Co3O4 Nanostructures Research Articles

Role of cobalt precursors in the synthesis of Co3O4 hierarchical nanostructures toward the development of cobalt‐based functional electrocatalysts for bifunctional water splitting in alkaline and acidic media

AbstractThe precursors have significant influence on the catalytic activity of nonprecious electrocatalysts for effective water splitting. Herein, we report active electrocatalysts based on cobalt oxide (Co3O4) hierarchical nanostructures derived from four different precursors of cobalt (acetate, nitrate, chloride, and sulfate salts) using the low‐temperature aqueous chemical growth method. It has been found that the effect of precursor on the morphology of nanostructured material depends on the synthetic method. The Co3O4 nanostructures exhibited cubic phase derived from these four precursors. The Co3O4 nanostructures obtained from chloride precursor have demonstrated improved oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) compared to other precursors due relatively higher content of Co3O4 nanostructures at the surface of material. An overpotential of 400 mV versus reversible hydrogen electrode (RHE) at 10 mA cm−2 was observed for HER. The Co3O4 nanostructures derived from the chloride precursor have shown favorable reaction kinetics via 34 mV dec−1 value of the Tafel slope for HER reaction. The Co3O4 nanostructures derived from chloride precursor have also shown an excellent HER durability for 15 hr in alkaline media. Furthermore, the OER functional characterization was carried out onto Co3O4 nanostructures derived from chloride precursor exhibited 220 mV overpotential at 10 mA cm−2 and Tafel slope of 56 mV dec−1. Importantly, the reason behind the favorable catalytic activity of Co3O4 nanostructures derived from chloride precursor was linked to one order of magnitude smaller charge transfer resistance and higher amount of Co3O4 content at the surface of nanostructures than the Co3O4 nanostructures derived from other precursors. The performance of Co3O4 nanostructures derived from chloride precursor via the wet chemical method suggests that cobalt chloride precursor could be of great interest for the development of efficient, stable, nonprecious, and environmentally friendly electrocatalysts for the chemical energy conversion and storage devices.

Nanostructuring Matters: Stabilization of Electrocatalytic Oxygen Evolution Reaction Activity of ZnCo2O4 by Zinc Leaching

Despite the enormous attention paid to cobalt oxide materials as efficient water splitting electrocatalysts, a deep understanding of their activity discrepancy is still elusive. In this work, we showed that stabilization of the internally generated oxygen evolution reaction (OER) active phase (oxyhydroxide) is crucial for ZnCo2O4 electrocatalysts. A systematic evaluation of the bulk and nanostructured ZnCo2O4 system concomitant with nanostructured Co3O4 showed that leaching of Zn is the driving force behind the near-surface transformation to the oxyhydroxide phase. The relative contribution to this near-surface reconstruction was found to be surface-sensitive. The electrochemical observations combined with Raman and impedance spectroscopy revealed that the good catalytic activity could be attributed to the formation of the cobalt oxyhydroxide phase, which was created by the dissolution of Zn from the nanostructured surface. Moreover, this study sheds light on previous contradicting postulates regarding the discrepancy of the OER activity of ZnCo2O4. Our finding regarding the formation of the OER active phase in spinel Zn-Co oxide will motivate researchers to focus more on the near-surface reconstruction behavior of cobalt-based oxide electrocatalysts in the future.

Synthesis of three-dimensional multifunctional Co3O4 nanostructures for electrochemical supercapacitors and H2 production

Synthesis of three-dimensional multifunctional Co3O4 nanostructures for electrochemical supercapacitors and H2 production

Templated Synthesis of Mesoporous Co3O4 Nanostructures for the Liquid-Phase Aerobic Oxidation of Benzyl Alcohol to Benzaldehyde

Mesoporous Co3O4 nanostructures, templated from different mesoporous silicas, SBA-3, SBA-5, and SBA-16, were used as catalysts for the liquid-phase selective oxidation of benzyl alcohol using molecular oxygen as the oxidant. The nanostructured Co3O4-16, templated from SBA-16, showed the best activity for the reaction, with 97.5% benzyl alcohol conversion and 100% benzaldehyde selectivity obtained after 3 h of reaction at 100 °C. This could be attributed to its large number of oxygen vacancies and low surface Co3+/Co2+ ratio that were beneficial to O2 activation, together with its three-dimensional nanostructure that facilitated the adsorption of benzyl alcohol, compared to Co3O4-3 and Co3O4-15. The material could be reused without losing activity if the organics adsorbed on the surface of the used sample were removed by calcination at 300 °C for 1 h. A mechanism for the reaction was proposed, considering that the activation of molecular oxygen was the rate-determining step of the reaction.

