Co3O4 Nanosheets Research Articles

Porous Co3O4 nanosheets as a high-performance non-enzymatic sensor for glucose detection.

Novel porous Co3O4 nanosheets (NSs) were synthesized on the flexible carbon cloth (CC) substrate by a facile hydrothermal method and applied to construct a non-enzymatic sensor for glucose detection. The sensor is based on the electro-catalytic oxidation of glucose on the surface of Co3O4 NSs. Since this particular nanostructure can provide large surface area and more active sites, the Co3O4 NSs non-enzymatic sensor exhibits excellent analytical performance, such as a high sensitivity (8506μAmM-1cm-2), a fast response time (less than 6s), low detection limit of 1μM, good selectivity, and long-term stability. The results suggest that the porous Co3O4 NSs have great potential applications in the development of sensors for enzyme-free detection of glucose.

Transforming Co3O4 nanosheets into porous N-doped Co O nanosheets with oxygen vacancies for the oxygen evolution reaction

Cobalt oxides have been widely investigated as promising replacements for noble metal-based catalysts for oxygen evolution reaction (OER). Herein, we, for the first time, have obtained porous CoxOy nanosheets with N-doping and oxygen vacancies by etching Co3O4 nanosheets with NH3 plasma. Comparing with the pristine Co3O4 nanosheets (1.79 V), the porous CoxOy nanosheets with N-doping and oxygen vacancies have a much lower potential of 1.51 V versus RHE to reach the current density of 10 mA cm−2. The obtained sample has a lower Tafel slope of 68 mV dec−1 than the pristine Co3O4 nanosheets (234 mV dec−1). The disclosed Co2+, which is responsible for the formation of active sites (CoOOH), N-doping and oxygen vacancies, gives rise to better performance of OER.

Design of porous Co3O4 nanosheets via one-step synthesis as high-performance anode materials for lithium-ion batteries

The morphology of Co-based zeolitic imidazolate framework is affected by the molar ratio of 2-methylimidazole and Co2+ used during the synthesis. In this study, we found that by further controlling the molar ratio of 2-methylimidazole and Co2+, hexagonal Co(OH)2 nanosheets can by formed. By calcination of such Co(OH)2 nanosheets, the original two-dimensional morphology was maintained and hierarchical pores were formed with 2-methylimidazole as the porogen. Such porous Co3O4 nanosheets exhibited good electrochemical performance and delivered a high specific capacity of 850 mAh g−1 at current density of 300 mA g−1 after 100 cycles when used as anode of lithium-ion batteries.

Graphene as an electrochemical transfer layer

The capability of graphene to adopt a property from an adjacent material is investigated by measuring the electrochemical performance of a monolayer graphene placed on top of thin cobalt oxide (Co3O4) nanosheets. In this assembly, monolayer graphene works as an interfacial layer which inhibits the direct contact of the actual electroactive material and electrolyte during electrochemical reaction. The results show that while graphene is electrochemically inert, it behaves as an active material to catalyze oxygen evolution reaction (OER) once placed on top of Co3O4 nanosheets. The graphene-covered Co3O4 model system shows electrochemical performance similar to Co3O4 indicating complete transference of the electrochemical property of the metal oxide to the graphene. Based on density functional theory (DFT) calculations, charge transfer from graphene to Co3O4 is the key factor for turning the electrochemically inactive graphene to an apparent active material.

Synthesis of Honeycomb-Like Co₃O₄ Nanosheets with Excellent Supercapacitive Performance by Morphological Controlling Derived from the Alkaline Source Ratio.

