Co3O4 Nanosheets Research Articles

Template-free Synthesis of Mesoporous and Crystalline Transition Metal Oxide Nanoplates with Abundant Surface Defects

Summary Mesoporous transition metal oxides with crystalline walls show promising applications in catalysis and energy storage. Syntheses of those crystalline mesoporous oxides, however, currently remain as an unmet challenge because of the large volume shrinkage during crystallization in a sol-gel process. Here, we demonstrate a facile and general template-free method to prepare six mesoporous transition metal oxides, e.g., CuO, CoO, and spinel MCo2O4 (M = Co, Cu, Mn, Zn), with highly crystalline walls and continuous mesopores in the forms of two-dimensional nanoplates or nanosheets. The method is based on the thermal crystalline transformation from basic carbonates to mesoporous metal oxides. The crystal interconversion not only endows the crystallinity and mesoporosity of oxides but also generates abundant surface-step defects that show remarkable enhancement of the catalytic activity of porous oxides. Our method likely provides an alternative paradigm for cost-effective and universal synthesis of crystalline mesoporous oxides beyond the traditional templating methods.

Non‐enzymatic glucose sensor based on three‐dimensional hierarchical Co 3 O 4 nanobooks

A new non-enzymatic glucose sensor is demonstrated successfully, based on three-dimensional (3D) hierarchical Co3O4 nanobooks (Co3O4 NBs). The 3D hierarchical Co3O4 NBs are assembled with porous and high crystalline 2D Co3O4 nanosheets. The electrochemical measurements reveal that the device exhibits outstanding performance for glucose detection, achieving a maximal sensitivity of 1068.85 μA mM−1cm−2 with a high R 2 of 0.9836, a low detection limit of 7.94 μM with a signal-to-noise of 3 and wide linear range up to 6 mM. The results demonstrate that the non-enzymatic glucose sensor can respond swiftly and selectively to glucose due to the high electrocatalytic activity of the 3D hierarchical Co3O4 NBs. The sensor also shows its high sensitivity and selectivity in detecting glucose in blood serum, confirming the practical application of the device with appealing accuracy.

1D/2D Cobalt‐Based Nanohybrids as Electrocatalysts for Hydrogen Generation

AbstractThe synergistic effects derived from optimizing the chemical and structural features of electrocatalysts permit them to attain remarkable activity and stability. Herein, 1D/2D cobalt‐based nanohybrid (CoNH) electrodes are developed; the structural design consists of Co3O4 electrospun nanoribbons (NRs) deposited onto a carbon fiber paper substrate where Co3O4 nanosheets are subsequently grown via an electrodeposition step and UV/ozone treatment. The content of noncovalently functionalized carbon nanotubes within the Co3O4 NRs is first tuned to enhance their charge transfer properties and mechanical stability. The electrocatalytic activity of the electrodes is further improved by a phosphorus modification of the 1D NRs, resulting in the formation of NaCoPO4. The optimized 1D/2D CoNH electrode, i.e., ED‐0.09 wt% fCNTs/P‐CoNHs, displays a similar performance to that of platinum in 0.25 m Na2S/0.35 m Na2SO3 (Tafel slope ≈102 mV dec−1 for the former and ≈96 mV dec−1 for the latter) and outstanding stability for up to 48 h. The versatility and high activity of this electrode is also demonstrated according to tests in a conventional water splitting system (cell voltage 1.55V, to produce 10 mA cm−2) and a solar‐driven electrolyzer (1 m KOH).

