Preparation and Characterization of Copper-Doped Cobalt Oxide Electrodes

Copper nanoparticles encapsulated in zeolitic imidazolate framework-8 as a stable and selective CO2 hydrogenation catalyst

Metal-organic frameworks have drawn attention as potential catalysts owing to their unique tunable surface chemistry and accessibility. However, their application in thermal catalysis has been limited because of their instability under harsh temperatures and pressures, such as the hydrogenation of CO2 to methanol. Herein, we use a controlled two-step method to synthesize finely dispersed Cu on a zeolitic imidazolate framework-8 (ZIF-8). This catalyst suffers a series of transformations during the CO2 hydrogenation to methanol, leading to ~14 nm Cu nanoparticles encapsulated on the Zn-based MOF that are highly active (2-fold higher methanol productivity than the commercial Cu-Zn-Al catalyst), very selective (>90%), and remarkably stable for over 150 h. In situ spectroscopy, density functional theory calculations, and kinetic results reveal the preferential adsorption sites, the preferential reaction pathways, and the reverse water gas shift reaction suppression over this catalyst. The developed material is robust, easy to synthesize, and active for CO2 utilization.

Low-Temperature Synthesis of Mesoporous Half-Metallic High-Entropy Spinel Oxide Nanofibers for Photocatalytic CO2 Reduction

High-entropy oxides (HEOs) exhibit great prospects owing to their varied composition, chemical adaptability, adjustable light-absorption ability, and strong stability. In this study, we report a strategy to synthesize a series of porous high-entropy spinel oxide (HESO) nanofibers (NFs) at a low temperature of 400 °C by a sol-gel electrospinning technique. The key lies in selecting six acetylacetonate salt precursors with similar coordination abilities, maintaining a high-entropy disordered state during the transformation from stable sols to gel NFs. The as-synthesized HESO NFs of (NiCuMnCoZnFe)3O4 show a high specific surface area of 66.48 m2/g, a diverse elemental composition, a dual bandgap, half-metallicity property, and abundant defects. The diverse elements provide various synergistic catalytic sites, and oxygen vacancies act as active sites for electron-hole separation, while the half-metallicity and dual-bandgap structure offer excellent light absorption ability, thus expanding its applicability to a wide range of photocatalytic processes. As a result, the HESO NFs can efficiently convert CO2 into CH4 and CO with high yields of 8.03 and 15.89 μmol g-1 h-1, respectively, without using photosensitizers or sacrificial agents.

A Polymer-Derived Co(Fe)Ox Oxygen Evolution Catalyst Benefiting from the Oxidative Dehydrogenative Coupling of Cobalt Porphyrins

Thin films of cobalt porphyrin conjugated polymers bearing different substituents are prepared by oxidative chemical vapor deposition (oCVD) and investigated as heterogeneous electrocatalysts for the oxygen evolution reaction (OER). Interestingly, the electrocatalytic activity originates from polymer-derived, highly transparent Co(Fe)Ox species formed under operational alkaline conditions. Structural, compositional, electrical, and electrochemical characterizations reveal that the newly formed active catalyst greatly benefited from both the polymeric conformation of the porphyrin-based thin film and the inclusion of the iron-based species originating from the oCVD reaction. High-resolution mass spectrometry analyses combined with density functional theory (DFT) calculations showed that a close relationship exists between the porphyrin substituent, the extension of the π-conjugated system cobalt porphyrin conjugated polymer, and the dynamics of the polymer conversion leading to catalytically active Co(Fe)Ox species. This work evidences the precatalytic role of cobalt porphyrin conjugated polymers and uncovers the benefit of extended π-conjugation of the molecular matrix and iron inclusion on the formation and performance of the true active catalyst.

