Synthesis of CoNi/SiO2 core-shell nanoparticles decorated reduced graphene oxide nanosheets for enhanced electromagnetic wave absorption properties

In this research, the nanocomposites, CoNi/SiO₂ core-shell nanoparticles decorated reduced graphene oxide (RGO) nanosheets, are successfully synthesized via liquid-phase reduction reactions combined with a sol-gel route. The structures, morphologies, chemical composition and magnetic properties of CoNi nanoparticles, CoNi/SiO₂ core-shell nanoparticles and RGO/CoNi/SiO₂ nanocomposites have been investigated in exhaustive detail. The electromagnetic (EM) parameters of RGO/CoNi/SiO₂ nanocomposites are measured using a vector network analyzer. The results reveal that the RGO/CoNi/SiO₂ nanocomposites display enhanced EM wave absorption properties with the maximum reflection loss (R_L) of ??46.3?dB at 6.2?GHz with a matching thickness of 4.2?mm. Additionally, the absorption bandwidth corresponding to the R_L less than ??10?dB is up to 14.3?GHz (3.7–18.0?GHz) with a matching thickness range of 2.0–5.0?mm. To comprehensively consider the absorption bandwidth and the maximum R_L, the integrational method which defines ΔS as the integration area of R_L (R_L < ??10?dB) and R_E as EM wave absorption efficiency is adopted to reveal that the RGO/CoNi/SiO₂ nanocomposites exhibit the excellent absorption properties with the matching thickness of only 2.0?mm. Accordingly, the as-prepared RGO/CoNi/SiO₂ nanocomposites could be applied as promising EM wave absorption materials.     

Facile synthesis of Co0.5Zn0.5Fe2O4 nanoparticles decorated reduced graphene oxide hybrid nanocomposites with enhanced electromagnetic wave absorption properties

Herein, reduced graphene oxide/cobalt-zinc ferrite (RGO/Co_0.5Zn_0.5Fe₂O₄) hybrid nanocomposites were fabricated by a facile hydrothermal strategy. Results revealed that the contents of RGO could affect the micromorphology, electromagnetic parameters and electromagnetic wave absorption properties. As the contents of RGO increased in the as-synthesized hybrid nanocomposites, the dispersibility of the particles was improved. Meanwhile, numerously ferromagnetic Co_0.5Zn_0.5Fe₂O₄ particles were evenly anchored on the wrinkled surfaces of flaky RGO. Besides, the obtained hybrid nanocomposites exhibited superior electromagnetic absorption in both X and Ku bands, which was achieved by adjusting the RGO contents and matching thicknesses. Significantly, when the content of RGO was 7.4 wt%, the binary nanocomposites showed the optimal reflection loss of -73.9 dB at a thickness of 2.2 mm and broadest effective absorption bandwidth of 6.0 GHz (12.0–18.0 GHz) at a thin thickness of merely 2.0 mm. The enhanced electromagnetic absorption performance was primarily attributed to the multiple polarization effects, improved conduction loss caused by electron migration, and magnetic loss derived from ferromagnetic Co_0.5Zn_0.5Fe₂O₄ nanoparticles. Our results could provide inspiration for manufacturing graphene-based hybrid nanocomposites as high-efficient electromagnetic wave absorbers.     

The effect of GO loading on electromagnetic wave absorption properties of Fe3O4/reduced graphene oxide hybrids

Ideal electromagnetic absorbing materials with lightweight and high efficiency have broad application outlook in military and civil fields. In this work, a 3D nanostructure material by hybridizing Fe₃O₄ nanocrystals and reduced graphene oxide (Fe₃O₄/rGO) were synthesized through an environmental-friendly one-pot solvothermal method. The effect of GO loading on electromagnetic (EM) wave absorption characteristic of Fe₃O₄/rGO was investigated. The introduction of rGO sheets not only prevented Fe₃O₄ from agglomerating, also improved the absorption performance of Fe₃O₄/rGO hybrids. With an appropriate addition, Fe₃O₄/rGO obtained a minimum reflection loss (RL) of −22.7 dB and the absorption bandwidth was 3.13 GHz (90% absorption).     

