Crystal Plane Effect of Co3O4 on Styrene Catalytic Oxidation: Insights into the Role of Co3+ and Oxygen Mobility at Diverse Temperatures

Multifunctional heterostructured CoS2@Co3O4 nanosheets synergistically enhance polysulfide adsorption and conversion in lithium-sulfur batteries

The practical application of lithium-sulfur (Li-S) batteries faces numerous challenges, primarily due to the shuttle effect of soluble lithium polysulfides (LiPSs) and the sluggish electrochemical reaction kinetics during their conversion to Li2S, resulting in poor cycling performance. To address these issues, this study employed a vapor deposition technique to in situ construct a CoS2@Co3O4 heterostructure with superior interfacial properties on a Co3O4 substrate, followed by crosslinking and optimization with reduced graphene oxide (rGO). Density functional theory (DFT) calculations reveal for the first time that the incorporation of S effectively modulates the d-band center of Co, which not only enhances the chemical adsorption capability of the heterointerface toward lithium polysulfides but also optimizes the catalytic pathway for sulfur species conversion. Comprehensive experimental results and theoretical calculations confirm that the CoS2@Co3O4 heterostructure exhibits multiple advantages, including strong adsorption capability, high catalytic activity, rapid Li+ transport efficiency, and excellent electrical conductivity. The CoS2@Co3O4 heterostructure not only significantly suppresses the LiPSs shuttle effect but also greatly accelerates the electrochemical reaction kinetics of LiPSs and Li2S. Compared to materials composed solely of CoS2 or Co3O4, the CoS2@Co3O4 heterostructure demonstrates synergistically enhanced electrochemical performance in Li-S batteries. At a current density of 2C, a representative Li-S battery achieves nearly 100 % Coulombic efficiency, with a reversible specific capacity of 827 mAh g-1 retained after 1000 cycles, corresponding to a capacity decay rate of only 0.007 % per cycle. Even under high sulfur loading conditions (5.1 mg cm-2), the battery maintains stable cycling performance. This work provides novel insights and directions for designing multifunctional heterostructures with synergistic effects for applications in lithium-ion batteries and catalytic fields.

Insight into the Synergistic Effect of Binary Nonmetallic Codoped Co3O4 Catalysts for Efficient Ethyl Acetate Degradation under Humid Conditions

The synthesis of high-performance catalysts for volatile organic compounds (VOCs) degradation under humid conditions is essential for their practical industrial application. Herein, a codoping strategy was adopted to synthesize the N-Co3O4-C catalyst with N, C codoping for low-temperature ethyl acetate (EA) degradation under humid conditions. Results showed that N-Co3O4-C exhibited great catalytic activity (T 90 = 177 °C) and water resistance (5.0 vol% H2O, T 90 = 178 °C) for EA degradation. Characterization results suggested that the C, N codoping weakened the Co-O bond strength, increased surface Co3+ and Oads species, and improved the low-temperature redox ability and the mobility of lattice oxygen species, which boosted the catalytic performance of N-Co3O4-C for EA degradation. Meanwhile, the N-doping-induced oxygen vacancies could interact with water vapor to generate extra active oxygen species, which enhanced the water resistance. Importantly, based on a series of characterization technologies, in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), and theoretical calculations, the synergistic effect of C, N codoping was systematically investigated and elucidated. The C doping induced the increase of surface area and the weakening of Co-O bond strength, which improved EA adsorption and lattice oxygen species activation to dissociate and oxidize EA, forming the key intermediate, acetate acid. N doping enhanced the adsorption and activation of gaseous oxygen species to form active oxygen species, attacking and breaking the C-C bond in acetate acid to accelerate EA deep oxidation, which synergistically facilitated EA degradation.

Weakening Mn-O Bond Strength in Mn-Based Perovskite Catalysts to Enhance Propane Catalytic Combustion

Exploring highly efficient and robust non-noble metal catalysts for VOC abatement is crucial but challenging. Mn-based perovskites are a class of redox catalysts with good thermal stability, but their activity in the catalytic combustion of light alkanes is insufficient. In this work, we modulated the Mn-O bond strength in a Mn-based perovskite via defect engineering, over which the catalytic activity of propane combustion was significantly enhanced. It demonstrates that the oxygen vacancy concentration and the Mn-O bond strength can be efficiently modulated by finely tuning the Ni content in SmNixMn1-xO3 perovskite catalysts (SNxM1-x), which in turn can enhance the redox ability and generate more active oxygen species. The SN0.10M0.90 catalyst with the lowest Mn-O bond strength exhibits the lowest apparent activation energy, over which the propane conversion rate increases by 3.6 times compared to that on the SmMnO3 perovskite catalyst (SM). In addition, a SN0.10M0.90/cordierite monolithic catalyst can also exhibit a remarkable catalytic performance and deliver excellent long-term durability (1000 h), indicating broad prospects in industrial applications. Moreover, the promotional effect of Ni substitution was further unveiled by density functional theory (DFT) calculations. This work brings a favorable guidance for the exploration of highly efficient perovskite catalysts for light alkane elimination.

