Zeolite Crystallization Inside Chemically Recyclable Ordered Nanoporous Co3O4 Scaffold: Precise Replication and Accelerated Crystallization.

The synthesis of mesoporous zeolites has garnered attention with regard to improving their catalytic and adsorption performances. While the hard-templating method provides opportunities to design precisely controlled hierarchical micro- and mesoporous structures, synthesizing mesoporous zeolites without external precipitation requires significant work. This is mainly due to the absence of usable templates other than carbon with hydrophobic surfaces. Herein, it is demonstrated that the Co3O4 template is valuable in preparing mesoporous silicalite-1 and ZSM-5 with a precisely controlled porous structure through hydrothermal synthesis. Unlike conventional carbon templates, the Co3O4 template is relatively hydrophilic, effective in suppressing external precipitation, and is reusable by dissolving in an acidic solution. The crystallization process also differs from that of the carbon template, as the silicate precipitates on a 3D ordered nanoporous Co3O4 scaffold, followed by crystallization and crystal growth. Furthermore, it is unexpectedly observed that the zeolite crystallization is accelerated in the Co3O4 template. The synthetic approach utilizing nanoporous metal oxides opens new doors for the control of the hierarchical structure of zeolites, as well as for the design of metal oxide-zeolite nanocomposite catalysts, due to the potential extensibility of the combination of metal oxides and zeolites.

A Green and Efficient Electrocatalytic Route for the Highly-Selective Oxidation of C-H Bonds in Aromatics over 1D Co3O4-Based Nanoarrays.

Electrocatalytic oxidation of C-H bonds in hydrocarbons represents an efficient and sustainable strategy for the synthesis of value-added chemicals. Herein, a highly selective and continuous-flow electrochemical oxidation process of toluene to various oxygenated products (benzyl alcohol, benzaldehyde, and benzyl acetate) is developed with the electrocatalytic membrane electrodes (ECMEs). The selectivity of target products can be manipulated via surface and interface engineering of Co3O4-based electrocatalysts. We achieved a high benzaldehyde selectivity of 90% at a toluene conversion of 47.6% using 1D-Co3O4 nanoneedles (NNs) loaded on a microfiltration (MF) titanium (Ti) membrane, i.e, Co3O4 NNs/Ti. In contrast, the main product shifted to benzyl alcohol with a selectivity of 90.1% at conversion of 32.1% after modifying MnO2 nanosheets (NSs) on Co3O4 NNs/Ti (Co3O4@MnO2/Ti) catalyst. Moreover, benzyl acetate product can be obtained with selectivity of 92% at a conversion of 58.5% at high current density (> 1.5mA cm-2), demonstrating that the pathway of toluene oxidation is readily maneuvered. DFT results reveal that modifying MnO2 on Co3O4 optimizes the electron structure of Co3O4@MnO2/Ti and modulates the adsorption behavior of intermediate species. This work demonstrates a sustainable, and continuous-flow process for precise control over production selectivity of value-added oxygenated derivatives in electrochemical oxidation of aromatic hydrocarbons.

One-pot, Solvent Free Synthesis of 2,5-Furandicarboxylic Acid from Deep Eutectic Mixtures of Sugars as Mediated by Bifunctional Catalyst.

Currently one-pot conversion of sugars to 2,5-furandicarboxylic acid (FDCA) is of significant interest due to the attainability of sugars as a feedstock and the enormous potential of FDCA as a bioplastic monomer. However, it remains challenging to construct efficient catalysts for this process. In this study, Co3O4 species were anchored to a sulfonated covalent organic framework thus affording a bifunctional catalyst (Co3O4@COF-SO3H). The sulfonic acid sites dehydrate sugars to 5-hydroxymethylfurfural (HMF), which is next oxidized to FDCA as catalyzed by the Co3O4 species. Such a process was applied in the conversion of various binary and ternary deep eutectic mixtures involving choline chloride and sugars without additional solvent. The maximum FDCA yield of 84% was obtained using glucose-fructose eutectic mixture as the substrates. Moreover, the catalyst was recyclable and stable under the applied reaction conditions. Our process eliminates the employment of organic solvents and expensive noble metal catalysts, resulting in green and economic biomass conversions.