Magnetic reduced graphene oxide nanocomposite as an effective electromagnetic wave absorber and its absorbing mechanism

A magnetic reduced graphene oxide (MRGO) composite consisting of graphene oxide and Fe₃O₄ particles in the range of 5–20 nm has been prepared by the one-pot hydrothermal process. RGO nanosheets provide flexible substrates for nanoparticle decoration, while Fe₃O₄ nanoparticles can also effectively prevent nanosheets to restack each other. Compared with previously literature, the synthesized RGO-Fe₃O₄ composite exhibits excellent electromagnetic wave absorption. The minimum reflection loss (R_L) value of −49.05 dB has been observed at 14.16 GHz with a thickness of 2.08 mm. The absorption bandwidth (R_L<−10 dB) corresponding to the minimum R_L is 4.60 GHz. The electromagnetic wave absorption properties of the RGO-Fe₃O₄ composite have been interpreted through the quarter-wavelength matching model.     

Fabrication of carbon-doped ZnCo2O4 yolk-shell microspheres compounded with magnetic graphene for enhanced electromagnetic wave absorption performance

Carbon-doped ZnCo₂O₄ (ZnCo₂O₄/C) yolk-shell microspheres are synthesized by a method of thermally decomposing precursor and then successfully compounded with magnetic graphene (MG) via co-precipitation in combination with a reduction pathway. The fabrication processes and characterizations (XRD, XPS, TEM, EDS and SEM) are described and explained in detail. It is confirmed that amorphous carbon (in situ decomposition from PVP) is uniformly doped into ZnCo₂O₄ yolk-shell microspheres. In addition, the reflection loss (RL) and electromagnetic (EM) wave absorption mechanisms of as-prepared ZnCo₂O₄/C/MG composites are calculated and analyzed exhaustively. The results show that absorption bandwidth with RL exceeding −10 dB reaches up to 4.48 GHz with a matching thickness of 3.5 mm while the maximum RL is up to −52.9 dB at 7.52 GHz with a matching thickness of 3.9 mm. Enhanced EM wave absorption performance can be attributed to good dielectric and magnetic loss, excellent impedance matching, diverse interfacial polarization and multiple reflections caused by special structures.     

Glycine-assisted solution combustion synthesis of NiCo2O4 electromagnetic wave absorber with wide absorption bandwidth

Design of high-performance electromagnetic (EM) wave absorbing materials has been regarded as an effective solution to excessive EM wave interference problem. As a promising candidate, NiCo₂O₄ absorbers have attracted enormous research attentions. However, currently reported morphology-manipulation synthetic methods of NiCo₂O₄ absorbers are time-consuming and require high energy consumption, which inhibit their practical applications. Herein, a more facile and cost-effective solution combustion synthesis was utilized to fabricate NiCo₂O₄ materials. The absorber prepared by using glycine as fuel displayed the best EM wave absorption performance. Impressively, ultra wide absorption bandwidth of 7.44 GHz from 10.56 GHz to 18 GHz could be achieved with relatively thin thickness of 2.1 mm NiCo₂O₄ sample fabricated in this work displayed the widest effective absorption bandwidth (EAB) among reported NiCo₂O₄-based EM wave absorbing materials so far. In view of its simple and low-cost synthetic process and excellent EM wave dissipation capacity, NiCo₂O₄ samples in this work showed great feasibility as practical absorber. In addition, our findings may also provide new sight for facile preparation of other high-performance EM wave absorbers by solution combustion synthesis instead of complex morphology-manipulation routes.     

One-step synthesis of Fe nanoparticles wrapped in N-doped carbon nanohorn microspheres as high-performance electromagnetic wave absorber

Designing cost-effective and eco-friendly electromagnetic absorbing materials is important for their widespread practical applications. Herein, Fe nanoparticles wrapped in carbon nanohorn microspheres enriched with N (Fe@NCNHs) were produced by a simple one-step method, which is a nonequilibrium strategy that involves evaporating a graphite anode and Fe wire in an arc plasma. The total pore volume for CNHs was calculated to be 0.38 cm³ g^?1, corresponding to its naturally inherited micropore and mesopore-dominate porosity. In addition, the N-doping content reached up to 9.3 at%. The electromagnetic wave-absorption performance of Fe@NCNHs can be controlled using the size and loading amount of Fe nanoparticles wrapped in CNHs, depending on the number of Fe wires inserted into the anode. When two Fe wires are inserted into the anode, Fe nanoparticles with uniform size are well wrapped in CNHs, exhibiting excellent electromagnetic wave absorption property with a minimum reflection loss (RL) of ?44.52 dB at 10.86 GHz matching an extremely low thickness of 1.6 mm at X band. The effective absorption bandwidth (RL < ?10 dB) was up to 13.86 GHz, and the matching thickness ranged between 1.2 and 5.0 mm. The results obtained in this study indicate that Fe@NCNHs are promising microwave-absorbing materials with enhanced dielectric loss and good impedance matching, which is attributed to the multiple reflections induced by the hollow structure of CNHs, interfacial polarization between the CNHs and Fe nanoparticles, dipole polarization induced by N-doping, and pentagonal and hexagonal defects on CNHs.     

