel oxide and chitosan. The composite is studied in an alkaline solution using electrochemistry techniques. The electrochemical activity towards ethylene glycol electrooxidation is studied as a function of anodic oxidation current density. Thus, the oxidation current values for NiCo2O4 and NiCo2O4@Chitosan in 1.0 M EG and 1.0 M KOH are 36 and 42 mA cm−2, respectively. The long-term stability of the electrode is measured by constant potential chronoamperometry. Kinetic parameters like diffusion coefficient, Tafel slope, surface coverage, and transfer coefficient are calculated. The density-functional theory estimates the adsorption of small molecules like ethylene glycol, urea, and carbon monoxide. The adsorption energy is studied on the top site of Ni and Co atoms of NiCo2O4. Forcite model is used to study the interaction between spinel oxide and chitosan. The energy calculation assumes that chitosan is adsorbed on the spinel oxide surface and enhances chitosan's ability for the adsorption of small molecules.

Enhancing asymmetric supercapacitor performance with NiCo2O4–NiO hybrid electrode fabrication

Spinel metal oxide with an extra crystalline phase is an active way to enhance the performance of the supercapacitor. Herein, a facile hydrothermal approach has been established for synthesizing nanocrystalline NiCo2O4 with an extra NiO phase material as the potential electrode for a supercapacitor. XRD analysis is executed to expose the crystalline environment and found to be dual phases ie. NiO and NiCo2O4. Further, the chemical environment of these phases is identified in FTIR, EDS, X-ray photoelectron spectroscopy, elemental mapping, and Raman analysis. The morphological analysis (SEM) of the material showed that the formation of tiny particulates aggregates become uniform in size, which consists of a nearly spherical structure. NiCo2O4–NiO showed a remarkable electrochemical performance in a 2 M potassium hydroxide. The maximum capacitance was achieved as 866 F/g at a sweep rate of 5 m V/s, which is quite higher than the normal pristine NiCo2O4. The material delivered a capacity retention of 85% over 5000 cycles. This high performance was attributed to the NiO phase in NiCo2O4 material inducing an additional charge at the boundary, prominent to synergistic effect and rapid electron and ion passage. Hence, overall, the superior performance with extra NiO phase could be beneficial for developing spinel metal oxide electrodes for battery-type supercapacitor applications.

Anionic defects engineering of NiCo2O4 for 5-hydroxymethylfurfural electrooxidation

Biomass electrooxidation reaction (BEOR) attracts worldwide attention due to its sustainable and carbon–neutral nature. The practical application of BEOR is, nevertheless, limited by the lack of electrocatalysts with high activity and selectivity. In this study, we demonstrate anionic defect engineering as an effective strategy to activate spinel NiCo2O4 to achieve outstanding performance towards 5-hydroxymethylfurfural electrooxidation reaction (HMFOR). F-dopants are successfully introduced into NiCo2O4, which spontaneously trigger oxygen vacancies formation in the lattice during synthesis. These anionic defects in NiCo2O4 result in the expansion of crystal structure, the increase of electron density and the weakened metal-O bond. The F-doped NiCo2O4 displays a 2,5-furandicarboxylic acid (FDCA) selectivity of 97% and Faradaic efficiency of 96.5%, which are noticeably higher than the pristine NiCo2O4. The strongly enhanced intrinsic activity is mainly attributed to the defect-facilitated adsorption of HMF. Our results provide critical insight into the role of anionic defects in determining the HMFOR activity, and the strategy can be applied for synthesizing high-performance electrocatalyst for other BEOR.

NiCo2O4@V2O5 nanobelts as electrode materials for efficient electrochemical charge storage

The development of novel nanostructured composites is of current interest for applications as electrode materials. In this regard, an attempt has been made to synthesize NiCo2O4@V2O5 nanocomposite and compare its charge storage performance with pristine NiCo2O4 nanoparticles. High-resolution scanning electron microscope micrographs reveal a mesoporous nanobelt like morphology of the nanocomposite with a Brunauer–Emmett–Teller surface area of ∼65 m2 g−1 and average mesopore size centered on ∼7.55 nm. Electrochemical measurements performed on both samples anticipate capacitive behavior with quasi-reversible redox reactions. However, NiCo2O4@V2O5 is found to demonstrate a strikingly high specific capacity of 194 mAh g−1 at 1 A g−1 along with a notable capacity retention of ∼90%, even after 3000 charge–discharge cycles, and a Coulombic efficiency >97% at 5 A g−1. These features are much superior to the properties of pristine NiCo2O4 nanoparticles. The results obtained in this work ascertain the functional robustness of NiCo2O4@V2O5 nanocomposites as electrode materials in supercapacitors.

