Undoped Co3O4 Research Articles

Insights of oxygen vacancies engineered structural, morphological, and electrochemical attributes of Cr-doped Co3O4 nanoparticles as redox active battery-type electrodes for hybrid supercapacitors

The global warming issue is spurring the development of renewable energy solutions, where supercapacitors are emerging as promising options for energy storage. Despite advancements in battery-type materials, doping is a practical approach to enhancing electrochemical performance. In this study, using the solution combustion method, we synthesized spinel Co3O4 nanoparticles doped with chromium (Cr) at 2.5 % and 5 % concentrations. The addition of Cr significantly modifies the structural, morphological, surface, and electrochemical properties of Co3O4 nanoparticles. Raman and X-ray photoelectron spectroscopy confirm that this doping method effectively regulates the oxygen vacancy defect level. Moreover, Cr dopants and oxygen vacancies modify electronic states, facilitating more accessible contact to active sites, improving electrical conductivity and more intricate redox chemistry. Notably, the 2.5 % Cr-doped Co3O4 configuration demonstrates substantially enhanced specific capacity (334.64 C g−1/92.95 mAh g−1 at 1 A g−1) and rate performance (59 %), surpassing those of 5 % Cr-doped Co3O4 and undoped Co3O4. Furthermore, the as-fabricated 2.5 % Cr-doped Co3O4//activated carbon (AC) hybrid supercapacitor (HSC) device exhibits a noteworthy energy density of 42.5 Wh kg−1 at 1295.73 W kg−1, withstanding 33.54 Wh kg−1 even at a power density of 5720.46 W kg−1. The HSC device showcases outstanding cyclic performance with 100 % capacity retention after 5000 cycles. Therefore, our work offers a viable way to improve the efficiency of hybrid supercapacitors by providing essential insights into the design of defect-engineered battery-type electrode materials.

Modification of Co3O4 by Al2O3: Influence on the reducibility

In this study, we used a coprecipitation method followed by calcination at 500 °C to synthesize undoped and Al3+-doped Co3O4 nanoparticles with different aluminum fractions (x = Al/(Co + Al) = 1/60, 1/30, 1/15, 1/75, 1/6 and 1/5). An addition of Al3+ ions led to a decrease in the average crystallite size from 29 to 11 nm, and growth of the specific surface area from 28 to 91 m2/g. TEM images indicated round and platelet shapes of the nanoparticles. According to HAADF-STEM combined with EDS elemental mapping, the platelet shape particles are Al3+-enriched, while the round shape particles are Al3+-depleted. The origin of Al3+ distribution over the oxide volume is conditioned by the state of the hydroxide precursor. It was shown by XRD that the coprecipitation yielded homogeneous hydroxides only for Al fractions x = 0 and x = 1/5. For the intermediate compositions, the precursors represent a mixture of Co6(CO3)2(OH)8*H2O and Co0.8Al0.2(OH)2(CO3)0.1*nH2O. On the TPR-H2 profiles, reduction peaks for three (Co,Al)3O4 oxides differing in the Al3+ concentration (y) can be found. Two of these oxides with y = 0 and y = 0.2 are formed from different hydroxides, and third one with y ∼0.05 is the result of their mutual interaction. In situ XRD allowed us to interpret the TPR peaks correctly and showed that the reduction of all the oxides occurs in two steps. In the first step, Co3+ → Co2+, and (Co1-yAly)3O4 oxides transform to (Co,Al)O. In the second step, Co2+ → Co0, and (Co,Al)O is reduced into metallic cobalt. In undoped Co3O4, Co3+ → Co2+ and Co2+ → Co0 reduction steps occur at T1 = 280 and T2 = 325 °C, respectively. For Al-depleted (Co1-yAly)3O4 (y ∼ 0.05 in the interior of particles), both reduction steps shift toward higher temperatures T1 = 305 and T2 = 405 °C, respectively. The reduction of Al-enriched (Co0.8Al0.2)3O4 is more difficult; first and second reduction steps occur at T1 = 345 and T2 = 610−690 °C. Therefore, Al3+ ions have a little effect on the first step and very significantly influence the second one. Additionally, it was shown by TEM that after the reduction at 700 °C metallic cobalt particles were surrounded by the Al-enriched oxide shell. Apparently, that is why the addition of even a small amount of Al3+ ions prevents a quick sintering of metallic cobalt observed for pure Co3O4.