Tunable design of ZnFe2O4@C@BPC hybrid with rich heterogeneous interfaces as a hydrophobic electromagnetic wave absorber

Environmentally friendly microwave absorbers with superior electromagnetic wave absorption, lightweight and hydrophobic ability have received considerable attention in practical applications. However, addressing the above-mentioned characteristics is simultaneously a tremendous challenge. Along these lines, in this work, a lightweight and efficient hybrid material was fabricated by employing simple self-assembly of core-shell ZnFe₂O₄@C nanospheres embedded within longan shell-derived honeycomb-like porous carbon. The results display that the carbon skeleton not only improves the conduction loss, but also promotes the reflection and scattering of EM wave. In addition, the core-shell ZnFe₂O₄@C microspheres are conducive to enhancing the ability of interface polarization and magnetic loss, and further improving the synergistic effect between the dielectric loss and magnetic loss. Furthermore, the unique structure of the ZnFe₂O₄@C@BPC endows it excellent hydrophobicity and avoids water vapor contamination in practical applications. Precisely, at a thickness of 3.4 mm, the minimum reflection loss (RL) is up to ?58.6 dB at 12.9 GHz. Notably, the effective absorption bandwidth (EAB) is as wide as 9.1 GHz (8.9–18.0 GHz), covering almost the entire X and Ku bands. Consequently, this outstanding performance renders the ZnFe₂O₄@C@BPC composite quite attractive for a broad range of applications in lightweight, hydrophobic microwave absorption materials.     

Controlled synthesis and electromagnetic wave absorption properties of core-shell Fe3O4@SiO2 nanospheres decorated graphene

Fe₃O₄/reduced graphene oxide (RGO) nanocomposite was synthesized by a simple hydrothermal method and then SiO₂ coated onto Fe₃O₄ by a modified Stӧber method. The transmission electron microscopy and field emission scanning electron microscopy characterization indicate that masses of Fe₃O₄@SiO₂ core-shell structure nanospheres attached to the RGO sheets, and that the thicknesses of SiO₂ shells are about 20–40 nm. The X-ray diffractograms and Raman spectra illustrate that the synthesized samples consist of highly crystallized cubic Fe₃O₄, amorphous SiO₂ and disorderedly stacked RGO sheets. The magnetic hysteresis loops reveal the ferromagnetic behavior of the samples at room temperature. In addition, the Fe₃O₄@SiO₂/RGO paraffin composite exhibit excellent electromagnetic wave absorption properties at room temperature in the frequency range of 2–18 GHz, which are attributed to the effective complementarities between the dielectric loss and magnetic loss. For Fe₃O₄@SiO₂/RGO-1 and Fe₃O₄@SiO₂/RGO-2 nanocomposite, the minimum reflection loss can reach −26.4 dB and −16.3 dB with the thickness of 1.5 mm, respectively. The effective absorption bandwidth of the samples can reach more than 10.0 GHz with the thickness in the range of 1.5–3.0 mm. It is demonstrated that such nanocomposite could be used as a promising candidate in electromagnetic wave absorption area.     