Honeycomb-like Co3O4 nanosheets with high specific surface area were successfully synthesized on porous nickel foam by the facile hydrothermal method followed by an annealing treatment (300 °C), which were used as high-performance supercapacitor electrodes. The effects of the mole ratio of hexamethylenetetramine (HMT) and Co(NO3)2 (1:1, 2:1, 3:1, 4:1, 5:1 and 6:1) as the reactants on the morphological evolution and electrochemical performance of the electrodes were investigated in detail. X-ray diffractometry (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM) were applied to characterize the structure and morphology of the products. The electrochemical performance was measured by cyclic voltammetry (CV) and galvanostatic charge/discharge. The mole ratio of HMT and Co(NO3)2 produced a significant effect on the morphological evolution of Co3O4. The morphological evolution of Co3O4 with the increase in the mole ratio was followed: the nanosheets accompanied with a large number of spherical nanoparticles → the formation of some strip-like particles due to the agglomeration of spherical nanoparticles → the formation of new nanosheets resulting from the growth of strip-like particles → the formation of coarse flower-like particles owing to the connection among the nanosheets → the nanosheets gradually covered with flower-like particles. Accompanied with the change, the specific surface area was increased firstly, and then decreased. A maximum was obtained at a HMT and Co(NO3)2 mole ratio of 4:1. The evolution in morphology of Co3O4 was responsible for the change in electrochemical performance of the electrode. The specific capacitance value of the electrode prepared at a HMT and Co(NO3)2 mole ratio of 4:1 was highest (743.00 F·g−1 at 1 A·g−1 in the galvanostatic charge/discharge test). The similar result was also observed in the CV test with a scanning rate of 5 mV·s−1. Moreover, the electrode also demonstrated an excellent cyclic performance, in which about 97% of the initial specific capacitance remained at 1 A·g−1 for 500 cycles in the galvanostatic charge/discharge test. This excellent electrochemical performance was ascribed to high specific surface area of Co3O4 nanosheets that provide added channels and space for the ions transportation.

Ionic-Liquid-Assisted One-Step Synthesis of CoO Nanosheets as Electrocatalysts for Oxygen Evolution Reaction.

The sluggish oxygen evolution reaction (OER) hinders the development of electrocatalytic water splitting for energy conversion and storage. Therefore, it is imperative to explore the cost-effective and highly efficient noble-metal-free electrocatalysts for OER. Herein, we are introducing such OER electrocatalyst based on Co, fabricated through an ionic-liquid-assisted one-step synthesis, where ionic liquid played a dual role as solvent cum structure-directing agent. Besides possessing large-accessible surface area and numerous active sites, the as-prepared stable CoO nanosheets exhibited excellent electrochemical activity through establishing an extensive contact with the electrolyte. Under alkaline conditions, the overpotential to achieve a current density of 10 mA cm–2 is only 320 mV, and the Tafel slope is as small as 70 mV dec–1. Thus, our work provides a new pathway for designing and engineering the highly efficient non-noble metal OER electrocatalysts by using ionic liquids.

Controllable 1D and 2D Cobalt Oxide and Cobalt Selenide Nanostructures as Highly Efficient Electrocatalysts for the Oxygen Evolution Reaction.

The relationship between controllable morphology and electrocatalytic activity of Co3 O4 and CoSe2 for the oxygen evolution reaction (OER) was explored in alkaline medium. Based on the time-dependent growth process of cobalt precursors, 1D Co3 O4 nanorods and 2D Co3 O4 nanosheets were successfully synthesized through a facile hydrothermal process at 180 °C under different reaction times, followed by calcination at 300 °C for 2 h. Subsequently, 1D and 2D CoSe2 nanostructures were derived by selenization of Co3 O4 , which achieved the controllable synthesis of CoSe2 without templating agents. By comparing the electrocatalytic behavior of these cobalt-based catalysts in 1 m KOH electrolyte toward the OER, both 2D Co3 O4 and 2D CoSe2 nanocrystals have lower overpotentials and better electrocatalytic stability than that of 1D nanostructures. The 2D CoSe2 nanosheets require overpotentials of 372 mV to reach a current density of 50 mA cm-2 with a small Tafel slope of 74 mV dec-1 . A systematic contrast of the electrocatalytic performances for the OER increase in the order: 1D Co3 O4 <2D Co3 O4 <1D CoSe2 <2D CoSe2 . This work provides fundamental insights into the morphology-performance relationships of both Co3 O4 and CoSe2 , which were synthesized through the same approach, providing a solid guide for designing OER catalysts.