Effect of Ce-Doping on the Structural, Morphological, and Electrochemical Features of Co3O4 Nanoparticles Synthesized by Solution Combustion Method for Battery-Type Supercapacitors

This study investigates the potential of cerium (Ce) doping to improve the performance of cobalt oxide (Co₃O₄) nanoparticles as battery-type supercapacitor electrodes. Pure Co₃O₄ nanoparticles were synthesized via a solution combustion method and then doped with 2.5% (Ce-Co3O4) and 5% Ce (CeO2-Co3O4). Comprehensive characterization, including X-ray diffraction (XRD), Raman spectroscopy, and field emission scanning electron microscopy (FESEM), was used to analyze the impact of Ce doping on the material properties. XRD analysis confirmed the successful incorporation of Ce into the Co₃O₄ structure, with distinct CeO2 phases forming at higher doping levels. Ce doping resulted in decreased crystallite size and peak intensity, indicating reduced crystallinity and increased defect concentration. Raman spectroscopy corroborated these findings, showing a redshift that suggests weakened metal-oxygen bonds and smaller grain sizes due to Ce³⁺ incorporation. FESEM images demonstrated that Ce doping effectively reduced nanoparticle agglomeration, with 2.5% doping leading to smaller particles and 5% doping promoting a 2D flake-like morphology with increased porosity. Nitrogen adsorption-desorption measurements revealed a significant increase in surface area and pore volume for CeO2-Co₃O₄, facilitating improved electrolyte diffusion and reduced resistance, thereby enhancing electrochemical performance. Evaluation of the electrochemical properties of undoped and Ce-doped Co₃O₄ materials revealed a battery-like response in a three-electrode configuration. Notably, the CeO2-Co3O4 exhibited a superior specific capacity of 603.3 C g-1 at a current density of 1 A g-1, significantly exceeding the values of 368.5 C g-1 and 127.1 C g-1 achieved by Ce-Co3O4 and undoped Co3O4, respectively. Furthermore, the CeO2-doped Co3O4 demonstrated exceptional cyclic stability, retaining 87% of its initial capacity after undergoing 5000 charge-discharge cycles at a high current density of 10 A g-1. These results suggest that Ce doping is a promising strategy for optimizing Co₃O₄-based battery-type electrode materials, potentially leading to the development of high-performance and cost-effective energy storage systems.

Modifications of some physical properties of nanostructured indium doped Co3O4 thin films

Using the chemical spray pyrolysis (CSP) technique, nanostructured undoped and Co3O4:In thin films are deposited. The effect of indium doping content in Cobalt ranged from 1% to 3% on optical, structural, and topographical properties of Co3O4 nanostructured thin films. No new peaks belonging to the In phase were seen, according to X-ray diffraction research, which revealed that pure and Co3O4: In thin films are polycrystalline in and cubic phase with (111), (311), (400), and (511) preferable orientation for all filmsThe Scherrer formula computation of average crystallite size shows that the size of Nano crystallites grows when doping is enhanced. AFM micrographs demonstrated how the surface shape of the films was discovered to be influenced by the inclusion of indium in the Co3O4 location.SEM images of Undoped Co3O4 and Co3O4:In films (CSP technique), showing separate semi-spherical blocks (120-200 nm) of nanoparticles (<30 nm). Band gap values for pure and doped were 2.52 to 2.38 eV. Resistance increases with increases Indium-doping, indicating more charge carriers and potential surface roughness influence. Sensitivity decreases with higher Indium concentrations, attributing to enhanced crystallinity and nano-crystalline size.

Modifications of some physical properties of nanostructured indium doped Co3O4 thin films

Using the chemical spray pyrolysis (CSP) technique, nanostructured undoped and Co3O4:In thin films are deposited. The effect of indium doping content in Cobalt ranged from 1% to 3% on optical, structural, and topographical properties of Co3O4 nanostructured thin films. No new peaks belonging to the In phase were seen, according to X-ray diffraction research, which revealed that pure and Co3O4: In thin films are polycrystalline in and cubic phase with (111), (311), (400), and (511) preferable orientation for all filmsThe Scherrer formula computation of average crystallite size shows that the size of Nano crystallites grows when doping is enhanced. AFM micrographs demonstrated how the surface shape of the films was discovered to be influenced by the inclusion of indium in the Co3O4 location.SEM images of Undoped Co3O4 and Co3O4:In films (CSP technique), showing separate semi-spherical blocks (120-200 nm) of nanoparticles (<30 nm). Band gap values for pure and doped were 2.52 to 2.38 eV. Resistance increases with increases Indium-doping, indicating more charge carriers and potential surface roughness influence. Sensitivity decreases with higher Indium concentrations, attributing to enhanced crystallinity and nano-crystalline size.

