Effect of sandblasting and acid surface pretreatment on the specific capacitance of CuO nanostructures grown by hot water treatment for supercapacitor electrode applications

Crystalline copper oxide (CuO) nanostructures with micro, nano, and micro-nano surface roughness were grown on Cu sheet substrates by a facile, scalable, low-cost, and low-temperature hot water treatment (HWT) method that simply involved immersing Cu sheet in DI water at 75 °C for 24 h without any chemical additives. Various morphological features and sizes of CuO nanostructures were tuned by using different surface pretreatment techniques including acid treatment, sandblasting, or a combination of those two. The surface morphology of the prepared samples was analyzed by scanning electron microscopy. The crystal structure of the CuO nanostructures was investigated by x-ray diffraction XRD and Raman spectroscopy. To study the pseudocapacitive behavior, their potential supercapacitor performance, and equivalent series resistance, electrochemical analysis was done by cyclic voltammetry and electrochemical impedance spectroscopy for all the CuO/Cu samples in 1 M of Na2SO4electrolyte. Among all, the best supercapacitive performance was achieved for CuO/Cu samples pretreated with Sandblasting followed by Acid treatment resulting in a specific capacitance of about 104 F g-1. The electrode with the sandblasted + acid pretreated sample showed a maximum of ∼69% capacitive retention after 2000 consecutive cycles. Our results indicate that CuO nanostructures on Cu substrates prepared with different surface pretreatment conditions and grown by HWT can be promising electrodes for supercapacitor device applications.

Chemical synthesis and super capacitance performance of novel CuO@Cu4O3/rGO/PANI nanocomposite electrode

Copper oxide-based nanocomposites are promising electrode materials for high-performance supercapacitors due to their unique properties that aid electrolyte access and ion diffusion to the electrode surface. Herein, a facile and low-cost synthesis in situ strategy based on co-precipitation and incorporation processes of reduced graphene oxide (rGO), followed by in situ oxidative polymerization of aniline monomer has been reported. CuO@Cu4O3/rGO/PANI nanocomposite revealed the good distribution of CuO@Cu4O3 and rGO within the polymer matrix which allows improved electron transport and ion diffusion process. Galvanostatic charge-discharge (GCD) results displayed a higher specific capacitance value of 508 F g-1 for CuO@Cu4O3/rGO/PANI at 1.0 A g-1 in comparison to the pure CuO@Cu4O3 278 F g-1. CuO@Cu4O3/rGO/PANI displays an energy density of 23.95 W h kg-1 and power density of 374 W kg-1 at the current density of 1 A g-1 which is 1.8 times higher than that of CuO@Cu4O3 (13.125 W h kg-1) at the same current density. The retention of the electrode was 93% of its initial capacitance up to 5000 cycles at a scan rate of 100 mV s-1. The higher capacitance of the CuO@Cu4O3/rGO/PANI electrode was credited to the formation of a fibrous network structure and rapid ion diffusion paths through the nanocomposite matrix that resulted in enhanced surface-dependent electrochemical properties.

Hydrothermal synthesis of CuO@MnO2 on nitrogen-doped multiwalled carbon nanotube composite electrodes for supercapacitor applications

Nitrogen-doped multiwalled carbon nanotubes (N-MWCNTs) have been used to fabricate nanostructured materials for various energy devices, such as supercapacitors, sensors, batteries, and electrocatalysts. Nitrogen-doped carbon-based electrodes have been widely used to improve supercapacitor applications via various chemical approaches. Based on previous studies, CuO@MnO₂ and CuO@MnO₂/N-MWCNT composites were synthesized using a sonication-supported hydrothermal reaction process to evaluate their supercapacitor properties. The structural and morphological properties of the synthesized composite materials were characterized via Raman spectroscopy, XRD, SEM, and SEM–EDX, and the morphological properties of the composite materials were confirmed by the nanostructured composite at the nanometer scale. The CuO@MnO₂ and CuO@MnO₂/N-MWCNT composite electrodes were fabricated in a three-electrode configuration, and electrochemical analysis was performed via CV, GCD, and EIS. The composite electrodes exhibited the specific capacitance of ~ 184 F g⁻¹ at 0.5 A g⁻¹ in the presence of a 5 M KOH electrolyte for the three-electrode supercapacitor application. Furthermore, it exhibited significantly improved specific capacitances and excellent cycling stability up to 5000 GCD cycles, with a 98.5% capacity retention.

