Solvothermal synthesis of ternary Cu2O-CuO-RGO composites as anode materials for high performance lithium-ion batteries

Electrochemically Dealloying Engineering toward Integrated Monolithic Electrodes with Superior Electrochemical Li-Storage Properties

Integrated monolithic electrodes (IMEs) free of inactive components demonstrate great potential in boosting energy-power densities and cycling life of lithium-ion batteries. However, their practical applications are significantly limited by low active substance loading (< 4.0 mg cm-2 and 1.0 g cm-3), complicated manufacturing process, and high fabrication cost. Herein, employing industrial Cu-Mn alloy foil as a precursor, a simple neutral salt solution-mediated electrochemical dealloying strategy is proposed to address such problems. The resultant Cu-Mn IMEs achieve not only a significantly larger active material loading due to the in situ generated Cu2O and MnOx (ca. 16.0 mg cm-2 and 1.78 g cm-3), simultaneously fast transport of ions and electrons due to the well-formed nanoporous structure and built-in Cu current collector, but also high structural stability due to the interconnected ligaments and suitable free space to relieve the volume expansion upon lithiation. As a result, they demonstrate remarkable performances including large specific capacities (> 5.7 mAh cm-2), remarkable pseudocapacitive effect despite the battery-type constitutes, long cycling life, and good working condition in a lithium-ion full cell. This study sheds new light on the further development of IMEs, enriches the existing dealloying techniques, and builds a bridge between the two.

Superior Electrochemical Performance of Two-Dimensional RGO/Cu/Cu2O Composite as Anode Material for Lithium-Ion Batteries

In recent years, graphene has attracted the interest of many researchers working on LIB anode materials owing to its unique 2D structure, thermal stability, and fast electron transfer. In this work, RGO/Cu/Cu2O nanocomposites were synthesized through a hydrothermal procedure. The as-prepared nanocomposites exhibited a high lithium storage capacity with improved cycling stability and great rate performance, i.e., the discharge capacity was 371.8 mAh/g after 100 cycles at a current density of 500 mA/g. These excellent properties were associated with the sheet structure symmetry of graphene enriched with the multifunctional Cu-Cu2O component, which prevented aggregation and accommodated the volume changes of the anode material during the charge–discharge tests. The RGO/Cu/Cu2O composite conferred to the LIB anode the ability to resist electrode cracking. The approach proposed in this paper can be also generalized for the synthesis of other carbon-based anode materials for LIBs.

The Thermal Expansion Exfoliation Technology and Lithium Promoter Assistant Enables CuOx/graphene as a High-Performance Anode for Lithium-Ion Batteries

The ability to rationally design the copper oxide anode with superior rate performance that possesses ultra-small particle size is highly desirable for lithium-ion batteries (LIBs). Herein, a rapid and effective...

Graphene-Based Nanomaterials for Flexible and Stretchable Batteries

Recently, as flexible and wearable electronic devices have become widely popular, research on light weight and large-capacity batteries suitable for powering such devices has been actively conducted. In particular, graphene has attracted considerable attention from researchers in the battery field owing to its good mechanical properties and its applicability in various processes to fabricate electrodes for batteries. Graphene is classified into two types: flake-type, fabricated from graphite, and film-type, synthesized using chemical vapor deposition. The unique processes involved in these two types enable the fabrication of flexible and stretchable batteries with various shapes and functions. In this article, the recent progress in the development of flexible and stretchable batteries based on graphene, as well as its important technical issues are reviewed.

Photoelectrochemical Water-Splitting Using CuO-Based Electrodes for Hydrogen Production: A Review

The cost-effective, robust, and efficient electrocatalysts for photoelectrochemical (PEC) water-splitting has been extensively studied over the past decade to address a solution for the energy crisis. The interesting physicochemical properties of CuO have introduced this promising photocathodic material among the few photocatalysts with a narrow bandgap. This photocatalyst has a high activity for the PEC hydrogen evolution reaction (HER) under simulated sunlight irradiation. Here, the recent advancements of CuO-based photoelectrodes, including undoped CuO, doped CuO, and CuO composites, in the PEC water-splitting field, are comprehensively studied. Moreover, the synthesis methods, characterization, and fundamental factors of each classification are discussed in detail. Apart from the exclusive characteristics of CuO-based photoelectrodes, the PEC properties of CuO/2D materials, as groups of the growing nanocomposites in photocurrent-generating devices, are discussed in separate sections. Regarding the particular attention paid to the CuO heterostructure photocathodes, the PEC water splitting application is reviewed and the properties of each group such as electronic structures, defects, bandgap, and hierarchical structures are critically assessed.