Rhombic Fe2O3 lumps doping hollow ZnFe2O4 spheres through oxidative decomposition process implanted into graphene conductive network with superior electromagnetic wave absorption properties

Conductor-dielectric-magnetic multicomponent coordination composites with rhombic Fe₂O₃ lumps doping hollow ZnFe₂O₄ spheres through oxidative decomposition process implanted into graphene conductive network (hollow ZnFe₂O₄ spheres/rhombic Fe₂O₃ lumps/rGO composites) were successfully constructed by a facile method. The countless hollow ZnFe₂O₄ spheres were compactly attached to the curled-paper rGO and larger sized-rhombic Fe₂O₃ lumps were relatively dispersed. Among, the hollow structure of ZnFe₂O₄ spheres could attenuate the electromagnetic wave by multiple reflections and scatterings. Intriguingly, hollow ZnFe₂O₄ spheres reacted with GO to form intermediate rhombic Fe₂O₃ lump products, which ameliorated the hetero-interfaces structure and helped to improve impedance matching by weakening the strong magnetic ZnFe₂O₄ (M_s = 91.2 emu/g) and high conductive rGO after the introduction of weakly magnetic Fe₂O₃ semiconductor. Moreover, all three components could induce dielectric polarization losses, such as multilayer or dipole polarization. Therefore, the maximum absorption of ternary composites was up to ?64.3 dB at 7 GHz and 3.4 mm, simultaneously, and a bandwidth exceeding ?10 dB was 4.2 GHz at 1.7 mm. Meanwhile, with a thin thickness range of 1.5–5 mm, the absorption bandwidth below ?10 dB was from 2 to 18 GHz which occupied for 91.5% of whole study frequency range. These results provided a new approach and reference for the design and property regulation of electromagnetic materials at electronic communications, aerospace and military radar flied.     

Microstructure and electromagnetic wave absorption property of reduced graphene oxide-SiCnw/SiBCN composite ceramics

In this account, RGO-SiC_nw/SiBCN composite ceramics were fabricated using polymer derived ceramic (PDC) combined with chemical vapor infiltration (CVI) technology. Dielectric property of as-obtained RGO-SiC_nw/SiBCN composite ceramics was significantly enhanced thanks to established conductive pathway through overlapped nanoscale SiC_nw and micro-sized RGO. The minimum RC of composite ceramics with 0.5 wt% GO and 2.29 wt% SiC_nw at thickness of 3.6 mm reached -42.02 dB with corresponding effective absorption bandwidth (EAB) of 4.2 GHz. As temperature rose from 25 to 400 °C, permittivity increased with enhanced charge carrier density and then it decreased due to oxidation process of RGO from 400 to 600 °C. The minimum reflection coefficient (RC) was recorded as -39.13 dB and EAB covered the entire X-band at 600 °C. EMW absorption ability was evaluated after high-temperature oxidation experiment under protective effect of wave-transparent Si₃N₄ coating. RGO-SiC_nw/SiBCN composite ceramics maintained outstanding EMW absorption ability with minimum RC of -10.41 dB after oxidation at 900 °C, indicating RGO-SiC_nw/SiBCN composite ceramics with excellent EMW absorption characteristic even at high temperatures and harsh environments.     

MOF-derived core-shell structured Cu9S5/NC@Co3S4/NC composite as a high-efficiency electromagnetic wave absorber

Constructing specific microstructures and designing multicomponent composites are regarded as effective approaches to obtaining high-efficiency electromagnetic (EM) wave absorbing materials. Herein, core-shell structured Cu₉S₅/N-doped carbon@Co₃S₄/N-doped carbon (Cu₉S₅/NC@Co₃S₄/NC) composites derived from Cu₃(BTC)₂@ZIF-67 were synthesized by facile carbonization and sulfidation processes. The Cu₉S₅ particles are embedded in the interior and surface of the carbon skeleton, and the Co₃S₄/NC particles are uniformly distributed on the surface of the carbon skeleton. Compared with Cu₉S₅/NC and Co₃S₄/NC, the Cu₉S₅/NC@Co₃S₄/NC composite displays improved impedance matching properties and much better EM wave absorbing properties. The minimum reflection loss (RL_min) reaches ?41.6 dB at 10.52 GHz with a thickness of 2 mm. In addition, the effective absorption bandwidth (EAB, RL < ?10 dB) is 4.08 GHz (12.73–16.81 GHz) with un ultrathin thickness of 1.5 mm. This work offers a facile strategy for synthesizing MOF-derived metal sulfides/carbon composites as EM wave absorption materials with strong absorption properties, a wide absorption bandwidth and ultrathin thickness.     