Comprehensive characterization of octahedral Co3O4 doped with Cu induces oxygen vacancies as a battery-type redox active electrode material for supercapacitors

The urgent need to combat global warming has spurred the exploration of renewable energy solutions, among which the supercapacitor has emerged as a promising contender for efficient energy storage in crucial applications. While battery-type electrode materials (BTMs), notably Co3O4, have shown impressive electrochemical performance in recent years, their inherent limitations, such as low conductivity, restricted surface area, and suboptimal electrochemical activity, pose challenges to their utility. Doping has emerged as a strategic solution to address these issues by modifying the crystal structure, surface morphology, specific surface area, electronic conductivity, and chemical stability of the host material, thereby enhancing its electrochemical performance. This study uses a combustion synthesis method to engineer octahedral Co3O4 with Cu-doping. We obtained three different samples of Co3O4: one undoped Co3O4, doped with 3 % Cu (3%Cu–Co3O4), and 6 % Cu (6%Cu–Co3O4). The addition of Cu not only changed the crystal structure and surface morphology but also impacted the surface area and defects (oxygen vacancies) in Co3O4, affecting its electrochemical performance. This doping method effectively controlled the oxygen vacancy defect content, as verified meticulously by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Raman spectroscopy, and UV–Vis diffuse reflectance spectroscopy (UV–Vis DRS). Particularly, the 6%Cu–Co3O4 configuration demonstrated significantly improved specific capacity (155.5 mA h g−1/559.8C g−1 at 1 A g−1) and rate performance (67 %), outperforming both 3%Cu–Co3O4 and undoped Co3O4. Additionally, it exhibited superior cycling stability with 91 % retention of the maximum specific capacity after 5000 cycles. Consequently, this study offers valuable insights into designing defect-engineered battery-type electrode materials for hybrid supercapacitors, which could significantly enrich their efficiency.

Improved hydrogen generation via NaBH4 hydrolysis: Synergistic role of sulfur and C4+-Doping unveils (440) high-index facets and modulates Co2+/Co3+ ratios in the Co3O4 lattice

Sodium borohydride (NaBH4) is crucial for eco-friendly “green” hydrogen (H2) storage, employing controlled release through catalyzed NaBH4 hydrolysis, mitigating its inherent sluggish self-hydrolysis. Precious metal catalysts enhance this process, but face scarcity and cost issues hindering widespread use, prompting interest in Co3O4, specifically with (311) orientation for abundant Co2+ sites. However, excess Co2+ on dominant (311) facets limits catalytic efficacy. This study presents a nuanced synthesis of sulfur (S)- and carbon (C4+)-doped Co3O4 that expose high-index (440) facets and optimize Co2+/Co3+ distribution. The catalytic performance of CoSC-0.1-700 on (440) facets demonstrates remarkable hydrogen generation rate of 4.1 L g−1. min−1 within 10.5 min, 1.81×, 2.42×, and 3.83× higher than control samples, and undoped Co3O4 with (311) dominance, and 1.24× higher than (220). An estimated activation energy (Ea) of 33.63 kJ mol−1, comparable to noble metals, indicates high performance and stability over ten (10) cycles. This approach promises sustainable future in "green" H2 production.

Metal-organic frameworks-derived Al/Mo co-doped porous Co3O4 hollow tetrahedrons for efficient triethylamine detection

Three-dimensional (3D) hollow porous structures have attracted great attention in surface-related fields due to their advantages such as large specific surface area, high gas permeability, and low agglomeration. In this work, Al/Mo co-doped porous Co3O4 hollow tetrahedrons derived from MOFs have been obtained using a simple solvothermal synthetic technique. Various characterizations have been used to analyze the crystalline and electronic structure. The results indicate that Al/Mo ions are successfully doped into the Co3O4 lattice and 0.2 at% Al/Mo co-doped Co3O4 shows the best sensing properties among the other Co3O4 based samples. In particular, 0.2% Al/Mo-Co3O4 exhibits the highest response values of 132–100 ppm TEA at 160 °C, which are 33 times as high as those of undoped Co3O4. Furthermore, 0.2% Al/Mo-Co3O4 also displays rapid response and recovery speed (4 s/36 s), low detection limit (0.5 ppm), good selectivity and long-term stability. The reason of enhanced TEA sensing properties is ascribed to the occurrence of 3D hollow porous structure and coupling effect of Al/Mo co-doping. Thus, 0.2 at% Al/Mo co-doped porous Co3O4 hollow tetrahedrons show promising applications in constructing high-performance chemical sensors for TEA detection.