Ionic liquid-derivatized hierarchical N-doped carbon-coated Co3O4 nanosheet array as high-performance anode materials for lithium-ion batteries

A novel nitrogen-doped carbon-coated graded Co3O4 nanosheets (NDC/Co3O4 NS) is synthesized by using a simple ionic liquid hydrothermal method. The as-prepared NDC/Co3O4 NS is composed of hexagonal nanosheets having different orientation and the thickness of 50–100 nm. Significantly, as an anode electrode for lithium-ion batteries (LIBs), the NDC/Co3O4 NS performed excellent cyclability. The NDC/Co3O4 NS delivers an initial discharge capacity of 1281.4 mAh g−1 at 445 mA g−1 and maintains a reversible high capacity of 929.4 mAh g−1 after 50 cycles, much higher than the unmodified Co3O4 nanosheets (230 mAh g−1). The superior excellent electrochemical performance can be attributed to the gradient structure and the nitrogen-doped carbon coating resulting in shorter ion transport distances and good electrical conductivity.

Highly sensitive electrochemical sensing platform: carbon cloth enhanced performance of Co3O4/rGO nanocomposite for detection of H2O2

Co3O4 is often used to detect H2O2. However, there are many problems such as low sensitivity and the long detection time when detecting H2O2 in various cobalt oxide composites. Therefore, it is a great challenge to develop different morphologies of the Co3O4 electrode to improve the detection performances of H2O2 effectively. In this paper, we had successfully prepared a novel Co3O4/reduced graphene oxide/carbon cloth (Co3O4/rGO/CC) composite. We used a simple template method. Co3O4 nanosheets with a diameter of about 47.7 nm were obtained by using graphene oxide as a template. Then, CC was used as a three-dimensional conductive support material. CC can inhibit the agglomeration of rGO to increase specific surface area and to enhance the conductivity of Co3O4. In this study, the electrochemical performances of the Co3O4/rGO/CC electrode were tested by the electrochemical workstation. The trigger response of the modified electrode was reduced by 0.067% and the relative standard deviation was 0.013% after 30 consecutive tests. The range of linearity was 0.387–63.523 mM. Besides, this electrode has the limit of detection (0.022 μM) and a higher sensitivity (0.9683 mA mM−1 cm−2). It indicated that the electrode has excellent electrochemical sensing performance and high stability. These excellent performances are mainly due to the synergistic effect of Co3O4 nanosheets, rGO, and CC.

Scalable and controlled synthesis of 2D nanoporous Co3O4 from bulk alloy for potassium ion batteries

ABSTRACT Potassium has attracted enormous attention as the promising resourceful alternative to lithium for rechargeable batteries. However, the developing of high-energy electrode materials remains a key challenge for potassium-ion batteries (KIBs). Herein, 2D nanoporous cobaltosic oxide (Co3O4) is synthesised by scalable chemical dealloying methods from bulk Al–Co alloy. It is found that the morphology of Co3O4 can be controlled by adjusting the dealloying time. As anode materials for KIBs, the as prepared Co3O4 nanosheets delivered a reversible capacity of 417 mA h g−1 at a constant current density of 89 mA g−1 and a good capacity retention even after 300 cycles. The special 2D nanoporous structure is beneficial to buffer volume expansion and enhance ionic diffusion, which is accounted for the good electrochemical performance. The synthesis method and the special structure may be interesting for researchers in other fields such as supercapacitor, catalyst, and sensors.

Layered hydrotalcite derived holey porous cobalt oxide nanosheets coated with nitrogen-doped carbon for high-mass-loading Li-ion storage

Transition metal oxides are promising for Li-ion batteries but suffer from sluggish Li-ion storage in thick electrodes. This work achieves high-mass-loading Li-ion storage by forming holey porous structures in CoO nanosheets using layered hydrotalcites as starting materials.

Integrating hierarchical porous nanosheets in the design of carbon cloth-based sandwiched sulfur cathodes to achieve high areal capacity in lithium sulfur batteries

Due to Co3O4 nanosheets grown on carbon fiber surface and within inter-fiber spaces (as shown in the graph), sulfur cathodes integrating the modified carbon cloth (CC@pCo3O4) demonstrate a superior areal capacity than most of previously reported CC-based sulfur cathodes.

Ultralow loading of nanostructured Mn species onto two-dimensional Co3O4 nanosheets for selective catalytic reduction of NOx with NH3

We report a facile method for dispersing Mn species onto two-dimensional Co3O4 nanosheets at the nanoscale for the selective catalytic reduction (SCR) of NOx with NH3.

