Co3O4 Surface Research Articles

Anchoring of porphyrins on atomically defined cobalt oxide: In-situ infrared spectroscopy at the electrified solid/liquid interface

In this work, we studied the interaction of 5-mono(4-phosphonatophenyl)-10–15–20-(triphenyl) porphyrin (MPTPP) with an atomically-defined Co3O4(111) surface in electrochemical environments. We prepared clean and well-defined Co3O4(111) films by physical vapor deposition in ultra-high vacuum (UHV) and transferred the samples into liquid environment without exposure to ambient conditions. We anchored MPTPP to Co3O4(111) in the liquid phase using two different solvents, namely ethanol and dichloromethane. After a second transfer step into an aqueous electrolyte (0.15 M ammonia buffer, pH 10), we investigated the interaction of the porphyrin with the oxide surface in a potential window from 0.3 to 1.3 VRHE using electrochemical infrared reflection absorption spectroscopy (EC-IRRAS). We observed that MPTPP binds via the phosphonate group to the Co2+ surface ions in the form of chelating tridentate. The binding motif remains unchanged in the entire potential region studied. While the binding motif was independent of the solvent used for anchoring, a higher coverage of anchored porphyrins was observed when adsorbing from ethanol.

Adsorption of D2O and CO on Co3O4(111): Water Stabilizes Coadsorbed CO

Water has a significant influence on the low-temperature CO oxidation on cobalt oxide. In this work, we studied the adsorption of CO and D2O on an atomically defined Co3O4(111) surface by infrared ...

Fabrication of Ni-Mn LDH/Co3O4 on carbon paper for the application in supercapacitors

In this work, the hydrothermal method is adopted to synthesize needle-like Co3O4 on the carbon fiber paper (CP) followed by the growth of nickel-manganese layered double hydroxide (Ni-Mn LDH) using the water bath method. Accordingly, the Ni-Mn LDH could be deposited onto the needle-like Co3O4 to form Ni-Mn LDH/Co3O4/CP composite electrode with a hierarchical structure. The electrochemical performance and the material properties are measured, and the influences of different concentrations of Ni(NO3)2∙6H2O, Mn(NO3)2∙4H2O on the performances of Ni-Mn LDH/Co3O4/CP are investigated. Based upon the results, it is concluded that although Co3O4 contributes some of the specific capacitance, Ni-Mn LDH and its uniform deposition on the Co3O4 surface play a key factor to enhance the specific capacitance. At a current density of 1 A/g, a specific capacitance of 219 F/g of the Co3O4/CP electrode is obtained, while an extremely high specific capacitance of 1327 F/g of the Ni-Mn LDH/Co3O4/CP electrode can be attained. In addition, the asymmetric supercapacitor which is built using the Ni-Mn LDH/Co3O4/CP electrode as the positive electrode and active carbon on CP electrode as the negative electrode, shown an energy density of 35.87 Wh/kg with a power density of 449.99 W/kg as well as a power density of up to 9000 W/kg and an energy density of 18.20 Wh/kg. By connecting two asymmetric supercapacitors in series, charging the supercapacitors for three seconds can light a 1.8 V red LED shine for 1320 s, indicating that the as-synthesized composite electrode possessing outstanding potential can be used in supercapacitors.

Mechanochemically Prepared Co3O4-CeO2 Catalysts for Complete Benzene Oxidation

Considerable efforts to reduce the harmful emissions of volatile organic compounds (VOCs) have been directed towards the development of highly active and economically viable catalytic materials for complete hydrocarbon oxidation. The present study is focused on the complete benzene oxidation as a probe reaction for VOCs abatement over Co3O4-CeO2 mixed oxides (20, 30, and 40 wt.% of ceria) synthesized by the more sustainable, in terms of less waste, less energy and less hazard, mechanochemical mixing of cerium hydroxide and cobalt hydroxycarbonate precursors. The catalysts were characterized by BET, powder XRD, H2-TPR, UV resonance Raman spectroscopy, and XPS techniques. The mixed oxides exhibited superior catalytic activity in comparison with Co3O4, thus, confirming the promotional role of ceria. The close interaction between Co3O4 and CeO2 phases, induced by mechanochemical treatment, led to strained Co3O4 and CeO2 surface structures. The most significant surface defectiveness was attained for 70 wt.% Co3O4-30 wt.% CeO2. A trend of the highest surface amount of Co3+, Ce3+ and adsorbed oxygen species was evidenced for the sample with this optimal composition. The catalyst exhibited the best performance and 100% benzene conversion was reached at 200 °C (relatively low temperature for noble metal-free oxide catalysts). The catalytic activity at 200 °C was stable without any products of incomplete benzene oxidation. The results showed promising catalytic properties for effective VOCs elimination over low-cost Co3O4-CeO2 mixed oxides synthesized by simple and eco-friendly mechanochemical mixing.

