Ultrathin Co3O4 Research Articles

An ultrathin defect-rich Co3O4 nanosheet cathode for high-energy and durable aqueous zinc ion batteries

A facile solvothermal reduction strategy is demonstrated to introduce oxygen defects into ultrathin Co3O4 nanosheets (R–Co3O4), which function as an advanced cathode for Zn//Co batteries.

MOFs-derived ultrathin holey Co3O4 nanosheets for enhanced visible light CO2 reduction

Reducing carbon dioxide (CO2) to various value-added chemical products by photocatalysis could effectively alleviate the serious problems of global warming and energy shortages. Currently, most commonly prepared photocatalysts present poor performance under visible light irradiation. In this study, we adopted a facile, scalable and controllable approach to prepare ultrathin two-dimensional (2D) porous Co3O4 catalysts (Co3O4-NS) by air calcining of the ultrathin metal-organic framework (MOFs) nanosheet templates to validly reduce CO2 with a Ru-based photosensitizer under visible light irradiation. Benefitting from the structural nature of MOFs precursors, the calcined Co3O4-NS inherit the morphology of 2D and well-developed porosity, which support the transport of electrons, enhance the adsorption of CO2 molecules, and render abundant catalytic sites for CO2 activation. As a result, the CO generation rate is approximately 4.52 μmol·h−1 with selectivity of 70.1%, which is superior to the Co3O4 bulk catalysts (Co3O4-BK). Additionally, density functional theory (DFT) calculations reveal that the model of Co3O4 monolayer has stronger CO2 adsorption energy than that of the Co3O4 bulk, which is beneficial for the CO2-to-CO conversion. This MOF-engaged strategy provides new insight into the controlled synthesis of advanced ultrathin holey nanosheets to improve the efficiency of photocatalytic CO2 reduction.

Pulsed Electrodeposition of Co3 O4 Nanocrystals on One-Dimensional ZnO Scaffolds for Enhanced Electrochemical Water Oxidation.

Invited for this month's cover are the collaborative groups of Dr. Yun Hau Ng at University of New South Wales, Australia and Dr. Yiming Tang at South China Normal University, China. The front cover picture shows ultrathin Co3 O4 nanoflakes that are deposited on ZnO nanorods by pulsed electrodeposition. The performance of the nanostructured hybrid Co3 O4 /ZnO anode in electrochemical O2 evolution is better than that of neat Co3 O4 . Well-aligned one-dimensional ZnO nanorod arrays are integrated as a scaffold which functions as a "highway" to facilitate improved charge transfer, while the porosity of the anode material allows the penetration of the electrolyte, thus promoting efficient utilization of the catalytically active species. Read the full text of the article at 10.1002/cplu.201800218.

Ultrathin mesoporous shell Co3O4 hollow spheres as high-performance electrode materials for lithium-ion batteries

Ultrathin mesoporous shell Co3O4 hollow spheres (T-CO) as nanostructured anode materials for lithium-ion batteries are synthesized using carbon sphere@Co-glycolate via a solvothermal reaction, followed by calcination process of 400 °C at a heating rate of 2 °C min−1. T-CO is composed of ultrathin shell of ∼45 nm thickness with highly mesoporous morphology and wide void of ∼700 nm distance with vastly macroporous morphology, leading to superior electrochemical performance. T-CO delivers outstanding specific capacity of 1612 mA h g−1 at the 200th cycle at a high current density of 1.5 A g−1 without any apparent capacity fading. Moreover, with the increase in 10 cycles, T-CO delivers 1560, 1620, 1650, 1640, 1460, 1010, and 635 mA h g−1 at the various current densities of 0.5, 1, 1.5, 2.5, 5, 8 and 10 A g−1, and then still maintains around 1320 mA h g−1 at 1.5 A g−1 at the 90th cycle. The reasons for showing superior electrochemical performance are as follows: (i) ultrathin mesoporous shell and wide void facilitating the redox reaction, (ii) ultrathin shell with highly mesoporous morphology increasing electrochemical sites, and (iii) wide void accommodating severe volume change and storing electrolyte for facile mass transfer; thereby maintaining the morphological integrity.