Structural, magnetic, and antibacterial activity of the pure, Zn-doped, and Zn-doped/sugar-assisted coprecipitation synthesized semicrystalline Co3O4 compound

Undoped, Zn-doped, and Zn-doped/sugar-assisted semi-crystalline structures of Co3O4 were made by introducing a facile precipitation approach. The synthesized compounds were tested for surface characteristics, magnetic properties, and antibacterial activity. Powder X-ray diffraction (XRD) analysis confirmed semi-crystalline behavior and spinel structure formation in all synthesized compounds. Using scanning electron microscopy (SEM) characterization, microstructure formation along with the large agglomeration of spherical particles, uniform distribution of spherical particles, and spherical-flake-like particle structures were noticed for the pure, Zn-doped, and Zn-doped/sugar-assisted Co3O4 samples, respectively. From the vibration sample magnetometry (VSM), Zn-doped/sugar-assisted Co3O4 was found to have relatively lower saturation magnetization when compared to pure Co3O4 and Zn-doped Co3O4 material. The antibacterial performance of the synthesized compounds against the bacteria Escherichia coli (E.coli) and Staphylococcus aureus (S. aureus) has been tested. The above-mentioned germicidal responses showed a relatively larger inhibition zone for the Zn-doped and Zn-doped/sugar-assisted Co3O4 compared to the undoped Co3O4 sample. The obtained diameter inhibition zone values of all synthesised compounds are comparable to the standard positive and negative control.

Nanocrystalline Ag-doped cobalt oxide as a flexible electrode material for high performance supercapacitor application

Co3-xAgxO4 (x = 0 ~ –0.4) nanocomposite with a spherical shape and porous surface has been synthesized using a simple, fast and scalable combustion method. The highly stable Ag-doped Co3O4 nanocomposite particles were found to be 20‐–50 nm in size with high surface area, crystallinity, and porosity. The specific capacitance value of the Co2.7Ag0.3O4 (CA3) electrode was observed to be higher than other electrodes. Doping of Ag provides a large Ag/Co3O4 interface which enhanced the electrical conductivity of the electrode by moulding ohmic contact. This contributes to a stable and straight passage for rapid charge transfer. The calculated specific capacitance value of CA3 nanocomposite was 648 F g‐−1 at a current density of 0.25A g‐−1 which was 6-fold greater than the undoped Co3O4 and 2‐–4-fold greater than Ag-doped Co3O4 nanocomposites prepared at other concentrations. The electrodes exhibited excellent cyclic stability with capacitance retention of 93% after 10,000 cycles having an energy density of 88.23 Wh kg‐−1 at 1.75 kW kg‐−1 power density indicating a promising material for supercapacitor application. Fabricated symmetric solid-state flexible device of Ag-doped Co3O4 also demonstrated reliable charge storage performance with a maximum energy density. The theoretical study also revealed that Ag doping into Co3O4 introduces additional localized states around the fermi level, between the highest occupied states and lowest unoccupied states. The presence of higher localized states near the Fermi level and smaller bandgap than Co3O4 enhanced the specific capacitance of the system, providing support to the experimental observation on improvement in energy charge storage.

Facile Synthesis of MOF-Derived Hierarchical Flower-Like Sr-Doped Co3O4 Structure for Effective TEA Sensing

Metal-organic framework (MOF)-derived metal oxide semiconductors (MOSs) have drawn great attention because of their abundant pore structures, large surface area, and good gas accessibility. Herein, hierarchical flower-like Sr-doped cobalt oxide (Co3O4) structure is obtained utilizing MOF as a self-sacrificing template. Compared with undoped Co3O4, the 2 mol% Sr-doped Co3O4 shows better triethylamine (TEA) sensing performance. It exhibits not only high response values of 52 (the response of undoped Co3O4 are about 3.3) and short response/recovery time (40/58 s) to 100 ppm TEA at a low working temperature of 160 °C, but also excellent selectivity and long-term stability, which show that the as-obtained flower-like Sr-doped Co3O4 structure is an effective material to detect TEA gas. The enhanced sensing properties are attributed to the synergistic effect of the creation of more oxygen vacancies and larger surface area of flower-like structure.