Electrochemical removal of nitrate using a nanosheet structured Co3O4/Ti cathode: Effects of temperature, current and pH adjusting

Co3O4 nanosheet film is synthesized through electrodeposition and used as cathode in electrochemical NO3– removal. The electrodeposition conditions are optimized and the NO3– removal rate is enhanced by 1.7 times in comparison with Co3O4 solid particle cathode, which mainly results from its large surface area and high efficient electron transfer and utilization capacities. The effects of reaction temperature and current are then deeply investigated. NO3– removal rate is enhanced from 0.00667 min−1 to 0.0156 min−1 at 0.08 A with reaction temperature rising from 5 °C to 45 °C, and it can further be enhanced to 0.0220 min−1 with current increasing to 0.16 A. Furthermore, the physical properties of Co3O4 nanosheet cathode are more stable during the reaction at high temperature. Low reaction temperature not only destroys nanosheet structure, but also changes the ratio of Co2+/Co3+ and the numbers of oxygen vacancy and lattice oxygen. Almost 60% TN removal is obtained under 0.16 A at 45 °C, however, most of which is obtained through NH3 escape instead of N2 generation. Adjusting the pH around neutral condition during the reaction can effectively fix NH3 in solution. The NH3 can then be oxidized to N2 in the presence of certain amount of Cl−.

Hierarchical porous arrays of mesoporous Co3O4 nanosheets grown on graphene skin for high-rate and high-capacity energy storage

The rate capability of an anode material is limited by slow Li-ion diffusion dynamics within the bulk, which leads to slow charging rates and low power densities in Li-ion batteries. To address this issue, we fabricated novel 3D hierarchical porous oxide arrays composed of mesoporous Co3O4 nanosheets grown on a thin layer of reduced graphene oxide “skin” as a stable buffering and conducting layer. The porous oxide-graphene hybrid anode shows the outstanding rate capability (∼1400 mAh g−1 at 2.0 A g−1) among all oxide anode materials, high cycling stability and high retention of 84.5% over 200 cycles. Besides, the anode material in sodium-ion batteries also delivers a high capacity of 757 mAh g−1 and a high retention of 89.7% over 400 cycles. The high electrochemical performances are mainly due to mesoporous Co3O4 nanosheets provide abundant accessible sites for electrolyte diffusion and intercalation of Li+/Na+ ions into the active phases while the graphene coating dramatically boosts the overall Li/Na storage performances of the Co3O4 nanosheets by enhancing the binding to and electrical contact with the current collector. Kinetic analysis reveals that the rational integration of battery-type and capacitor-type electrochemical energy storage in the same anode material (the distinct 3D hierarchical porous structure) enables to offer excellent rate capability. This novel graphene-metal oxide nanopore array could be applied in high-performance Li-ion and Na-ion batteries.

Hybrid architecture design enhances the areal capacity and cycling life of low-overpotential nanoarray oxygen electrode for lithium–oxygen batteries

Abstract Transition metal oxide (TMO) nanoarrays are promising architecture designs for self-supporting oxygen electrodes to achieve high catalytic activities in lithium-oxygen (Li−O2) batteries. However, the poor conductive nature of TMOs and the confined growth of nanostructures on the limited surfaces of electrode substrates result in the low areal capacities of TMO nanoarray electrodes, which seriously deteriorates the intrinsically high energy densities of Li−O2 batteries. Herein, we propose a hybrid nanoarray architecture design that integrates the high electronic conductivity of carbon nanoflakes (CNFs) and the high catalytic activity of Co3O4 nanosheets on carbon cloth (CC). Due to the synergistic effect of two differently featured components, the hybrid nanoarrays (Co3O4−CNF@CC) achieve a high reversible capacity of 3.14 mA h cm−2 that cannot be achieved by only single components. Further, CNFs grown on CC induce the three-dimensionally distributed growth of ultrafine Co3O4 nanosheets to enable the efficient utilization of catalysts. Thus, with the high catalytic efficiency, hybrid Co3O4−CNF@CC also achieves a more prolonged cycling life than pristine TMO nanoarrays. The present work provides a new strategy for improving the performance of nanoarray oxygen electrodes via the hybrid architecture design that integrates the intrinsic properties of each component and induces the three-dimensional distribution of catalysts.

