Pristine Co3O4 Research Articles

Fe2O3-Co3O4 nanocomposite gas sensor for ethanol sensing studies

This study focused on pristine Fe2O3, pristine Co3O4, and Fe2O3-Co3O4 composite using the Pechini sol-gel method for ethanol gas sensing applications. Advanced characterization techniques were used to analyze the phase, morphology, and composition of the synthesized materials. Gas sensors were then fabricated and used for ethanol gas sensing at different temperatures. The results indicated that Fe2O3-Co3O4 composite gas sensor crystallized at 600 °C, had higher response compared to both pristine Fe2O3 and pristine Co3O4 gas sensors. The composite sensor manifested a high response of 26.2–100 ppm ethanol at 250 °C, while maximum responses of pristine Co3O4 gas sensor was only 4.4 at 200 °C and that of pristine Fe2O3 sensor was 11.4 at 300 °C. The boosted sensing performance of the composite sensor was related to the formation of p-n heterojunctions between Co3O4 and Fe2O3 in composite sensor, the formation of dangling bonds at interfaces, and high intrinsic ethanol sensing properties of Fe2O3.

Hydroxylation of an ultrathin Co3O4(111) film on Ir(100) studied by in situ ambient pressure XPS and DFT

In the present work, we have studied the interaction of water with spinel cobalt oxide (Co3O4), an effect which has been considered a major cause of its catalytic deactivation. Employing a Co3O4(111) model thin film grown on Ir(100) in (ultra)high vacuum, and ambient pressure X-ray photoelectron spectroscopy (APXPS), hydroxylation in 0.5 mbar H2O vapor at room temperature was monitored in real time. The surface hydroxyl (OH) coverage was determined via two different models based (i) on the termination of a pristine and OH-covered Co3O4(111) surface as derived from density functional theory (DFT) calculations, and (ii) on a homogeneous cobalt oxyhydroxide (CoO(OH)) overlayer. Langmuir pseudo-second-order kinetics were applied to characterize the OH evolution with time, suggesting two regimes of chemisorption at the mosaic-like Co3O4(111) film: (i) plateaus, which were quickly saturated by OH, followed by (ii) slow hydroxylation in the “cracks” of the thin film. H2O dissociation and OH formation, blocking exposed Co2+ ions and additionally consuming surface lattice oxygen, respectively, may thus account for catalyst deactivation by H2O traces in reactive feeds.

Broadband dielectric spectroscopy studies of Co3O4 and Co2TiO4 two-phase spinel composites

Broadband dielectric spectroscopy studies of the two-phase composites, (1 – x) Co3O4 + x Co2TiO4, have been reported over a wide range of compositions (0 ≤ x ≤ 1) and temperatures (80 K ≤ T ≤ 573 K). Normal spinel Co3O4 and inverse spinel Co2TiO4 phases are well distinguishable with ∼4.6 % variation in the lattice parameter of the Co3O4 phase with an increase of x from 0 to x = 1. The ac-conductivity (σ) of this composite follows Johnscher's power law (∼Aωs) variation with frequency exponent factor ‘s’ both greater than as well as less than unity. The temperature dependence of ‘σ’ reveals the Arrhenius-like behavior instead of variable range hopping of charge carriers with activation energy in the 2–1800 meV range. Systematic analysis of such conductivity mechanisms for all the compositions is compared with the pristine Co3O4 system.

Photothermal Assisted Biomass Oxidation for Pairing Carbon Dioxide Electroreduction with Low Cell Potential.