Rational Design of Self-Supported CuO x -Decorated Composite Films as an Efficient and Easy-Recycling Catalyst for Styrene Oxidation

The applications of graphene-based materials in catalysis are limited by their strong tendency to aggregate, which may lead to a decrease in active sites. Herein, we propose a facile and controllable strategy to fabricate a series of heterogeneous catalysts with a unique nanostructure wherein CuO _x -decorated reduced graphene oxide (rGO) sheets are incorporated into a solid matrix composed of poly(vinylpyrrolidone) (PVP) and carboxymethyl cellulose (CMC). The resultant materials are self-supported films and could be directly used as catalysts for the liquid-phase oxidation of styrene without the requirement for extra substrates. The employment of PVP-CMC (PC) as the support for CuO _x -decorated rGO sheets successfully inhibits their aggregation. Benefiting from the dispersion of copper species, these films exhibit good catalytic activity and recyclability under mild reaction conditions. Especially, they can be conveniently removed from the reaction mixture by tweezers due to their structural stability. For catalyzing multiple reactions with high efficiency and facile recyclability, this study offers a universal strategy to design heterogeneous catalysts based on graphene materials and provides a promising platform.

Direct Utilization of Photoinduced Charge Carriers to Promote Electrochemical Energy Storage

Electrochemical energy storage has been regarded as one of the most promising strategies for next-generation energy consumption. To meet the increasing demands of urban electric vehicles, development of green and efficient charging technologies by exploitation of solar energy should be considered for outdoor charging in the future. Herein, a light-sensitive material (copper foam-supported copper oxide/nickel copper oxides nanosheets arrays, namely CF@CuO_x @NiCuO_x NAs) with hierarchical nanostructures to promote electrochemical charge storage is specifically fabricated. The as-fabricated NAs have demonstrated a high areal specific capacity of 1.452 C cm^-2 under light irradiation with a light power of 1.76 W, which is 44.8% higher than the capacity obtained without light. Such areal specific capacity (1.452 C cm^-2 ) is much higher than that of the conventional supercapacitor structure using a similar active redox component reported recently (NiO nanosheets array@Co₃ O₄ -NiO FTNs: maximum areal capacity of 623.5 mF cm^-2 at 2 mA cm^-2 ). This photo-enhancement for charge storage can be attributed to the combination of photo-sensitive Cu₂ O and pseudo-active NiO components. Hence, this work may provide new possibilities for direct utilization of sustainable solar energy to realize enhanced capability for energy storage devices.

A nanocomposite consisting of cuprous oxide supported on graphitic carbon nitride nanosheets for non-enzymatic electrochemical sensing of 8-hydroxy-2'-deoxyguanosine