Construction of F-doped Co3O4/Co3O3.69F0.31 nanocomposite for boosting photocatalytic removal of organics from industrial waste H2O under visible-light

Visible-light (λ ≥ 420 nm) active fluorine (F) doped composite photocatalyst Co3O4/Co3O3.69F0.31 was prepared through substitution method. In this process, cobaltic oxide, Co3O4 was synthesized first; subsequently, F was introduced into Co3O4. The prepared Co3O4/Co3O4-xFx heterocomposite photocatalysts were characterized through X-ray Diffractometry (XRD), Scanning Electron Microscopy (SEM), EDX-mapping, UV–visible Spectrophotometry, X-ray Photoelectron Spectroscopy (XPS). Zeta potential indicates that the photocatalysts carrying negative charge on its surface which make the catalyst more suspended compare to undoped Co3O4. The Co3O4/Co3O4-xFx composite with several atom % of F demonstrated better photocatalytic activity compare to Co3O4 and TiO2 nanoparticles towards the decomposition of methyl blue (MB) and phenol in aqueous medium under visible light irradiation. The composition of Co3O4/Co3O4-xFx was optimized to 0.31 atom% (i.e., x = 0.31) of F doping with respect to degradation of organics in aqueous medium. After 2 h of visible irradiation, 33% decomposition MB and 45% degradation of phenol were achieved with Co3O4/Co3O3.69F0.31 composite photocatalyst whereas, Co3O4 and TiO2 demonstrated negligible decomposition efficiency. Due to F doping, the valence band (VB) level of Co3O4 was up-lifted which enhanced the absorption of visible light and made possible excitation of more and more VB electrons Co3O4/Co3O3.69F0.31 towards its conduction band (CB) and, thus CB electrons (e−) and VB holes (h+) are spatially separated. Experimental study proved that both the excited electrons (e−) and holes (h+) of Co3O4/Co3O3.69F0.31 composite took part in degrading photocatalytic reactions as well as enhanced photocatalytic efficiency.

Rapid synthesis and magnetic property characterization of Mg2+ doped Co3O4 nanostructures

Utilizing combustion method Mg substituted Co3O4 nanoparticles were prepared using the fuel L-alanine. The formation of the cubic spinel structure in the prepared undoped Co3O4 and Mg substituted Co3O4 is assured by X-ray diffraction (XRD) studies. The average crystallite size was observed to lie within 48.6 nm to 17.3 nm. The microstructural analysis shown that the prepared nanoparticles are porous in nature comprising of intragranular pores and melded grains with distinct grain boundaries. The bandgap values were determined using Kubelka–Munk (K–M) technique which was found to fall within 1.87–3.64 eV range. Interestingly, para-/superpara- magnetic characteristics was seen at ±15KOe by the magnetic studies. The FT-IR bands at 662 and 569 cm−1are attributed to the Co–O stretching mode of cubic spinel Co3O4 structure for the prepared samples. .

Toxic Gas Response for Nanostructured Cobalt Oxide Thin Films

The gas sensing properties of undoped Co3O4 and doped with Y2O3 nanostructures were investigated. The films were synthesized using the hydrothermal method on a seeded layer. The XRD, SEM analysis and gas sensing properties were investigated for the prepared thin films. XRD analysis showed that all films were polycrystalline, of a cubic structure with crystallite size of (12.6) nm for cobalt oxide and (12.3) nm for the Co3O4:6% Y2O3. The SEM analysis of thin films indicated that all films undoped Co3O4 and doped possessed a nanosphere-like structure.
 The sensitivity, response time and recovery time to H2S reducing and NO2 oxidizing gases were tested at different operating temperatures. The resistance changed with exposure to the test gas. The results revealed that the Co3O4:6%Y2O3 possessed the highest sensitivity around 90% (at room temperature) and 62.5% (at 150 oC) when exposed to the reducing gas H2S and oxidizing gas NO2, respectively with 0.8sec for both recovery and response times.

