Structure Of Co3O4 Research Articles

Co3O4/rGO based nanocomposite architectures as electrodes for advanced energy storage and their pseudocapacitive attributes

In response to escalating global challenges in energy storage, this study embarked on captivating exploration of electrochemically proficient Co3O4 composites, seamlessly integrated with varying concentrations of reduced graphene oxide (5 %, 10 %, and 15 %). Using a single-step hydrothermal method, Co3O4 was synthesized, followed by a solvothermal process to produce Co3O4/rGO composites. These composites were then applied to Nickel Foam to fabricate electrodes. The structural properties of these novel Co3O4/rGO/NF electrodes were analyzed using X-ray Diffractometer, which confirmed the distinctive crystalline structure of Co3O4 and indicated no phase transformation after the introduction of rGO. Morphological analysis through a Field Emission Electron Microscope and Transmission Electron Microscope revealed layered structures and increasing porosity correlated with higher rGO concentrations. Electrochemical performance was rigorously tested through cyclic voltammetry, which verified the pseudocapacitive attributes of the samples. Additionally, galvanostatic charge-discharge studies highlighted that the electrode containing 15 % rGO demonstrated highest (Cs = 1360 Fg−1) at 1.7 Ag−1, with 86 % of cyclic retention after 5000 cycles. Electrochemical impedance spectroscopy further demonstrated superior conductivity, underscoring the potential of these electrodes'for supercapacitor applications.

Operando Surface X‐Ray Diffraction Studies of Epitaxial Co3O4 and CoOOH Thin Films During Oxygen Evolution: pH Dependence

AbstractTransition metal oxides, especially cobalt oxides and hydroxides, are of great interest as precious metal free electrode materials for the oxygen evolution reaction (OER) in electrochemical and photoelectrochemical water splitting. Here, we present detailed studies of the potential‐ and pH‐dependent structure and structural stability of Co3O4 and CoOOH in neutral to alkaline electrolytes (pH 7 to 13), using operando surface X‐ray diffraction, atomic force microscopy, and electrochemical measurements. The experiments cover the pre‐OER and OER range and were performed on epitaxial Co3O4(111) and CoOOH(001) films electrodeposited on Au(111) single crystal electrodes. The CoOOH films were structurally perfectly stable under all experimental conditions, whereas Co3O4 films exhibit at all pH values reversible potential‐dependent structural transformations of a sub‐nanometer thick skin layer region at the oxide surface, as reported previously for pH 13 (F. Reikowski et al., ACS Catal. 2019, 9, 3811). The intrinsic OER activity at 1.65 V versus the reversible hydrogen electrode decreases strongly with decreasing pH, indicating a reaction order of 0.2 with respect to [OH−]. While the Co3O4 spinel is stable at pH 13, intermittent exposure to electrolytes with pH≤10 results in dissolution as well as gradual degradation of its OER activity in subsequent measurements at pH 13.

Tuning structural and optical properties of GO@Mn-doped Co3O4 hybrid nanocomposite by a facile synthesis

Metal and metal oxide materials are mostly used to tune the optical characteristics. The optical and systemic effects of pure Cobalt Oxide (Co3O4) are examined by knocking out the dissimilar assemblage of Manganese (Mn) ions using the co-precipitation method. Graphene oxide (GO) reduces the optical band gap and enhances the effects of ethical Co3O4 and MnCo3O4 by hydrothermal procedure. The percentage of Mn over pure Co3O4 was 0.09wt.%, 0.18wt.%, 0.27wt.%, and GO doped over MnCo3O4 was 1wt.%. Remarkably, spinel-type cobalt oxide has two participation band gaps at 494nm and 772nm of nanocomposites which then shifted from 494nm to 510nm and 772nm to 779nm with the doping of GO. The result describes that the band gap was minimized from 1.76eV to 1.59eV respectively to accommodate the density of states by doping of Mn ions and GO. Conductivity and optical absorbance were also increased by doping assemblage of Mn ions and GO. XRD peaks show the FCC crystalline structure of Co3O4, and the GO peak disappeared for @MnCo3O4, indicating that GO was completely reduced to rGO during the synthesis process.