A hybrid FeOx/CoOx/Pt ternary nanocatalyst for augmented catalysis of formic acid electro-oxidation.

Platinum-based catalysts that have long been used as the anodes for the formic acid electro-oxidation (FAO) in the direct formic acid fuel cells (DFAFCs) were susceptible to retrogradation in performance due to CO poisoning that impaired the technology transfer in industry. This work is designed to overcome this challenge by amending the Pt surface sequentially with nanosized cobalt (nano-CoOx, fibril texture of ca. 200 nm in particle size) and iron (nano-FeOx, nanorods of particle size and length of 80 and 253 nm, respectively) oxides. This enriched the Pt surface with oxygenated groups that boosted FAO and mitigated the CO poisoning. The unfilled d-orbitals of the transition metals and their tendency to vary their oxidations states presumed their participation in a faster mechanism of FAO. Engineering the Pt surface in this FeOx/CoOx/Pt hierarchy resulted in a remarkable activity toward FAO, that exceeded four times that of the Pt catalyst with up to ca. 2.5 times improvement in the catalytic tolerance against CO poisoning. This associated a ca. - 32 mV shift in the onset potential of FAO which increased to - 40 mV with a post-activation of the same catalyst at - 0.5  in 0.2 mol L-1 NaOH, displaying the catalyst's competitiveness in reducing overpotentials in DFAFCs. It also exhibited a favorable amelioration in the catalytic durability in long-termed chronoamperometric electrolysis. The electrochemical impedance spectroscopy and the CO stripping voltammetry were employed to elucidate the origin of enhancement.

Dose-Dependent Attenuation of the Efficacy of Clitoria ternatea by Cobalt Oxide Nanoparticles Against Diabetes-Induced Cognitive Impairment.

Diabetes mellitus is a metabolic disorder caused by insulin deficiency, insulin resistance, genetic alterations, and oxidative stress. The high glucose levels may impair the functioning of nerve cells, leading to neurodegenerative diseases, including cognitive impairment. Clitoria ternatea has various pharmacological activities, including antioxidant, anti-inflammatory, antidiabetic, and neuroprotective effects. The present study evaluates the efficacy of fresh flower aqueous extract of Clitoria ternatea against diabetes-induced cognitive impairment. The challenges in delivering drugs targeting the brain possess the limitations of crossing the blood-brain barrier. Metal nanoparticles are considered the most reliable brain drug delivery systems. Considering the neurotoxicity of cobalt oxide, whether it can be used to improve brain delivery is also evaluated. Cobalt oxide nanoparticles (Co3O4 NPs) of fresh flower aqueous extract of Clitoria ternatea are prepared by green synthesis and characterized. The effect of these nanoparticles is compared with Clitoria ternatea extract against Streptozotocin (STZ)-induced cognitive impairment. The behavioral, biochemical, in vivo antioxidant, total thiol content, estimation of proinflammatory cytokines, acetylcholine esterase, and nitrite levels in the brain of STZ-induced diabetic rats revealed that cobalt oxide nanoparticles showed neurotoxicity, whereas C. ternatea showed neuroprotective effect and also improved the cognitive function. The lower dose of cobalt oxide nanoparticles of C. ternatea (2 mg/kg) exhibited a neuroprotective and cognition improvement effect. However, the higher dose (4 mg/kg) of cobalt oxide nanoparticles of C. ternatea showed a neurotoxic effect. Since Co3O4 NPs are neuroprotective at low doses, they can be used for neuroprotective actions. However, dose optimization studies are required.

Electro-Chemo-Mechanical Evolution at the Garnet Solid Electrolyte-Cathode Interface.

