Co3O4 Surface Research Articles

Activation of formyl C[sbnd]H and hydroxyl O[sbnd]H bonds in HMF by the CuO(1 1 1) and Co3O4(1 1 0) surfaces: A DFT study

The first principle calculations with on-site Coulomb repulsion U terms were carried out to investigate the 5-hydroxymethylfurfural (HMF) adsorption on the CuO(1 1 1) and Co3O4(1 1 0) surfaces, two widely used oxidation catalysts. The adsorption of HMF molecule is energetically favoured in both cases, and HMF is more inclined to bridge adsorption via hydroxyl and formyl groups binding with surface O and metal sites. Moreover, the adsorption energy relies on both the coordination type of surface lattice oxygen to which the H atom binds and the formation of H-bond involving hydroxyl and formyl groups on the adsorbed HMF. Also, the hydroxyl OH bond breaking is very easy and is likely to be the first step in HMF oxidation, and then the OH insertion reaction to produce 2,5-furandicarboxylic acid (FDCA). The corresponding experimental results also show that the CuO and Co3O4 surfaces are promising candidate catalysts.

Enhancing the electrochemical performances of LiNi0.5Mn1.5O4 by Co3O4 surface coating

A Co3O4 coating is formed on the surface of LiNi0.5Mn1.5O4 particles via an ethanol mediated precipitation method. The existence of the uniform Co3O4 coating is clearly observed by scanning electron microscopy and transmission electron microscopy. The results of electrochemical performance testing prove that the Co3O4 coating can greatly enhance the cycling stability and rate performance of LiNi0.5Mn1.5O4. The optimal sample 5% Co3O4-coated LiNi0.5Mn1.5O4 delivers a discharge capacity 126 mAh g−1 at 1 C rate with a capacity retention 96.8% after 300 cycles and a high discharge capacity 97.5 mAh g−1 at 10 C rate. The causes to the improvement are discussed based on elemental analysis, X-ray photoelectron spectroscopy and electrochemical impedance spectroscopy.

Enhanced Gas‐Sensing Performances of Ru‐Loaded p‐Type Co3O4 Nanoparticles

Co3O4 nanoparticles (NPs) and Co3O4 NPs‐functionalized with 0.25, 0.50, and 1.00 wt.% Ruthenium (Ru) are synthesized by the precipitation and impregnation methods. X‐ray diffraction data confirm that all samples are highly crystalline with a typical cubic Co3O4 NPs structure. Electron microscopic images show spherical morphologies of Co3O4 nanoparticles with the diameters of 10–30 nm and Ru nanoparticles with relatively small diameters of 2–4 nm loaded on Co3O4 surfaces. The gas‐sensing results reveal that Ru loading at an optimally low Ru content of 0.25 wt.% led to significantly enhanced ethanol sensing performances. Specifically, the 0.25 wt.%Ru/Co3O4 sensor exhibits a good p‐type response of ≈30 to 100 ppm C2H5OH, short response time (0.08 s), good recovery time (a few minutes) and high C2H5OH selectivity against H2S, H2, NH3, NO2, and SO2. Therefore, the Ru‐loaded Co3O4 sensor is a promising alternative p‐type gas sensor for ethanol detection.

Phosphonic Acids on an Atomically Defined Oxide Surface: The Binding Motif Changes with Surface Coverage.

We have studied the anchoring mechanism of a phosphonic acid on an atomically defined oxide surface. Using time-resolved infrared reflection absorption spectroscopy, we investigated the reaction of deuterated phenylphosphonic acid (DPPA, C6H5PO3D2) with an atomically defined Co3O4(111) surface in situ during film growth by physical vapor deposition. We show that the binding motif of the phosphonate anchor group changes as a function of coverage. At low coverage, DPPA binds in the form of a chelating tridentate phosphonate, while a transition to a chelating bidentate occurs close to monolayer saturation coverage. However, the coverage-dependent change in the binding motif is not associated with a major change of the molecular orientation, suggesting that the rigid phosphonate linker always maintains the DPPA in a strongly tilted orientation irrespective of the surface coverage.