Structure and oxygen vacancy engineered CuCo-layered double oxide nanotube arrays as advanced bifunctional electrocatalysts for overall water splitting

In recent years, as a green renewable energy production technology, electrochemical water splitting has demonstrated high development potential. Many materials have been reported as successful catalysts in the water-splitting field. However, it is still a huge challenge to produce bifunctional electrocatalysts for the efficient and sustainable generation of hydrogen and oxygen simultaneously. Herein, we successfully developed oxygen vacancies abundant CuCo layered double oxide (O_v-CuCo-LDO) hollow nanotube arrays (HNTAs) loaded on nickel foam as advanced electrocatalysts for total water splitting. When the current density was 10 mA cm^-2, the O_v-CuCo-LDO HNTAs exhibited outstanding onset overpotentials of 53.9 and 72.5 mV for the hydrogen evolution and oxygen evolution reactions (HER and OER) in alkaline medium, respectively, because of the bimetallic synergistic effect between the cobalt and copper and the unique hollow porous structure. In addition, an as-assembled O_v-CuCo-LDO||O_v-CuCo-LDO electrolytic cell showed a small potential of 1.55 V to deliver a current density of 10 mA cm^-2. Moreover, it also showed remarkable durability after long-term overall water splitting for more than 20 h. The research results in this paper are of great interest to practical applications of the water decomposition process, providing clear and in-depth insights into preliminary robust and efficient multifunctional electrocatalysts for overall water splitting.

How to Change the Reaction Chemistry on Nonprecious Metal Oxide Nanostructure Materials for Electrocatalytic Oxidation of Biomass-Derived Glycerol to Renewable Chemicals

Au and Pt are well-known catalysts for electrocatalytic oxidation of biomass-derived glycerol. Although some nonprecious-metal-based materials to replace the costly Au and Pt are used for this reaction, the fundamental question of how the nonprecious catalysts affect the reaction chemistry and mechanism compared to Au and Pt catalysts is still unanswered. In this work, both experimental and computational methods are used to understand how and why the reaction performance and chemistry for the electrocatalytic glycerol oxidation reaction (EGOR) change with electrochemically-synthesized CuCo-oxide, Cu-oxide, and Co-oxide catalysts compared to conventional Au and Pt catalysts. The Au and Pt catalysts generate major glyceric acid and glycolic acid products from the EGOR. Interestingly, the prepared Cu-based oxides produce glycolic acid and formic acid with high selectivity of about 90.0%. This different reaction chemistry is related to the enhanced ability of CC bond cleavage on the Cu-based oxide materials. The density functional theory calculations demonstrate that the formic acids are mainly formed on the Cu-based oxide surfaces rather than in the process of glycolic acid formation in the free energy diagram. This study provides critical scientific insights into developing future nonprecious-based materials for electrochemical biomass conversions.

Catalytic performance of mixed MxCo3−xO4 (M = Cr, Fe, Mn, Ni, Cu, Zn) spinels obtained by combustion synthesis for preferential carbon monoxide oxidation (CO-PROX): insights into the factors controlling catalyst selectivity and activity

A series of mixed cobalt spinel catalysts (MxCo3−xO4 (M = Cr, Fe, Mn, Ni, Cu, Zn)) was synthesized and tested in the CO-PROX reaction and in sole CO oxidation and H2 oxidation as references.

The role of synthesis vis-à-vis the oxygen vacancies of Co3O4 in the oxygen evolution reaction

The combustion synthesized Co3O4 due to high oxygen vacancies exhibited a significant oxygen evolution reaction as has been probed by electrocatalytic experiments and DFT calculations.

Electrochemical performance of transition metal based CoB2O4 (B = Co and Fe) oxides as an electrode material for energy storage devices

A high capacitance of 1039 F g−1 for Co3O4 as compared to 527 F g−1 for CoFe2O4 along with a capacity retention of 86% for up to GCD 5000 cycles, confirm it's potential to be used as an electrode for practical energy storage devices.

Carbon Material and Cobalt-Substitution Effects in the Electrochemical Behavior of LaMnO3 for ORR and OER

LaMn_1−xCo_xO₃ perovskites were synthesized by a modified sol-gel method which incorporates EDTA. These materials’ electrochemical activity towards both oxygen reduction (ORR) and oxygen evolution reactions (OER) was studied. The cobalt substitution level determines some physicochemical properties and, particularly, the surface concentration of Co and Mn’s different oxidation states. As a result, the electroactivity of perovskite materials can be tuned using their composition. The presence of cobalt at low concentration influences the catalytic activity positively, and better bifunctionality is attained. As in other perovskites, their low electrical conductivity limits their applicability in electrochemical devices. It was found that the electrochemical performance improved significantly by physically mixing with a mortar the active materials with two different carbon black materials. The existence of a synergistic effect between the electroactive component and the carbon material was interpreted in light of the strong carbon–oxygen–metal interaction. Some mixed samples are promising electrocatalysts towards both ORR and OER.