PEG-templated assembling of Co3O4 nanosheets with nanoparticles for enhanced sensitive non-enzymatic glucose sensing performance

The porous Co3O4 nanosheets have been prepared by a hydrothermal and subsequent calcination processes using polyethylene glycol as soft morphology controlled template. The morphology, structure, and composition of the materials were characterized by SEM, TEM, HRTEM, XRD and XPS. The as prepared Co3O4 have a porous sheet-like structure composed of nanoparticles with average diameter less than 100 nm. Moreover, the as-prepared Co3O4 nanosheets exhibited greatly improved electrochemical performance than that of Co3O4 spheres, which may be due to the porous sheet-like structures beneficial for high efficiency of charge transfer and analytes diffusion. The Co3O4 modified electrode exhibited excellent electrochemical performance with a wide linear range from 2 to 3420 µM, sensitivity of 745.26 µA mM− 1cm− 2 and detection limit of 0.65 µM. The higher electrocatalytic activity of Co3O4 nanosheets to glucose oxidation demonstrated it may be a favorable candidate for the development of non-enzymatic sensor.

Tailoring oxygen vacancy on Co3O4 nanosheets with high surface area for oxygen evolution reaction

Electrochemical water splitting requires efficient water oxidation catalysts to accelerate the sluggish kinetics of water oxidation reaction. Here, we designed an efficient Co3O4 electrocatalyst using a pyrolysis strategy for oxygen evolution reaction (OER). Morphological characterization confirmed the ultra-thin structure of nanosheet. Further, the existence of oxygen vacancies was obviously evidenced by the X-ray photoelectron spectroscopy and electron spin resonance spectroscopy. The increased surface area of Co3O4 ensures more exposed sites, whereas generated oxygen vacancies on Co3O4 surface create more active defects. The two scenarios were beneficial for accelerating the OER across the interface between the anode and electrolyte. As expected, the optimized Co3O4 nanosheets can catalyze the OER efficiently with a low overpotential of 310 mV at current density of 10 mA/cm2 and remarkable long-term stability in 1.0 mol/L KOH.

Soliton mode-locked thulium-doped fiber laser with cobalt oxide saturable absorber

Abstract In this work, we propose and demonstrate a mode-locked thulium doped fiber laser (TDFL) with an integrated cobalt oxide (Co3O4) saturable absorber (SA). The SA is fabricated by suspending Co3O4 nanosheets in a polymer film before being secured between two fiber ferules. The laser operates in the anomalous dispersion regime, confirmed by the Kelly sidebands observed in the obtained optical spectrum. Mode-locking operation is obtained at a low threshold pump power of 77.32 mW, with further optimizations made using a polarization controller The laser generates pulses with a repetition rate of 11.36 MHz and a pulse width of 1.39 ps. The generated pulses are highly stable, with a high signal-to-noise ratio of 46.00 dB and minimum power fluctuations indicating a long-term stability. This work demonstrates a simple and a low-cost laser that would have potential applications for operation near the 2.0-µm region, especially for medical applications.

A Single Energy Conversion and Storage Device of Cobalt Oxide Nanosheets and N-Doped Reduced Graphene Oxide Aerogel

The hybridization between energy conversion and energy storage materials in a single cell (HECS) is proposed in this work. The HECS cell consists of photoactive cobalt oxide (Co3O4) positive electrode as the energy conversion material and N-doped reduced graphene oxide aerogel (N-rGOAE) as the energy storage material. The photoactive Co3O4 nanosheets were prepared by using various calcination temperatures for which the in situ electrochemical XAS suggests that the Co3O4 nanosheets calcined at 300oC exhibit the highest change in oxidation state compared to other conditions. The HECS cell using photoactive Co3O4 film calcined at 300oC and N-rGOAE exhibits 1.7-fold higher specific capacitance under LED light illumination than that of the dark condition. Under white LED light illumination, the photovoltaic effect can be generated in the Co3O4 electrode with electron-hole pairs, while the N-rGOAE can balance all the charges generated from the Co3O4 via both electrochemical double-layer and pseudocapacitive behaviours.