La0.1Ca0.9MnO3/Co3O4 for oxygen reduction and evolution reactions (ORER) in alkaline electrolyte

Non-precious metal bifunctional catalysts are of great interest for metal–air batteries, electrolysis, and regenerative fuel cell systems due to their performance and cost benefits compared to the Pt group metals (PGM). In this work, metal oxides of La0.1Ca0.9MnO3 and nano Co3O47 catalyst as bifunctional catalysts were used in oxygen reduction and evolution reactions (ORER). The catalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and N2 adsorption isotherms. The electrocatalytic activity of the perovskite-type La0.1Ca0.9MnO3 and Co3O4 catalysts both as single and mixtures of both were assessed in alkaline solutions at room temperature. Electrocatalyst activity, stability, and electrode kinetics were studied using cyclic voltammetry (CV) and rotating disk electrode (RDE). This study shows that the bifunctional performance of the mixed La0.1Ca0.9MnO3 and nano Co3O4 was superior in comparison to either La0.1Ca0.9MnO3 or nano Co3O4 alone for ORER. The improved activity is due to the synergistic effect between the La0.1Ca0.9MnO3 and nano Co3O4 structural and surface properties. This work illustrates that hybridization between these two metal oxides results in the excellent bifunctional oxygen redox activity, stability, and cyclability, leading to a cost-effective application in energy conversion and storage, albeit to the cost of higher catalyst loadings.

Trends of Alkane Activation on Doped Cobalt (II, III) Oxide from First Principles

AbstractThe surface doping of a metal oxide can tune its catalytic performance, but it remains unclear how the tuning depends on the dopant type and the surface facet. Herein we study doped Co3O4 (1 1 1) and (3 1 1) surface facets using first‐principles density functional theory (DFT) to obtain general descriptors for oxygen reactivity (which include vacancy formation energy and hydrogen adsorption energy) and correlate them to ethane C−H activation energy as a measure of the catalytic performance. The periodic trends of the dopants are investigated for a total of 20 dopants, namely, the elements from K to Ge. We find strong linear correlations between the oxygen reactivity descriptors and the computed energy barriers. We also discover a strong surface facet sensitivity among certain dopants such that different surface orientations and sites lead to different or even the opposite dopant performance. This work provides a useful guide for dopant performance in ethane activation on the two very different Co3O4 surfaces.

An electrochemical sensing platform of cobalt oxide@gold nanocubes interleaved reduced graphene oxide for the selective determination of hydrazine

Reduced graphene oxide-cobalt oxide nanocube@gold (rGO-Co3O4@Au) nanocomposite was prepared using a one-pot hydrothermal synthesis. The nanocomposite was characterized using the UV-Vis absorption spectroscopy, field emission scanning electron microscopy (FESEM), high resolution transmission electron microscopy (HRTEM), energy dispersive X-ray (EDX) mapping, X-ray diffraction (XRD) and Raman analyses. The EDX mapping analysis showed the uniform distribution of Au nanoparticles on the Co3O4 surface that made the surface more roughness. The higher degree of reduction of GO was confirmed from the increased intensity ratio of the D and G bands (ID/IG) of the Raman spectrum during the hydrothermal synthesis. The rGO-Co3O4@Au nanocomposite exhibited good electrocatalytic activity towards the oxidation of hydrazine in phosphate buffer (pH 7.2). The detection of hydrazine was carried out using amperometry technique and the current response was linear in the range of 10–620 μM. The limit of detection was found to be 0.443 μM. The selectivity of the nanocomposite for the sensing of hydrazine was studied with the interferents such as NO3−, SO42−, Cl−, Ag+, Na+, K+, ethanol, 4-nitrophenol, ascorbic acid and glucose. The sensing of different concentration of hydrazine present in the real water samples was analysed and an appreciable recovery was found.