Cerium functionalized graphene nano-structures and their applications; A review

Graphene-based nanomaterials with remarkable properties, such as good biocompatibility, strong mechanical strength, and outstanding electrical conductivity, have dramatically shown excellent potential in various applications. Increasing surface area and porosity percentage, improvement of adsorption capacities, reduction of adsorption energy barrier, and also prevention of agglomeration of graphene layers are the main advantages of functionalized graphene nanocomposites. On the other hand, Cerium nanostructures with remarkable properties have received a great deal of attention in a wide range of fields; however, in some cases low conductivity limits their application in different applications. Therefore, the combination of cerium structures and graphene networks has been widely invesitaged to improve properties of the composite. In order to have a comprehensive information of these nanonetworks, this research reviews the recent developments in cerium functionalized graphene derivatives (graphene oxide (GO), reduced graphene oxide (RGO), and graphene quantum dot (GQD) and their industrial applications. The applications of functionalized graphene derivatives have also been successfully summarized. This systematic review study of graphene networks decorated with different structure of Cerium have potential to pave the way for scientific research not only in field of material science but also in fluorescent sensing, electrochemical sensing, supercapacitors, and catalyst as a new candidate.

Novel Au nanorod/Cu2O composite nanoparticles for a high-performance supercapacitor

Metal-oxide nanomaterials have attracted great interest in recent years due to their novel characteristics such as surface effect and quantum confinement. A fascinating Au nanorod (NR)/cuprous oxide core-shell composite (AuNR/Cu2O) was directly synthesized using a moderate one-pot facile green redox method and further utilized for energy storage applications in a supercapacitor. The synthesis mechanism is based on the use of reducing agents to form the core shell. The resultant composite was deposited on the surface of nickel foam as a result of redox reactions between Au and Cu via a hydrothermal method. AuNR/Cu2O composite nanoparticles (NPs) were characterized using various spectroscopic and microscopic techniques, including UV-vis and X-ray photoelectron spectroscopies, Brunauer-Emmett-Teller surface area analysis, X-ray diffractometry, and transmission electron microscopy. The AuNR/Cu2O composite NPs grow via the depositing of a 20-50 nm Cu2O shell on an AuNR core with dimensions of 5-20 nm in width and 40-70 nm in length. The as-synthesized AuNR/Cu2O composite NPs were effectively used as electrode materials in a supercapacitor, and their electrochemical performance was determined by cyclic voltammetry, galvanostatic charge-discharge measurements, and electrochemical impedance spectroscopy in 2 M KOH aqueous solution as an electrolyte. The composite NPs showed excellent average specific capacitance of 235 F g-1 at a current density of 2 A g-1 and durable cycling stability (96% even after 10 000 cycles). The higher efficiency of the AuNR/Cu2O composite NPs can be attributed to the presence of AuNR in the core. The AuNR/Cu2O composite NPs exhibit a high surface area and high electrical conductivity, which consequently result in their excellent specific capacitance and outstanding rate as an all-solid-state supercapacitor electrode.

Copper Oxide/Functionalized Graphene Hybrid Nanostructures for Room Temperature Gas Sensing Applications

Oxide semiconductors are conventionally used as sensing materials in gas sensors, however, there are limitations on the detection of gases at room temperature (RT). In this work, a hybrid of copper oxide (CuO) with functionalized graphene (rGO) is proposed to achieve gas sensing at RT. The combination of a high surface area and the presence of many functional groups in the CuO/rGO hybrid material makes it highly sensitive for gas absorption and desorption. To prepare the hybrid material, a copper oxide suspension synthesized using a copper acetate precursor is added to a graphene oxide solution during its reduction using ascorbic acid. Material properties of the CuO/rGO hybrid and its drop-casted thin-films are investigated using Raman, FTIR, SEM, TEM, and four-point probe measurement systems. We found that the hybrid material was enriched with oxygen functional groups (OFGs) and defective sites, along with good electrical conductivity (Sheet resistance~1.5 kΩ/□). The fabricated QCM (quartz crystal microbalance) sensor with a thin layer of the CuO/rGO hybrid demonstrated a high sensing response which was twice the response of the rGO-based sensor for CO2 gas at RT. We believe that the CuO/rGO hybrid is highly suitable for existing and future gas sensors used for domestic and industrial safety.