Facile electrochemically induced vacancy modulation of NiCo2O4 cathode toward high-performance aqueous Zn-based battery

Transition metal oxides are highly promising cathode materials in rechargeable Zn-based batteries owing to their low cost, high theoretical capacity and good reversibility. Nevertheless, intrinsically low conductivity and sluggish redox reaction kinetics normally result in their inferior specific capacity and poor rate capability, which critically constrains the practical performance of Zn-based batteries. Herein, an ultrafast and controllable electrochemical activation (EA) process is developed to effectively enhance the electrochemical performance of NiCo2O4 cathode. Systematic studies reveal EA process triggers in situ reconstruction of NiCo2O4 lattice by weakening the coordination of Co-O bonds, resulting in the formation of abundant oxygen vacancies (octahedral Co2+). These oxygen vacancies increase the charge carrier density and endow the superficial metallic active sites with higher electrochemical activity, which synergistically accelerates the electrochemical reaction kinetics. The oxygen-deficient NiCo2O4 exhibits a remarkable capacity of 418.9 mAh/g at 1 A/g, which is nearly 5-fold higher than that of pristine NiCo2O4. Furthermore, the oxygen-deficient NiCo2O4//Zn battery presents an extremely high energy density (682.4 Wh kg−1) and excellent power density (50.8 kW kg−1), surpassing most of the reported aqueous rechargeable batteries. This work provides a facile and effective vacancy modulation strategy for the development of advanced materials utilized in energy and catalysis fields.

Nanoribbon-like NiCo2O4/reduced graphene oxide nanocomposite for high-performance hybrid supercapacitor

Nanoribbon-like NiCo2O4/reduced graphene oxide (RGO) nanocomposites were in situ prepared by an oxalate-assisted hydrothermal method. The various RGO contents (10, 20, and 30 wt%) were added during oxalate precipitation. The plate-like shape of oxalate precipitates was thermally decomposed into the nanoribbon-like morphology in which the NiCo2O4 nanoparticles were aligned in one direction. A network of pores between nanoparticles (∼21–14 nm) is caused by exhausting a large volume of gases during calcination at 450 °C. The specific capacity increases from 418 to 758 C g−1 at 1 A g−1 with the amounts of RGO up to 30 wt%. Furthermore, the NiCo2O4/RGO nanocomposites exhibit higher rate capability than the pristine NiCo2O4 nanoparticles. The NiCo2O4-30 wt% RGO//active carbon hybrid capacitor has a high energy density of 61 Wh kg−1 at the current density of 1 A g−1 and excellent cycling stability of 92% at 3 A g−1 after 5000 cycles.

Recent Research of NiCo2O4/Carbon Composites for Supercapacitors

Supercapacitors have played an important role in electrochemical energy storage. Recently, researchers have found many effective methods to improve electrode materials with more robust performances through the increasing volume of scientific publications in this field. Though nickel cobaltite (NiCo2O4), as a promising electrode material, has substantially demonstrated potential properties for supercapacitors, its composites usually show much better performances than the pristine NiCo2O4. The combination of carbon-based materials and NiCo2O4 has been implemented recently due to the dual mechanisms for energy storage and the unique advantages of carbon materials. In this paper, we review the recent research on the hybrids of NiCo2O4 and carbon nanomaterials for supercapacitors. Typically, we focused on the reports related to the composites containing graphene (or reduced graphene oxide), carbon nanotubes, and amorphous carbon, as well as the major synthesis routes and electrochemical performances. Finally, the prospect for the future work is also discussed.

Multi-defects engineering of NiCo2O4 for catalytic propane oxidation

High-performance non-noble metal catalyst development is always the pursuit for the VOCs oxidation. Herein, a multi-defective spinel catalyst was intelligently built with a mechano-chemical strategy by Na assisted milling of NiCo2O4, wherein, the incorporation of Ni into the spinel oxide could introduce cationic defects, the etching by Na brought anionic defects, while the milling process fractured the bulk and facilitated the exposure of surface defects. Thereout, the obtained D-NiCo2O4 was endowed with a significantly elevated oxygen vacancies, raised active oxygen species, enhanced oxygen mobility and an increased specific surface area. The beneficial features promise D-NiCo2O4 a superb activity for propane catalytic oxidation, exhibiting a T50 (temperature at 50% propane conversion) of 187 °C and T90 (temperature at 90% propane conversion) of 194 °C at propane space velocity of 60,000 mL·g−1·h−1, which outperformed that of pristine NiCo2O4 and Co3O4 catalyst, making itself one of the most outstanding non-noble metal catalysts for propane oxidation. This work set the paradigm to enhance the VOCs oxidation performance of metal oxide catalyst by multi-defects engineering.