Graphitic carbon nitrides supported cuprous oxide architecture is reported as an efficient electrode material for supercapacitors, especially due to its high charge-transfer conductivity of the electrochemical devices. Herein, we present an electrochemical sensor to specifically detect 8-hydroxy-2'-deoxyguanosine (8-HDG) oxidative stress biomarker using graphitic carbon nitrides that decorate a cuprous oxide cubes modified electrode. The fabricated electrochemical sensor was characterized and proved by electrochemical methods, EDX, FESEM, and amperometry (i-t). In the presence of 8-hydroxy-2'-deoxyguanosine (8-HDG), the effective interaction between graphitic carbon nitrides and 8-HDG favors the accumulation on the Cu₂O/g-C₃N₄/GCE, which increases the electrocatalytic property and amperometric response. The proposed electrochemical sensor exhibits a wide linear range for 8-HDG in 0.1 M phosphate buffer (pH 7.0) from 25 nM to 0.91 mM, and the limit of detection (LOD) is 4.5 nM. The stability of the Cu₂O/g-C₃N₄/GCE is improved when stored at 4 °C. The repeatability and reproducibility of this electrochemical sensor is good and the sensor retains its  current response for 8-HDG detection also after long time storage. The modified sensor proved high selectivity and sensitivity for 8-HDG, which made it possible to determine 8-HDG in biological samples. Furthermore, the Cu₂O/g-C₃N₄/GCE offered a favorable electron transfer between the Cu₂O/g-C₃N₄ and the electrode interface compared to Cu₂O/GCE, g-C₃N₄/GCE, and unmodified GCE. Graphical abstract Electrochemical detection of oxidative stress marker based on Cu₂O@g-C₃N₄ materials modified electrode.

Structure-tunable supraparticle assemblies of hollow cupric oxide sheathed with nanographenes

Self-assembled supraparticles (SPs), a secondary structure of clustered nanoparticles, have attracted considerable interest owing to their highly tunable structure, composition, and morphology from their primary nanoparticle constituents. In this study, hierarchically assembled hollow Cu2O SPs were prepared using a cationic polyelectrolyte poly(diallyl dimethylammonium chloride) (PDDA) during the formation of Cu2O nanoparticles. The concentration-dependent structural transformation of PDDA from linear chains to assembled droplets plays a crucial role in forming a hollow colloidal template, affording the self-assembly of Cu2O nanoparticles as a secondary surfactant. The use of the positively charged PDDA also affords negatively charged nanoscale graphene oxide (NGO), an electrical and mechanical supporter to uniformly coat the surface of the hollow Cu2O SPs. Subsequent thermal treatment to enhance the electrical conductivity of NGO within the NGO/Cu2O SPs allows for the concomitant phase transformation of Cu2O to CuO, affording reduced NGO/CuO (RNGO/CuO) SPs. The uniquely structured hollow RNGO/CuO SPs achieve improved electrochemical properties by providing enhanced electrical conductivity and electroactive surface area.

MoS2 nanoflowers encapsulated into carbon nanofibers containing amorphous SnO2 as an anode for lithium-ion batteries

SnO₂ with high abundance, large theoretical capacity, and nontoxicity is considered to be a promising candidate for use as advanced electrodes. However, the poor electronic conductivity and large volume variations hinder the practical applications of SnO₂-based electrodes for use in lithium-ion batteries (LIBs). Herein, the MoS₂-SnO₂ heterostructures were encapsulated into carbon nanofibers (CNFs) via facile solvothermal and electrospinning methods. Remarkably, when the binder-free and robust MoS₂-SnO₂@CNF is employed as the anode for LIBs, such a clever structure yields a discharge capacity of 983 mA h g^-1 at a current density of 200 mA g^-1 after 100 cycles and a capacity of 710 mA h g^-1 after 800 cycles at a current density of 2000 mA g^-1. Moreover, full cells and flexible full cells were constructed, which exhibited high flexibility and delivered a high reversible capacity of 463 mA h g^-1 after 100 cycles at 500 mA g^-1. The exceptional performance of MoS₂-SnO₂@CNF could be attributed to the rational design of the electrode structure. On one hand, the robust structure of the amorphous SnO₂ and MoS₂ nanoflowers in the conductive carbon network not only provides direct current pathways, but also enhances electron transfer. On the other hand, the abundance of p-n heterogeneous interfaces considerably reduces the charge transfer resistance and enhances the surface reaction kinetics. This work proposes a feasible strategy to enhance the capacity and stability of SnO₂-based electrodes and opens up a new avenue for the potential applications of SnO₂ anode materials.