Na-doped cobalt spinel electrocatalysts prepared by programmed electrostatic spraying for improving OER activity and durability in acidic media

The daunting challenge to establish a trade-off among the activity, durability, and cost of electrocatalysts for oxygen evolution reaction (OER) with sluggish reaction kinetics impedes the practical green energy conversion. Hereby, a non-noble metal-based electrocatalyst (i.e., Na-doped Co3O4) was in-situ prepared by programmed electrostatic spraying as an advanced alternative to the costly and scarce state-of-the-art IrO2 and RuO2-based electrocatalysts. The utilization of this sprayer facilitates intimate contact with the substrate electrode and provides short ion diffusion paths, facilitating efficient electron transport. Additionally, the doping of Na ions into the Co3O4 structure results in structural distortion and charge redistribution, leading to the generation of oxygen vacancies (OVs). These OVs enhance the activity of lattice oxygen atoms, thus enabling rapid and durable oxygen evolution in an acidic media (0.5 M H2SO4). The optimal Na-Co3O4 (AA) exhibits a notably low overpotential of 360 mV@10 mA·cm−2 and at least 200 h stability. In addition, density functional theory (DFT) calculations confirm that the incorporation of Na ions significantly elevates electrical conductivity by decreasing the energy band gap and reduces the free energy barrier for the conversion of *O to *OOH, thereby improving the intrinsic OER activity. Finally, by implanting the catalyst in a single-cell proton exchange membrane water electrolyzer (PEMWE), the current density of 100 mA·cm−2 is achieved at a voltage of 1.62 V. This innovative non-noble metal catalyst holds great potential for scalable PEMWE anodes.

Metal-organic framework derived porous nanosheets-like Co3O4 electrodes on stainless steel with high-performance for supercapacitors

In this work, three-dimensional (3D) nanoporous MOF-derived Co3O4 was successfully prepared by a facile, easy, and rapid solvothermal method on a stainless steel substrate using 1, 4-BDC organic linker and a precursor. Additionally, the effects of the Co-precursor and organic linker on the structure, composition, and morphology of the prepared MOF-derived Co3O4 samples were investigated through an XRD study, which indicated that the MOF-derived Co3O4 thin films exhibited crystalline nature upon deposition on the stainless steel substrate. FE-SEM revealed a porous nanosheet-like morphology. EDAX analysis confirmed the formation of the MOF-derived Co3O4 structure, indicating the presence of cobalt, oxygen, and carbon elements. The oxidation states of the prepared MOF-derived Co3O4 thin films were determined by X-ray photoelectron spectroscopy. Furthermore, the electrochemical performance of the MOF-derived Co3O4 samples was evaluated in a three-electrode system using 1 M KOH electrolyte. Consequently, optimized MOF-derived Co3O4 exhibited excellent electrochemical performance attributed to these advantages. The C3 sample demonstrated an outstanding specific capacitance of 1210 F/g at a current density of 0.5 mA/cm², along with remarkable cyclic stability retention of 94.30 % after 4000 charging/discharging cycles. Additionally, the MOF-derived Co3O4 (C3) electrode showed an excellent energy density of 35.70 Wh/kg and a power density of 4.5 kW/kg. As a result, the unique hierarchical porous structure of MOF-derived Co3O4 also offers effective pathways and excellent electrochemical performance, making it a promising candidate for advanced electrode materials in high-performance supercapacitors.