Co3 O4 Nanowire Arrays toward Superior Water Oxidation Electrocatalysis in Alkaline Media by Surface Amorphization.

It is highly desirable to develop a simple, fast and straightforward method to boost the alkaline water oxidation of metal oxide catalysts. In this communication, we report our recent finding that the generation of amorphous Co-borate layer on Co3 O4 nanowire arrays supported on Ti mesh (Co3 O4 @Co-Bi NA/TM) leads to significantly boosted OER activity. The as-prepared Co3 O4 @Co-Bi NA/TM demands overpotential of 304 mV to drive a geometrical current density of 20 mA cm-2 in 1.0 M KOH, which is 109 mV less than that for Co3 O4 NA/TM, with its catalytic activity being preserved for at least 20 h. It suggests that the existence of amorphous Co-Bi layer promotes more CoOx (OH)y generation on Co3 O4 surface.

Interaction of Ester-Functionalized Ionic Liquids with Atomically-Defined Cobalt Oxides Surfaces: Adsorption, Reaction and Thermal Stability.

Hybrid materials consisting of ionic liquid (ILs) films on supported oxides hold a great potential for applications in electronic and energy materials. In this work, we have performed surface science model studies scrutinizing the interaction of ester-functionalized ILs with atomically defined Co3 O4 (111) and CoO(100) surfaces. Both supports are prepared under ultra-high vacuum (UHV) conditions in form of thin films on Ir(100) single crystals. Subsequently, thin films of three ILs, 3-butyl-1-methyl imidazolium bis(trifluoromethyl-sulfonyl) imide ([BMIM][NTf2 ]), 3-(4-methoxyl-4-oxobutyl)-1-methylimidazolium bis(trifluoromethyl-sulfonyl) imide ([MBMIM][NTf2 ]), and 3-(4-isopropoxy-4-oxobutyl)-1-methylimidazolium bis(trifluoromethyl-sulfonyl) imide ([IPBMIM][NTf2 ]), were deposited on these surfaces by physical vapor deposition (PVD). Time-resolved and temperature-programmed infrared reflection absorption spectroscopy (TR-IRAS, TP-IRAS) were applied to monitor in situ the adsorption, film growth, and thermally induced desorption. By TP-IRAS, we determined the multilayer desorption temperature of [BMIM][NTf2 ] (360±5 K), [MBMIM][NTf2 ] (380 K) and [IPBMIM][NTf2 ] (380 K). Upon deposition below the multilayer desorption temperature, all three ILs physisorb on both cobalt oxide surfaces. However, strong orientation effects are observed in the first monolayer, where the [NTf2 ]- ion interacts with the surface through the SO2 groups and the CF3 groups point towards the vacuum. For the two functionalized ILs, the [MBMIM]+ and [IPBMIM]+ interact with the surface Co2+ ions of both surfaces via the CO group of their ester function. A very different behavior is found, if the ILs are deposited above the multilayer desorption temperature (400 K). While for [BMIM][NTf2 ] and [MBMIM][NTf2 ] a molecularly adsorbed monolayer film is formed, [IPBMIM][NTf2 ] undergoes a chemical transformation on the CoO(100) surface. Here, the ester group is cleaved and the cation is chemically linked to the surface by formation of a surface carboxylate. The IL-derived species in the monolayer desorb at temperatures around 500 to 550 K.

Carbon nanotube/Co3O4 nanocomposites selectively coated by polyaniline for high performance air electrodes

We herein report the preparation of carbon nanotube (CNT)/Co3O4 nanocomposites selectively coated with polyaniline (PANI) via an electropolymerization method, for use as an effective electrode material for Li-air (Li-O2) batteries. The Co3O4 catalyst attached to the CNTs facilitated the dissociation of reaction products and reduced the overpotential of the cells. As the carbon surface activates the side reactions, the PANI coating on the carbon surface of the electrode suppressed the side reaction at the electrode/Li2O2 and electrode/electrolyte interfaces, thus enhancing the cycle performance of the electrode. In addition, the catalytic activity of Co3O4 on the CNT/Co3O4 nanocomposites remained unaffected, as the Co3O4 surface was not covered with a PANI layer due to the nature of the electropolymerization method. Overall, the synergic effect of the PANI layer and the Co3O4 catalyst leads to a superior cyclic performance and a low overpotential for the electrode based on selectively PANI-coated CNT/Co3O4 nanocomposites.