Free-Standing Selenium Impregnated Carbonized Leaf Cathodes for High-Performance Sodium-Selenium Batteries

A novel approach of carbonizing leaves by thermal pyrolysis with melt diffusion followed by selenium vapor deposition is developed to prepare the carbon-selenium composite cathodes for sodium-selenium batteries. The carbonized leaf possesses internal hierarchical porosity and high mass loading; therefore, the composite is applied as a binder- and current collector-free cathode, exhibiting an excellent rate capability and a high reversible specific capacity of 520 mA h g^-1 at 100 mA g^-1 after 120 cycles and 300 mA h g^-1 even at 2 A g^-1 after 500 cycles without any capacity loss. Moreover, the unique natural three-dimensional structure and moderate graphitization degree of leaf-based carbon facilitate Na⁺/e^- transport to activate selenium which can guarantee a high utilization of the selenium during discharge/charge process, demonstrating a promising strategy to fabricate advanced electrodes toward the sodium-selenium batteries.

Template synthesis of the Cu2O nanoparticle-doped hollow carbon nanofibres and their application as non-enzymatic glucose biosensors

The cuprous oxide nanoparticle (Cu₂O NP)-doped hollow carbon nanofibres (Cu₂O/HCFs) were directly synthesized by the anodic aluminium oxide (AAO) template. The doped Cu₂O NPs were formed by in situ deposition by direct reduction reaction of precursor carbonization in thermal decomposition and could act as functionalized nanoparticles. The synthesized Cu₂O/HCFs were characterized in detail by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and inductively coupled plasma mass spectrometry (ICP-MS). The results reveal that Cu₂O/HCFs have a tubular structure with an average diameter of approximately 60 nm. The shape of the Cu₂O/HCFs is straight and Cu₂O NPs are uniformly distributed and highly dispersed in HCFs. Cu₂O/HCFs have good dispersibility. The electrochemical activity of Cu₂O/HCFs was investigated by cyclic voltammetry (CV), the glucose sensors display high electrochemical activity towards the oxidation of glucose. Cu₂O/HCFs can effectively accelerate the transmission of electrons on the electrode surface. Cu₂O/HCFs are applied in the detection of glucose with a detection limit of 0.48 µM, a linear detection range from 7.99 to 33.33 µM and with a high sensitivity of 1218.3 µA cm^-2 mM^-1. Moreover, the experimental results demonstrate that Cu₂O/HCFs have good stability, reproducibility and selectivity. Our results suggest that Cu₂O/HCFs could be a promising candidate for the construction of non-enzymatic sensor.

Optimum Preferential Oxidation Performance of CeO2-CuO x-RGO Composites through Interfacial Regulation

Interfacial regulation offers a promising route to rationally and effectively design advanced materials for CO preferential oxidation. Herein, we initiated an interfacial regulation of CeO₂-CuO _x-RGO composites by adjusting the addition sequence of the components during the support formation. The presence of RGO along with the sequence tuning of the components is confirmed to survey the changes of the oxidation state of copper species, the content and distribution of the Cu⁺ site, and the synergistic interactions between Cu-Ce mixed oxides and reduced graphene oxide (RGO) over the catalysts. These catalysts were systematically characterized by inductively coupled plasma, X-ray diffraction, transmission electron microscopy/high-resolution transmission electron microscopy, hydrogen temperature-programmed reduction, X-ray photoelectron spectra, thermal gravimetric analysis, Raman spectra, and in situ diffuse reflectance infrared Fourier transform spectroscopy measurements. The results show that RGO is favorable for the generation of Cu⁺ and the dispersion of copper-cerium species in the as-prepared catalysts. Furthermore, by multi-interfacial regulation of the CeO₂-CuO _x-RGO composites, the catalyst CeO₂/CuO _x-RGO exhibits a strikingly high catalytic oxidation activity at a low temperature coupled with a broader operation temperature window (i.e., CO conversion >99.0%, 140-220 °C) in the CO-selective oxidation reaction, which has been attributed to the high content of the active species Cu⁺ enriched on the surface, the highly dispersed copper oxide clusters subjected to a strong interaction with ceria, and the synergistic interactions between Cu-Ce mixed oxides and RGO.

The influence of copper addition on the electrical conductivity and charge transfer resistance of reduced graphene oxide (rGO)

The possible explanations on how the existence of copper, CuO, or Cu₂O influences the electrical conductivity and electrochemical properties of rGO.