Effect of Copper Cobalt Oxide Composition on Oxygen Evolution Electrocatalysts for Anion Exchange Membrane Water Electrolysis

Copper cobalt oxide nanoparticles (CCO NPs) were synthesized as an oxygen evolution electrocatalyst via a simple co-precipitation method, with the composition being controlled by altering the precursor ratio to 1:1, 1:2, and 1:3 (Cu:Co) to investigate the effects of composition changes. The effect of the ratio of Cu²⁺/Co³⁺ and the degree of oxidation during the co-precipitation and annealing steps on the crystal structure, morphology, and electrocatalytic properties of the produced CCO NPs were studied. The CCO_1:2 electrode exhibited an outstanding performance and high stability owing to the suitable electrochemical kinetics, which was provided by the presence of sufficient Co³⁺ as active sites for oxygen evolution and the uniform sizes of the NPs in the half cell. Furthermore, single cell tests were performed to confirm the possibility of using the synthesized electrocatalyst in a practical water splitting system. The CCO_1:2 electrocatalyst was used as an anode to develop an anion exchange membrane water electrolyzer (AEMWE) cell. The full cell showed stable hydrogen production for 100 h with an energetic efficiency of >71%. In addition, it was possible to mass produce the uniform, highly active electrocatalyst for such applications through the co-precipitation method.

Sinterability and Dielectric Properties of LiTaO3-Based Ceramics with Addition of CoO

Lithium tantalite (LiTaO₃) is a common piezoelectric and ferroelectric crystal, but the LiTaO₃ polycrystalline ceramics have rarely been reported, and their refractory character presents difficulties in their fabrication. In this study, LiTaO₃-based ceramics with different amounts of CoO were prepared by pressureless sintering at 1250 °C, and the effects of the amount of sintering aid on the sinterability, microstructure, and dielectric properties of the ceramics were investigated. The relative densities of the LiTaO₃-based ceramics were significantly improved by the addition of CoO powder. The LiTaO₃-based ceramics achieved the highest relative density (89.4%) and obtained a well-grained microstructure when the added amount of CoO was 5 wt.%. Only the LiTaO₃ phase in the ceramics was observed, indicating that the ions Co diffused into the LiTaO₃ lattices and mainly existed in two forms: Co²⁺ and Co³⁺. The effects of the added amount of CoO on the dielectric properties of the LiTaO₃-based ceramics were studied thoroughly. Consequently, the dielectric constant was enhanced, and the dielectric loss decreased in the LiTaO₃-based ceramics with the addition of CoO. The optimal value was obtained at 5 wt.% of CoO-added LiTaO₃-based ceramics.

Effect of Co(II) dopant on the removal of Methylene Blue by a dense copper terephthalate

In this research, for the first time, a series of Co(II) doped copper terephthalate (CoX-CuBDC, where X is doping percentage) were successfully synthesized via solvothermal method and were tested for dye removal application. The physical properties of CoX-CuBDC were studied by several techniques including X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy-dispersive spectroscopy (EDS), thermogravimetric analysis (TGA) and Brunauer-Emmett-Teller (BET) surface area analysis. The incorporation of Co(II) dopant leads to isomorphic substitution of Cu(II) in the CuBDC framework with the maximum doping percentage of 22. Doping and parent MOFs which are non-porous were used for removal of Methylene Blue (MB) from aqueous solution. Adsorption capacity of Co22-CuBDC and CuBDC are 52 and 58 mg/g, respectively, both of which are higher than the adsorption capacity recorded from several high porosity MOFs. Adsorption kinetic studies indicate that adsorption process follows pseudo-second order model while the adsorption mechanism is dominated by electrostatic attraction. Overall, even though these materials show non-porous characteristic, it can be used effectively in wastewater treatment application.