First-principles Study of Surface and Solution Model of Li-O2 Reactions in Lithium-air Batteries

Lithium-air batteries are promising competitors to replace traditional lithium ion batteries due to the extremely high theoretical energy density. However, the development is limited by the cathode properties, which should be stable, conductive, and reactive in oxygen-rich environments. Here, we employ two different systems of 1) Co3O4-based cathode and vacuum center, and 2) Co3O4-based cathode and DMSO electrolyte to study the mechanisms of Li-air discharge and charge reactions. The structure, stability, and electronic properties of different surface reconstructions of the Co3O4 (100) facet are investigated by static DFT calculations and ab initio Grand Canonical Monte Carlo method. The Co3O4 (100)-O (Oxidized) surface is found as the most stable one at standard conditions. In addition, the mechanisms of multi-step reactions between Li+/e- and O2 are studied, where lithium suboxide products (Li2O2 or Li3O2) are formed on the different Co3O4 (100) terminations. Finally, we also simulate reaction pathways involving only the surface (“surface model”) as well as pathways involving DMSO-based electrolyte (“solution model”) for the discharging/charging process on the Co3O4 (100) surfaces. In the co-designed system of Co3O4 (100)-O cathode and DMSO electrolyte, the solution model pathway for Li-O2 discharge reaction is energetically favorable, providing a low constant overpotential of 0.17 V for the toroid Li2O2 formation. However, the discharge overpotential will be gradually increased from 0.17 V to 0.33 V in the surface model after the cathode surface being fully covered. The charge overpotential we found at the interface of DMSO electrolyte and Co3O4 (100) surface can be low to 0 V but with slow decomposition rate. Instead, 0.36 V overpotential is always required to rapidly decompose the Li2O2 from itself surface in both solution and surface model of charging process. Moreover, a even higher charge overpotential (1 V) is always observed in experiments, which is due to the voltage demand for other side reactions (including Li2CO3 decomposition). In this aspect, increasing the stability of the aprotic electrolytes (including DMSO) is a key technical issue to prohibit the formation of side carbonate products during operation. Our results help shed fundamental insight on the electrolyte assisted Li-O2 reactions on the transition metal oxides and can potentially lead to a new nanomaterials design dimension towards Lithium batteries.

Interface Engineering of Heterogeneous CeO2-CoO Nanofibers with Rich Oxygen Vacancies for Enhanced Electrocatalytic Oxygen Evolution Performance.

The development of highly efficient and cheap electrocatalysts for the oxygen evolution reaction (OER) is highly desirable in typical water-splitting electrolyzers to achieve renewable energy production, yet it still remains a huge challenge. Herein, we have presented a simple procedure to construct a new nanofibrous hybrid structure with the interface connecting the surface of CeO2 and CoO as a high-performance electrocatalyst toward the OER through an electrospinning-calcination-reduction process. The resultant CeO2-CoO nanofibers exhibit excellent electrocatalytic properties with a small overpotential of 296 mV at 10 mA cm-2 for the OER, which is superior to many previously reported nonprecious metal-based and commercial RuO2 catalysts. Furthermore, the prepared CeO2-CoO nanofibers display remarkable long-term stability, which can be maintained for 130 h with nearly no attenuation of OER activity in an alkaline electrolyte. A combined experimental and theoretical investigation reveals that the excellent OER properties of CeO2-CoO nanofibers are due to the unique interfacial architecture between CeO2 and CoO, where abundant oxygen vacancies can be generated due to the incomplete matching of atomic positions of two parts, leading to the formation of many low-coordinated Co sites with high OER catalytic activity. This research provides a practical and promising opportunity for the application of heterostructured nonprecious metal oxide catalysts for high-efficiency electrochemical water oxidation.