Facile synthesis of rGO@ CoO nanocomposites electrode material for photocatalytic hydrogen generation and supercapacitor applications

Herein this work, a simple one-step hydrothermal method for decorating CoO nanostructures uniformly on rGO surfaces. The produced CoO/rGO electrode material was uniformly characterised physiochemical techniques to determine its structure and its morphological behaviour. The CoO nanostructures deposited on rGO surfaces could act effectively as a highly conductive material that aids in uniform redox reactions. Electrochemical measurements indicate that the CoO/rGO nancomposite modified electrode has a specific capacitance value of 592 F g−1 at 2 A g−1 in 1 M aqueous KOH with a good stability of 90% capacitance stability even after 3000 charge-discharged cycles, making it an attractive material for use in electrochemical energy storage devices. Furthermore, the RGO has mainly double role as electron mediator to improve the charge transportation and improving the light absorption behaviour in the visible light region. The constructed CoO/rGO nanocomposite applied as photocatalyst for water splitting exhibits improved H2 production (830 μmol h−1 g−1) under the visible light. The major findings of this work offer a unique opportunity for constructing visible light response photoactive material, and electrochemical redox capacitors for energy needs.

Room temperature synthesis and ammonia sensing of monodispersed hierarchical 1 and 3-dimensional Co3O4 nanostructures: switching from p to n-type sensing

Room temperature synthesis and ammonia sensing of monodispersed hierarchical 1 and 3-dimensional Co3O4 nanostructures: switching from p to n-type sensing

Highly-efficient degradation of ensulizole using monopersulfate activated by nanostructured cobalt oxide: A comparative study on effects of different nanostructures

The most extensively used sunscreen protecting agent, Ensulizole, has been proven to exhibit hormone disrupting effects. To establish efficient processes to destruct Ensulizole in water, SO4•−-involved advanced oxidation processes using monopersulfate (MPS) seem useful. Since cobalt (Co) is the most capable of metal for activating MPS, Co3O4 appears as a promising heterogeneous catalyst for activating MPS to degrade Ensulizole. As catalytic activities of metal oxide catalysts are strongly associated with their morphologies, and surficial properties, nanoscale Co3O4 with functional nanostructures would be expected as advantageous catalysts for activating MPS. Therefore, three Co3O4 materials with distinct nanostructures and shapes were fabricated in this study, including Co3O4 cone ball (COCB), Co3O4 plate lump (COPL), and Co3O4 needle sheaf (CONS). Their surficial properties are also noticeably distinct with different fractions of Co2+, and Co3+, various oxygen vacancies, textural features and surface defects. Through comparing these three nanostructured Co3O4 for activating MPS to degrade Ensulizole, CONS exhibits the tremendously higher catalytic activity than COCB and COPL for activating MPS to eliminate Ensulizole completely and rapidly. The Ea value of Ensulizole degradation of CONS is also significantly low as 9.8 kJ/mol, which is the lowest Ea ever reported in literatures. CONS could also retain its catalytic activities over 5 continuous cycles to rapidly degrade Ensulizole. The activation mechanism of MPS by CONS and Ensulizole degradation pathway are also comprehensively elucidated via experimental evidences and the theoretical calculation to offer insightful information of development of Co-based heterogeneous catalysts for Ensulizole degradation.