Copper-Doped Cobalt Spinel Electrocatalysts Supported on Activated Carbon for Hydrogen Evolution Reaction

The development of electrocatalysts based on the doping of copper over cobalt spinel supported on a microporous activated carbon has been studied. Both copper–cobalt and cobalt spinel nanoparticles were synthesized using a silica-template method. Hybrid materials consisting of an activated carbon (AC), cobalt oxide (Co₃O₄), and copper-doped cobalt oxide (CuCo₂O₄) nanoparticles, were obtained by dry mixing technique and evaluated as electrocatalysts in alkaline media for hydrogen evolution reaction. Physical mixtures containing 5, 10, and 20 wt.% of Co₃O₄ or CuCo₂O₄ with a highly microporous activated carbon were prepared and characterized by XRD, TEM, XPS, physical adsorption of gases, and electrochemical techniques. The electrochemical tests revealed that the electrodes containing copper as the dopant cation result in a lower overpotential and higher current density for the hydrogen evolution reaction.

Aerobic oxidation of fluorene to fluorenone over Co–Cu bimetal oxides

Aerobic oxidation of fluorene to fluorenone was achieved over Co–Cu bimetal oxides using O₂ as an oxidant in the absence of a radical initiator. Co–Cu bimetal oxides showed better catalytic performance than CuO and Co₃O₄.

Metal–organic framework derived hollow porous CuO–CuCo2O4 dodecahedrons as a cathode catalyst for Li–O2 batteries

Metal–organic framework derived porous CuO–CuCo₂O₄ dodecahedrons as a cathode catalyst for Li–O₂ batteries with significantly enhanced rate and cyclic performance.

The high efficient catalytic properties for thermal decomposition of ammonium perchlorate using mesoporous ZnCo2O4 rods synthesized by oxalate co-precipitation method

Mesoporous ZnCo₂O₄ rods have been successfully prepared via oxalate co-precipitation method without any template. The nano-sized spinel crystallites connected together to form mesoporous structure by annealing homogeneous complex oxalates precursor at a low rate of heating. It is found that the low anneal rate plays an important role for the formation of mesoporous ZnCo₂O₄ rods. The effects of the heat temperature on the phase, morphology and catalytic properties of the products were studied. The XRD, SEM TEM, and N₂ absorption/desorption have been done to obtain compositional and morphological information as well as BET surface area of the as-prepared sample. Catalytic activities of mesoporous ZnCo₂O₄ rods toward the thermal decomposition of ammonium perchlorate (AP) were investigated with differential scanning calorimetry (DSC) and thermogravimetry (TG) techniques. The results show that the addition of ZnCo₂O₄ rods to AP dramatically reduces the decomposition temperature. The ZnCo₂O₄ rods annealed at 250 °C possesses much larger specific area and exhibits excellent catalytic activity (decrease the high decomposition temperature of AP by 162.2 °C). The obtained mesoporous ZnCo₂O₄ rods are promising as excellent catalyst for the thermal decomposition of AP.

Room-Temperature Ammonia Gas Sensing Using Mixed-Valent CuCo2O4 Nanoplatelets: Performance Enhancement through Stoichiometry Control

We report the sensing properties of an interesting ternary oxide CuCo₂O₄ (CCO) which comprises two earth-abundant transition elements, both capable of supporting multiple valence states. We have used a synthesis protocol, which renders unique nanoplatelet-type morphology but with a degree of biphasic character (CuO as a secondary phase in addition to the defect-spinel Cu_1-x Co₂O₄). This sample constitution can be controlled through the use of cation off-stoichiometry, and the same also influence the sensing response significantly. In particular, a Co 10 at. % excess CCO (CCO-Co(10)) case exhibits a good response (∼7.9% at 400 ppm) for NH₃ gas with a complete recovery at room temperature (23 °C, ±1 °C) in 57% RH. The material performance was investigated for other gases such as H₂S, NO₂, and CO. A good response is observed for H₂S and NO₂ gases but without a recovery; however, for CO, a poor response is noted. Herein, we discuss the specific results for ammonia sensing for the CCO-Co(10) case in detail via the use of different characterizations and outline the difference between the cases of the single-phase defect-stabilized material versus nonpercolating biphasic material.