Mesoporous and macroporous Ag-doped Co3O4 nanosheets and their superior photo-catalytic properties under solar light irradiation

An ideal photocatalyst should have a wider absorption capacity, a larger surface area, a narrow optical band gap, a better electronic conductivity, a lower load transfer resistance and a minimum charge recombination probability. Herein, mesoporous and macroporous nanosheets of Ag·Co3O4 have been synthesized via a two-step hydrothermal and post-annealing approach. The catalytic activities of the doped and undoped Co3O4 samples were tested and compared using Methylene Blue dye (MB) as a model pollutant. The specific surface area, optical band gap, electrical conductivity, and charge transfer resistance of the fabricated samples were analyzed using BET, UV/Visible, I–V, and EIS analyses. The Ag·Co3O4 sample showed a higher catalytic aptitude than the pristine Co3O4 sample because it degrades comparatively higher concentration of MB dye at a faster rate under natural sunlight irradiation. Specifically, the Ag·Co3O4 sample eliminated 88.4% MB dye at the rate constant (k) of 2.1 × 10−2 min−1 in only 90 min of solar irradiation. The outstanding removal efficiency and higher rate performance of the Ag·Co3O4 sample is attributed to its novel bimodal-porous structure, higher surface area (258 m2 g-1), narrow bandgap (1.55 eV), good electrical conductivity (1.5 × 105 Sm−1) and smaller charge transfer resistance. The exceptional activity of the Ag·Co3O4 sample under solar irradiation reveal its greatest potential to eliminate toxic and harmful dyes from industrial effluents.

On the Stability of Co3O4 Oxygen Evolution Electrocatalysts in Acid

AbstractOxygen evolution reaction (OER) electrocatalysts suitable to work in acid are typically restricted to platinum group noble metal oxides because of their high activity and, especially, stability. Co3O4 is currently explored as an alternative OER catalyst. Herein we prepared Co3O4 films on fluorine‐doped Sn oxide (FTO) glass and Ti foil via thermal decomposition of nitrate salts and evaluated their activity and stability in 0.05 M H2SO4. Crystalline Co3O4 films deposited on FTO were stable during chronopotentiometry at 10 mA cm−2 for over 16 hours. The dissolution rate was 61 ngCo cm−2 min−1. The choice of a stable support such as FTO is essential to ensure the stability of the catalyst‐substrate interface and to prevent substrate passivation under OER conditions. Doping Co3O4 with Li resulted in a higher OER activity under acidic conditions to be attributed to the larger electrochemical surface area, although the stability was impeded compared to undoped Co3O4.

Study of the Structural and Optical Properties of Ni-doped Co3O4 Thin Films Using Chemical Spray Pyrolysis Technique

Undoped and Ni-doped Cobalt oxide thin films (Co3O4:Ni) with doping percentage (3, 6, and 9%) have been prepared by chemical spray pyrolysis technique on glass substrates at (400 °C). The structural, surface morphology and optical properties were studied. XRD results showed that all the films were polycrystalline and had a cubic structure with preferred orientation (111) plane for all doping. The AFM images appear to be smooth and homogenous films. The optical properties showed that the transmittance decreased by increasing the percentage of Ni, and the direct optical band gap decreased from (2.53 eV) to (2.32 eV) for undoped Co3O4 with increasing the doping percentage to (9%).

A tunable bifunctional hollow Co3O4/MO3 (M = Mo, W) mixed-metal oxide nanozyme for sensing H2O2 and screening acetylcholinesterase activity and its inhibitor.