Magnesium doped spinel NiCo2O4 for improved hole extraction in efficient inverted perovskite solar cells

In recent years, p-type oxide semiconductors have been widely used as hole transport materials (HTMs) in halide perovskite solar cells (PSCs). Spinel NiCo2O4 has attracted much attention in this regard due to its environmental friendliness and rich elemental composition. In this work, a solution-processed Mg-doped NiCo2O4 film was prepared for the first time as HTM for inverted planar PSCs. The density functional theory calculations reveal that the Mg doping increases the electronic states at the Fermi energy level of NiCo2O4 to promote the carrier transport. Ultraviolet photoelectron spectroscopy (UPS) further shows that the valance band maximum (VBM) of the Mg-doped NiCo2O4 is increased by 0.08 eV compared to that of pristine NiCo2O4, thus reducing the energy level mismatch at the HTM/perovskite interface. As a result, the Mg-doped NiCo2O4 HTM enables a promising power conversion efficiency (PCE) of 16.71% for the inverted MAPbI3 PSCs, which is 18% higher than that of the pristine NiCo2O4 devices (14.07%). The improved PCE is attributed to the improved hole extraction and better matching of the interfacial energy levels of the Mg-doped NiCo2O4. Our result provides novel prospect for the electronic structure manipulation of spinel NiCo2O4 by element doping.

Co-doped Ni–Fe spinels for electrocatalytic oxidation over glycerol

A series of Co-doped Ni–Fe spinels (NiCoxFe(2-x)O4, x = 0.2, 0.4, 0.6, 0.8, 1.0, 1.4, 1.8, 2) were prepared at optimum calcination temperature (700 °C) by the sol-gel method and then applied for the electrocatalytic oxidation over glycerol. Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), Tafel curve, and chronoamperometry (i-t) were performed to investigate electrochemical performance of as-prepared spinel catalysts. The results showed that NiCo0·8Fe1·2O4 exhibited distinct redox peaks and the larger CV area (626.2 ± 0.03 μV A cm−2), lower Rct (42.42 ± 0.03 Ω) and Tafel slope (21 mV dec−1) than that of pristine NiFe2O4 and NiCo2O4, signifying Co-doped NiFe2O4 is beneficial to accelerate the catalytic oxidation of glycerol. Moreover, the ECSA and stability of NiCo0·8Fe1·2O4 were also observably improved. This excellent performance is comparable to that of commercial Pt/C (20 wt.%)-SA. The enhanced electrocatalytic property of NiCo0·8Fe1·2O4 is ascribed to the uneven distribution of oxygen in NiFe2O4 structure caused by Co doping, thus forming oxygen defect sites.

Reduced graphene oxide/hierarchal spinel nickel cobaltite nanoflowers composites for supercapacitor electrodes with ultrahigh capacitive and excellent rate performance

Researchers are extensively investigating transition metal oxides due to their unique porous architectural structure and remarkable electrochemical properties, which are suitable to boost the energy storage capabilities. In present work, facile chemical route was used to synthesize hierarchal spinel nickel cobaltite nanoflowers anchored reduced graphene oxide (NiCo2O4-rGO) as high performance electrode material. NiCo2O4 anchored rGO demonstrated specific capacitance of 2695 Fg-1 at 1 Ag-1, which is greater than pristine NiCo2O4 nanoflowers specific capacitance. NiCo2O4-rGO showed excellent stability and retention capability of 96% after 2500 cycles at 5 Ag-1. Furthermore, NiCo2O4–rGO exhibited maximum energy density of 93.57 WhKg−1 at power density of 250 WKg-1. We have achieved specific capacitance and retention capability which is higher than previously reported results. This enhancement is mainly attributed to the spinel structure of NiCo2O4 and its robust structural affinity with rGO. Moreover, rGO possesses extended surface area provided ample of active sites and exceptional synergetic effect which helped to enhance the induction and consequently transportation of e−/h+. More importantly due to its special morphological effects, in future NiCo2O4 anchored rGO nanoflowers may open new avenue in research but also used as an efficient electrode material for the construction of high performance supercapacitors.

Ruthenium-modified porous NiCo2O4 nanosheets boost overall water splitting in alkaline solution

Exploring efficient oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) electrocatalysts is crucial for developing water splitting devices. The composition and structure of catalysts are of great importance for catalytic performance. In this work, a heterogeneous Ru modified strategy is engineered to improve the catalytic performance of porous NiCo2O4 nanosheets (NSs). Profiting from favorable elements composition and optimized structure property of decreased charge transfer barrier, more accessible active sites and increased oxygen vacancy concentration, the Ru-NiCo2O4 NSs exhibits excellent OER activity with a low overpotential of 230 mV to reach the current density of 10 mA/cm2 and decent durability. Furthermore, Ru-NiCo2O4 NSs show superior HER activity than the pristine NiCo2O4 NSs, as well. When assembling Ru-NiCo2O4 NSs couple as an alkaline water electrolyzer, a cell voltage of 1.60 V can deliver the current density of 10 mA/cm2. This work provides feasible guidance for improving the catalytic performance of spinel-based oxides.