Solid-state batteries promise higher energy density and improved safety compared with lithium-ion batteries. However, electro-chemomechanical instabilities at the solid electrolyte interface with the cathode and the anode hinder their large scale implementation. Here, we focus on resolving electro-chemo-mechanical instability mechanisms and their onset conditions between a state-of-the-art cathode, LiNi0.6Mn0.2Co0.2O2 (NMC622), and the garnet Li7La3Zr2O12 (LLZO) solid electrolyte. We used thin-film NMC622 on LLZO pellets to place the interfacial region within the detection depth of the X-ray characterization techniques. The experimental probes of the near-interface region included in operando X-ray absorption spectroscopy and ex situ focused ion beam scanning electron microscopy. Electrochemical degradation was not observable during cycling at room temperature with 4.3 V versus Li/Li+ charge voltage cutoff, or with stepwise potentiostatic hold up to 4.1 V versus Li/Li+. In contrast, secondary phases including reduced transition metal species (Ni2+, Co2+) were found after cycling up to 4.3 V versus Li/Li+ at 80 °C and during potentiostatic hold at 4.3 V versus Li/Li+ (Ni2+). Intergranular cracks between NMC622 grains and delamination at the NMC622|LLZO interface occurred readily after the first charge. These interface reaction products and mechanical failure lowered the capacity and cell efficiency due to partial loss of the NMC622 phase, partial loss of contact at the interface, and a higher polarization resistance. Electrochemical instability between delithiated NMC622 and LLZO could be mitigated by using a low charge voltage cutoff or cycling at lower temperature. Ways to engineer the mechanical properties to avoid crack deflection and delamination at the interface are also discussed for enhancing mechanical stability.

Highly efficient electrocatalytic oxidation of levodopa as a Parkinson therapeutic drug based on modified screen-printed electrode.

The current study presents the creation of a straightforward and sensitive sensor based on ZnO/Co3O4 nanocomposite modified screen-printed electrode (ZnO/Co3O4NC/SPE) for levodopa determination. At ZnO/Co3O4NC/SPE, an oxidative peak for levodopa solution in pH 6.0 phosphate buffer solution (PBS) were seen that were both more resolved and more enhanced. Levodopa was measured using differential pulse voltammetry (DPV), which showed an excellent linear range (0.001-800.0 µM) and detection limit (0.81 nM). The presence of interference did not affect the electrochemical response of levodopa at ZnO/Co3O4NC/SPE, demonstrating high selectivity. Levodopa in a real samples have been successfully detected using the manufactured sensor.

Synthesis of Amorphous Nickel-Cobalt Hydroxides for Ni-Zn Batteries.

In this work we developed a hydrothermal method for synthesizing amorphous Ni-Co hydroxide (NC(OH)) and in the subsequent step crystalline NiCo2O4 (NCO) has been produced using water as the solvent. For nickel-zinc batteries, NC(OH) was found to have superior performance to its NCO prepared by two-step process. The thermal stability analysis exhibited the optimum temperature to obtain the NC(OH), and NCO electrode materials. The XRD pattern showed mixed phases containing both Ni and Co hydroxides (during the initial step) and in the subsequent step (calcined) the formation of cubic spinel structure was noticed. For NC(OH), aggregated particles with irregular morphology were observed while clustered nanorod-like shapes were noticed for NCO samples. To be noted, that the nanorod morphology was obtained through a facile approach without employing any structure-directing agent. Both NC(OH) and NCO were employed as cathodes for Ni-Zn battery studies against Zn foil anode with a polyamide-based separator soaked in 6 M KOH saturated with ZnO additive was used as electrolyte. The Ni-Zn cell was fabricated in CR2032 coin cell configuration. The electrochemical studies such as cyclic voltammetry (CV) showed the characteristic redox peaks for NC(OH) sample exhibiting high peak current compared to its NCO counterpart. The NC(OH) had a capacity of 268 mAh g-1 against 120 mAh g-1 for NCO at a current density of 1 Ag-1. The cell was able to retain 85 % of the capacity at the end of 500 cycles and showed remarkable rate capability. The Ni-Zn battery presents energy and power densities of 428.8 Wh Kg-1 and 2.68 kW Kg-1, respectively surpassing the normal values reported for aqueous rechargeable batteries. Owing to the presence of Ni and Co in hydroxide form (reduced crystallinity) the NC(OH) sample showed improved electrochemical activity. This work provides a facile approach and effective strategy for developing bimetallic hydroxides for optimal energy storage performance.