A New Approach to In-Situ Co3o4 Nanostructure Decorated Free-Standing Carbon Foam Derived from Phenolic Resin for High-Performance Supercapacitor

A New Approach to In-Situ Co3o4 Nanostructure Decorated Free-Standing Carbon Foam Derived from Phenolic Resin for High-Performance Supercapacitor

Synthesis and characterizations of highly responsive H2S sensor using p-type Co3O4 nanoparticles/nanorods mixed nanostructures

High-quality p-type semiconducting Co3O4 with mixed morphology of nanoparticles/nanorods are synthesized using a hydrothermal route for high response and selective hydrogen sulphide (H2S) sensor application. XRD and Raman studies revealed the crystal structure and molecular bonding for obtained Co3O4, respectively. The nanoparticles/nanorods-like structures were confirmed for Co3O4 using FESEM and TEM analysis. The EDS and XPS spectra analysis were carried out for elemental composition and chemical atomic states of Co3O4. The Co3O4 sensor is investigated for gas sensing properties in dynamic conditions. The sensor exhibited the highest selectivity towards H2S among various hydrogen-contained gases at 225 °C. The sensor revealed a high response of 357% and 44% for 100 and 10 ppm H2S gas concentrations, respectively. The Co3O4 sensor exhibited a systematic dynamic resistance response for 100–10 ppm range H2S gas. The excellent dynamic resistance repeatability of the sensor was shown towards 25 ppm H2S gas. The response of Co3O4 sensor was investigated at different operating temperatures and H2S concentrations. The sensor stability and H2S sensing mechanism for the Co3O4 sensor have been reported. Highly uniform and mixed nanostructures of Co3O4 can be the potential sensor material for real-time high-performance H2S sensor application.

NiCo2O4 nanostructures loaded onto pencil graphite rod: An advanced composite material for oxygen evolution reaction

Driving oxygen evolution reaction (OER) at extremely low overpotential and the blockage of oxygen gas inside the catalytic material leads to the deactivation of catalytic activity, therefore it is an essential step in electrochemical energy conversion systems, but still very challenging task. The clay minerals including bentonite and kaolinite are rich with plenty of active centers and favorable chemical composition for the catalysis applications but limited by the insulating properties, thus they cannot be used as an electrode material for the water splitting. The unique presence of clay minerals in the form of pencil graphite rod (PGR) and its attractive architecture enabled us to exploit advantageous features and use them as an in situ electrode for growth of metal oxide nanostructures for the electrolysis applications. The naturally inherent presence of SiO2 favors the catalytic properties and durability of the electrode whereas the MgO produces the abundant oxygen vacancies and Co3+ ions for OER process. Herein, we present a facile approach of using PGR as host substrate and co-catalyst for the loading of Co3O4, NiCo2O4 and NiO nanostructures and the modified electrode carried high porosity for easily bubbling of oxygen gas, plenty of intrinsic active centers coming from both clay minerals and metal oxides for excellent OER process. The fabricated electrode is physically well-characterized, and it has a natural ability to sustain a long term stability even at higher current densities and industrial electrolyzer conditions. The NiCo2O4/PGR, Co3O4/PGR, and NiO/PGR electrodes exhibit an overpotential of 234, 242 and 272 mV respectively at a current density of 100 mAcm−2 in 1.0 M KOH electrolytic solution. The presence of large number of oxygen vacancies through SiO2 and MgO, high Ni2+/Ni3+ and Co3+/Co2+ ratios, multi metal centers, large specific surface area, high pore volume, high electrochemical active surface area and fast charge transport within the NiCo2O4/PGR are the main reasons for its superfast OER kinetics. Thus, the proposed method of electrode design will pave a potential way for high performance electrochemical devices like metal air batteries, fuel cell and supercapacitors.

Electrochemical Performance of Iron-Doped Cobalt Oxide Hierarchical Nanostructure

In this study, hydrothermally produced Fe-doped Co3O4 nanostructured particles are investigated as electrocatalysts for the water-splitting process and electrode materials for supercapacitor devices. The results of the experiments demonstrated that the surface area, specific capacitance, and electrochemical performance of Co3O4 are all influenced by Fe3+ content. The FexCo3-xO4 with x = 1 sample exhibits a higher BET surface (87.45 m2/g) than that of the pristine Co3O4 (59.4 m2/g). Electrochemical measurements of the electrode carried out in 3 M KOH reveal a high specific capacitance of 153 F/g at a current density of 1 A/g for x = 0.6 and 684 F/g at a 2 mV/s scan rate for x = 1.0 samples. In terms of electrocatalytic performance, the electrode (x = 1.0) displayed a low overpotential of 266 mV (at a current density of 10 mA/cm2) along with 52 mV/dec Tafel slopes in the oxygen evolution reaction. Additionally, the overpotential of 132 mV (at a current density of 10 mA/cm2) and 109 mV with 52 mV/dec Tafel slope were obtained for x = 0.6 sample towards hydrogen evolution reaction (HER). According to electrochemical impedance spectroscopy (EIS) measurements and the density functional theory (DFT) study, the addition of Fe3+ increased the conductivity at the electrode–electrolyte interface, which substantially impacted the high activity of the iron-doped cobalt oxide. The electrochemical results revealed that the mesoporous Fe-doped Co3O4 nanostructure could be used as potential electrode material in the high-performance electrochemical capacitor and water-splitting catalysts.