Degradation of atrazine in heterogeneous Co3O4 activated peroxymonosulfate oxidation process: Kinetics, mechanisms, and reaction pathways

Herbicide atrazine (ATZ) has caused great environmental concern due to its long-term application in agriculture and persistence nature. This study examined the degradation of ATZ in heterogeneously activated peroxymonosulfate (PMS) oxidation processes, using Co3O4 as the catalyst, finding that high PMS concentrations and near neutral pH (pH 6.0) were beneficial for ATZ degradation. ATZ degradation rate was influenced by functional groups present on the Co3O4 surface at varying pH. Complete removal of 20μM ATZ was achieved in 15min, with 2.0mM PMS and 0.4g/L Co3O4 at pH 6.0. Minimal cobalt leaching occurred during reaction, shown by a maximum dissolved Co concentration (0.06mg/L) found at pH 3.0 and decreasing with increasing pH. During the reaction, Co3O4 showed high potential for reusability. Structural properties of the pristine and used Co3O4 catalysts were characterized by scanning electron microscope; X-ray diffraction; and X-ray photoelectron spectroscopy, with no changes observed post-reaction. A total of 7 intermediate products of ATZ were detected by liquid chromatography-tandem mass spectrometry, with quantification of intermediate products allowing the contribution of different pathway for ATZ degradation, to be accessed. Transformation pathways including dealkylation, dechlorination-hydroxylation, and alkylic-oxidation were proposed for catalytic decomposition of ATZ in the Co3O4/PMS system.

Elektronni ta mahnitni xarakterystyky poverxni shpineli Co3O4 (111) v nablyzhenni GGA + U

The atomic structure and electronic properties of the spinel Co3O4 (111) surface are calculated within the methods of density functional theory. Possible types of the surface are analyzed, and their formation energies are calculated. Electron states formed at the surface by broken bonds are studied in detail, and their partial density of states is calculated. It is shown that, unlike the bulk of spinel, its surface has nontrivial magnetic properties, because Co atoms acquire an additional magnetic moment under near-surface conditions.

The Mechanism of Skutterudite Acid Leaching: A DFT Study of H<sup>+</sup> Effect on CoO (010) Surface

A DFT study of H+ effect on CoO(0 1 0) surface was carried out. What could be seen from the inter atomic distance and the density of states (DOS) was: Co-O bonds were broken strongly and H-O bonds formed strongly when one H+ was adsorbed on the O atom, and Co-O bonds were not broken and H-O bond not formed strongly when two H+ were adsorbed on the O atom, so the Skutterudite acid leaching process cannot be described as two H+ were adsorbed on the O atom and formed the H2O molecules to enter the solution. But that can be described as one H+ was adsorbed on the O atom and formed the OH- to enter the solution, the OH- was combined with the H+ in the solution to form the H2O molecule.

Comparative studies of leached Pt-Fe and Pt-Co catalysts for CO oxidation reactions

Leached Pt-Fe and Pt-Co catalysts were prepared by acid leaching the reduced catalysts in acid solution. Oxidation treatments of leached catalysts produced the structure of metal oxides decorating the surface of nanoparticles. The fully oxidized Fe 2 O 3 and Co 3 O 4 species on Pt nanoparticle surfaces result in the low performance of the CO complete oxidation (COOX) reaction. In contrast, unsaturated FeO and CoO surface species can be formed during exposure to the CO preferential oxidation (CO-PROX) reaction with an excess of H 2 , leading to a high O 2 activation ability and enhancing the CO-PROX activity. The FeO x surface structures can be transformed between these two states by varying the reactive gas environments, exhibiting oscillating activity in these two reactions. Conversely, the CoO surface structure formed in the H 2 -rich atmosphere is stable when exposed to the COOX reaction and exhibits similar activity in these two reactions. It is hoped that this work may assist in understanding the important role of surface oxides in real reactions. The structure of metal oxides on nanoparticle surfaces can be obtained by oxidizing the leached Pt-Fe and Pt-Co catalysts. The relationship between surface oxides and the catalytic performance for CO oxidation reactions was studied.