Effect of Ce-Doping on the Structural, Morphological, and Electrochemical Features of Co3O4 Nanoparticles Synthesized by Solution Combustion Method for Battery-Type Supercapacitors

This study investigates the potential of cerium (Ce) doping to improve the performance of cobalt oxide (Co₃O₄) nanoparticles as battery-type supercapacitor electrodes. Pure Co₃O₄ nanoparticles were synthesized via a solution combustion method and then doped with 2.5% (Ce-Co3O4) and 5% Ce (CeO2-Co3O4). Comprehensive characterization, including X-ray diffraction (XRD), Raman spectroscopy, and field emission scanning electron microscopy (FESEM), was used to analyze the impact of Ce doping on the material properties. XRD analysis confirmed the successful incorporation of Ce into the Co₃O₄ structure, with distinct CeO2 phases forming at higher doping levels. Ce doping resulted in decreased crystallite size and peak intensity, indicating reduced crystallinity and increased defect concentration. Raman spectroscopy corroborated these findings, showing a redshift that suggests weakened metal-oxygen bonds and smaller grain sizes due to Ce³⁺ incorporation. FESEM images demonstrated that Ce doping effectively reduced nanoparticle agglomeration, with 2.5% doping leading to smaller particles and 5% doping promoting a 2D flake-like morphology with increased porosity. Nitrogen adsorption-desorption measurements revealed a significant increase in surface area and pore volume for CeO2-Co₃O₄, facilitating improved electrolyte diffusion and reduced resistance, thereby enhancing electrochemical performance. Evaluation of the electrochemical properties of undoped and Ce-doped Co₃O₄ materials revealed a battery-like response in a three-electrode configuration. Notably, the CeO2-Co3O4 exhibited a superior specific capacity of 603.3 C g-1 at a current density of 1 A g-1, significantly exceeding the values of 368.5 C g-1 and 127.1 C g-1 achieved by Ce-Co3O4 and undoped Co3O4, respectively. Furthermore, the CeO2-doped Co3O4 demonstrated exceptional cyclic stability, retaining 87% of its initial capacity after undergoing 5000 charge-discharge cycles at a high current density of 10 A g-1. These results suggest that Ce doping is a promising strategy for optimizing Co₃O₄-based battery-type electrode materials, potentially leading to the development of high-performance and cost-effective energy storage systems.

Asymmetric defective sites-mediated high-valent cobalt-oxo species in self-suspension aerogel platform for efficient peroxymonosulfate activation

The main pressing problems should be solved for heterogeneous catalysts in activation of peroxymonosulfate (PMS) are sluggish mass transfer kinetics and low intrinsic activity. Here, oxygen vacancies (Vo)-rich of Co3O4 nanosheets were anchored on the superficies of spirulina-based reduced graphene oxide-konjac glucomannan (KGM) aerogel (R-Co3O4-x/SRGA). The porous structure and superhydrophilicity conferred by KGM maximized the diffusion and transport of reactant. More interestingly, R-Co3O4-x/SRGA came true self-suspension rather than conventional self-floating without the aid of external force, maximizing space utilization and facilitating catalysts recovery. Anchored R-Co3O4-x nanosheets acted as “engines” to drive the reaction. Density functional theory (DFT) manifested Vo was capable of breaking the symmetry of the electronic structure of Co3O4. The formation of asymmetric active sites (Vo) was revealed to modulate the d-band center, enhanced affinity for PMS, and promoted evolution of high-valent cobalt-oxo (Co(IV)=O) species. R-Co3O4-x/SRGA achieved complete removal of sulfamethoxazole (SMX) within 12 min. Furthermore, R-Co3O4-x/SRGA demonstrated exceptional stability in the presence of various environmental interference factors and continuous flow device. This insightful work cleverly integrates the macroscopic design of structure, and the microscopic regulation of active sites is expected to open up new opportunities for the development of water treatment.