Insight into the Surface-Tuned Activity and Cl2/HCl Selectivity in the Catalytic Oxidation of Vinyl Chloride over Co3O4(110) versus (001): A DFT Study

Co3O4 has received tremendous attention in the oxidation of chlorinated volatile organic compounds (CVOCs) for its general catalytic oxidation ability. However, to rationally optimize the Co3O4-based catalysts, ascertaining the reaction mechanism and active-site-specific activity variation at the molecular level remains an open issue. Herein, we performed the first-principles calculations to systematically explore the catalytic oxidation process of vinyl chloride (VC) on two representative (110) and (001) surfaces of Co3O4. The reaction pathways of VC oxidation are thoroughly calculated, mainly consisting of three subprocesses, namely, the C–Cl bond scission, CH2CH oxidation, and the elimination of Cl species. Results show that the oxygen vacancy is indispensable to break the C–Cl bond on Co3O4(110), whereas the C–Cl bond cleavage can be achieved by the collaboration of two adjacent Co5c sites at a lower barrier on Co3O4(001). Both surfaces are reactive for the oxidation of the CH2CH group, indicative of the excellent oxidative ability of the Co3O4 catalyst. More importantly, we identify the rate-determining step in the overall VC oxidation as the elimination of Cl species, and HCl is the preferential chlorine-containing product rather than Cl2. In comparison with Co3O4(110), the Co3O4(001) surface gives a lower energy barrier for Cl elimination and indicates its potentially superior performance for VC oxidation. Finally, some propositions are made for how to improve the VC oxidation on Co3O4 catalysts. These fundamental insights identified in this work may provide a theoretical basis for the design and synthesis of Co3O4-based catalysts in CVOC oxidation.

Theoretical study on W-Co3O4 (1 1 1) surface: Acetone adsorption and sensing mechanism

Volatile organic compounds are highly toxic, and need advanced sensing technology for detection. The morphology, composition and surface characteristics are critical parameters to enhance the gas sensing of metal oxide-based sensors. However, the experimental results only reflect macroscopic phenomena, but cannot explain the sensing mechanism in depth. In this study, the acetone sensing performance of pristine and W modified Co3O4 (111) surface have been studied using DFT methods. Various adsorption sites have been investigated on top of the clean and O adsorped W-Co3O4 (111) surfaces. Our results show the decorated W atom in direct vicinity of pre-adsorbed oxygen is the best site for acetone adsorption. The modification of W atom makes energy band-gap narrower, alters the electronic properties, and enhances the number of transferred electrons. Our study provides a theoretical basis for finding better modified p-type semiconductor sensors toward acetone.

Metal organic framework-templated fabrication of exposed surface defect-enriched Co3O4 catalysts for efficient toluene oxidation

Exposed surface defect-enriched Co3O4 catalysts derived from metal organic framework (MOF) were fabricated by the promotion of surface Mn species for toluene oxidation. The incorporation of Mn species into Co3O4 surface lattice could give rise to the local lattice distortion in spinel structure, resulting in highly exposed surface defect rather than bulk defect. More Co3+ species were also exposed on the surface of MnOx/Co3O4 samples owing to the electron transfer from Co to Mn species by the occupation of surface Mn in octahedral Co3+ sites. Accordingly, the low-temperature reducibility and high mobility of lattice oxygen were significantly improved in virtue of the highly exposed surface defect and predominately surface Co3+ sites, thus promoting the catalytic activity and stability for toluene oxidation. Moreover, the toluene conversion decreased with the increase of weight hourly space velocity (WHSV). In situ DRIFTS results confirmed the continuous oxidation process for toluene degradation, and the conversion of benzoate into maleic anhydride should be the rate-controlling step.

Increased Ion Conductivity in Composite Solid Electrolytes With Porous Co3O4 Cuboids

Compared with the fagile ceramic solid electrolyte, Li-ion conducting polymer electrolytes are flexible and have better contact with electrodes. However, the ionic conductivity of the polymer electrolytes is usually limited because of the slow segment motion of the polymer. In this work, we introduce porous Co3O4 cuboids to Poly (Ethylene Oxide)-based electrolyte (PEO) to investigate the influence of these cuboids on the ionic conductivity of the composite electrolyte and the performance of the all-solid-state batteries. The experiment results showed the porous cuboid Co3O4 fillers not only break the order motion of segments of the polymer to increase the amorphous phase amount, but also build Li+ continuous migration pathway along the Co3O4 surface by the Lewis acid-base interaction. The Li+ conductivity of the composite polymer electrolyte reaches 1.6 × 10−4 S cm−1 at 30°C. The good compatibility of the composite polymer electrolyte to Li metal anode and LiFePO4 cathode ensures good rate performance and long cycle life when applying in an all-solid-state LiFePO4 battery. This strategy points out the direction for developing the high-conducting composite polymer electrolytes for all-solid-state batteries.