Effect of Pd doping on CH4 reactivity over Co3O4 catalysts from density-functional theory calculations

Palladium oxide (PdOx) and cobalt oxide (Co3O4) are efficient catalysts for methane (CH4) combustion, and Pd-doped Co3O4 catalysts have been found to exhibit better catalytic activities, which suggest synergism between the two components. We carried out first-principles calculations at the PBE+U level to investigate the Pd-doping effect on CH4 reactivity over the Co3O4 catalyst. Because of the structural complexity of the Pd-doped Co3O4 catalyst, we built Pd-doped catalyst models using Co3O4(001) slabs with two different terminations and examined CH4 reactivity over the possible Pd–O active sites. A low energy barrier of 0.68 eV was predicted for CH4 dissociation over the more reactive Pd-doped Co3O4(001) surface, which was much lower than the 0.98 and 0.89 eV that was predicted previously over the more reactive pure Co3O4(001) and (011) surfaces, respectively. Using a simple model, we predicted CH4 reaction rates over the pure Co3O4(001) and (011) surfaces, and Co3O4(001) surfaces with different amounts of Pd dopant. Our theoretical results agree well with the available experimental data, which suggests a strong synergy between the Pd dopant and the Co3O4 catalyst, and leads to a significant increase in CH4 reaction rate.

Metal organic framework-mediated synthesis of potassium-promoted cobalt-based catalysts for higher oxygenates synthesis

Syngas to higher oxygenates conversion was carried out on a series of potassium-promoted cobalt-based catalysts. Catalysts with different potassium composition were prepared by metal organic framework-mediated synthesis, which is the calcination of the ZIF-67 metal organic framework (MOF). Cobalt skeleton structure that originated from the MOF is preserved after the calcination. The calcined catalysts consist of Co3O4 nanoparticles and surface carbon. The catalysts were reduced by H2/He prior to the reaction. CO hydrogenation was carried out at various temperatures (270°C, 300°C and 325°C) and at 40bar, with H2/CO=1/1. The formation of methane and higher hydrocarbons is suppressed by potassium, and cobalt carbide is formed from metallic cobalt during the reaction. Thus, the K-promoted cobalt based catalyst synthesized by the MOF-mediated synthesis shows higher selectivity to ethanol, acetaldehyde and higher oxygenates, even at high temperatures.

Ultrafast Charge Transfer between Light Absorber and Co3O4 Water Oxidation Catalyst across Molecular Wires Embedded in Silica Membrane.

The mechanism of visible light-induced hole transfer from a molecular light absorber, in the form of a free-base porphyrin, coupled to a Co3O4 nanoparticle catalyst for water oxidation by a molecular wire (p-oligo(phenylenevinylene) featuring three aryl units) is investigated by transient absorption spectroscopy. The wires are covalently anchored on the Co3O4 surface and embedded in a dense, yet ultrathin (2 nm), silica layer that separates light absorber and catalyst. The porphyrin is electrostatically adsorbed on the silica surface, and aqueous colloidal solutions of the core-shell particles are used for transient optical measurements. Pulsed optical excitation of the porphyrin results in rapid injection of the photogenerated hole onto the molecular wire and concurrent formation of reduced light absorber in less than 1 picosecond (ps). Ultrafast charge separation was monitored by transient absorption of the wire radical cation, which is given by bands in the 500 to 600 nm region and at 1130 nm, while formation of reduced porphyrin was characterized by absorption at 700 nm. Forward transfer of the hole to Co3O4 catalyst proceeds in 255 ± 23 ps. Ultrafast transfer of positive charge from the molecular assembly to a metal oxide nanoparticle catalyst for water oxidation is unprecedented. Holes on Co3O4 recombined with electrons of the reduced sensitizer with biphasic kinetics on a much longer time scale of ten to several hundred nanoseconds. The unusually efficient hole transfer coupling of a molecular light absorber with an Earth-abundant metal oxide catalyst by silica-embedded p-oligo(phenylenevinylene) offers an approach for integrated artificial photosystems featuring product separation on the nanoscale.