Integrating anodic biomass valorization with carbon dioxide electroreduction (CO2RR) can produce value-added chemicals on both the cathode and anode; however, anodic oxidation still suffers from high overpotential. Herein, a photothermal-assisted method was developed to reduce the potential of 5-hydroxymethyl furfural (HMF) electrooxidation. Capitalizing on the copious oxygen vacancies, defective Co3O4 (D-Co3O4) exhibited a stronger photothermal effect, delivering a local temperature of 175.47 °C under near infrared light illumination. The photothermal assistance decreased the oxidation potential of HMF from 1.7 V over pristine Co3O4 to 1.37 V over D-Co3O4 to achieve a target current density of 30 mA cm-2, with 2,5-furandicarboxylic acid as the primary product. Mechanistic analysis disclosed that the photothermal effect did not change the HMF oxidation route but greatly enhanced the adsorption capacity of HMF. Meanwhile, faster electron transfer for direct HMF oxidation and the surface conversion to cobalt (oxy)hydroxide, which contributed to indirect HMF oxidation, was observed. Thus, rapid HMF conversion was realized, as evidenced by in situ surface-enhanced infrared spectroscopy. Upon coupling cathodic CO2RR with an atomically dispersed Ni-N/C catalyst, the Faradaic efficiencies of CO (cathode) and 2,5-furandicarboxylic acid (FDCA, anode) exceeded 90.0 % under a low cell potential of 1.77 V.

A vertically aligned flake like CuO/Co3O4 nanoparticle@g-C3N4 ternary nanocomposite: A heterojunction catalyst for efficient photo electrochemical water splitting

Efficient utilization of solar energy for the conversion of water into hydrogen via photoelectrochemical (PEC) water splitting holds tremendous promise for sustainable energy production. In this study, we report a novel vertically aligned flake-like CuO/Co3O4 nanoparticle@g-C3N4 sheets ternary nanocomposite as a heterojunction catalyst for enhancing PEC water splitting efficiency. The ternary nanocomposite was synthesized via a facile and scalable method, resulting in a unique structure with vertically aligned CuO/Co3O4 nanoparticles in tight interface interaction with g-C3N4 sheets. The resulting heterojunction exhibited enhanced light absorption, efficient charge separation, and improved charge transfer kinetics, leading to significantly enhanced PEC water splitting performance. The as-synthesized ternary nanocomposite, such as CuO/Co3O4@g-C3N4 nanocomposite, demonstrated superior PEC activity with an enhanced photocurrent density, i.e., 0.88 mA/cm2, which is higher than that of the pristine CuO (0.65 mA/cm2), Co3O4 (0.7 mA/cm2), and CuO-Co3O4 (0.77 mA/cm2) structures with linear sweep voltammetry under light irradiation. Additionally, the ternary nanocomposite exhibited excellent stability during 2 h PEC water splitting measurements under 1 h time interval chopped conditions. The remarkable performance of the vertically aligned CuO/Co3O4 nanoparticle@g-C3N4 ternary nanocomposite underscores its potential as a promising catalyst for efficient solar-driven hydrogen generation. This study not only provides insights into the design of advanced heterojunction catalysts but also contributes to the development of sustainable energy conversion technologies.

Construction of Co3O4/Bi5O7I heterojunction derived from ZIF-67/BiOI with enhanced photodegradation ability

Recently, the degradation of expired and unused antibiotics has been a great concern for human health, and it has become a serious environmental hazard. Photocatalysis technology has treated the most promising ways to degrade antibiotics in the environment with high efficiency and low cost. A series of Co3O4/Bi5O7I composites were successfully synthesized via the calcination method derived from Zeolitic imidazolate frameworks-67 and Bismuth oxyiodide, and chatacerized by spectroscopic and also X-ray diffraction (XRD) processes. Co3O4/Bi5O7I composites exhibited enhanced photocatalytic performance for tetracycline degradation, which is about 6 times higher than that of the pristine Co3O4. The Co3O4/Bi5O7I can remove 86.67% tetracycline in 90 min and shows enhanced photocatalytic activities, which are about 6 times higher than those of the pristine Co3O4. The possible mechanisms of photocatalytic degradation were analyzed by trapping experiments, electron paramagnetic resonance, photocurrent, and electrochemical impedance measurements. The direct Z-scheme structure of Co3O4/Bi5O7I composites facilitated the charge separation and transportation of the photogenerated electrons and holes.