Surface dynamics and electrochemical examination of Co3O4 films by iron doping

This study focused on Co3O4 films, which were prepared by cost-effective chemical bath deposition on In:SnO2 (ITO) substrates with iron doping concentrations ranging from 2 to 6 mol %. Structural properties were investigated by XRD as well as nanotexture of Fe: Co3O4 films was captured via SEM and detailed fractal analysis was analyzed in each prepared film. Effective using of prepared Fe: Co3O4 electrodes for electrochemical charge storage applications has been examined by using CV and EIS. From x-ray patterns, spinel cubic structure of Co3O4 was observed in all samples, while peaks with Co2O3 and substrate indexed peaks were also shown. Pure and iron doped Co3O4 surfaces have spherical agglomerative forms while porous structures were observed in 4% Co3O4 samples. Redox peaks induced by Faradaic reactions in the CV plots present pseudo- capacitive nature for all electrodes and improves charge transfer process in 4% Co3O4 and 6% Co3O4 from EIS measurements. Additionally, using scaling theory, the coverage ratio, fractal dimensions, cluster sizes and interface critical exponent values of the superficial hetero morphology of the samples are calculated. While the coating rate decreases according to the iron concentration, fractal dimensions increase. However, as the number of clusters increases, the average cluster size decreases. The interface critical exponent value shows an irregular change.

Boosting Acidic Water Oxidation on Hematite Photoanodes with Synergistic Effects of Ce‐Doped Co3O4 Nanoparticles

AbstractPhotoelectrochemical (PEC) water splitting is pivotal for addressing the clean and renewable energy demands. However, developing low‐cost, efficient, and robust non‐precious metal catalysts for the acidic oxygen evolution reaction (OER) remains a significant challenge. In this study, we introduced Ce to modulate the electronic structure of Co3O4, enhancing the stability of Co3O4 without compromising its activity. Ce‐doped Co3O4 nanoparticles were electrodeposited onto Ti‐doped hematite surfaces (Ce : Co3O4/Fe2O3), significantly enhancing the PEC performance for water splitting under acidic conditions. These catalysts achieved high photocurrent densities and exhibited prolonged stability. Functioning as p‐type semiconductors, the Ce : Co3O4 nanoparticles not only boosted light absorption but also formed a p‐n heterojunction with the Ti‐doped hematite. This heterojunction generated a built‐in electric field that facilitated the separation and transfer of photogenerated carriers, thereby improving charge separation efficiency. Additionally, these nanoparticles expanded the active surface area of hematite and served as a co‐catalyst, markedly accelerating the OER kinetics. The Ce : Co3O4/Fe2O3 photoanode achieved an impressive photocurrent density of 1.08 mA cm−2 at 1.23 VRHE in acidic media, demonstrating its enhanced activity and stability.

A vertically aligned flake like CuO/Co3O4 nanoparticle@g-C3N4 ternary nanocomposite: A heterojunction catalyst for efficient photo electrochemical water splitting

Efficient utilization of solar energy for the conversion of water into hydrogen via photoelectrochemical (PEC) water splitting holds tremendous promise for sustainable energy production. In this study, we report a novel vertically aligned flake-like CuO/Co3O4 nanoparticle@g-C3N4 sheets ternary nanocomposite as a heterojunction catalyst for enhancing PEC water splitting efficiency. The ternary nanocomposite was synthesized via a facile and scalable method, resulting in a unique structure with vertically aligned CuO/Co3O4 nanoparticles in tight interface interaction with g-C3N4 sheets. The resulting heterojunction exhibited enhanced light absorption, efficient charge separation, and improved charge transfer kinetics, leading to significantly enhanced PEC water splitting performance. The as-synthesized ternary nanocomposite, such as CuO/Co3O4@g-C3N4 nanocomposite, demonstrated superior PEC activity with an enhanced photocurrent density, i.e., 0.88 mA/cm2, which is higher than that of the pristine CuO (0.65 mA/cm2), Co3O4 (0.7 mA/cm2), and CuO-Co3O4 (0.77 mA/cm2) structures with linear sweep voltammetry under light irradiation. Additionally, the ternary nanocomposite exhibited excellent stability during 2 h PEC water splitting measurements under 1 h time interval chopped conditions. The remarkable performance of the vertically aligned CuO/Co3O4 nanoparticle@g-C3N4 ternary nanocomposite underscores its potential as a promising catalyst for efficient solar-driven hydrogen generation. This study not only provides insights into the design of advanced heterojunction catalysts but also contributes to the development of sustainable energy conversion technologies.