Co3O4@CoNi-LDH core/shell nanosheet arrays for high-performance battery-type supercapacitors

Co3O4@CoNi-layered double hydroxide (LDH) core/shell nanosheet array on Ni foam was prepared as an integrated battery-type electrode for supercapacitors by growth of CoNi-LDH nanosheets shell on the surface of Co3O4 plates core. The resulting composite material exhibits high specific capacitance (2676.9 F g−1 at 0.5 A g−1) and excellent cycling stability. The improved electrochemical behavior is benefited from the typical mesoporous structure, which shorten the diffusion distance of OH− in the electrolyte and the strong core/shell binding interaction among Co3O4 and CoNi-LDH nanosheet arrays. Additionally, an assembled asymmetric supercapacitor (ASCs) device using as-fabricated Co3O4@CoNi-LDH as positive electrode and activated carbon (AC) as negative electrode also exhibits a high energy density of 61.23 Wh kg−1 at a high power density of 750 W kg−1, furthermore, still remains 24.8 Wh kg−1 even at a higher power density of 7500 W kg−1. Most importantly, a red light-emitting diode (LED) can be illuminated by two connected ASCs, indicating that as-synthesized Co3O4@CoNi-LDH possesses great potential for practical applications. As a result, this work demonstrates a feasible strategy for the design and fabrication of metal oxides/LDH composites for applications in energy storage systems.

Gradual “OH−-incursion” outside-inside strategy in construction of 3D flower-like Co3O4-CNT>N-PEGm hierarchical microspheres for supercapacitors

We have synthesized a novel dodecyl benzene sulfate (DBS)-intercalated 3D flower-like α-Co(OH)2-CNT>N-PEGm hierarchical microsphere composites as the precursor by a gradual “OH−-incursion” with an outside-inside strategy, in which the incorporating CNT>N-PEGm were modified by Nitrene Chemistry with the methoxypolyethylene glycol (mPEG). Based on the sintering process, the Co3O4-CNT>N-PEGm composites exhibit close function of CNT>N-PEGm with Co3O4 nanostructures, due to the coordination bonds formed between the lone pair of electrons on ether-oxygen groups of the polymer chains on the CNTs surface and cobalt ions. Moreover, the as-prepared Co3O4-CNT>N-PEGm can provide a range of hierarchical mesoporous as short ion-diffusion channels in the Co3O4 nanosheets at the exterior of the composites, meanwhile the CNT>N-PEGms provide electron transport channels to improve the electron transport in the interior of Co3O4 microspheres. Hence, the high specific capacitance value of 1513.2 F g−1 at a current density of 0.5 A g−1 was achieved for Co3O4-CNT>N-PEGm in 6 M KOH solution. Furthermore, an asymmetric supercapacitor fabricated with Co3O4-CNT>N-PEGm as positive electrode material and active carbon as negative electrode material showed an excellent capacitance of 119.9 F g−1 at a current density of 0.5 A g−1 and an energy density of 42.6 Wh kg−1 at the power density of 400 kW kg−1.

Co3O4 Nanosheet Arrays on Ni Foam as Electrocatalyst for Oxygen Evolution Reaction

Co3O4 nanosheet arrays on Ni foam (Co3O4 NS/NF) were designed, fabricated, and utilized as electrocatalysts for electrochemical oxygen evolution reaction (OER). The electrocatalytic performance of the Co3O4 NS/NF for OER was systematically evaluated by cyclic voltammetry, linear polarization, and Tafel curve measurements. Compared to the bare Ni foam, free-standing Co3O4 nanosheets, and commercialized Pt/C electrodes, Co3O4 NS/NF exhibits excellent OER activity in water-alkaline electrolyte with low onset overpotential (~ 50 mV), large anodic current density, and excellent durability. The compatible electrocatalytic activity for OER of the Co3O4 NS/NF is attributed to the unique nanosheet structure and the interconnected nanoarrays configuration of Co3O4 that provides plentiful catalytic active sites, in addition to the inherent catalytic activity of Co3O4. The electron transportation capability of the supporter Ni foam makes the composite a potential electrocatalyst for OER.