Utilizing the oxygen-atom trapping effect of Co3O4 with oxygen vacancies to promote chlorite activation for water decontamination

Heterogeneous high-valent cobalt-oxo [≡Co(IV)=O] is a widely focused reactive species in oxidant activation; however, the relationship between the catalyst interfacial defects and ≡Co(IV)=O formation remains poorly understood. Herein, photoexcited oxygen vacancies (OVs) were introduced into Co3O4 (OV-Co3O4) by a UV-induced modification method to facilitate chlorite (ClO2-) activation. Density functional theory calculations indicate that OVs result in low-coordinated Co atom, which can directionally anchor chlorite under the oxygen-atom trapping effect. Chlorite first undergoes homolytic O-Cl cleavage and transfers the dissociated O atom to the low-coordinated Co atom to form reactive ≡Co(IV)=O with a higher spin state. The reactive ≡Co(IV)=O rapidly extracts one electron from ClO2- to form chlorine dioxide (ClO2), accompanied by the Co atom returning a lower spin state. As a result of the oxygen-atom trapping effect, the OV-Co3O4/chlorite system achieved a 3.5 times higher efficiency of sulfamethoxazole degradation (~0.1331 min-1) than the pristine Co3O4/chlorite system. Besides, the refiled OVs can be easily restored by re-exposure to UV light, indicating the sustainability of the oxygen atom trap. The OV-Co3O4 was further fabricated on a polyacrylonitrile membrane for back-end water purification, achieving continuous flow degradation of pollutants with low cobalt leakage. This work presents an enhancement strategy for constructing OV as an oxygen-atom trapping site in heterogeneous advanced oxidation processes and provides insight into modulating the formation of ≡Co(IV)=O via defect engineering.

O-Vacancy Mediated Partially Inverted Ferrospinels for Enhanced Activity in the Sulfuric Acid Decomposition for Hydrogen Production

Understanding the characterization of a tailored Co3O4 spinel with Fe3+ doping poses a challenge due to the surface state complexity in bifunctional catalysts with higher cation diversity. Doping with secondary metal results in a double spinel structure (a hybrid of normal and inverted spinels). This enhances the catalytic properties by generating more active oxygen vacancies. The cobalt-rich (FeCo2O4) hybrid spinel and iron-rich (CoFe2O4) inverted spinel are synthesized using a wet impregnation method, supported over oxidized SiC (SiC-Pretrt) for an improved metal-support interaction. FeCo2O4 on pretreated SiC exhibits the highest catalytic activity (90% conversion at 1173 K) and stability (over 100 h) in sulfuric acid decomposition of the iodine-sulfur process for hydrogen production. This improved performance is attributed to the high electronegativity of Co3+, oxygen vacancies, and strong metal-support interaction. The high electronegativity of Co3+ weakens the S-O bond in M-S-O, enhancing the catalytic activity of the spinels. These results are further corroborated by detailed characterization and density functional theory calculations.

Constructing a Pd-Co Interface to Tailor a d-Band Center for Highly Efficient Hydroconversion of Furfural over Cobalt Oxide-Supported Pd Catalysts

Cobalt is an alternative catalyst for furfural hydrogenation but suffers from the strong binding of H and furan ring on the surface, resulting in low catalytic activity and chemoselectivity. Herein, by constructing a Pd-Co interface in cobalt oxide-supported Pd catalysts to tailor the d-band center of Co, the concerted effort of Pd and Co boosts the catalytic performance for the hydroconversion of furfural to cyclopentanone and cyclopentanol. The increased dispersion of Pd on acid etching Co3O4 promotes the reduction of Co3+ to Co0 by enhancing hydrogen spillover, favoring the creation of the Pd-Co interface. Both experimental and theoretical calculations demonstrate that the electron transfer from Pd to Co at the interface results in the downshift of the d-band center of Co atoms, accompanied by the destabilization of H and furan ring adsorption on the Co surface, respectively. The former improves the furfural hydrogenation with TOF on Co elevating from 0.20 to 0.62 s-1, and the latter facilitates the desorption of formed furfuryl alcohol from the Co surface for subsequently hydrogenative rearrangement of the furan ring to cyclopentanone on acid sites. The resultant Pd/Co3O4-6 catalyst delivers superior activity with a 99% furfural conversion and 85% overall selectivity toward cyclopentanone/cyclopentanol. We anticipate that such a concept of tailoring the d-band center of Co via interface engineering provides novel insight and feasible approach for the design of highly efficient catalysts for furfural hydroconversion and beyond.