氧化石墨烯对SiO2多孔陶瓷吸波性能的影响

采用颗粒堆积法,以石英砂为骨料,甲基纤维素为黏结剂干压成型后,在1300℃保温1 h烧结制备得到SiO₂多孔陶瓷样品。通过对样品吸波性能的测试,发现样品的吸波带较宽达到9 GHz,反射率约-3 dB。经过浸渍氧化石墨烯后,样品的吸波性能发生较大改变。在氧化石墨烯质量分数为0.004%时,由于氧化石墨烯的涡流损耗,样品的吸波性能较纯SiO₂多孔陶瓷样品的吸波性能提高75%,反射率达到-5 dB。过量的氧化石墨烯使多孔陶瓷样品呈现出对电磁波的全反射。     

Fabrication of hexagonal cerium oxide nanoparticles decorated nitrogen-doped reduced graphene oxide hybrid nanocomposite as high-performance microwave absorbers in the Ku band

With the aim to obtain microwave absorbers simultaneously possessing broad absorption bandwidth, strong absorption intensity and thin matching thickness, nitrogen-doped reduced graphene oxide decorated by cerium oxide particles (NRGO/CeO₂) hybrid nanocomposite was prepared through a hydrothermal and calcination two-step route. Results of micromorphology analysis showed that numerous hexagonal CeO₂ nanoparticles were evenly anchored on the crumpled surfaces of NRGO. Moreover, both nitrogen doping and hybridization with RGO could notably strengthen the microwave absorption capacity of CeO₂. Remarkably, the NRGO/CeO₂ hybrid nanocomposite exhibited the minimum reflection loss of ?57.2 dB at 13.4 GHz (Ku band) under a matching thickness of 1.66 mm and maximum absorption bandwidth of 4.6 GHz (from 13.2 to 17.8 GHz) at an ultrathin thickness of only 1.5 mm. Meanwhile, the hybrid nanocomposites displayed strong absorption intensity (≤-20 dB, 99% absorption) in almost the whole measured thicknesses range. Furthermore, the relationship between absorption intensity and filler loadings was uncovered. The potential microwave absorption mechanisms were further revealed. Therefore, this work opened a novel idea for designing RGO-based hybrid nanocomposites as high-performance microwave absorbers.     

还原的氧化石墨烯/CoFe2O4的膜分散-水热法制备及其吸波性能

基于双膜分散技术与水热法相结合的思想,在较低温度条件下,短时间内合成了还原的氧化石墨烯(rGO)/CoFe₂O₄纳米复合材料,并研究了rGO/CoFe₂O₄的吸波性能。通过 XRD、SEM、EDS、TEM、TG/DSC、IR测试手段对rGO/CoFe₂O₄进行表征,采用矢量网络分析仪测定了复合材料在2~18GHz范围内复介电常数和复磁导率的变化,并利用计算机模拟材料在不同厚度下电磁波的衰减性能。结果表明:在透明绢丝状石墨烯的表面及边缘负载了粒度均匀的纳米CoFe₂O₄粒子;单一纳米CoFe₂O₄的反射率损耗为-3.59dB。而mCoFe₂O₄:mGO为10:7的样品的吸波层厚度在2~3mm之间变化时,微波吸收效果显著增强,厚度为3mm时,出现最大微波衰减值-9.2dB,并且微波吸收峰随着吸波层厚度的增加而向低频移动。相比于单一纳米CoFe₂O₄粉体,rGO/CoFe₂O₄纳米复合材料对电磁波的吸收效果有了大幅度的提高。     

Facile synthesis of Mn3O4 hollow polyhedron wrapped by multiwalled carbon nanotubes as a high-efficiency microwave absorber

Investigating lightweight and high-efficiency electromagnetic wave (EM) absorbers is evolving as a desirable approach to solve the electromagnetic pollution. In this study, Mn₃O₄ hollow polyhedron wrapped by multiwalled carbon nanotubes (Mn₃O₄/MWCNTs) was successfully prepared by one-step hydrothermal treatment. Interestingly, the Mn₃O₄ polyhedron as a unique hollow structure can serve as a microwave receiver and the incident EM waves hardly escape in the intricate networks, which could be repetitiously attenuated and consumed. The Mn₃O₄/MWCNTs composite with a filler loading of 20 wt% exhibits most outstanding EM absorption performance over the whole frequency of 2–18 GHz. The optimal reflection loss (R_L) achieves −53.8 dB at 11 GHz, and the effective absorption bandwidth (R_L exceeding −10 dB) reaches 4.1 GHz (9.1–13.2 GHz) with a thickness of 2.5 mm. The effective absorption bandwidth (R_L < −10 dB) up to 13.7 GHz (85% absorption over 2–18 GHz) was achieved by adjusting the thickness from 1.5 to 4 mm. The remarkable EM absorption performances benefit from the synergistic effects of suitable impedance matching, dielectric loss, interfacial polarizations and relaxation polarizations. These results indicate that Mn₃O₄/MWCNTs composite with lightweight and high-efficiency microwave absorption properties could serve as a prospective microwave absorber in practical applications.     