A self-templated strategy was adopted to design hollow Co3O4/MO3 (M = Mo, W) mixed-metal oxides via the Mo or W doping of ZIF-67, and subsequent pyrolysis under an atmosphere of air at a low temperature of 450 °C. The hollow Co3O4/MO3 (M = Mo, W) mixed-metal oxides displayed tunable oxidase-like and peroxidase-like activities able to efficiently catalyze the oxidation of TMB to generate a deep blue color in the absence or presence of H2O2. Relative to that of the un-doped Co3O4, the oxidase mimic activity of the Mo-doped Co3O4 increased to 1.3 to 2.1-fold, while its peroxidase mimic activity increased to 7.1 to 19.9-fold, depending on different Mo doping amounts. The oxidase mimic activity of the W-doped Co3O4 increased to 2.1 to 2.3-fold, while its peroxidase mimic activity increased to 4.8 to 5.9-fold, depending on the different W doping amounts. The Mo- and W-doped Co3O4 nanohybrid exhibited both higher O2 and H2O2 activating capability, and their H2O2 activating capacity was superior to the O2 activating capability. Furthermore, the Mo- and W-doped Co3O4 nanohybrids exhibited similar O2 activating abilities, while the Mo-doped one displayed a higher H2O2 activating capability than the W-doped one. The discrepant peroxidase-like nature of Mo- and W-doped Co3O4 nanohybrids is likely attributed to their different catalytic mechanisms. The peroxidase-like activity of Mo-doped Co3O4 is highly related to the ˙OH free radical, while that of W-doped Co3O4 is likely ascribed to the electron transfer between TMB and H2O2. The Km values of Co3O4/MoO3 for TMB and H2O2 were 0.0352 mM and 0.134 mM, which were 3.2- and 1.9-fold lower than that of pure Co3O4, respectively. A Co3O4/MoO3-based colorimetric platform was developed for the determination of H2O2 in the 0.1-200 μM range, with a limit of detection of 0.08 μM (3σ). Based on the thiocholine (TCh) inhibition of the excellent peroxidase-like activity of Co3O4/MoO3 and the TCh generation via acetylcholinesterase (AChE) catalyzed hydrolysis of acetylthiocholine chloride (ATCh), the colorimetric platform was extended to screen AChE activity and its inhibitor.

Manganese doped Co3O4 mesoporous nanoneedle array for long cycle-stable supercapacitors

Long–term cycling stability is an important criterion and big challenge for pseudocapacitive materials. Ultra-stable manganese doped Co3O4 mesoporous nanoneedles were synthesized via one-step hydrothermal reaction followed by annealing grown on nickel foam (noted as MnxCoyO/NF, x + y = 2.25) for supercapacitors. The Mn doping in Co3O4 was confirmed by several techniques. Among various MnxCoyO/NF electrodes, the Mn1.5Co0.75O/NF demonstrated the superior electrochemical performance, with an excellent cycling stability of 104% capacitance retention after 10 000 charge–discharge cycles at 6 A g−1, as well as a good capability (668.4 F g−1 at 1 A g−1 compared to that of undoped Co3O4 which is 201.3 F g−1). Moreover, the assembled asymmetric supercapacitor based on Mn1.5Co0.75O/NF//graphene performs a high energy density of 25.88 Wh kg−1 (at 359.5 W kg−1) and a high power density of 14.7 kW kg−1(at 10.63 Wh kg−1). The improved electrochemical properties are mainly owing to the enhanced intrinsic conductivity and electrochemical activity of Co3O4 after doped with appropriate Mn concentration. The three-dimensional nanostructure of mesoporous nanoneedle array grown on NF also provides short ion diffusion path and large active surface areas, contributing to the high rate performance and high energy density. This study may offer a new approach to fabricate the unique 3D nanostructured electrode materials based on doped metal oxides for supercapacitors with long-term cycling stability and high energy density.

Characterization of Mn-Doped Co3O4 Thin Films Prepared by Sol Gel-Based Dip-Coating Process

Abstract In this article, manganese-doped cobalt oxide (Mn-doped Co3O4) thin films have been prepared on glass substrates using sol gel-based dip-coating technique in order to investigate their optical, structural and electrical properties. The Mn concentration was changed from 0 % to 9 %. The synthesized samples were characterized by ultraviolet-visible spectroscopy (UV-visible), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and complex impedance spectroscopy to elucidate the optical, structural, vibrational and electrical properties. Our optical results show that the transmittance of Mn-doped Co3O4 films decreases with increasing doping levels. The optical band gaps were found to be ( E g 1 = 1.51 e V , E g 2 = 2.12 e V ) ({E_{g1}} = 1.51{\ }eV, {E_{g2}} = 2.12{\rm{ eV}}) and ( E g 1 = 1.23 e V , E g 2 = 1.72 e V ) ({E_{g1}} = 1.23{\ }eV, {E_{g2}} = 1.72{\rm{ eV}}){\ } for the case of undoped Co3O4 and 9 % Mn-doped Co3O4, respectively. This shift means that the impurities would create energy levels. The structural analysis provides evidence that obtained powders were crystallized in cubic spinel structure. The complementary phase information is provided by FTIR spectroscopy. The FTIR study depicted the presence of four distinct bands characterizing Mn-doped Co3O4 cubic spinel-type structure. The Nyquist plots suggest that the equivalent circuit of Mn-doped Co3O4 films is an RpCp parallel circuit. It was found that the effective resistance Rp decreases, whereas the effective capacitance Cp increases with doping.