Rational design of KCu7S4@NiCo2O4 in-situ growth on nickel foam for high performance supercapacitor electrode

The application of NiCo2O4 as electrode materials for supercapacitors has attracted widespread attention. However, pristine NiCo2O4 always suffer from poor electrical conductivity and rate performance that limit their electrochemical performance in supercapacitors. In order to overcome the deficiencies of NiCo2O4, in this study, we successfully synthesized KCu7S4@NiCo2O4 core–shell structure in-situ grown on Ni foam with good electrochemical performance. The morphologies of KCu7S4@NiCo2O4 composite could be controlled by electrochemical deposition time. According to the electrochemical testing results, an optimal composite was obtained with the deposition time of 10 min, and the corresponding KCu7S4@NiCo2O4 composite possessed the high specific capacitance of 18.4 F cm−2 (2008 F g−1) at a current density of 3 mA cm−2 and good cycling stability (80% capacitance retention after 4000 cycles at a current density of 40 mA cm−2). Moreover, the investigation demonstrates the great potential application of KCu7S4 @NiCo2O4 in supercapacitor. The asymmetric supercapacitor fabricated with KCu7S4@NiCo2O4 and activated carbon delivers a high energy density of 125.56 Wh kg−1 at the power density of 105.5 W kg−1.

Synthesis of 3D nanoflower-like mesoporous NiCo2O4 N-doped CNTs nanocomposite for solid-state hybrid supercapacitor; efficient material for the positive electrode

In this research work, we report a novel method for developing ternary NiCo2O4 compounds using deep eutectic solvents (DESs) and a strategy for improving their pseudocapacitive performance. NiCo2O4 composites with N-doped carbon nanotubes (NCNTs) were fabricated on Ni foam using a hydrothermal method. The electrochemical performance of the NiCo2O4 was altered with the change in the reaction temperature. The composite of NiCo2O4 and NCNTs demonstrated a maximum value of specific capacity of 303 mAh g−1 at a scan rate of 5 mV s−1. The specific capacity for the composite compound was 1.3-fold greater than that of the pristine NiCo2O4 sample. For practical applications, we constructed a flexible solid-state hybrid supercapacitor comprised of NiCo2O4/NCNTs//activated carbon (AC) cells with an excellent energy density of 12.31 Wh kg−1, outstanding power density of 8.96 kW kg−1, and tremendous electrode stability. The three-dimensional mesoporous nanoflowers and nanotubes-like nanostructures of NiCo2O4 are well-suited for use in hybrid devices as well as convenient for flexible electronic devices.

Improved electrochemical performance of nickel cobaltite/ multi-walled carbon nanotube composite as a hybrid electrode for supercapacitors

Metal oxide and carbon nanotubes (CNT) interactions are deep-seated to activate high energy storage ability in energy storage devices. In the present study, NiCo2O4/MWCNT composite is synthesized by the sonochemical method and employed as a hybrid electrode in supercapacitors. The NiCo2O4/MWCNT hybrid electrode delivers a specific capacitance of 418.1 F g−1 (or specific capacity 57.22 mAh g−1) at 2 A g−1 in 6 M KOH electrolyte, which is more than two and half times higher than pristine NiCo2O4. Furthermore, the hybrid electrode displays the high-rate capability (73.1% @10A g−1) and cycling stability (95.2% after 2000 charge-discharge cycles) owing to improved electrical conductivity, low charge transfer resistance, and the good synergistic effect that emerges due to complementary effect. These remarkable electrochemical properties suggest that NiCo2O4/MWCNT composite expected to be a note-worthy supercapacitor electrode material.

Enhancing the supercapacitor performance of NiCo2O4 microflowers by reduced graphene oxide nano-sheets

This work presented the preparation and supercapacitor performance of a spinel nickel-cobalt oxide (NiCo2O4) microflowers mixed with nano-sized reduced graphene oxide (rGO) sheets. The hybrid material (NiCo2O4/rGO), pure NiCo2O4 and nano-sized rGO samples were characterized and confirmed by several techniques, such as XRD, SEM and EDS. The supercapacitive properties of all prepared samples were also studied using an electrochemical measurement technique (CV and GCD). The results revealed that the NiCo2O4/rGO (484.1 F.g−1) hybrid electrode exhibited much higher specific capacitance than those of pristine NiCo2O4 (358.3 F.g−1) and nano-sized rGO (113.8 F.g−1) electrodes, respectively. Hence, this work indicates that the supercapacitor performance of NiCo2O4 mixed rGO hybrid materials is more superior to the pure NiCo2O4 microflowers and nano-sized rGO sheets.