Co3 O4 -CeO2 Nanocomposites for Low-Temperature CO Oxidation.

In an effort to combine the favorable catalytic properties of Co3O4 and CeO2, nanocomposites with different phase distribution and Co3O4 loading were prepared and employed for CO oxidation. Synthesizing Co3O4‐modified CeO2 via three different sol‐gel based routes, each with 10.4 wt % Co3O4 loading, yielded three different nanocomposite morphologies: CeO2‐supported Co3O4 layers, intermixed oxides, and homogeneously dispersed Co. The reactivity of the resulting surface oxygen species towards CO were examined by temperature programmed reduction (CO‐TPR) and flow reactor kinetic tests. The first morphology exhibited the best performance due to its active Co3O4 surface layer, reducing the light‐off temperature of CeO2 by about 200 °C. In contrast, intermixed oxides and Co‐doped CeO2 suffered from lower dispersion and organic residues, respectively. The performance of Co3O4‐CeO2 nanocomposites was optimized by varying the Co3O4 loading, characterized by X‐ray diffraction (XRD) and N2 sorption (BET). The 16–65 wt % Co3O4−CeO2 catalysts approached the conversion of 1 wt % Pt/CeO2, rendering them interesting candidates for low‐temperature CO oxidation.

Influence of Fe and Ni Doping on the OER Performance at the Co3O4(001) Surface: Insights from DFT+UCalculations

Using density functional theory calculations with an on-site Hubbard U term, we study the oxygen evolution reaction (OER) at the Co3O4(001) surface. The stability of different surface terminations ...

Surface reconstruction of CoO (111) and its effects on the formation of oxygen vacancy and OER activity

The surface reconstruction and its effect on the oxygen vacancy (VO) formation and OER performance of CoO (111) surface are studied using the first principles calculations. The surface reconstruction from the CoO6 octahedrons to the CoO4 tetrahedrons is revealed at CoO (111) surface, which enhances the OER activity and the stability of VO at the surface of CoO (111). The existence of VO changes the electron accumulation around the Co atoms and the bonding state between Co and O atoms, and thus, affects the adsorption of OH and deprotonation process. By analyzing the electron structure, the nature of the activity changes at Co sites due to the surface reconstruction and the introduction of VO is revealed. Our investigation provides a theoretical basis for the design and application of Co-based OER catalysts.

Effect of Complexing Agents on Surface Composition for Co Post-CMP Cleaning Process

The effect of surface composition change based on complexing agents on cobalt (Co) post-chemical mechanical polishing cleaning (cleaning) is investigated. The change in chemical composition of the Co surface significantly affects Co cleaning performance, as well as dissolution capacity of the complexing agent and pH of cleaning solution. Oxide composition of the Co surface was manipulated using different types of complexing agents. Addition of citric acid and glycine in cleaning solution resulted in predominant formation of Co3O4 and CoOOH on the Co surface, respectively. The citric acid-derived Co3O4 surface embraces abundant –O– terminates, which attracts the complexing agent and silica abrasive relatively weakly, resulting in suppression of recess formation and reduction of surface particle residue after cleaning. On the contrary, the –OH terminated CoOOH surface formed by glycine bound strongly with silica. Therefore, preferential development of Co3O4 on the surface considerably enhances Co cleaning performance, which is achieved by introducing citric acid in the cleaning solution. To sum up, we suggested an unconventional insight to understand the effect of Co surface chemical state on cleaning performance.

Preparation of Co3O4 self-cleaning nanocoatings: Investigation of ZnO seeded steel meshes

In this study, superhydrophobic Co3O4 surfaces with micro/nano hierarchical structures were synthesized on the stainless steel mesh (type: 304, size: #50) by the chemical bath deposition (CBD) method. Taguchi L9 experimental design was applied to evaluate the influence of the type and concentration amounts of the additives, the zinc salt solution concentration as the seeding medium, and the reaction time. After surface modification, the sample synthesized under the optimized conditions showed superhydrophobic properties with the water contact angle (WCA) of 162.6±2.6° and contact angle hysteresis (CAH) of 2˚. X-ray Diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM), Fourier Transform Infrared (FTIR), and Energy Dispersive X-ray (EDX) analyses were used to characterize the synthesized samples. The FESEM images of the optimum sample confirmed the formation of the flower-like structures assembled from numerous petals with thicknesses of ~50 nm to 95 nm. The chemical stability and the self-cleaning characteristics of the obtained superhydrophobic surface were also investigated. Results of the assessments showed that the Co3O4 superhydrophobic surfaces were exhibited an excellent self-cleaning performance.