Synergistic coupling of NiCo2O4 nanorods onto porous Co3O4 nanosheet surface for tri-functional glucose, hydrogen-peroxide sensors and supercapacitor

Spinel-oxide-based mixtures have been explored for rapid and efficient biological molecule detection and energy storage applications. Porous Co3O4 nanosheets were used as growth sites, where NiCo2O4 nanorods were anchored to the Co3O4 surface to form porous Co3O4–NiCo2O4 nanosheets to achieve accurate glucose or hydrogen-peroxide monitoring and potential supercapacitor applications. The nanostructure and composition were confirmed by scanning-electron microscopy, transmission-electron microscopy and X-ray photoelectron spectroscopy. Under optimal preparation and sensing conditions, porous Co3O4–NiCo2O4 nanosheets exhibited a preeminent sensitivity towards glucose oxidation (1463.13 μA mM−1cm−2) and hydrogen-peroxide reduction (303.42 μA mM−1cm−2), with a low detection limit of 0.112 μM and 0.596 μM, respectively, and a good selectivity and reproducibility. Such porous mixture-coated Ni foam electrodes are suitable for supercapacitor performances with a high specific capacitance of 1041.2 F/g at a current density of 2 A/g and no obvious capacitance attenuation after 5000 cycles at a current density of 5 A/g, which will promote the exploration of nanocomposites in multi-purpose fields.

Phosphate ion functionalized Co3O4 nanosheets/RGO with improved electrochemical performance

By using surfactants P123 as directional growth agent of Co(OH)2 nanosheets, Co3O4 nanosheet/reduced graphite oxide (RGO) hybrid material was prepared by calcining precursor Co(OH)2/graphite oxide (GO) at 275 °C for 2 h and followed by thermal annealing at 500 °C for 1.5 h in Ar atmosphere. With a mass ratio of Co3O4/RGO to NaH2PO2·H2O being 10, phosphate-ion functionalized Co3O4 nanosheets/RGO (denoted as P-Co3O4/RGO-10) was finally prepared by phosphating treating Co3O4/RGO at 225 °C for 30 min. The phase transition from Co(OH)2 nanosheets to Co3O4 nanosheets was a topochemical process and Co3O4 nanosheets with porous characteristic were uniformly dispersed on the surface of RGO. Phosphating treatment not only improved the surface reaction activity of Co3O4 nanosheets and rate performance of the obtained electrode materials, but also caused thin nanosheet pores favorable to the transport of electrolyte ions. P-Co3O4/RGO-10 hybrid electrode showed improved specific capacitance (448 F g-1) at a current density of 1 A g-1, extremely outstanding rate capability (78 %) at various current densities from 1 to 10 A g-1 and good cycling performance after continuous 5000 cycles. Phosphating treatment technology is an effective surface engineering technology to improve rate capability and specific capacitance for pseudocapacitive materials.

Two-dimensional Cd-doped porous Co3O4 nanosheets for enhanced room-temperature NO2 sensing performance