Synergistic doping and de-doping of Co3O4 catalyst for effortless formaldehyde oxidation

The pursuit of high-performance non-precious metal catalysts for Volatile Organic Compounds (VOCs) abatement is paramount in meeting stringent environmental regulations. In this study, we present a groundbreaking approach by crafting a highly defective Co3O4 catalyst through a strategic process involving Mg doping and subsequent partial de-doping. The catalyst exhibited an exceptional activity in the oxidation of formaldehyde (HCHO), achieving a remarkable conversion rate of 2.92 μmol·m−2·h−1, which is 3.1 times that of the pristine Co3O4 at 100 °C and an HCHO space velocity of 75,000 mL·g−1·h−1. Our methodology involves a dual-action process of doping and de-doping, orchestrating the introduction of significant structural and surface defects. These include surface cracks, lattice distortions, cationic vacancies, oxygen vacancies, lower metal coordination, and more. This orchestrated creation of defects serves to amplify the generation of active oxygen sites, thereby enhancing the intrinsic oxidative ability of the catalyst. The net result is a lowered activation energy barrier for HCHO, further contributing to the catalyst performance enhancement. This study not only establishes a new benchmark for Co3O4 catalysis but also provides insightful paradigms for the role of defects engineering in promoting non-noble metal-catalyzed volatile organic compounds oxidation.

Regulating surface properties of Co3O4@MnO2 catalysts through Co3O4-MnO2 interfacial effects for efficient toluene catalytic oxidation

Interface engineering between Co3O4 and MnO2 shows distinct advantages in regulating the surface properties of catalysts. However, there is still doubt about whether the interfacial effects originate from the interaction between heterogeneous metals and Co3+ or Co2+. Herein, Co3O4-MnO2 interface was successfully constructed on Co3O4 primarily exposed different crystal planes to design Co ions that were directly linked to MnO2 at Co3O4-MnO2 interface. Combining the results of systematic characterizations and catalytic performance evaluation, it is found that the oxidative decomposition of toluene over Co3O4@MnO2 catalysts is significantly accelerated in comparison with the pristine Co3O4, which can be attributed to the greatly increased Co3+ and adsorbed oxygen species as well as specific surface area after the successful construction of Co3O4-MnO2 heterointerface. However, Co3O4-MnO2 interface shows much greater influence on Co3O4@MnO2-100 where Co ions mainly exist in the form of Co2+ than that on Co3O4@MnO2-110 dominated by Co3+. Furthermore, catalytic performance evaluation results illustrate that the T90 of Co3O4@MnO2-110 has only decreased by 11 °C compared to Co3O4-110, while the T90 of Co3O4@MnO2-100 is 50 °C lower than that of Co3O4-100. Therefore, based on the above results it speculates that the strong interaction between MnO2 and Co3O4 at Co3O4-MnO2 hetero-interface may originate more from the synergistic effect between MnO2 species and Co2+ ions. In addition, the in-situ DRIFTS demonstrate that the oxidation of toluene over Co3O4@MnO2 catalysts follows the path of toluene → benzaldehyde → benzoate → maleic anhydride → water and carbon dioxide.

Deep eutectic solvent-assisted synthesis of transition metal oxide and its integration into polymer matrix for supercapacitor

Transition metal oxide-based materials continue to attract interest in energy and environmental applications due to their unique characteristics. However, their integration with polymers needs to be explored to achieve enhanced capacitance values. To address this issue, two step strategy is utilized wherein the first step involves preparation of a pristine transition metal oxide (Co3O4) by a deep eutectic solvent (DES) consisting of choline chloride and hydrogen donor ethyelene glycol in the ratio of 2:1. In the second step the environmentally friendly high energy ball milling is utilized with strong mechanical forces producing desired poly-3-dodecyl thiophene (P3DDT)-wrapped cobalt oxide (Co3O4). The structural and morphological properties of the prepared Co3O4 and its composite (P3DDT-Co3O4) are determined by aid of X-ray diffraction (XRD) studies, Field emission scanning electron microscope (FESEM), and X-ray photoelectron spectroscopy (XPS). The synthesized Co3O4 exhibited petal-like morphology, whereas in P3DDT-Co3O4 the polymer appears to be completely wrapped on transition metal oxide. The electrochemical characteristics of electrodes were studied. The P3DDT-Co3O4 exhibited higher specific capacitance (294F/g) than pristine Co3O4 (174F/g) at a current density of 1 A/g and its retention capacity increased (96%) and then decreased (93%) over 5000 cycles in a three-electrode cell assembly. The lowest capacitance (136F/g) was obtained for P3DDT. Experimental results demonstrate that the design is suitable for upgrading favorably active electrochemical spots in Co3O4 during the incorporation of P3DDT by the ball-milling procedure, showing outstanding performance in energy-storage applications.