Co3O4-Based Materials as Potential Catalysts for Methane Detection in Catalytic Gas Sensors.

The present work deals with the development of Co3O4-based catalysts for potential application in catalytic gas sensors for methane (CH4) detection. Among the transition-metal oxide catalysts, Co3O4 exhibits the highest activity in catalytic combustion. Doping Co3O4 with another metal can further improve its catalytic performance. Despite their promising properties, Co3O4 materials have rarely been tested for use in catalytic gas sensors. In our study, the influence of catalyst morphology and Ni doping on the catalytic activity and thermal stability of Co3O4-based catalysts was analyzed by differential calorimetry by measuring the thermal response to 1% CH4. The morphology of two Co3O4 catalysts and two NixCo3-xO4 with a Ni:Co molar ratio of 1:2 and 1:5 was studied using scanning transmission electron microscopy and energy dispersive X-ray analysis. The catalysts were synthesized by (co)precipitation with KOH solution. The investigations showed that Ni doping can improve the catalytic activity of Co3O4 catalysts. The thermal response of Ni-doped catalysts was increased by more than 20% at 400 °C and 450 °C compared to one of the studied Co3O4 oxides. However, the thermal response of the other Co3O4 was even higher than that of NixCo3-xO4 catalysts (8% at 400 °C). Furthermore, the modification of Co3O4 with Ni simultaneously brings stability problems at higher operating temperatures (≥400 °C) due to the observed inhomogeneous Ni distribution in the structure of NixCo3-xO4. In particular, the NixCo3-xO4 with high Ni content (Ni:Co ratio 1:2) showed apparent NiO separation and thus a strong decrease in thermal response of 8% after 24 h of heat treatment at 400 °C. The reaction of the Co3O4 catalysts remained quite stable. Therefore, controlling the structure and morphology of Co3O4 achieved more promising results, demonstrating its applicability as a catalyst for gas sensing.

Self-supporting nanosheet electrode for efficient oxygen evolution in a wide pH range: engineering electronic structure of Co3O4 by Fe doping

Self-supporting nanosheet electrode for efficient oxygen evolution in a wide pH range: engineering electronic structure of Co3O4 by Fe doping

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.

Special atmosphere annealed Co3O4 bifunctional catalysts with oxygen defects for high-efficient water splitting

Electrochemical water splitting is widely recognized as an economical and sustainable method for producing high-purity hydrogen using renewable energy sources. Herein, we prepared 3D urchin-like sphere structures of Co3O4 to serve as an excellent bifunctional catalyst for overall water splitting. Different Co3O4 samples were directly synthesized on Ni foam through hydrothermal and annealing processes under various atmospheric conditions, leading to the formation of oxygen vacancies with varying concentrations. Specifically, the Co3O4/NF-Ar/O2 demonstrates outstanding catalytic performance for both OER (η20 = 269 mV) and HER (η10 = 135 mV), while maintaining excellent durability in 1 M KOH. Electrolysis cells employing Co3O4/NF-Ar/O2 as both anode and cathode demonstrate a low cell voltage of 1.56 V to achieve 10 mV cm−2 in alkaline conditions. The excellent catalytic performance can be mainly attributed to the urchin-like nanostructure and the appropriate concentration of oxygen vacancies. This research provides further insights into the application of the method to induce oxygen vacancies in low-cost and high-efficiency transition metal oxides (TMOs)-based catalysts for electrochemical reaction.