Synthesis of Fe3O4 and Pt nanoparticles on reduced graphene oxide and their use as a recyclable catalyst

A bifunctional Fe(3)O(4)-Pt/reduced graphene oxide (rGO) composite, i.e. Fe(3)O(4) nanoparticles (~4.8 nm in size) and Pt nanoparticles (~5 nm in size) loaded on a rGO surface, has been synthesized. It shows great catalytic performance for the reduction of methylene blue. Recycling of the composite can be achieved by simply applying an external magnetic field. In addition, the Fe(3)O(4)-Pt/rGO composite exhibits a higher catalytic activity and selectivity for aqueous-phase aerobic oxidation of benzyl alcohol than does the FeO(x)-Pt on carbon nanotubes (i.e. FeO(x)-Pt/CNT composite). Moreover, the approach for the synthesis of Fe(3)O(4)-Pt/rGO composite is simple, and can be widely employed to produce other rGO-based composites with special properties. Our work indicates that the rGO-based bifunctional composite has great potential for practical applications in various fields, such as catalytic reaction, electrochemical sensing, clean energy, etc.     

Microstructure and enhanced electromagnetic wave absorbing performance of Zn0.6Ni0.3Cu0.1Fe2O4 ferrite glass-ceramic

Here we introduce a controllable route for the efficient synthesis of Zn_0.6Ni_0.3Cu_0.1Fe₂O₄ ferrite glass-ceramic with enhanced electromagnetic wave (EMW) absorbing performance. By adding a certain amount of Zn, Ni, Cu and Fe oxides into the SiO₂–Al₂O₃–B₂O₃–CaO-R₂O glass system, the microstructure of three-dimensional dendritic ferrites combined with amorphous SiO₂-rich phase is constructed through a high-temperature melt and quenching route. The good EMW absorption performance is attributed to the unique combination of amorphous glass and spinel ferrite, which improves the impedance matching of the material and absorbs EMW by the dielectric loss and magnetic loss. Moreover, the dendritic ferrite crystal phase is compounded with the SiO₂-rich amorphous phase to form grain boundaries and crystal-amorphous interfaces, which enhances the interfacial polarization and builds multiple transmission-absorption mechanisms. The results show that the reflection loss peak value of the glass-ceramics containing 60 wt% Zn_0.6Ni_0.3Cu_0.1Fe₂O₄ spinel is ?42.16 dB with the sample thickness of 2 mm, and the effective absorption band range (reflection loss ≤ -10 dB) is 3.76 GHz (13.6–17.36 GHz) at 1.5 mm. This approach presents a scalable and low-cost solution that may be applied to the design of high-efficiency EMW consumption components in the future.     

Polydopamine-assisted formation of Co3O4-nanocube-anchored reduced graphene oxide composite for high-performance supercapacitors

Tailoring transition-metal oxide nanoparticles with two-dimensional carbon has become a favorite way to improve their electrochemical performance. In this study, a composite of reduced graphene oxide was anchored by Co₃O₄ nanocubes and easily prepared with the assistance of polydopamine (PDA), using a combination of hydrothermal reaction and pyrolysis (Co₃O₄@PDA-rGO). Polydopamine, which possesses abundant catechol and amine groups, could be easily grafted onto graphene oxide to reduce the aggregation of graphene particles. Furthermore, PDA provided active sites, i.e., catechol and amine groups, which coordinated with Co²⁺, enabling enrichment of metal ions on the surface of graphene. After the pyrolysis of Co²⁺-containing PDA-grafted graphene at 400 °C, the Co²⁺ ions were converted into Co₃O₄ nanocubes, while the PDA carbonized to form N-doped porous carbon on the surface of graphene. The resulting product, Co₃O₄@PDA-rGO, demonstrated extraordinary supercapacitive behavior with good cycling stability owing to its unique porous structure as well as the intimate contact between Co₃O₄ and the carbon matrix.