Ultrathin Mesoporous Co3O4 Nanosheet Arrays for High-Performance Lithium-Ion Batteries.

Transition metal oxides, such as Co3O4, have attracted great attention for lithium-ion batteries (LIBs) due to their high theoretical capacity and satisfactory chemical stability. However, the slow kinetics of Li-ion and electron transport as well as poor cycling stability still largely restrains their applications. Here, we report the rational design of well-defined mesoporous ultrathin Co3O4 nanosheet arrays (NSAs) by topological transformation of layered double hydroxides nanosheet arrays (NSAs), which demonstrate significantly enhanced performance as anode for LIBs. The as-obtained Co3O4 NSAs with suitable thickness and abundant mesopores show excellent electrochemistry performance for LIBs, giving a high specific charge capacity of 2019.6 mAh g–1 at 0.1 A g–1, a good rate capability, and a remarkable cycling stability (1576.9 mAh g–1 after the 80th cycle), which is much superior to that of Co3O4 with thicker or thinner nanosheets as well as to that of the reported results. This facile strategy may be extended to the synthesis of other transition metal oxide NSAs, which can be potentially used in energy storage and conversion devices.

Ultrathin Co3O4 Nanomeshes for the Oxygen Evolution Reaction

Ultrathin transition-metal-based nanomeshes can perfectly combine the advantages of two-dimensional (2D) ultrathin nanosheets and porous nanostructures, which have wide applications in energy storage and conversion. In this work, we present an etch-free one-step approach to directly synthesize the ultrathin Co3O4 nanomeshes (Co-UNMs) by employing a CoCl2/K3Co(CN)6 cyanogel as the reaction precursor. The 2D planar structural unit and solid properties of the cyanogel result in the preferential assembly of generated crystal nuclei at the solid–liquid interface (i.e., cyanogel–solution interface) in the 2D direction, which plays a key role in the formation of nanomeshes. The as-prepared Co-UNMs with 1.5 nm thickness and abundant pores have high surface area and numerous defect atoms, resulting in enhanced activity for the oxygen evolution reaction (OER) in alkaline media, such as a low overpotential of 307 mV at 10 mA cm–2, a small Tafel slope of 76 mV dec–1, and attractive durability in 1 M KOH electrolyte.

Generalized Synthesis of Ultrathin Cobalt-Based Nanosheets from Metallophthalocyanine-Modulated Self-Assemblies for Complementary Water Electrolysis.

The development of effective approaches for preparing large-area, self-standing, ultrathin metal-based nanosheets, which have proved to be favorable for catalytic applications such as water electrolysis, is highly desirable but remains a great challenge. Reported herein is a simple and versatile strategy to synthesize ultrathin Co3 O4 and CoP NSs consisting of close-packed nanoparticles by pyrolyzing cobalt(II) phthalocyanine/graphene oxide (CoPc/GO) assemblies in air and subsequent topotactic phosphidation while preserving the graphene-like morphology. The strong π-π stacking interactions between CoPc and GO, and the inhibiting effect of the tetrapyrrole-derived macrocycle for grain growth during the catalytic carbon gasification contribute to the NSs forming. The resulting homologous Co3 O4 and CoP NSs display outstanding catalytic activity in alkaline media toward the oxygen evolution reaction and the hydrogen evolution reaction, respectively, ascribed to the richly exposed active sites, and the expedited electrolyte/ion transmission path. The integrated asymmetrical two-electrode configuration also presents a superior cell voltage of 1.63 V at 10 mA cm-2 for overall water splitting, accompanied with the excellent durability during long-term cycling. Further evidences validate that this strategy is appropriate to fabricate graphene-like ultrathin NSs of many other metal oxides, such as Fe2 O3 , NiO, MoO3 , and mixed-metal oxides, for various applications.

Green Fabrication of Ultrathin Co3O4 Nanosheets from Metal-Organic Framework for Robust High-Rate Supercapacitors.