Interfacial electron interactions governed photoactivity and selectivity evolution of carbon dioxide photoreduction with spinel cobalt oxide based hollow hetero-nanocubes

In this work, an efficient CO2 photoreduction catalyst based on Co3O4/ZnIn2S4 hollow hetero-nanocubes is precisely constructed via an in-situ transformation of cobalt-organic framework followed by a solvothermal reaction. Comprehensive in-situ spectroscopic analyses and theoretical calculations have revealed that the critical interfacial electron interactions (IEIs) effects on both photoactivity evolution and selectivity modulation in the Co3O4/ZnIn2S4 hetero-structure. As the content of ZnIn2S4 increases in the hetero-structure, the photoactivity exhibits a volcano-like evolution profile but the CH4 selectivity reduces monotonously. The improved photoactivity is attributed to the IEIs-promoted charge separation as well as the specific-surface-area effect in terms of electron unitization rate, and the electronic structure of Co3O4 is tuned and the energy barrier for the key reaction intermediate *CHO is reduced, leading to improved CH4 selection in comparison with bare Co3O4. The IEIs-mediated production selectivity is further verified by a Co3O4/CeO2 heterojunction, indicating a certain universality of the IEI effect.

A novel dual S-scheme Co9S8/MnCdS/Co3O4 heterojunction for photocatalytic hydrogen evolution under visible light irradiation.

Rational design and synthesis of a unique heterojunction photocatalyst structure is an important strategy to enhance its performance and structural stability. Herein, Co9S8/MnCdS/Co3O4 photocatalysts with double S-scheme heterojunctions were successfully prepared by coupling Co9S8 and Co3O4 sheet structures with n-type MnCdS nanoparticles through a simple solvothermal and mechanical mixing method. The construction of the dual S-scheme heterostructure offers the possibility to expand the light absorption range, extend the carrier lifetime and maximise the redox capacity. In addition, the mechanism of charge transfer and the reason for the improvement of photocatalytic activity were explored through photoelectrochemical characterization. The lamellar structures of Co9S8 and Co3O4 not only provide excellent dispersion and slow down the agglomeration of MnCdS nanoparticles, but also promote charge transfer, which improves the photocatalytic hydrogen production effect. Under simulated solar irradiation, the evolution rate of H2 after 5 h was as high as 46.44 μmol, which was 3.49 and 1.49 times higher than those of pristine MnCdS and MnCdS/Co3O4, respectively. Meanwhile, it has good stability under 20 h irradiation. This work demonstrates a novel idea for the rational design of double S-scheme photocatalysts with efficient space separation.

Application of dandelion-like Sm2O3/Co3O4/rGO in high performance supercapacitors.

Novel 2D material-based supercapacitors are promising candidates for energy applications due to their distinctive physical, chemical, and electrochemical properties. In this study, a dandelion-like structure material comprised of Sm2O3, Co3O4, and 2D reduced graphene oxide (rGO) on nickel foam (NF) was synthesised using a hydrothermal method followed by subsequent annealing treatment. This dandelion composite grows further through the tremella-like structure of Sm2O3 and Co3O4, which facilitates the diffusion of ions and prevents structural collapse during charging and discharging. A substantial number of active sites are generated during redox reactions by the unique surface morphology of the Sm2O3/Co3O4/rGO/NF composite (SCGN). The maximum specific capacity the SCGN material achieves is 3448 F g-1 for 1 A g-1 in a 6 mol L-1 KOH solution. Benefiting from its morphological structure, the prepared composite (SCGN) exhibits a high cyclability of 93.2% over 3000 charge-discharge cycles at 10 A g-1 and a coulombic efficiency of 97.4%. Additionally, the assembled SCGN//SCGN symmetric supercapacitors deliver a high energy density of 64 W h kg-1 with a power density of 300 W kg-1, which increases to an outstanding power density of 12 000 W kg-1 at 28.7 W h kg-1 and long cycle stability (80.9% capacitance retention after 30 000 cycles). These results suggest that the manufactured SCGN electrodes could be viable active electrode materials for electrochemical supercapacitors.

Poly[(2-methacryloyloxy)Ethyl]Trimethylammonium Chloride Supported Cobalt Oxide Nanoparticles as an Active Electrocatalyst for Efficient Oxygen Evolution Reaction.