Unveiling the diverse bioactivity of cobalt oxide nanoparticles produced through carboxymethyl cellulose extraction.

This study explores an eco-friendly method for synthesizing Cobalt oxide nanoparticles (Co3O4NPs) using extracted carboxymethyl cellulose (CMC) as a reducing and stabilizing agent. The Co3O4NPs, characterized via various analyses, demonstrated a crystalline structure with sizes ranging from 10.9 to 28.2 nm. Microscopic imaging confirmed a uniform spherical morphology with an average diameter of 27.2 nm. The biological activities of Co3O4NPs were investigated extensively, highlighting their superior antibacterial efficacy compared to amoxicillin-clavulanic acid. These nanoparticles exhibited potent antioxidant properties and demonstrated safety for potential applications based on erythrocyte viability results. Additionally, Co3O4NPs displayed significant potency against Michigan Cancer Foundation-7 (MCF-7) breast cancer cells and showed promising α-amylase enzyme inhibitory activity, highlighting their multifunctional therapeutic potential as antioxidant, antibacterial, anticancer, and alpha-amylase inhibition assay.

The catalytic efficacy of modified manganese-cobalt oxides for room-temperature oxidation of formaldehyde in air.

Formaldehyde (FA) is a hazardous indoor air pollutant with carcinogenic propensity. Oxidation of FA in the dark at low temperature (DLT) is a promising strategy for its elimination from indoor air. In this light, binary manganese-cobalt oxide (0.1 to 5 mol L-1-MnCo2O4) is synthesized and modified in an alkaline medium (0.1-5 mol L-1 potassium hydroxide) for FA oxidation under room temperature (RT) conditions. Accordingly, 1-MnCo2O4 achieves 100 % FA conversion at RT (50 ppm and 7022 h-1 gas hourly space velocity (GHSV)). The catalytic activity of 1-MnCo2O4 is assessed further as a function of diverse variables (e.g., catalyst mass, relative humidity, FA concentration, molecular oxygen (O2) content, flow rate, and time on-stream). In situ diffuse reflectance infrared Fourier-transform spectroscopy confirms that FA molecules are adsorbed onto the active surface sites of 1-MnCo2O4 and oxidized into water (H2O) and carbon dioxide (CO2) through dioxymethylene (DOM) and formate (HCOO-) as the reaction intermediates. According to the density functional theory simulations, the higher catalytic activity of 1-MnCo2O4 can be attributed to the combined effects of its meritful surface properties (e.g., the firmer attachment of FA molecules, lower energy cost of FA adsorption, and lower desorption energy for CO2 and H2O). This work is the first report on the synthesis of alkali (KOH)-modified MnCo2O4 and its application toward the FA oxidative removal at RT in the dark. The results of this study are expected to provide valuable insights into the development of efficient and cost-effective non-noble metal catalysts against indoor FA at DLT.

Cobalt-Imidazole Complexes: Effect of Anion Nature on Thermochemical Properties.

A solvent-free method was proposed for the synthesis of hexaimidazolecobalt(II) nitrate and perchlorate complexes-[Co(C3H4N2)6](NO3)2 and [Co(C3H4N2)6](ClO4)2-by adding cobalt salts to melted imidazole. The composition, charge state of the metal, and the structure of the resulting complexes were confirmed by elemental analysis, XPS, IR spectroscopy, and XRD. The study of the thermochemical properties of the synthesized complexes showed that [Co(C3H4N2)6](NO3)2 and [Co(C3H4N2)6](ClO4)2 are thermally stable up to 150 and 170 °C, respectively. When the critical temperature of thermal decomposition is reached, oxidative two-stage gasification is observed. In this case, the organic component of the [Co(C3H4N2)6](NO3)2 complex undergoes almost complete gasification to form Co3O4 with a slight admixture of CoO, which makes it attractive as a component of gas-generation compositions, like airbags.