Two-dimensional cobalt oxide (Co3O4) is a promising candidate for robust electrochemical capacitors with high performance. Herein, we use 2,3,5,6-tetramethyl-1,4-diisophthalate as a recyclable ligand to construct a Co-based metal-organic framework of UPC-9, and subsequently, we obtain ultrathin hierarchical Co3O4 hexagonal nanosheets with a thickness of 3.5 nm through a hydrolysis and calcination process. A remarkable and excellent specific capacitance of 1121 F·g-1 at a current density of 1 A·g-1 and 873 F·g-1 at a current density of 25 A·g-1 were achieved for the as-prepared asymmetric supercapacitor, which can be attributed to the ultrathin 2D morphology and the rich macroporous and mesoporous structures of the ultrathin Co3O4 nanosheets. This synthesis strategy is environmentally benign and economically viable due to the fact that the costly organic ligand molecules are recycled, reducing the materials cost as well as the environmental cost for the synthesis process.

Engineering 2D Nanofluidic Li‐Ion Transport Channels for Superior Electrochemical Energy Storage

Rational surface engineering of 2D nanoarchitectures-based electrode materials is crucial as it may enable fast ion transport, abundant-surface-controlled energy storage, long-term structural integrity, and high-rate cycling performance. Here we developed the stacked ultrathin Co3 O4 nanosheets with surface functionalization (SUCNs-SF) converted from layered hydroxides with inheritance of included anion groups (OH- , NO3- , CO32- ). Such stacked structure establishes 2D nanofluidic channels offering extra lithium storage sites, accelerated Li-ion transport, and sufficient buffering space for volume change during electrochemical processes. Tested as an anode material, this unique nanoarchitecture delivers high specific capacity (1230 and 1011 mAh g-1 at 0.2 and 1 A g-1 , respectively), excellent rate performance, and long cycle capability (1500 cycles at 5 A g-1 ). The demonstrated advantageous features by constructing 2D nanochannels in nonlayered materials may open up possibilities for designing high-power lithium ion batteries.

Single‐Crystalline Ultrathin Co3O4 Nanosheets with Massive Vacancy Defects for Enhanced Electrocatalysis

AbstractThe role of vacancy defects is demonstrated to be positive in various energy‐related processes. However, introducing vacancy defects into single‐crystalline nanostructures with given facets and studying their defect effect on electrocatalytic properties remains a great challenge. Here this study deliberately introduces oxygen defects into single‐crystalline ultrathin Co3O4 nanosheets with O‐terminated {111} facets by mild solvothermal reduction using ethylene glycol under alkaline condition. As‐prepared defect‐rich Co3O4 nanosheets show a low overpotential of 220 mV with a small Tafel slope of 49.1 mV dec−1 for the oxygen evolution reaction (OER), which is among the best Co‐based OER catalysts to date and even more active than the state‐of‐the‐art IrO2 catalyst. Such vacancy defects are formed by balancing with reducing environments under solvothermal conditions, but are surprisingly stable even after 1000 cycles of scanning under OER working conditions. Density functional theory plus U calculation attributes the enhanced performance to the oxygen vacancies and consequently exposed second‐layered Co metal sites, which leads to the lowered OER activation energy of 2.26 eV and improved electrical conductivity. This mild solvothermal reduction concept opens a new door for the understanding and future designing of advanced defect‐based electrocatalysts.

Ultrathin Co3O4 Layers with Large Contact Area on Carbon Fibers as High‐Performance Electrode for Flexible Zinc–Air Battery Integrated with Flexible Display