Mechanistic Aspects of Wet and Dry CO Oxidation on Co3O4 Nanorod Surfaces: A NAP-UPS Study.

Catalytic activity, electronic structure, and the mechanistic aspects of Co3O4 nanorod (NR) surfaces have been explored for CO oxidation in dry and wet atmosphere using near-ambient pressure ultraviolet photoelectron spectroscopy. Presence of water with CO + O2 plummets the catalytic activity because of the change in the electronic nature from predominantly oxide (without water in feed) to a Co3O4 surface covered by a few intermediates. However, at ≥375 K, the Co3O4 surface recovers and regains the oxidation activity, at least partially, even in the presence of water. This is fully supported by the changes observed in the work function of Co3O4 under wet (H2O + CO + O2) conditions compared with dry (CO + O2) conditions. This study focuses on the comparative CO oxidation rate on Co3O4 NR surfaces and highlights the changes in the electronic structure that occur in the catalyst during the CO oxidation reaction.

Activity and stability of Co3O4-based catalysts for soot oxidation: The enhanced effect of Bi2O3 on activation and transfer of oxygen

Bi2O3-Co3O4 catalysts were prepared by sol-gel method and tested for soot oxidation by O2. The composite oxides showed excellent activity under both tight and loose contact when compared with individual Co3O4 or Bi2O3, and the maximum activity was obtained over catalyst with Bi/Co molar ratio of 0.2. The samples were characterized by means of XRD, N2 adsorption, FE-SEM, XPS, FT-IR, C-TPR and O2-TPD. It was found that Bi2O3 with low melting point deposited on Co3O4 surface could not only promote the contact state between soot and catalyst, but also produce more oxygen species with high mobility and reactivity at Bi-Co interface layer. Oxygen activation channel and reaction pathway were discussed based on the results of isothermal anaerobic titrations and 18O-isotopic tests, which confirmed that soot was more likely to react with lattice oxygen species rather than O2, especially at low temperatures. The high mobility of lattice oxygen species was attributed to a combination of the O2− conductivity of Bi2O3 and the accelerative formation of oxygen vacancies at Bi-Co interface. A feasible reaction mechanism over the binary catalysts for soot oxidation was proposed. The stability tests were also studied and the results indicated that Bi-modified Co3O4 showed prominent tolerance against thermal shock, H2O and SO2, thus being a promising active component for practical application.

Oxygen Deficiency and Reactivity of Spinel NiCo2O4 (001) Surfaces

We carried out density functional theory (DFT) calculations with on-site Hubbard U corrections to investigate the structure, defects, and reactivity of (001) surfaces of spinel NiCo2O4 (NCO), a promising catalyst for CO and methane oxidation. By examining surfaces with different Co/Ni compositions, we find that the formation of surface oxygen vacancies (VOs) on NCO(001) is strongly affected by the neighboring cation in the third layer, the computed formation energy being largest (∼1.2 eV) for O vacancies coordinated to third layer Co and smallest (∼0.5 eV) for VOs coordinated to a Ni neighboring another Ni ion. As a result, VO formation is generally much easier on NCO (001) than on Co3O4 (001) surfaces, suggesting that NCO may be a better catalyst than Co3O4 for oxidation reactions based on the Mars–Van Krevelen mechanism. Surface oxygen vacancies on reduced NCO surfaces can be healed through dissociative water adsorption at room temperature. In contrast, adsorption of molecular oxygen at VOs is energetic...