Nickel Cobaltite Nanoplate-Based Electrochemical Sensing Platform from Printable Inks for Simultaneous Detection of Dopamine and Uric Acid.

2D metal oxide-based nanomaterials have emerged as an exciting area of research owing to their rich electrochemical properties and diverse applications, including biosensors. In this work, we have synthesized ultra-thin Co3 O4 , NiO, and NiCo2 O4 nanostructures supported on a carbon cloth and printed graphite/Kapton substrates following thermal reduction of self-assembled metal alkanethiolates. These nanostructures act as a sensing platform for simultaneous detection of dopamine (DA) and uric acid (UA), important biological molecules in physiological and pathological tests. The ultrathin 2D nanoplates of NiCo2 O4 spinel formed in this study exhibit high electrochemical activity than pristine NiO and Co3 O4 . The electrochemical characterization studies indicate that NiCo2 O4 possesses a high potential for DA and UA with a peak separation of ∼140 mV, high sensitivity, and excellent selectivity. The low-cost and disposable, single-shot probe biosensors fabricated in this work possess a wide working range of 0.001-1000 μM with detection limits of 0.33 and 0.49 nM for DA and UA, respectively, with a practically achievable limit of quantification of ∼1 nM. Multiple sensing electrodes are printed on graphite/Kapton all at once following this method with improved reproducibility for DA and UA sensing further extending the scope of work towards mass fabrication and practical usage.

Design of open-porous three-dimensional starfish-like Co3O4/Ni forest electrode for efficient energy storage devices

A binder-free positive electrode material of 3D starfish-like Co3O4/Ni forest is fabricated via a novel and facile hydrothermal process followed by thermal treatment. The morphological studies clearly showed the construction of starfish-like micro-flowers of Co3O4 nanostructure forest densely covered on the entire Ni current collector. The 3D-Co3O4/Ni electrode displayed an areal capacity as high as 143.28 mC cm−2 at 0.5 mA cm−2 and higher stability of 88.4% after 5000 cycles. Moreover, the fabricated 3D-Co3O4/Ni||3D-Bi2O3/Ti supercapattery delivered a maximum areal capacitance of 24.73 mF cm−2, the energy density of 6.73 μWh cm−2 and power density of 5250 μW cm−2 with good cycling stability> 71% capacity retention after 5000 cycles. The higher electrochemical performance of the electrode is delivered due to the availability of abundant electrochemically active sites in the 3D starfish-like Co3O4 microflower, which facilitates a higher electrochemical reaction. The starfish-like forest architectures allow rapid ion diffusion, and the binder-free electrode reduces the contact resistance, which fasten the electron transport. These tolerable results prompt the as-prepared electrode with 3D starfish-like Co3O4 microflower morphology as an auspicious positive electrode material for electrochemical energy storage devices.

Optical and electrochemical properties of spinel cubic nanostructured thin film Co3O4 prepared by spray pyrolysis