A facile and binder‐free method is developed for the in situ and horizontal growth of ultrathin mesoporous Co3O4 layers on the surface of carbon fibers in the carbon cloth (ultrathin Co3O4/CC) as high‐performance air electrode for the flexible Zn–air battery. In particular, the ultrathin Co3O4 layers have a maximum contact area on the conductive support, facilitating the rapid electron transport and preventing the aggregation of ultrathin layers. The ultrathin feature of Co3O4 layers is characterized by the transmission electron microscopy, Raman spectra, and X‐ray absorption fine structure spectroscopy. Benefiting from the high utilization degree of active materials and rapid charge transport, the mass activity for oxygen reduction and evolution reactions of the ultrathin Co3O4/CC electrode is more than 10 times higher than that of the carbon cloth loaded with commercial Co3O4 nanoparticles. Compared to the commercial Co3O4/CC electrode, the flexible Zn–air battery using ultrathin Co3O4/CC electrode exhibits excellent rechargeable performance and high mechanical stability. Furthermore, the flexible Zn–air battery is integrated with a flexible display unit. The whole integrated device can operate without obvious performance degradation under serious deformation and even during the cutting process, which makes it highly promising for wearable and roll‐up optoelectronics.

Facile Preparation of Ultrathin Co3 O4 /Nanocarbon Composites with Greatly Improved Surface Activity as a Highly Efficient Oxygen Evolution Reaction Catalyst.

The efficient catalytic oxidation of water to dioxygen plays a significant role in solar fuel and artificial photosynthetic systems. It remains highly challenging to develop oxygen evolution reaction (OER) catalysts with high activity and low cost under mild conditions. Here, a new composite material is reported based on ultrathin 2D Co3 O4 nanosheets and reduced graphene oxides (rGO) by means of a one-pot hydrothermal strategy. The ultrathin Co3 O4 /rGO nanocomposite shows superior stability under alkaline conditions and exhibits an overpotential of 290 mV with a Tafel slope of 68 mA dec-1 , which is much smaller than that of bare Co3 O4 catalyst. Extensive experiments were also carried out using 0D CS and 1D CNTs (CS=carbon spheres, CNTs=carbon nanotubes) in place of the 2D rGO. The overpotentials of as-prepared nanocomposites decrease with the increase of the dimension of nanocarbons, suggesting the electrochemistry activity is closely related to the surface area of carbon substrates. In addition, compared with ultrathin 2D Co3 O4 nanosheets with a Co2+ /Co3+ ratio of 1.2, the as-prepared ultrathin Co3 O4 /rGO nanocomposite with a Co2+ /Co3+ ratio of 1.4 contributes to the better OER performance as more oxygen vacancies can be formed in the ultrathin Co3 O4 /rGO nanocomposite under the experimental conditions. Compared with other Co3 O4 -containing composite materials reported so far, the ultrathin Co3 O4 /rGO nanocomposites show excellent OER performance.

Ultrathin mesoporous Co3O4 nanosheets-constructed hierarchical clusters as high rate capability and long life anode materials for lithium-ion batteries

Herein, Ultrathin mesoporous Co3O4 nanosheets-constructed hierarchical clusters (UMCN-HCs) have been successfully synthesized via a facile hydrothermal method followed by a subsequent thermolysis treatment at 600°C in air. The products consist of cluster-like Co3O4 microarchitectures, which are assembled by numerous ultrathin mesoporous Co3O4 nanosheets. When tested as anode materials for lithium-ion batteries, UMCN-HCs deliver a high reversible capacity of 1067mAhg−1 at a current density of 100mAg−1 after 100 cycles. Even at 2Ag−1, a stable capacity as high as 507mAhg−1 can be achieved after 500 cycles. The high reversible capacity, excellent cycling stability, and good rate capability of UMCN-HCs may be attributed to their mesoporous sheet-like nanostructure. The sheet-layered structure of UMCN-HCs may buffer the volume change during the lithiation-delithiation process, and the mesoporous characteristic make lithium-ion transfer more easily at the interface between the active electrode and the electrolyte.

Galvanic displacement assembly of ultrathin Co3O4 nanosheet arrays on nickel foam for a high-performance supercapacitor

High-performance supercapacitors are very desirable for many portable electronic devices, electric vehicles and high-power electronic devices. Herein, a facile and binder-free synthesis method, galvanic displacement of the precursor followed by heat treatment, is used to fabricate ultrathin Co3O4 nanosheet arrays on nickel foam substrate. When used as a supercapacitor electrode the prepared Co3O4 on nickel foam exhibits a maximum specific capacitance of 1095 F g−1 at a current density of 1 A g−1 and good cycling stability of 71% retention after 2000 cycling tests. This excellent electrochemical performance can be ascribed to the high specific surface area of each Co3O4 nanosheet that comprises numerous nanoparticles.