P-type Co3O4 has received ever-growing interest as a promising gas-sensing material due to the unique advantages of low-cost, earth abundance and considerable electrical conductivity at relatively low temperature. Herein, we designed and fabricated two-dimensional (2D) Cd-doped porous Co3O4 nanosheets through a microwave-assisted solvothermal method and subsequently in-situ annealing process. It is found that as-prepared 5 %-Cd-Co3O4-based gas sensor shows a significantly improved response value of 3.38 (Ra/Rg) and a relatively lower recovery time of 620 s for NO2 detection at room temperature (25 °C). Additionally, the sensor displays a wide detection range for NO2 detection low to 154 ppb (low theoretical limit of detection), outstanding selectivity compared with some volatile organic compounds, and excellent long-term stability for 6 months. The results of experiments and the corresponding Lewis acid-base theory reveal that the excellent room-temperature sensing performance is mainly promoted by the Cd dopant through a combined set of factors, including enhanced electronic conductivity, increased oxygen vacancy concentration and formed Co2+−O2− to improve NO2 adsorption. However, the further increased concentration of Cd2+ as Lewis acid sites will decrease the adsorption of NO2 that can benefit for improving recovery performance. Thus, the demonstration of such 2D Cd-doped porous Co3O4 nanosheets provides valuable insights for the p-type metal oxide semiconductor-based room-temperature gas sensors.

Room-temperature sulfurization for obtaining Co3O4/CoS core-shell nanosheets as supercapacitor electrodes

Creating a hybrid cobaltous-based oxide/sulfide core-shell composite is an effective strategy to improve the composites conductivity thus enhance the electrochemical performance of cobaltous oxide. By using Co3O4 nanosheets (NSs) as precursor, a room-temperature sulfurization for obtaining Co3O4/CoS core-shell NSs via anion exchange is developed which show better supercapacitor performance in contrast to the most high-temperature material process required in synthesis of CoS. The study demonstrates that the preceding step of introducing oxygen vacancies to Co3O4 by NaBH4 solution reduction is crucial, which allows S2− to facilitate entering the position of O2− in the solid phase successfully at room temperature. The as-obtained Co3O4/CoS NSs preserve the porous morphology and have larger accessible active surface area and better conductivity than those of Co3O4 and CoS composite. In this report, the Co3O4/CoS NSs exhibit an improved specific capacitance of 1658 F g−1 at 1 A g−1 which can be maintained at 92.3% after 10,000 cycles. The corresponding assembled asymmetric supercapacitor with activated carbon as anode displays a high energy density of 23.6 Wh kg−1 at a power density of 250 W kg−1.

Co3O4 nanosheet decorated nickel foams as advanced lithium host skeletons for dendrite-free lithium metal anode

Lithium metal batteries (LMBs) have been regarded as the most promising battery system for the next-generation high energy density batteries due to the extremely high specific capacity of the lithium (Li) metal anode. Unfortunately, the commercial application has been hindered by sharp dendrite Li growth and infinite relative volume change during the repeated charge/discharge process, which lead to severe safety issues and poor cyclability of the battery. Herein, a novel composite Lithium anode is fabricated via thermally infusion molten Li into three-dimensional (3D) nickel foam (NF) framework decorated by lithiophilic Co3O4 nanosheet arrays. The universalized growth of Co3O4 nanosheet on the Ni foam can provide superior wettability between the molten Li and Ni foam, and facilitate more convenient infusion process (5 s). Benefitting from uniform distribution of Li in the 3D host and homogeneous Li+ flux on the surface of the electrode, excellent Li stripping/plating performance (1000 h at 3 mA cm−2 and 275 h at 5 mA cm−2) and dendrite-suppressed morphology are achieved for the Li–Co3O4/NF composite anode. When utilized in full cells paired with a LiFePO4 cathode, the Li–Co3O4/NF composite anode demonstrates greater cyclability and rate performance than bare Li anode. As a result, the obtained Co3O4/NF demonstrates excellent electrochemical performance as a lithium host skeleton for advanced Li metal battery.