In this present, a spinel cubic Co3O4 nanostructured thin film has been deposited by a simple and inexpensive spray pyrolysis method on preheated FTO substrate at different temperatures of the substrate (TS = 350 ̊C, 400 ̊C, 450 ̊C, and 500 ̊C). The surface, optical and structural properties of these films have been studied by FESEM, UV–Vis, and XRD analyses. According to these results the film has been deposited at TS = 400 ̊C chooses for electrochemical tests. The surface morphology investigated by FESEM and structural properties has been studied by XRD patterns. The grain size of samples was calculated by XRD patterns and FESEM images. The average grain size was about 30 nm, and the results of XRD and FESEM confirmed each other. UV–vis spectroscopy of these films shows that they have two absorption edges with direct and indirect bandgap at 2.2 and 1.5 eV, respectively. The electrochemical properties of this electrode have been analyzed by CV, impedance, and charge/discharge curve. The CV curve was investigated at different scan rates: 100, 80, 60, 40, 20, and 10 mv.s-1. The specific capacitance of the above electrode was decreased by increasing the scan rate. The specific capacitance of this electrode was calculated by CV and charge/discharge curve and it was 1800 F/g. The electrochemical analysis shows that the capacity of this electrode decreases only 4% after 5000 cycles therefore it is a very stable electrode.

Nanostructured Co3O4 electrocatalyst for OER: The role of organic polyelectrolytes as soft templates

Designing an efficient electrocatalyst for the oxygen evolution reaction (OER) in alkaline media is highly needed but very challenging task. Herein, we used organic polyelectrolytes such as (carboxymethyl cellulose) CMC and polyacrylamide polymers for the growth of Co3O4 nanostructures by aqueous chemical growth method. The morphology and composition studies were performed on scanning electron microscopy (SEM), energy dispersive X-ray (EDX), powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and high-resolution transmission electron microscopy (HRTEM) techniques. The structural properties and the surface chemistry of the Co3O4 electrocatalysts were correlated to the OER performance, and the enhancement mechanism with respect to pristine Co3O4 was observed to be specifically related to the polyelectrolyte templating role.Co3O4@CMC composites displayed reduced crystallite size, producing OER overpotential as low as 290 mV at 10 mAcm−2 in 1.0 KOH and Tafel slope of 71 mVdec−1, suggesting fast transfer of intermediates and electrons during water electrolysis. On the other hand, the use of polyacrylamide and its different templating mechanism resulted in similar crystallite size, but preferential exposed faces and larger surface vacancies content, as demonstrated by HR-TEM and XPS, respectively. Consistently, this material displays cutting-edge OER performance, such as overpotential of 260 mV at 10 mAcm−2 and a low Tafel slope of 63 mVdec−1. The proposed strategy for the preparation of Co3O4 nanostructures in the presence of CMC and polyacrylamide is facile, mass production, thus it could equally contributed towards the realization of hydrogen energy. Therefore, these nanostructures of Co3O4 can be regarded as an alternative and promising materials for the different electrochemical applications including fuel cells, metal air batteries, overall water electrolysis and other energy storage devices.

Metal Oxide Nanostructure-Based Gas Sensor for Carbon Dioxide Detection

Abstract To increase the sensitivity and efficiency of a gas sensor, nanostructured ZnO and Co3O4 layers were obtained by hydrothermal synthesis directly on the electrode surface, eliminating the use of binders. Scanning electron microscope images showed that the resulting nanostructured coatings were characterised by good adhesion to the surface and high porosity, which opened up the possibility of their further use in the process of developing a gas sensor. The efficiency of the obtained nanostructured coatings and their sensitivity at room temperature to various concentrations of CO2 were determined. The resistance curves of the samples were obtained as a function of gas concentration in the chamber, for Co3O4 and ZnO nanostructures.

Nanostructure modulation of Co3O4 films by varying anion sources for pseudocapacitor applications

We controllable designed and synthesized four kinds of three-dimensional (3D) hierarchical nanostructured Co3O4 thin films directly deposited on the nickel foam surface by a facile chemical bath deposition method. The morphologies of the Co3O4 films were regulated by using different anions (SO42−, NO3−, Cl−, and CH3COO−) originated from the precursors. The effect of different anions on the surface morphologies and pseudocapacitance behaviors of Co3O4 films was investigated by multiple electrochemical methods, including cyclic voltammetry (CV), galvanostatic charge-discharge cycles (GCD) and electrochemical impedance spectroscopies (EIS). The results indicated that the anions in the precursor salts greatly affected the morphology and porosity of the Co3O4 thin film, and consequently exhibited the different electrochemical performances in 2.0 M KOH electrolyte. The Co3O4 thin film prepared from cobalt acetate shown excellent electrochemical performance among the four different Co3O4 thin films electrodes, such as a high specific capacitance (743.8 F·g−1) and nice cycling stability (95.8% retention after 1000 charge-discharges at a high current density of 5 A·g−1). Furthermore, this work also provides a facile large-scale fabrication method to prepare secondary nanostructure on pseudocapacitance materials, such as graphene, transition metal oxides, carbon fibers, for enhancing the electrochemical performance of supercapacitor at low operation temperature.