Ultrathin Titanium Dioxide Coating Enables High-Rate and Long-Life Lithium Cobalt Oxide.

Lithium cobalt oxide (LCO) has been widely used as a leading cathode material for lithium-ion batteries in consumer electronics. However, unstable cathode electrolyte interphase (CEI) and undesired phase transitions during fast Li+ diffusivity always incur an inferior stability of the high-voltage LCO (HV-LCO). Here, an ultra-thin amorphous titanium dioxide (TiO2) coating layer engineered on LCO by an atomic layer deposition (ALD) strategy is demonstrated to improve the high-rate and long-cycling properties of the HV-LCO cathode. Benefitting from the uniform TiO2 protective layer, the Li+ storage properties of the modified LCO obtained after 50 ALD cycles (LCO-ALD50) are significantly improved. The results show that the average Li+ diffusion coefficient is nearly tripled with a high-rate capability of 125 mAh g-1 at 5C. An improved cycling stability with a high-capacity retention (86.7%) after 300 cycles at 1C is also achieved, far outperforming the bare LCO (37.9%). The in situ XRD and ex situ XPS results demonstrate that the dense and stable CEI induced by the surface TiO2 coating layer buffers heterogenous lithium flux insertion during cycling and prevents electrolyte, which contributes to the excellent cycling stability of LCO-ALD50. This work reveals the mechanism of surface protection by transition metal oxides coating and facilitates the development of long-life HV-LCO electrodes.

An electrochemical sensing potential of cobalt oxide nanoparticles towards citric acid integrated with computational approach in food and biological media.

Although citric acid (CA) has antioxidant, antibacterial, and acidulating properties, chronic ingestion of CA can cause urolithiasis, hypocalcemia, and duodenal cancer, emphasizing the need for early detection. There are very few documented electrochemical-based sensing methods for CA detection due to the challenging behavior of electrode fouling caused by reactive oxidation products. In this study, a novel, non-enzymatic, and economical electrochemical sensor based on cobalt oxide nanoparticles (CoOxNPs) is successfully reported for detection CA. The CoOxNPs were synthesized through a simple thermal decomposition method and characterized by SEM, FT-IR, EDX, and XRD techniques. The proposed sensing platform was optimized by various parameters, including pH (7.0), time (15 min), and concentration of nanoparticles (100 mM) etc. In a linear range of 0.05-2500 µM, a low detection limit (LOD) of 0.13 µM was achieved. Theoretical calculations (ΔRT), confirmed hydrogen bonding and electrostatic interactions between CoOxNPs and CA. The detection method exhibited high selectivity in real media like food and biological samples, with good recovery values when compared favorably to the HPLC method. To facilitate effective on-site investigation, such a sensing platform can be assembled into a portable device.

Synthesis Pathway of Layered-Oxide Cathode Materials for Lithium-Ion Batteries by Spray Pyrolysis.

We report the synthesis of LiCoO2 (LCO) cathode materials for lithium-ion batteries via aerosol spray pyrolysis, focusing on the effect of synthesis temperatures from 600 to 1000 °C on the materials' structural and morphological features. Utilizing both nitrate and acetate metal precursors, we conducted a comprehensive analysis of material properties through X-ray diffraction (XRD), Raman spectroscopy, thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). Our findings reveal enhanced crystallinity and significant oxide decomposition within the examined temperature range. Morphologically, nitrate-derived particles exhibited hollow, spherical shapes, whereas acetate-derived particles were irregular. Guided by high-temperature X-ray diffraction (HT-XRD) data, the formation of a layered LCO oxide structure, with distinct spinel Li2Co2O4 and layered oxide LCO phases was shown to emerge at different annealing temperatures. Optimally annealed particles showcased well-defined layered structures, translating to high electrochemical performance. Specifically, nitrate-based particles annealed at 775 °C for 1 h demonstrated initial discharge capacities close to 179 mAh/g, while acetate-based particles, annealed at 750 °C for 3 h, achieved 136 mAh/g at a 0.1C discharge rate. This study elucidates the influence of synthesis conditions on LCO cathode material properties, offering insights that advance high throughput processes for lithium-ion battery materials synthesis.