MOF-derived Co3O4 nanosheets rich in oxygen vacancies for efficient all-solid-state symmetric supercapacitors

Co3O4 is a promising pseudocapacitive material with a high theoretical capacity. We demonstrate herein a facile interfacial engineering toward Co-metal organic frameworks (Co-MOFs) derived Co3O4 nanosheets for improving the overall capacitive performance. Firstly, a thin hydrophilic carbon layer was coated onto carbon cloth (CC) to stablize the interfacial coordination effect between Co3O4 and carbon fibres. Secondly, oxygen vacancies by reducing Co3O4 was introduced to improve the electron and ions transfer on the interface between Co3O4 and electrolyte. The unique Co3O4 structure and composition endow the optimal v-Co3O4/CC composite with significantly improved specific capacity (414 C g−1 at 1 A g−1) and excellent stability (0.00174% capacity loss per cycle for 15000 cycles). Asymmetric supercapacitor by assembling v-Co3O4/CC composite as positive electrode with the same MOF derived carbon nanosheets as negative electrode demonstrates a high volumetric and gravimetric energy density of 0.74 mWh cm−3 (14.7 mW cm−3) and 45.3 Wh kg−1 (915 W kg−1), respectively. This work might provide a simple but efficient approach for boosting the pseudocapacitive performance of transition metal oxides.

Oxygen Vacancy-rich Porous Co3O4 Nanosheets toward Boosted NO Reduction by CO and CO Oxidation: Insights into the Structure-Activity Relationship and Performance Enhancement Mechanism.

Oxygen vacancy-rich porous Co3O4 nanosheets (OV-Co3O4) with diverse surface oxygen vacancy contents were synthesized via facile surface reduction and applied to NO reduction by CO and CO oxidation. The structure-activity relationship between surface oxygen vacancies and catalytic performance was systematically investigated. By combining Raman, X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, and O2-temperature programmed desorption, it was found that the efficient surface reduction leads to the presence of more surface oxygen vacancies and thus distinctly enhance the surface oxygen amount and mobility of OV-Co3O4. The electron transfer towards Co sites was promoted by surface oxygen vacancies with higher content. Compared with the pristine porous Co3O4 nanosheets, the presence of more surface oxygen vacancies is beneficial for the catalytic performance enhancement for NO reduction by CO and CO oxidation. The OV-Co3O4 obtained in 0.05 mol L-1 NaBH4 solution (Co3O4-0.05) exhibited the best catalytic activity, achieving 100% NO conversion at 175 °C in NO reduction by CO and 100% CO conversion at 100 °C in CO oxidation, respectively. Co3O4-0.05 exhibited outstanding catalytic stability and resistance to high gas hour space velocity in both reactions. Combining in situ DRIFTS results, the enhanced performance of OV-Co3O4 for NO reduction by CO should be attributed to the promoted formation and transformation of dinitrosyl species and -NCO species at lower and higher temperatures. The enhanced performance of OV-Co3O4 for CO oxidation is due to the promotion of oxygen activation ability, surface oxygen mobility, as well as the enhanced CO2 desorption ability. The results indicate that the direct regulation of surface oxygen vacancies could be an efficient way to evidently enhance the catalytic performance for NO reduction by CO and CO oxidation.

Ultrathin Co3O4 nanosheets anchored on multi-heteroatom doped porous carbon derived from biowaste for high performance solid-state supercapacitors

Low-cost multi-heteroatom doped porous carbons derived from agricultural waste were prepared as the base material. Then, the cobalt oxides nanosheets were anchored to the surface of the carbon material to obtain the composites. It was found that the adoption of porous carbon is of great significance for the improvement of materials properties. The presence of porous structure derived from carbon materials not only increases the stability of the material, but also facilitates the diffusion and transfer of electrolyte ions. Meanwhile, the flaky Co3O4 endows the material with high energy density and high charge transport efficiency. The resulted composite materials exhibit high specific surface area with low electrochemical impedance. Both aqueous and solid-state SCs were assembled separately. The energy density of aqueous SC can reach up to 42.5 Wh kg−1 at a power density of 746 W kg−1 and even with power density up to 30 kW kg−1 as the energy density still maintained 25 Wh kg−1. As for solid-state SC, the energy density can reach 40.6 μWh cm−2. The retention of solid-state SC can maintain at 87.1% even after 3000 cycle numbers. The excellent performance of composites enables them to be promising electrode materials for energy storage.