Catalysing a sustainable future: Harnessing solar energy with novel Co3O4@VO2 nanocomposites for enhanced photocatalytic hydrogen generation and dye degradation

This study focuses on the hydrothermal synthesis and characterization of Concentration dependent Co3O4@VO2 nanocomposites with varying molar ratios of Co3O4 to VO2 (2:1, 1:1, and 1:2) for efficient hydrogen generation and dye degradation. The structural and morphological characteristics of the prepared nanocomposites were analysed using x-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). Crystallographic analysis using XRD confirmed the formation of crystalline Co3O4 with a monoclinic structure, while the presence of VO2 was identified by characteristic peaks in the XPS. Microscopic analysis using SEM and TEM revealed well-dispersed nanocomposites with nanoscale dimensions. Photocatalytic activities were evaluated for hydrogen evolution and dye degradation, with the nanocomposite featuring a 2:1 ratio of Co3O4 to VO2 (CV-21) demonstrating significantly enhanced performance. CV-21 exhibited a lower onset potential and higher current density for hydrogen evolution (2270μmol/h/g), indicating improved photocatalytic activity. Additionally, it displayed rapid and superior dye degradation (93% within 10 min) under sunlight compared to Victoria blue B (VBB) dye. The Co3O4@VO2 nanocomposites, particularly CV-21, demonstrate enhanced photocatalytic performance for hydrogen generation and dye degradation compared to pristine VO2 and Co3O4. This improvement possibly due to synergistic effects between Co3O4 and VO2, optimized structural characteristics, and improved interfacial properties in the nanocomposite structure. These findings highlight the promising potential of Co3O4@VO2 nanocomposites, particularly CV-21, for environmental remediation applications.

Three-Dimensional Network of Highly Uniform Cobalt Oxide Microspheres/MXene Composite as a High-Performance Electrocatalyst in Hydrogen Evolution Reaction.

Due to its affordable cost, excellent redox capability, and relatively effective resistance to corrosion in alkaline environments, spinel Co3O4 demonstrates potential as a viable alternative to noble-metal-based electrocatalysts. Nevertheless, these materials continue to exhibit drawbacks, such as limited active surface area and inadequate intrinsic conductivity. Researchers have been trying to increase the electrical conductivity of Co3O4 nanostructures by integrating them with various conductive substrates due to the low conductivity of pristine Co3O4. In this study, uniform cobalt glycerate solid spheres are first synthesized as the precursor and subsequently transformed into cobalt oxide microspheres by a simple annealing procedure. Co3O4 grown on the surface of Ti3C2Tx-MXene nanosheets (Co3O4/MXene) was successfully synthesized through electrostatic attraction. In order to create a positively charged surface, the Co3O4 microspheres were treated with aminopropyltriethoxysilane. The Co3O4/MXene exhibited a low overpotential of 118 mV at 10 mA cm-2 and a Tafel slope of 113 mV dec-1 for the hydrogen evolution reaction, which is much lower than the pristine Co3O4 at 232 and 195.3 mV dec-1.