Biocompatible Cobalt Oxide Nanoparticles for X-ray Fluorescence Microscopy.

The synthesis of water-soluble nanoparticles is a well-developed field for ferrite-based nanoparticles with the majority consisting of iron oxide or mixed metal iron oxide nanoparticles. However, the synthesis of non-agglomerated non-ferrite metal/metal oxide NPs is not as well established. The synthesis and characterization of uniform 20 nm, biologically compatible cobalt oxide (CoO) nanoparticles (NPs) is described. These nanoparticles have two principle components: 1) a CoO core of suitable size to contain enough cobalt atoms to be visualized by X-ray fluorescence microscopy (XFM) and 2) a robust coating that inhibits NP aggregation as well as renders them water-soluble and biocompatible (i.e. stealth coatings). Stable cobalt oxide NPs are obtained with octadecyl amine coatings as reported by Bhattacharjee. Two strategies for solubilizing these NPs in water were investigated with varying degrees of success. Exchanging the octadecyl amine coating for a nitrodopamine anchored PEG coating yielded the desired water-soluble NPs but in very low yield. Alternately, leaving the octadecyl amine coating on the NP and interdigitating this with a maleic anhydride-vinyl copolymer with different hydrophobic sidechains followed by opening the maleic anhydride ring with amine substituted PEG polymers (the water solubilizing component), yielded the desired water soluble NPS were obtained in good yield. Characterization data for the nanoparticles and the components of the coatings required for bioorthogonal reactions to ligate them with biotargeting agents are also described.

Synthesis and characterization of nitrogen-doped-MWCNT@cobalt oxide for nerve agent simulant detection.

Organophosphorus nerve agents are toxic compounds that disrupt neuromuscular transmission by inhibiting the neurotransmitter enzyme, acetylcholinesterase, leading to rapid death. A hybrid composite was synthesized using a hydrothermal process for the early detection of dimethyl methyl phosphonate (DMMP), a simulant of the G-series nerve agent, sarin. Quartz crystal microbalance (QCM) and surface acoustic wave (SAW) sensors were used as detectors. Nitrogen-doped multiwalled carbon nanotubes (N-MWCNTs), cobalt oxide (Co3O4), and N-MWCNT@Co3O4 were compared to detect DMMP concentrations of 25-150 ppm. At 25 ppm, the differential frequencies (Δf) of the N-MWCNT, Co3O4, and N-MWCNT@Co3O4 sensors were 5.8, 2.3, and 99.5 Hz, respectively. The selectivity results revealed a preference for the DMMP rather than potential interference. The coefficients of determination (R2) of the N-MWCNT, Co3O4, and N-MWCNT@Co3O4 sensors for detecting 25-150 ppm DMMP were 0.983, 0.986, and 0.999, respectively. The response times of the N-MWCNT, Co3O4, and N-MWCNT@Co3O4 sensors for detecting 100 ppm DMMP were 25, 27, and 34 s, respectively, while the corresponding recovery times were 85, 105, and 181 s. The repeatability results revealed the reversible adsorption and desorption phenomena for the fixed DMMP concentration of 100 ppm. These unique findings show that synthesized materials can be used to detect organophosphorus nerve agents.

Combined effect of grooves and nanoflower structured Co3O4 coating on bamboo wood for highly efficient solar steam generation at indoor and outdoor conditions.