Ultrathin Co3O4 nanofilm as an efficient bifunctional catalyst for oxygen evolution and reduction reaction in rechargeable zinc-air batteries.

Two-dimensional (2D) nanocatalysts with a large specific surface area and efficient charge conductivity are promising candidates for catalyzing the sluggish oxygen evolution reaction (OER) and oxygen reduction reaction (ORR), which are at the heart of various electrochemical energy conversion and storage technologies. Here, we report the synthesis of an ultrathin Co3O4 nanofilm with a thickness of nearly 1.8 nm via a surfactant- and template-free facile hydrothermal route. The proposed synthesis strategy can be extended to the preparation of 2D NixCo3-xO4 and FexCo3-xO4 nanostructures. The synthesized Co3O4 nanofilm exhibited bifunctional activity that was superior to that of the counterpart Co3O4 nanoparticles, including a lower overpotential and higher reduction and evolution current densities, and demonstrated faster catalytic kinetics over the 2D nanofilm surface. In comparison with precious metal-based catalysts, to achieve an OER current density of 40 mA cm-2 the overpotential of the nanofilm (461 mV) was lower than that of RuO2 (526 mV), whereas the ORR on the nanofilm proceeded via a dominant 4e- transfer mechanism, which is similar to that of commercial carbon-supported Pt (Pt/C). The Co3O4 nanofilm enabled the assembly of rechargeable Zn-air batteries with a lower overpotential (0.72 V), higher round-trip efficiency (62.7%), and a longer cycle lifetime (175 cycles). The remarkable bifunctional activity contributes to an increase in the number of electrochemically active sites, a large interfacial contact area with the electrolyte, and the enrichment of Co3+ ions on the surface, which facilitates the adsorption and activation of oxygen-containing species. This study should shed light on the future development of new electroactive materials with optimized 2D nanostructures to enhance the overall bifunctional ORR/OER performance of rechargeable metal-air batteries.

Ultrathin Co3O4 nanosheets highly dispersed on reduced graphene oxide: An efficient bi-functional catalyst for Li-O2 battery

ABSTRACTUltrathin Co3O4 nanosheets grown on the reduced graphene oxide (Co3O4/rGO) was synthesized by a simple hydrothermal method and was investigated as a cathode in a Li-O2 battery. Benefited from the synergistic effect between Co3O4 and rGO, the hybrid exhibits a high initial capacity of 10,528 mAh g−1 along with a high coulombic efficiency (84.4%) at 100 mA g−1. In addition, the batteries show an enhanced cycling stability and after 113 cycles, the cut-off discharge voltage remains above 2.5 V. The outstanding performance is intimately related to the high surface area of rGO, which not only provide carbon skeleton for the uniform distribution of Co3O4 nanosheets but also facilitate the reversible formation and decomposition of insoluble Li2O2. The results of electrochemical tests confirm that the Co3O4/rGO hybrid is a promising candidate for the Li-O2 batteries.

Electrochemical Partial Reforming of Ethanol into Ethyl Acetate Using Ultrathin Co3O4 Nanosheets as a Highly Selective Anode Catalyst

Electrochemical partial reforming of organics provides an alternative strategy to produce valuable organic compounds while generating H2 under mild conditions. In this work, highly selective electrochemical reforming of ethanol into ethyl acetate is successfully achieved by using ultrathin Co3O4 nanosheets with exposed (111) facets as an anode catalyst. Those nanosheets were synthesized by a one-pot, templateless hydrothermal method with the use of ammonia. NH3 was demonstrated critical to the overall formation of ultrathin Co3O4 nanosheets. With abundant active sites on Co3O4 (111), the as-synthesized ultrathin Co3O4 nanosheets exhibited enhanced electrocatalytic activities toward water and ethanol oxidations in alkaline media. More importantly, over the Co3O4 nanosheets, the electrooxidation from ethanol to ethyl acetate was so selective that no other oxidation products were yielded. With such a high selectivity, an electrolyzer cell using Co3O4 nanosheets as the anode electrocatalyst and Ni–Mo nanopowders as the cathode electrocatalyst has been successfully built for ethanol reforming. The electrolyzer cell was readily driven by a 1.5 V battery to achieve the effective production of both H2 and ethyl acetate. After the bulk electrolysis, about 95% of ethanol was electrochemically reformed into ethyl acetate. This work opens up new opportunities in designing a material system for building unique devices to generate both hydrogen and high-value organics at room temperature by utilizing electric energy from renewable sources.