Effortless Fabrication of Bi2O3‐Co3O4 Nanocomposite Catalyst: Harnessing Photocatalytic Power for Efficient Cationic Dye Degradation

AbstractA cost‐effective and simple co‐precipitation approach was used to create an efficient photocatalyst Co3O4‐Bi2O3 with identical stoichiometry (1 : 1 of both Co3O4 and Bi2O3). XRD, FTIR, TEM, SEM‐EDS, XPS, UV‐DRS, PL, BET, and TGA were used to characterize the produced material‘s structural and optical properties. The presence of a single phase spinel structure with a distinctive plane (311) was verified by the XRD peak of 2 at 36.9° for Co3O4‐Bi2O3. The SEM pictures revealed clustered consolidated spheres, suggesting particle homogeneity and high interconnectedness. The HR‐TEM and SAED pictures revealed an average crystallite size of 28 nm for the Co3O4‐Bi2O3 heterojunction. The UV‐DRS spectral data demonstrated a 2.1 eV reduction in band gap energy for Co3O4‐Bi2O3 (whereas Co3O4 is 2.4 eV and Bi2O3 is 2.7 eV). Under solar light irradiation, pristine Co3O4, Bi2O3, and Co3O4‐Bi2O3 composites were investigated for photocatalytic degradation of Methylene Blue (MB) and Malachite green (MG) dyes. By adjusting factors such as pH, starting dye concentration, catalyst dosage, and agitation duration, the optimal efficiency was determined. The acquired results showed Co3O4‐Bi2O3 ′s superior activity over both precursors. The composite obtained maximal degradation of 98 % (at pH=11) and 97 % (at pH=9) for MB and MG, respectively. The enhanced photo degradation activity of Co3O4‐Bi2O3 can be due to larger visible light absorption, increased surface area, and decreased h+/e− recombination. The reactive species trapping study was performed to determine the importance of superoxide and hydroxyl radicals during photo degradation. Dye degradation was governed by a pseudo‐first‐order kinetic model. The reusability and stability of Co3O4‐Bi2O3 were confirmed by utilizing the same material for five consecutive runs with both MB and MG dyes. Mass spectra analysis provided insights into the successful degradation of dyes, elucidating intermediate products. The synthesized Co3O4‐Bi2O3 nanocomposite offers unrivalled advantages in terms of structural and optical properties, superior photocatalytic activity, and remarkable stability, making it a promising candidate for efficient dye degradation applications without the formation of toxic by‐products.

Dual Applications of Cobalt-Oxide-Grafted Carbon Quantum Dot Nanocomposite for Two Electrode Asymmetric Supercapacitors and Photocatalytic Behavior.

Carbon materials, such as graphene, carbon nanotubes, and quantum-dot-doped metal oxides, are highly attractive for energy storage and environmental applications. This is due to their large surface area and efficient optical and electrochemical activity. In this particular study, a composite material of cobalt oxide and carbon quantum dots (Co3O4-CQD) was prepared using cobalt nitrate and ascorbic acid (carbon source) through a simple one-pot hydrothermal method. The properties of the composite material, including the functional groups, composition, surface area, and surface morphology, were evaluated by using various methods such as ultraviolet, Fourier transform infrared, X-ray diffraction, Raman, X-ray photoelectron spectroscopy, Brunauer-Emmett-Teller, scanning electron microscopy, and transmission electron microscopy analysis. The electrochemical performance of the Co3O4-CQD composite has been studied using a three-electrode system. The results show that at 1 A g-1, the composite delivers a higher capacitance of 1209 F g-1. The asymmetric supercapacitor (Co3O4-CQD//AC) provided 13.88 W h kg-1 energy and 684.65 W kg-1 power density with a 96% capacitance retention. The Co3O4-CQD composite also demonstrated excellent photocatalytic activity (90% in 60 min) for the degradation of methylene blue dye under UV irradiation, which is higher than that of pristine Co3O4 and CQD. This demonstrates that the Co3O4-CQD composite is a promising material for commercial energy storage and environmental applications.