Currently, interfacial solar steam generation (ISSG) in desalinating water has become very popular for obtaining purified water from polluted water. However, finding an efficient evaporator with low cost is a challenging task for researchers. In this work, we introduce natural bamboo wood (BW) that acts as an interfacial evaporator for obtaining purified water. Four different wood evaporators namely, flat wood (BW-FW), two-cut grooved wood (BW-2G), four-cut grooved wood (BW-4G), and four-cut grooved with Co3O4-coated wood (BW-4G/Co3O4) are used to study the mass loss (ML), evaporation rate (ER), and evaporation efficiency (EY). From the observations, BW-4G/Co3O4 gives an admirable ML, ER, and EY of 4.4 g, 3.366 kg m-2 h-1, and 91.34% under 1 sun illumination for 60 min. Also, the BW-4G/Co3O4 evaporator is kept under natural sun illumination. It achieves 17.8 g of ML, 1.92 kg m-2 h-1 of ER, and 76% of EY respectively under 604.762 W/m2 solar illumination for 8 h. The reasons for the observed results are as follows: (i) the presence of grooves increases the exposing area for solar illuminations, (ii) super hydrophilicity nature of wood gives continuous replenishment of water from the bottom to the evaporative surface, (iii) the excellent salt rejection property of wood aids in continuous water transportation without salt accumulations. As a result of the condensed seawater samples, the ion concentrations (zinc, magnesium, cadmium, lead, copper, and sodium) come under WHO standards. Consequently, it gives better dye water separation from polluted water.

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.

Co and Co3O4 in the Hydrolysis of Boron-Containing Hydrides: H2O Activation on the Metal and Oxide Active Centers.

This work focuses on the comparison of H2 evolution in the hydrolysis of boron-containing hydrides (NaBH4, NH3BH3, and (CH2NH2BH3)2) over the Co metal catalyst and the Co3O4-based catalysts. The Co3O4 catalysts were activated in the reaction medium, and a small amount of CuO was added to activate Co3O4 under the action of weaker reducers (NH3BH3, (CH2NH2BH3)2). The high activity of Co3O4 has been previously associated with its reduced states (nanosized CoBn). The performed DFT modeling shows that activating water on the metal-like surface requires overcoming a higher energy barrier compared to hydride activation. The novelty of this study lies in its focus on understanding the impact of the remaining cobalt oxide phase. The XRD, TPR H2, TEM, Raman, and ATR FTIR confirm the formation of oxygen vacancies in the Co3O4 structure in the reaction medium, which increases the amount of adsorbed water. The kinetic isotopic effect measurements in D2O, as well as DFT modeling, reveal differences in water activation between Co and Co3O4-based catalysts. It can be assumed that the oxide phase serves not only as a precursor and support for the reduced nanosized cobalt active component but also as a key catalyst component that improves water activation.

Hierarchically Structured Graphene Aerogel Supported Nickel-Cobalt Oxide Nanowires as an Efficient Electrocatalyst for Oxygen Evolution Reaction.

The rational design of a heterostructure electrocatalyst is an attractive strategy to produce hydrogen energy by electrochemical water splitting. Herein, we have constructed hierarchically structured architectures by immobilizing nickel-cobalt oxide nanowires on/beneath the surface of reduced graphene aerogels (NiCoO2/rGAs) through solvent-thermal and activation treatments. The morphological structure of NiCoO2/rGAs was characterized by microscopic analysis, and the porous structure not only accelerates the electrolyte ion diffusion but also prevents the agglomeration of NiCoO2 nanowires, which is favorable to expose the large surface area and active sites. As further confirmed by the spectroscopic analysis, the tuned surface chemical state can boost the catalytic active sites to show the improved oxygen evolution reaction performance in alkaline electrolytes. Due to the synergistic effect of morphology and composition effect, NiCoO2/rGAs show the overpotential of 258 mV at the current density of 10 mA cm-2. Meanwhile, the small values of the Tafel slope and charge transfer resistance imply that NiCoO2/rGAs own fast kinetic behavior during the OER test. The overlap of CV curves at the initial and 1001st cycles and almost no change in current density after the chronoamperometric (CA) test for 10 h confirm that NiCoO2/rGAs own exceptional catalytic stability in a 1 M KOH electrolyte. This work provides a promising way to fabricate the hierarchically structured nanomaterials as efficient electrocatalysts for hydrogen production.