High-performance solid state asymmetric supercapacitor based on electrochemically decorated 3D network-like Co3O4 architecture on NiO nanoworms

The unique 3D network-like cobalt oxide architecture was electrochemically deposited on nickel oxide nanoworms (NiONWs) with nickel foil (NF) substrate. After the anodic polarization of NF and its activation, a very thin film of NiO nanoworms with the average diameter of 30 nm and the length of 100 nm was successfully grown on anodized Ni foil (a-NF) by using a facile hydrothermal method under the mild conditions including a saturated alkaline solution of Ni2+ at 65 °C to prepare a-NF/NiONWs. Then, 3D network-like Co3O4 nanosheets with the average thickness of 25 nm were directly electrodeposited on a-NF/NiONWs by using cyclic voltammetry under the optimized experimental conditions. The morphologies and detailed geometrical structures of the electrodes were conducted by FE-SEM. The fabricated a-NF/NiONWs/Co3O4 electrode provides a high areal specific capacitance of 1320 mF cm-2 at a current density of 4 mA cm−2 and high mass specific capacitance of 2000 F g−1 at the current density of 6 A g−1. By using a-NF/NiONWs/Co3O4 as a positive electrode and reduced graphene oxide-deposited NF (RGO/NF) as a negative electrode, a solid-state asymmetric a-NF/NiONWs/Co3O4//RGO/NF supercapacitor was assembled and it exhibited a high specific capacitance of 471.4 mF cm-2 at a current density of 3 mA cm−2. The fabricated solid-state supercapacitor also showed good rate capacity and long-term cycling performance of 2000 cycles.

Platinum Cluster/Nanoparticle on CoO Nanosheets with Coupled Atomic Structure and High Electrocatalytic Durability

Seeking electrocatalysts with a low Pt content, high activity, and durability in oxygen reduction reaction (ORR) remains one major challenge for fuel cell applications. Herein, by chemical dealloying of AlCoPt ternary alloys, CoO nanosheets with evenly doped ultrasmall Pt clusters/nanoparticles have been obtained. Thanks to the coherent atomic structure between CoO and Pt, the Pt-doped CoO (Pt/CoO) can work stably for ORR in 0.1 M HClO4 after tens of thousands of electrochemical cycles and exhibits a 13.5-fold enhancement in the electrochemically active surface area normalized ORR activity over that of commercial Pt/C catalyst.

Co3 O4 Nanosheets as Active Material for Hybrid Zn Batteries.

The rapid development of electric vehicles and modern personal electronic devices is severely hindered by the limited energy and power density of the existing power sources. Here a novel hybrid Zn battery is reported which is composed of a nanostructured transition metal oxide-based positive electrode (i.e., Co3 O4 nanosheets grown on carbon cloth) and a Zn foil negative electrode in an aqueous alkaline electrolyte. The hybrid battery configuration successfully combines the unique advantages of a Zn-Co3 O4 battery and a Zn-air battery, achieving a high voltage of 1.85 V in the Zn-Co3 O4 battery region and a high capacity of 792 mAh gZn-1 . In addition, the battery shows high stability while maintaining high energy efficiency (higher than 70%) for over 200 cycles and high rate capabilities. Furthermore, the high flexibility of the carbon cloth substrate allows the construction of a flexible battery with a gel electrolyte, demonstrating not only good rechargeability and stability, but also reasonable mechanical deformation without noticeable degradation in performance. This work also provides an inspiring example for further explorations of high-performance hybrid and flexible battery systems.