Preparation of a high-performance H2S gas sensor based on CuO/Co3O4 composite derived from bimetallic MOF

The bimetallic metal–organic frameworks (MOFs), Cu/Co-MOF, was synthesized through a solvothermal method and calcined to obtain CuO/Co3O4 composites. By adjusting the molar ratio between Cu and Co ions, a composite material of CuO/Co3O4 (Cu:Co = 1:1) was developed and showed excellent sensing capabilities, and the response reached as high as 196.3 for 10 ppm H2S detection. Furthermore, the optimal operating temperature as low as 40 °C was found. In comparison with the sensors prepared by pristine CuO and pristine Co3O4, the sensor based on CuO/Co3O4 composite exhibited a significant response. Additionally, the sensor can detect H2S gas down to 300 ppb. The gas sensing mechanism is discussed in depth from the perspective of p–p heterojunction formation between the p-type CuO and p-type Co3O4. The as-prepared CuO/Co3O4 composite-based sensor is expected to find practical application in the low-power monitoring of H2S.

Electronic Reconstruction via Low‐Degree Fluorination for High‐Performance Zinc‐Ion Battery

AbstractThe development of transition metal oxide cathodes with high capacity and ultralong lifespan is one of the keys to promoting the performance of aqueous zinc–ion batteries, but it remains a crucial challenge. Herein, cobalt oxide is applied as an example to demonstrate that low‐degree fluorination is a novel approach to synergistically boost charge storage kinetics and stability. Specifically, partial substitution of O2− with F− intensifies electron delocalization of Co 3d orbitals, which reduces bulk charge transfer impedance and endows surface active sites with higher reactivity, thus achieving boosted redox kinetics and energy density. Moreover, the modification of coordination structure with the highest‐electronegativity F− can effectively inhibit irreversible phase transition and structural deformation, which assures significantly optimized cycling stability. As a result, the fluorinated Co3O4 demonstrates a distinctly improved specific capacity of 406 mAh g−1 at 1 A g−1, approximately a threefold increase compared to one of pristine Co3O4 (131 mAh g−1). The assembled fluorinated Co3O4//Zn battery delivers an ultrahigh energy density of 658 Wh kg−1 at 3.5 kW kg−1 and 95.7% capacity retention after 10 000 cycles. This work offers a new understanding of the electronic engineering of metal oxides toward high‐performance energy storage applications.

Engineering of Co3O4 electrode via Ni and Cu-doping for supercapacitor application.

Although cobalt oxides show great promise as supercapacitor electrode materials, their slow kinetics and low conductivity make them unsuitable for widespread application. We developed Ni and Cu-doped Co3O4 nanoparticles (NPs) via a simple chemical co-precipitation method without the aid of a surfactant. The samples were analyzed for their composition, function group, band gap, structure/morphology, thermal property, surface area and electrochemical property using X-ray diffraction (XRD), ICP-OES, Fourier transform infrared (FTIR) spectroscopy, Ultraviolet-visible (UV-Vis), Scanning electron microscopy (SEM), Thermogravimetric analysis (TGA) and/or Differential thermal analysis (DTA), Brunauer-Emmett-Teller (BET), and Impedance Spectroscopy (EIS), Cyclic voltammetry (CV), respectively. Notably, for the prepared sample, the addition of Cu to Co3O4 NPs results in a 11.5-fold increase in specific surface area (573.78m2g-1) and a decrease in charge transfer resistance. As a result, the Ni doped Co3O4 electrode exhibits a high specific capacitance of 749Fg-1, 1.75 times greater than the pristine Co3O4 electrode's 426Fg-1. The electrode's enhanced surface area and electronic conductivity are credited with the significant improvement in electrochemical performance. The produced Ni doped Co3O4 electrode has the potential to be employed in supercapacitor systems, as the obtained findings amply demonstrated.

An in situ phase transformation induced mesoporous heterointerface for the alkaline hydrogen evolution reaction.

The phase structure of a catalyst plays a crucial role in determining the catalytic activity. In this study, a facile phosphorization process is employed to achieve the in situ phase transformation from single-phase Co3O4 to CoO/CoP hybrid phases. Characterization techniques, including XRD, BET, SEM, and TEM, confirm the retention of the mesoporous nature during the phase transformation, forming porous CoO/CoP heterointerfaces. Strong charge transfer is observed across the CoO/CoP heterointerface, indicating a robust interaction between the hybrid phases. The CoO/CoP hybrid exhibits significantly enhanced catalytic activity for the alkaline hydrogen evolution reaction (HER) compared to pristine Co3O4. Density Functional Theory (DFT) calculations reveal that the elimination of the band gap in the spin-down band of Co in CoO/CoP contributes to the observed high HER activity. The findings highlight the potential of CoO/CoP hybrids as efficient catalysts for HER, and contribute to the advancement of catalyst design for sustainable energy applications.