Plasma‐Assisted Synthesis of Co3O4‐Based Electrocatalysts on Ni Foam Substrates for the Oxygen Evolution Reaction

AbstractElectrocatalytic oxygen evolution reaction (OER) plays a key role in sustainable energy conversion and storage, but is severely hampered by the lack of efficient catalysts, whose development remains a critical and challenging issue. Herein, it is reported for the first time that pure and Fe2O3‐containing Co3O4‐based OER electrocatalysts are grown on highly porous Ni foams by plasma enhanced‐chemical vapor deposition and/or radiofrequency sputtering. Thanks to the inherent advantages of cold plasma synthesis routes, Ni foam supports are efficiently infiltrated by Co3O4 nanostructures and eventually nanosized Fe2O3, allowing a fine‐tuning of their mutual content, nano‐organization, and oxygen defectivity. For Co3O4‐Fe2O3 systems, these issues enable current densities up to ≈120 mA cm−2 at 1.79 V versus the reversible hydrogen electrode, an overpotential of ≈350 mV at 10 mA cm−2 and a Tafel slope as low as 60 mV dec−1, favorably comparing with literature values for most cobalt‐based OER catalysts reported so far. Such features, accompanied by a good time stability, represent an important goal for eventual practical applications and candidate the proposed fabrication route as a valuable tool for the design of efficient electrocatalysts with precisely engineered properties and based on naturally abundant transition elements.

Co–Co3O4 nanostructure with nitrogen-doped carbon as bifunctional catalyst for oxygen electrocatalysis

In view of the development of advanced bi-functional oxygen electrodes for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), herein, we report the synthesis of Co–Co3O4 nanostructure encased in N-doped carbon (Co–Co3O4/NC) by carbothermal reduction followed by controlled oxidative treatment. The formation of a protective-active oxide layer on the metallic-Co not only facilitated the effective charge separation and transport but also displayed improved stability of Co–Co3O4/NC in an alkaline operating condition. The Co–Co3O4/NC catalyst afforded 0.810 V overvoltage between ORR and OER in 0.1 M KOH solution, consequently, this lower reversible overvoltage would result in energy saving of around 0.246 V if Co–Co3O4/NC is used as an oxygen electrode instead of commercially available 40 wt % Pt/C. Furthermore, in comparison with the use of Pt/C + IrO2 as an ORR and OER catalyst, respectively the single bi-functional electrocatalyst i.e., Co–Co3O4/NC would result in energy saving of around 0.13 V.

Fast, sensitive and low-cost chemical sensor based on manufacturing nanostructured Co3O4 using Raman Spectroscopy

Nanostructured Co3O4 has novel properties, so it can be manufactured with simple, fast preparation of samples, and a low-cost process. FESEM field emission electron microscope scanning, XRD diffraction, and Raman spectroscopy characterized Co3O4 nanostructured tetrahedral structures with multiple branches. Good sensitivity and selectivity and high stability can be seen for the nanostructured Co3O4. Cationic surfactant (CTAB) and anionic surfactant (PVP) both have a guiding effect on Co3O4 production. The self-assembled Co3O4 particles in Methylene Blue (MB) exhibit excellent Surface Enhanced Raman Spectroscopy efficiency. An average enhancement factor (EF) of 50 × 106 was achieved for the Co3O4 in PVP on 135 gsm printing paper and 41 ×106 for the Co3O4 in CTAB on 240 gsm printing paper.The results showed Co3O4 in PVP produced the highest sensitivity, specificity, and the lowest limit of detection LOD which was 0.52 nM for MB as Raman reporter molecule, and the sensitivity offered almost 98% with selectivity equal to 92%. To the best of the author’s knowledge, this is the first demonstration of Co3O4 in PVP paper-based as a chemical sensor by enhanced Raman spectroscopy signal.