Construction of a Cu-Based Metal-Organic Framework by Employing a Mixed-Ligand Strategy and Its Facile Conversion into Nanofibrous CuO for Electrochemical Energy Storage Applications

Recently, metal-organic frameworks (MOFs) have been widely employed as a sacrificial template for the construction of nanostructured materials for a range of applications including energy storage. Herein, we report a facile mixed-ligand strategy for the synthesis of a Cu-MOF, [Cu₃(Azopy)₃(BTTC)₃(H₂O)₃·2H₂O]_n (where BTTC = 1,2,4,5-benzenetetracarboxylic acid and Azopy = 4,4'-azopyridine), via a slow-diffusion method at room temperature. X-ray analysis authenticates the two-dimensional (2D)-layered framework of Cu-MOF. Topologically, this 2D-layered structure is assigned as a 4-connected unimodal net with sql topology. Further, nanostructured CuO is obtained via a simple precipitation method by employing Cu-MOF as a precursor. After analysis of their physicochemical properties through various techniques, both materials are used as surface modifiers of glassy carbon electrodes for a comparative electrochemical study. The results reveal a superior charge storage performance of CuO (244.2 F g^-1 at a current density of 0.8 A g^-1) with a high rate capability compared to Cu-MOF. This observation paves the pathway for the strategic design of high-performing supercapacitor electrode materials.

A SnO2QDs/GO/PPY ternary composite film as positive and graphene oxide/charcoal as negative electrodes assembled solid state asymmetric supercapacitor for high energy storage applications

The work demonstrates tin oxide quantum dots/graphene oxide/polypyrrole (SnO2QDs/GO/PPY) ternary composite deposited on titanium foil as a positive electrode and graphene oxide (GO)/charcoal on titanium foil as negative electrode separated by polyvinyl alcohol/potassium hydroxide (PVA/KOH) gel-electrolyte as a solid-state asymmetric supercapacitor for high energy storage applications. Here, tin oxide quantum dots (SnO2QDs) were successfully synthesized by a hydrothermal technique, and SnO2QDs/GO/PPY ternary composite was synthesized by an in situ method with pyrrole monomer, SnO2, and GO. A pH value controlled, which maintained the uniform size of SnO2QDs dispersed on PPY, through GO ternary composite was used for fabricating the asymmetric supercapacitor electrode with the configuration (SnO2QDs/GO/PPY)/GO/charcoal (85 : 10 : 5). The device achieved the highest specific capacitance of 1296 F g-1, exhibited an energy density of 29.6 W h kg-1 and the highest power density of 5310.26 W kg-1 in the operating voltage from 0 to 1.2 V. The device also possessed excellent reliability and retained the capacitance of 90% after 11 000 GCD cycles. This ternary composite is a prominent material for potential applications in next-generation energy storage and portable electronic devices.

Rapid design of a core–shell-like metal hydroxide/oxide composite and activated carbon from biomass for high-performance supercapattery applications

Core–shell-like 2D Ni(OH)₂ on a Cu₂O custard apple-like composite and biomass-derived activated carbon materials were used for the construction of a supercapattery device.

Enhanced photocatalytic dye degradation and hydrogen production ability of Bi25FeO40-rGO nanocomposite and mechanism insight

A comprehensive comparison between BiFeO3-reduced graphene oxide (rGO) nanocomposite and Bi25FeO40-rGO nanocomposite has been performed to investigate their photocatalytic abilities in degradation of Rhodamine B dye and generation of hydrogen by water-splitting. The hydrothermal technique adapted for synthesis of the nanocomposites provides a versatile temperature-controlled phase selection between perovskite BiFeO3 and sillenite Bi25FeO40. Both perovskite and sillenite structured nanocomposites are stable and exhibit considerably higher photocatalytic ability over pure BiFeO3 nanoparticles and commercially available Degussa P25 titania. Notably, Bi25FeO40-rGO nanocomposite has demonstrated superior photocatalytic ability and stability under visible light irradiation than that of BiFeO3-rGO nanocomposite. The possible mechanism behind the superior photocatalytic performance of Bi25FeO40-rGO nanocomposite has been critically discussed.