Porous Cobalt Oxynitride Nanosheets for Efficient Electrocatalytic Water Oxidation.

Exploring efficient and cheap oxygen evolution reaction (OER) electrocatalysts is of great significance for electrochemical water splitting. Herein, we successfully prepared an efficient ternary electrocatalyst of porous cobalt oxynitride (Co3 Ox Ny ) nanosheets by a simple nitridation strategy. Specifically, CoON PNS-400 (cobalt oxynitride with porous nanosheet structure obtained at 400 o C) offered a low OER overpotential of 0.23 V to achieve the catalytic current density of 10 mA cm-2 and a small Tafel slope of 48 mV dec-1 in alkali media, outperforming most of the first-row transition-metal-based OER electrocatalysts. The calculated density of states (DOS) analysis and electron spin resonance (ESR) measurements revealed that the introduction of foreign N atoms into pristine Co3 O4 nanosheets can optimize the electronic structure and create more oxygen vacancies, thus leading to enhanced electrical conductivity. Density functional theory (DFT) calculations demonstrated that the foreign N atoms can also improve the energetics for OER by modulating the free energy for adsorbed intermediates (OOH*, OH*, O*), further improving the OER electrocatalytic activity of CoON PNS-400. This work provides a possibility for rationally designing ternary transition-metal compounds as advanced OER electrocatalysts.

Wet chemical synthesis of S doped Co3O4 nanosheets/reduced graphene oxide and their application in dye sensitized solar cells

Despite the fact that Co3O4 nanomaterials have gained much attention due to their excellent electrochemical properties, the poor conductivity and catalytic reduction ability for I3− ion hinder their application as counter electrode (CE) of dye sensitized solar cells (DSSCs). Herein, a facile ion exchange approach is developed to prepare S-doped Co3O4 nanosheet. S doping strategy significantly improves the catalytic activity of Co3O4 nanosheets for the reduction of I3− ion and their charge transport ability. For the sake of doping S into Co3O4 and rGO simultaneously, the similar wet chemical process is adopted in the presence of graphene oxide (GO) to synthesize S-doped Co3O4/reduced graphene oxide (rGO) composites. The power conversion efficiency (PCE) of Co3O4-DSSC is only 1.98%. Using S-doped Co3O4 as CE, the PCE can be dramatically improved to 6.76%. Moreover, the S-doped Co3O4/rGO-DSSC shows higher PCE (8.24%) than that of Pt (7.79%). Electrochemical measurement results indicate that the S-doped Co3O4/rGO composites not only show excellent electrocatalytic activity, but also show high cycling stability. The outstanding improved performance of DSSCs with S-doped Co3O4 nanosheet and S-doped Co3O4/rGO composite as CEs demonstrates that the surface atomic configurations of CE materials have significant influence on their electrocatalytic activity.

Enhanced performance of solid-state Li–O2 battery using a novel integrated architecture of gel polymer electrolyte and nanoarray cathode

The present work proposes a novel strategy to fabricate an integrated architecture of gel polymer electrolyte (GPE)–nanoarray cathode for lithium–O2 batteries (LOBs). As a proof-of-concept experiment, the photo-initiated in situ polymerization of GPE was carried out via incorporating the precursor solution in advance into a self-standing binder-free oxygen electrode of Co3O4 nanosheets array grown on carbon cloth (Co3O4@CC), forming an integrated GPE–Co3O4@CC architecture. The performance of the solid-state LOBs using the GPE–Co3O4@CC assembly is greatly enhanced compared to the counterparts with a traditional cell structure, in which GPE was sandwiched by a lithium metal and a cathode. The enhanced performance is ascribed to the combination of the in situ polymerization of GPE and the versatile structure of nanoarray electrode, which results in abundant interfacial contacts between GPE and electrode. This work presents an alternative way to develop high-performance solid-state LOBs by combining the advantages of both gel polymer electrolytes and nanoarray electrodes.