Coffee-Waste Templating of Metal Ion-Substituted Cobalt Oxides for the Oxygen Evolution Reaction

A facile and scalable method using coffee waste grounds as a hard template has been developed to fabricate nanostructured Co₃ O₄ for the oxygen evolution reaction (OER). Co₃ O₄ incorporating metals with different valences (M/Co=1:4; M=Cu, Ni, Fe, Cr, and W) were also prepared with similar sheet-like structures comprising nanosized crystallites. After detailed characterization by X-ray diffraction, electron microscopy, and nitrogen sorption, the oxides were employed as OER electrocatalysts. Substitution of octahedral and tetrahedral sites of the spinel structure with divalent and trivalent transition metals (Cu, Ni, Fe, and Cr) increased the activity of Co₃ O₄ for the OER, whereas incorporation of hexavalent W led to formation of a second crystal phase and significantly higher electrocatalytic performance. Furthermore, this method is easily scaled up for mass production of Co₃ O₄ with the same nanostructure, which is highly desirable for large-scale application.

Degradation of dyes by peroxymonosulfate activated by ternary CoFeNi-layered double hydroxide: Catalytic performance, mechanism and kinetic modeling

Ternary CoFeNi-layered double hydroxide (CoFeNi-LDH) was synthesized and initially applied to activate peroxymonosulfate (PMS) for the degradation of Congo red (CR) and Rhodamine B (RhB). The results show that the CoFeNi-LDH/PMS system can efficiently degrade nearly 100% of 20 mg/L CR or 20 mg/L RhB within 6- and 10-min reaction times, respectively. And the catalyst exhibits higher degradation efficiency on CR than on RhB under identical conditions, which is confirmed by electron clouds of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) performed by DFT calculations. Quenching tests reveal that SO₄^- is the dominant active species participating in the degradation process. Mechanism investigation demonstrates that Co(II)-Co(III)-Co(II) cycle is responsible for activating PMS to generate radicals for dyes degradation. A dynamic kinetic model is successfully developed to simulate the concentration profiles of CR and RhB degradation in CoFeNi-LDH/PMS system. The empirical second order rate constants between SO₄^- and CR (k_SO4-/CR), HO and CR (k_OH/CR), SO₄^- and RhB (k_SO4-/RhB), HO and RhB (k_HO/RhB) are determined to be 2.47 × 10⁷, 3.44 × 10⁶, 8.39 × 10⁶ and 2.62 × 10⁷ M^-1s^-1, respectively. In addition, toxic assessment using ECOSAR program suggests that the overall toxicity of CR and RhB decreased after treatment with CoFeNi-LDH/PMS system. Repeating tests and application of CoFeNi-LDH in different water sources give us adequate confidence that the as-synthesized CoFeNi-LDH is favorable for the purification of dye-contaminanted waters in practical.

Enhanced Fenton-like catalytic performance of N-doped graphene quantum dot incorporated CuCo2O4

In the present study, a novel nanocomposite based on CuCo₂O₄ and N-doped graphene quantum dots (N-GQDs) as an iron-free heterogeneous Fenton-like catalyst was prepared by a two-step solvothermal method.

Promoting effect of solvent on Cu/CoO catalyst for selective glycerol oxidation under alkaline conditions

Cu/CoO catalysts were employed for the selective oxidation of glycerol in the aqueous phase under basic conditions.