Influence of the particle size on selective 2-propanol gas-phase oxidation over Co3O4 nanospheres

Co3O4 nanospheres with a preferential (110) surface orientation showed excellent catalytic properties in the selective gas-phase oxidation of 2-propanol. A preferential Mars–van Krevelen mechanism on the Co3O4(110) surface was identified by DFT + U.

Temperature Dependence of the Artificial Photosynthesis Reactions Catalyzed by Nanostructured Co/CoO.

Carbon dioxide (CO2) and water (H2O) have been converted into hydrocarbons at temperature ranging from 58 to 242 °C through an artificial photosynthesis reaction catalyzed by nanostructured Co/CoO. The experimental results show that chain hydrocarbons (alkane hydrocarbons) (CnH2n+2, where 3 ≤ n ≤ 16) mainly form at a temperature higher than about 60 °C, the production rate reaches a maximum at 130 °C, and abruptly decreases above 130 °C, and then gradually increases until 220 °C. While the temperature is higher than 220 °C, benzene (C6H6) and its derivatives such as toluene (C7H8), p-xylene (C8H10), and C9H12 form. The modeling of temperature dependence of the reaction rate reveals that the vaporization of the adsorbed water contributes to the sharp peak; the activation energy is estimated as about 1 eV, which is in agreement with the reaction of CO and H2 to synthesize chain hydrocarbons. The experimental results support the mechanism that the chemisorbed CO2 and physisorbed H2O on the CoO surface are disassociated or excited with light, and the disassociated or excited molecules then synthesize hydrocarbons. When most of the water molecules leave from the CoO at temperature higher than 220 °C, the hydrogen source is of very low concentration while the carbon source remain the same because of the chemisorption, and thus benzene and its derivatives with low hydrogen atom number form.

Oxygen Evolution Reaction on a N-Doped Co0.5-Terminated Co3o4 (001) Surface

Abstract Recent experimental findings suggest that the catalytic activity of Co3O4 for oxygen evolution reaction (OER) could be improved by nitrogen doping. We present preliminary OER modelling on a N-doped Co3O4 surface, with varying concentration of the dopant and its spatial distribution around Cooct and Cotet adsorption sites. The overpotential was calculated for two adsorption sites on seven types of N-doped Co3O4 surface. The largest calculated overpotential value for a N-doped surface was ~1V.

The coralline cobalt oxides compound of multiple valence states deriving from flower-like layered double hydroxide for efficient hydrogen generation from hydrolysis of NaBH4

Efficient hydrogen storage, transportation and generation are key-technology for future hydrogen economy. Sodium borohydride (NaBH4) stands out as promising hydrogen energy carrier with merits of high volumetric density and environmentally benign hydrolysis products. Flower-like layered double hydroxide α-Co(OH)2 with intercalation of B species was synthesized via hydrothermal crystallization method using sodium tetraphenylboron as source of B and alkaline, which makes it different from the previous supporting materials. Pure or mixed cobalt oxides with different valence states containing B (CoO/B, Co3O4/B, Co+CoO/B, CoO+Co3O4/B) were subtly prepared via controlling calcination temperature, time and atmosphere for sodium borohydride hydrolysis. Coral-like CoO+Co3O4/B displayed superior hydrogen generation rate (6478 mlH2·min−1·g−1metal) with arrhenius activation energies of 41.14 kJ/mol for NaBH4 hydrolysis in alkaline solutions compared to those reported pure precious metals. The out-standing catalytic performance of CoO+Co3O4/B may be attributed to electron transfer among cobalt oxide. DFT calculation indicates NaBH4 hydrolysis undergoes a reaction path on CoO+Co3O4 surface with lower relative energies.

Structure and Stability of the (001) Surface of Co3O4

Atomic-scale structures and energetics of the Co3O4 (001) surface are studied combining high-resolution transmission electron microscopy observations and density functional theory calculations. The...