Synthesis of graphene-transition metal oxide hybrid nanoparticles and their application in various fields

Single layer graphite, known as graphene, is an important material because of its unique two-dimensional structure, high conductivity, excellent electron mobility and high surface area. To explore the more prospective properties of graphene, graphene hybrids have been synthesised, where graphene has been integrated with other important nanoparticles (NPs). These graphene-NP hybrid structures are particularly interesting because after hybridisation they not only display the individual properties of graphene and the NPs, but also they exhibit further synergistic properties. Reduced graphene oxide (rGO), a graphene-like material, can be easily prepared by reduction of graphene oxide (GO) and therefore offers the possibility to fabricate a large variety of graphene-transition metal oxide (TMO) NP hybrids. These hybrid materials are promising alternatives to reduce the drawbacks of using only TMO NPs in various applications, such as anode materials in lithium ion batteries (LIBs), sensors, photocatalysts, removal of organic pollutants, etc. Recent studies have shown that a single graphene sheet (GS) has extraordinary electronic transport properties. One possible route to connecting those properties for application in electronics would be to prepare graphene-wrapped TMO NPs. In this critical review, we discuss the development of graphene-TMO hybrids with the detailed account of their synthesis. In addition, attention is given to the wide range of applications. This review covers the details of graphene-TMO hybrid materials and ends with a summary where an outlook on future perspectives to improve the properties of the hybrid materials in view of applications are outlined.

Facile In Situ Fabrication of Nanostructured Graphene-CuO Hybrid with Hydrogen Sulfide Removal Capacity

A simple and scalable synthetic approach for one-step synthesis of graphene-CuO (TRGC) nanocomposite by an in situ thermo-annealing method has been developed. Using graphene oxide (GO) and copper hydroxide as a precursors reagent, the reduction of GO and the uniform deposition of in situ formed CuO nanoparticles on graphene was simultaneously achieved. The method employed no solvents, toxic-reducing agents, or organic modifiers. The resulting nanostructured hybrid exhibited improved H2S sorption capacity of 1.5 mmol H2S/g-sorbent (3 g S/100 g-sorbent). Due to its highly dispersed sub-20 nm CuO nanoparticles and large specific surface area, TRGC nanocomposite exhibits tremendous potential for energy and environment applications.

Graphene-Based Materials for Lithium-Ion Hybrid Supercapacitors

Lithium-ion hybrid supercapacitors (LIHSs), also called Li-ion capacitors, have attracted much attention due to the combination of the rapid charge-discharge and long cycle life of supercapacitors and the high energy-storage capacity of lithium-ion batteries. Thus, LIHSs are expected to become the ultimate power source for hybrid and all-electric vehicles in the near future. As an electrode material, graphene has many advantages, including high surface area and porous structure, high electric conductivity, and high chemical and thermal stability, etc. Compared with other electrode materials, such as activated carbon, graphite, and metal oxides, graphene-based materials with 3D open frameworks show higher effective specific surface area, better control of channels, and higher conductivity, which make them better candidates for LIHS applications. Here, the latest advances in electrode materials for LIHSs are briefly summarized, with an emphasis on graphene-based electrode materials (including 3D graphene networks) for LIHS applications. An outlook is also presented to highlight some future directions.

Hierarchical Cu2O/CuO/Co3O4 core-shell nanowires: synthesis and electrochemical properties

We prepared hierarchical Cu2O/CuO/Co3O4 core-shell nanowires (NWs) via a facile chemical deposition method followed by calcination for use as the electrode of supercapacitors. The Cu2O/CuO/Co3O4 electrode showed a specific capacitance of 318 F g(-1) at a current density of 0.5 A g(-1). 80% of the original specific capacitance was retained after 3000 cycles at a current density of 5 A g(-1). An asymmetric supercapacitor cell using Cu2O/CuO/Co3O4 NWs as the positive electrode and activated graphene as the negative electrode exhibited a maximum energy density of 12 Wh kg(-1). The electrochemical properties of the electrode were strongly related to the hierarchical nanostructure, which not only provided rich active sites but also shortened ion transport pathways.

3D ordered nanoporous NiMoO4 for high-performance supercapacitor electrode materials

3D ordered nanocrystalline nanoporous NiMoO₄ with high surface area and bimodal pore size distribution has been synthesized by nanocasting from mesoporous silica KIT-6, and applied as high-performance supercapacitor electrode material.

Fabrication, mechanical properties, and biocompatibility of reduced graphene oxide-reinforced nanofiber mats

Graphene-based nanofibers with superior electrical and mechanical properties have been developed for application in tissue engineering.