To combat with energy crisis considering clean energy, oxygen evolution reaction (OER) is crucial to implement electrolytic hydrogen fuel production in real life. Here, straightforward chemical synthesis pathways are followed to prepare cobalt tetraoxide nanoparticles (Co3O4NPs) in an alkaline OER process using poly[(2-methacryloyloxy)ethyl]trimethylammonium chloride (Co3O4NPs@PMTC) as support to prevent aggregation. In material characterization, the X-ray diffraction (XRD) pattern confirms the crystallinity of the synthesized Co3O4NPs@PMTC, and Raman spectroscopy indicates that the Co3O4NPs contain cubic close-packed oxides. The morphological analysis reveals the wrinkle-like disruption which is distributed evenly owing to the folded nanosheet arrays. Energy-dispersive X-ray spectroscopy indicates the presence of a significant number of cobalt atoms in the Co3O4NPs, and elemental mapping analysis demonstrates the composition of the NPs. At a current density of 10 mA cm-2, oxygen is emitted at 1.67 V delivering an overpotential of 440 mV. This unique structure of Co3O4NPs@PMTC provides beneficial functions that are responsible for a large number of active sites and the rapid release of oxygen gas with long-term stability. Through kinetic study, we found a Tafel slope of 48.9 mV dec-1 which proves the catalytic behavior of Co3O4NPs@PMTC is promising toward the OER process.

Atomically Confined Ru Sites in Octahedral Co3O4 for High‐Efficiency Hydrazine Oxidation

AbstractHydrazine‐assisted water electrolyzer is a promising energy‐efficient alternative to conventional water electrolyzer, offering an appealing path for sustainable hydrogen (H2) production with reduced energy consumption. However, such electrolyzer is presently impeded by lacking an efficient catalyst to accelerate the kinetics of pivotal half‐reaction, that is, hydrazine oxidation reaction (HzOR). Herein, a ruthenium (Ru) single‐atom on an octahedral cobalt oxide (Co3O4) substrate (Ru‐Co3O4) catalyst, guided by theoretical calculations is developed. Those lattice‐confined Ru sites within octahedral structure of spinel Co3O4 effectively lower the energy barrier required for the formation of N2H2* intermediate and desorption of H* species in HzOR. As a result, the Ru‐Co3O4 catalyst achieves superior HzOR performance with a low potential of −0.024 V versus (vs.)reversible hydrogen electrode (RHE) at 100 mA cm−2 and remarkable stability for over 200 h at 200 mA cm−2. Importantly, a modular H2 production achieves an output of 0.48 kWh electricity per m3 H2 by decoupling and pairing the HzOR and hydrogen evolution reaction (HER) half‐reaction with a Zinc (Zn) redox reservoir. The work represents a significant advancement in the field, offering substantial flexibility for on‐demand H2 production and energy output.

Modulated Electronic Structure of Co3O4 by Single Atoms for Efficient Anodic Oxygen Evolution in Acid.

The challenge of the practical application of a water electrolyzer system lies in the development of low-manufacturing cost, highly active, and stable electrocatalysts to replace the noble metal ones, in order to enable environmentally friendly hydrogen production on a large scale. Herein, a facile method is proposed for boosting the performance of Co3O4 through the incorporation of large-sized single atoms. Due to the larger ionic radius of rare earth metals than that of Co, the incorporation elongates the bond length of Co─O, resulting in the narrowed d-p band centers and the high spin configuration, which is favorable for the interaction and charge transfer with absorbent (*OH). As a result, the Ce-incorporated Co3O4 with the longest Co─O bond length exhibits the best oxygen evolution reaction (OER) performance, specifically, the turnover frequency is over 17 times higher than that of pristine Co3O4 nanosheet under an overpotential of 400mV. Powered by a commercial Si solar cell, a two-electrode solar water-splitting device combining Ce-incorporated Co3O4 and Pt delivers a solar-to-hydrogen conversion efficiency of 13.53%. The strategy could provide a new insight for improving the performance of OER electrocatalysts in acid toward practical applications.