Interconnected Copper Cobaltite Nanochains as Efficient Electrocatalysts for Water Oxidation in Alkaline Medium

The present work is focused on the protective-agent-free synthesis of interconnected copper cobaltite (Cu_0.3Co_2.7O₄) nanochains by temperature-controlled solvothermal method followed by post-thermal treatment of the precursors. Furthermore, Cu_0.3Co_2.7O₄ interconnected nanochains are employed as electrocatalyst for water oxidation in alkaline medium for the first time. Extensive studies of physiochemical properties showed the formation of interconnected 1D nanochains of Cu_0.3Co_2.7O₄ exhibiting a larger specific surface area (139.5 m² g^-1) and enhanced electrochemical water oxidation ability. It delivered excellent mass activity (∼50.0 A g^-1), high anodic current density (∼124.9 mA cm^-2 at 1.75 V versus reversible hydrogen electrode), and turnover frequency (∼4.26 × 10^-2 s^-1) in 1.0 M KOH. These Cu_0.3Co_2.7O₄ nanochains also demonstrated low overpotential (∼351 mV) and good cycling stability (1000 cycles) in strong alkaline media. The fabricated Cu_0.3Co_2.7O₄ nanochains could be a good alternative to the commercial OER electrocatalysts (RuO₂ and IrO₂) and also advantageous to the development of efficient, cost-effective, and durable electrocatalysts for electrochemical water splitting.

Influence of annealing temperature on microstructure and lithium storage performance of self-templated CuxCo3−xO4 hollow microspheres

Spinel Cu_xCo_3−xO₄ (x ≤ 0.30) hollow microspheres have been readily prepared via a self-templated solvothermal reaction followed by a thermal annealing step.

Partial conversion of current collectors into nickel copper oxide electrode materials for high-performance energy storage devices

A novel substrate sacrifice process is proposed and developed for converting part of a current collector into supercapacitor active materials, which provides a new route in achieving high energy density of supercapacitor device. Part of a copper foam current collector is successfully converted into highly porous nickel copper oxide electrode for light- and high-performance supercapacitors. Remarkably, this strategy circumvents the problem associated with poor contact interface between electrode and current collector. Meanwhile, the overall weight of the supercapacitor could be minimized. The charge transfer kinetics is improved while the advantage of the excellent mechanical properties of metal current collector is not traded off. By virtue of this unique current collector self-involved architecture, the material derived from the current collector manifests large areal capacitance of 3.13 F cm(-2) at a current density of 1 A g(-1). The capacitance can retain 2.97 F cm(-2) at a much higher density (4 A g(-1)). Only a small decay of 6.5% appears at 4 A g(-1) after 1600 cycles. The strategy reported here sheds light on new strategies in making additional use of the metal current collector. Furthermore, asymmetric supercapacitor using both solid-state gel electrolyte and liquid counterpart are obtained and analyzed. The liquid asymmetric supercapacitor can deliver a high energy density up to 0.5 mWh cm(-2) (53 Wh kg(-1)) at a power density of 13 mW cm(-2) (1.4 kW kg(-1)).

Tuning emission and Stokes shift of CdS quantum dots via copper and indium co-doping

Cu and In co-doped CdS QDs are synthesized and exhibit large Stokes shifts and tunable emission from green to near-infrared.

Near-ambient XPS characterization of interfacial copper species in ceria-supported copper catalysts

Catalysts based on combinations of copper and cerium oxides are interesting alternatives to noble metal ones for processes involved in the production/purification of hydrogen produced from hydrocarbons or biomass like the water–gas shift or the preferential oxidation of CO reactions.

Temperature effect on the binder-free nickel copper oxide nanowires with superior supercapacitor performance

Although the use of nickel oxide in supercapacitor electrodes has been reported extensively, the effect of incorporating copper in the binary compound is not known. Arrays of nickel copper oxide nanowires on the current collector via a simple and industrially compatible route have been successfully synthesized. A systematic study on the effect of temperature is also presented. Strikingly, through conductivity modification and binder-free growth, the as-grown nanowires show high specific capacitance (2.24 F cm(2) at 10 mA; 1955 F g(-1) at 1 mV s(-1)), good rate capability (still 2.18 F cm(2) at 50 mA, 1542 F g(-1) at 50 mV s(-1)), and excellent cycle life (90% after 1000 cycles at a high charging-discharging rate 10 A g(-1)). An asymmetric full cell is then prepared and tested, and very high energy density (30 Wh kg(-1)) is achieved. Ideal capacitive behavior (rectangular shape of cyclic voltammetry) is shown with this tailored architecture of the full cell.