MOF-derived Al3+-doped Co3O4 nanocomposites for highly n-butanol gas sensing performance at low operating temperature

High-performance gas sensors based on metal oxides for detecting Volatile Organic Compounds (VOCs) at low operating temperatures have garnered considerable attention due to their practical utility and energy efficiency. In this study, we synthesized the Al/Co metal-organic framework (MOF) by using a hydrothermal method. Subsequently, Al3+-doped Co3O4 (Al3+-Co3O4) nanocomposites with varying Al3+ concentrations were obtained through calcination. When applied to gas sensors, the Al3+-Co3O4 nanocomposites-based gas sensors exhibited excellent sensing properties toward n-butanol at a low operating temperature (100 ℃). Specifically, the response of the 10% Al3+-Co3O4 nanocomposite to 20 ppm n-butanol reached 116.7, representing an approximately 5.5-fold improvement compared to pristine Co3O4. The gas sensor based on the 10% Al3+-Co3O4 nanocomposite also demonstrated commendable repeatability, selectivity, and stability. This suggests that Al3+ doping results in Al3+-Co3O4 possessing a more intact spherical morphology. Doping significantly enhances the gas-sensing performance of Al3+-Co3O4 due to increased oxygen vacancies and a narrower band gap energy. These findings inspire the development of new p-type metal oxide semiconductor gas sensors operating at low temperatures.

Modulated Electronic Structure of Co3O4 by Single Atoms for Efficient Anodic Oxygen Evolution in Acid.

The challenge of the practical application of a water electrolyzer system lies in the development of low-manufacturing cost, highly active, and stable electrocatalysts to replace the noble metal ones, in order to enable environmentally friendly hydrogen production on a large scale. Herein, a facile method is proposed for boosting the performance of Co3O4 through the incorporation of large-sized single atoms. Due to the larger ionic radius of rare earth metals than that of Co, the incorporation elongates the bond length of Co─O, resulting in the narrowed d-p band centers and the high spin configuration, which is favorable for the interaction and charge transfer with absorbent (*OH). As a result, the Ce-incorporated Co3O4 with the longest Co─O bond length exhibits the best oxygen evolution reaction (OER) performance, specifically, the turnover frequency is over 17 times higher than that of pristine Co3O4 nanosheet under an overpotential of 400mV. Powered by a commercial Si solar cell, a two-electrode solar water-splitting device combining Ce-incorporated Co3O4 and Pt delivers a solar-to-hydrogen conversion efficiency of 13.53%. The strategy could provide a new insight for improving the performance of OER electrocatalysts in acid toward practical applications.

Tuning selectivity of CO2 hydrogenation over Co catalysts by surface decoration of Sn

Hydrogenation of CO2 to valuable chemicals is in great attention while modulating the selectivity of catalyst is still a challenging issue. Herein, the selectivity tuning from CH4 to CO was achieved over the Co-based catalysts through Sn decoration. The pristine Sn-doped Co3O4 was prepared by a hydrothermal method, and was found to convert as an exposed metal Co phase along with the segregation and accumulation of Sn on the surface after the reduction pretreatment. Through a combination of experimental and density functional theory calculations, the role of Sn was illustrated to modify the Co sites chemically instead of directly participating into catalysis, leading to a weaken dissociation activity of CO and H2 occurring preferably on the pure Co sites. As a result, it promotes the desorption of intermediate CO from catalyst surface as a main product, thereby achieving high CO selectivity (∼100 %) over the Sn-Co catalyst, in sharply contrast to the predominant CH4 selectivity (>90 %) over the un-modified Co site. This work provides an understanding of chemical modulation of the metal sites through a bimetallic architecture, especially in tailoring catalytic selectivity of CO2 hydrogenation.