Uniform Deposition of Co3O4 Nanosheets on Exfoliated MoS2 Nanosheets as Advanced Catalysts for Water Splitting

Sluggish oxygen evolution reaction (OER) is the bottleneck for water splitting. Herein, an ultrathin Co3O4 nanosheet is uniformly deposited on the chemical exfoliated MoS2 nanosheet (ex-MoS2) via an in-situ hydrolysis and epitaxial growth. These novel noble-metal-free OER catalysts were proposed as an excellent platform for water splitting to promote the oxygen evolution activity and stability. MoS2 introduction can improve the conductivity of Co3O4 nanosheets, generate more Co3+ species in Co3O4 nanosheets during electrochemical activation and render high durability against dissolution of Co3O4 nanosheets in high potential polarization. As a result, these novel Co3O4/ex-MoS2 hybrids exhibit an excellent OER activity with a remarkable low Tafel slope (ca. 36mVdec−1), and a substantially small overpotential (ca. 290mV required for 10mAcm−2). Their OER stability is also outstanding, with 95.2% OER activity retention for 10000 potential cyclings. The superior OER performance is compatible to, and even better than state of art OER catalysts reported recently.

Facile synthesis ultrathin mesoporous Co3O4 nanosheets for high-energy asymmetric supercapacitor

Highly ultrathin mesoporous Co3O4 nanosheets have been successfully designed and constructed on nickel foam substrate via a facile two-step approach, including a hydrothermal technique without any surfactant and followed calcination of precursor. Owing to the unique mesoporous ultra-thin structural features, the capacitance of Co3O4 nanosheets electrode was as high as 610 mF cm−2 at a current density of 1 mA cm−2, and the cycling stability remained about 94.5% after 3000 cycles at current density of 4 mA cm−2. In addition, an asymmetric supercapacitor device based on the ultrathin mesoporous Co3O4 nanosheets was fabricated and has shown promising energy densities of 136 Wh kg−1 at power density of 0.75 kW kg−1. These results demonstrated that the ultrathin mesoporous Co3O4 nanosheets were excellent candidate for electrochemical supercapacitor devices.

Co@Co3 O4 @PPD Core@bishell Nanoparticle-Based Composite as an Efficient Electrocatalyst for Oxygen Reduction Reaction.

Durable electrocatalysts with high catalytic activity toward oxygen reduction reaction (ORR) are crucial to high-performance primary zinc-air batteries (ZnABs) and direct methanol fuel cells (DMFCs). An efficient composite electrocatalyst, Co@Co3 O4 core@shell nanoparticles (NPs) embedded in pyrolyzed polydopamine (PPD) is reported, i.e., in Co@Co3 O4 @PPD core@bishell structure, obtained via a three-step sequential process involving hydrothermal synthesis, high temperature calcination under nitrogen atmosphere, and gentle heating in air. With Co@Co3 O4 NPs encapsulated by ultrathin highly graphitized N-doped carbon, the catalyst exhibits excellent stability in aqueous alkaline solution over extended period and good tolerance to methanol crossover effect. The integration of N-doped graphitic carbon outer shell and ultrathin nanocrystalline Co3 O4 inner shell enable high ORR activity of the core@bishell NPs, as evidenced by ZnABs using catalyst of Co@Co3 O4 @PPD in air-cathode which delivers a stable voltage profile over 40 h at a discharge current density of as high as 20 mA cm(-2) .