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Co3O4 nanocubes are evaluated concerning their intrinsic electrocatalytic activity towards the oxygen evolution reaction (OER) by means of single‐entity electrochemistry. Scanning electrochemical cell microscopy (SECCM) provides data on the electrocatalytic OER activity from several individual measurement areas covering one Co3O4 nanocube of a comparatively high number of individual particles with sufficient statistical reproducibility. Single‐particle‐on‐nanoelectrode measurements of Co3O4 nanocubes provide an accelerated stress test at highly alkaline conditions with current densities of up to 5.5 A cm−2, and allows to derive TOF values of up to 2.8×104 s−1 at 1.92 V vs. RHE for surface Co atoms of a single cubic nanoparticle. Obtaining such high current densities combined with identical‐location transmission electron microscopy allows monitoring the formation of an oxy(hydroxide) surface layer during electrocatalysis. Combining two independent single‐entity electrochemistry techniques provides the basis for elucidating structure–activity relations of single electrocatalyst nanoparticles with well‐defined surface structure. [ABSTRACT FROM AUTHOR]

In recent years, catalytic hydrolysis of sodium borohydride is considered to be a promising approach for hydrogen generation towards fuel cell devices, and highly efficient and noble-metal-free catalysts have attracted increasing attention. In our present work, Co 3 O 4 nanocubes are synthesized by solvothermal method, and then vapor-phase phosphorization treatment is carried out for the preparation of novel Co−O−P composite nanocatalysts composed of multiple active centers including Co, CoO, and Co 2 P. For catalyst characterization, field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), energy dispersive spectrometry (EDS), X-ray diffraction (XRD) and X-ray photoelectric spectroscopy (XPS) are conducted. Optimal conditions for catalyst preparation and application were investigated in detail. At room temperature (25 °C), maximum hydrogen generation rate (HGR) is measured to be 4.85 L min−1 g−1 using a 4 wt% NaBH 4 − 8 wt% NaOH solution, which is much higher than that of conventional catalysts with single component reported in literature. It is found that HGR remarkably increases with the increasing of reaction temperature, and apparent activation energy for catalytic hydrolysis of NaBH 4 is calculated to be 63 kJ mol−1. After reusing for five times, the Co−O−P composite nanocatalysts still retains 78% of the initial activity. • Novel Co-O-P composite nanocatalysts were developed for NaBH 4 hydrolysis to generate H 2. • The catalysts were prepared by a combined processing consisted of solvothermal method and vapor phase phosphorization. • The catalysts were composed of multiple active components including Co, CoO and Co 2 P.4. • The catalysts present much higher catalytic activity than that of single-component catalysts in literature. [ABSTRACT FROM AUTHOR]

Abstract Cobalt (II, III) oxide (Co 3 O 4) nanostructures have attracted much attention as a candidate for anode materials in lithium-ion batteries (LIBs) due to its unique physical/chemical properties and high specific capacity. However, critical issues, such as low electronic conductivity, inefficient ionic diffusion, and large volume change during battery operation, have to be addressed before practical applications. In this work, we report a facile chemical reduction approach to modify Co 3 O 4 nanocubes by NaBH 4 solution treatment. The microstructure and chemical composition analysis indicate that the modified Co 3 O 4 nanocubes are oxygen deficient and other secondary phases are not formed during the processing. The degree of oxygen deficiency can be well controlled by altering the concentration of NaBH 4 solution. When evaluated as the anodes for LIBs, the optimized sample shows a reversible capacity of 873.5 mAhg−1 after 50 cycles at a current density of 0.1 Ag−1, and a charge-discharge capacity of 569.1 mAhg−1 at a higher current density of 5 Ag−1. The balanced oxygen deficiency and crystallinity in the chemically reduced nanostructured electrodes are supposed to be responsible for the improved lithium storage properties. We believe that the facile solution-based chemical reduction strategy provides an alternative way to control the defects in different functional nanostructures for broader applications. Graphical abstract Chemical reduction in NaBH 4 solution generates oxygen deficiency in Co 3 O 4 nanocubes, which provides a new way to tune lithium storage properties. Unlabelled Image Highlights • Chemical reduction in solution generates oxygen deficiency in Co 3 O 4 nanocubes. • The amount of oxygen deficiency can be controlled by NaBH 4 concentration. • The optimized sample (Co 3 O 4 -10 mM) shows good lithium storage properties. • The improved performance is attributed to the balanced oxygen deficiency and crystallinity. [ABSTRACT FROM AUTHOR]

A new La3+-doped Co 3 O 4 nanocubes based screen printed electrochemical sensor was effectively used to determine sulfite. The electrochemical oxidation activity of sulfite was considered in PBS (pH 7.0) with voltammetry method. The obtained results presented that the new electrode has an electrocatalytic behavior in oxidizing sulfite resulting in a significant enhancement in its oxidation current. There is a linear correlation between the peak currents and the level of sulfite in the range of 0.7–1000.0 μM with a limit of detection of 0.090 (±0.001) μM. The suggested sensor showed good selectivity, sensitivity and outstanding recovery results for real samples with considerable constancy and precision suggesting practical efficacy of the La3+-doped Co 3 O 4 nanocubes/SPE as an efficient and reliable electrochemical sensor for determining sulfite. • La3+ doped Co 3 O 4 nanocubes as a nanocomposite was synthesized and used for modification of graphite screen-printed electrode • This modified electrode was used for determination of sulfite • It was used for real sample analysis. [ABSTRACT FROM AUTHOR]

Developing facile strategies to construct free-standing flexible electrodes with extremely sensitive and stable electrochemical response towards analytes is of huge demand and it is still highly challenging. Herein, we design a unique and cost-effective hybrid electrode comprising of cobalt oxide (Co 3 O 4) directly grown on highly conducting MXene based carbon fiber electrode (CFE) as a self-standing electrode using a simple hydrothermal-annealing method, where MXene nanosheets on electrode support facilitate the growth of uniform-sized Co 3 O 4 nanocubes. Our results demonstrate that the synergetic effects of conductive MXene support and catalytically active Co 3 O 4 nanocubes provide a superior response towards glucose oxidation in an alkaline medium (0.1 M KOH). The resultant Co 3 O 4 /MXene@CFE demonstrates remarkable sensitivity (19.3 μA mM−1 cm−2), wide linear range (0.05 μM to 7.44 mM) and lower detection limits (10 nM), thus providing excellent selectivity over interfering species and good electrochemical stability for an extended shelf-life. Therefore, the obtained self-standing Co 3 O 4 /MXene@CFE flexible electrode establishes a promising platform for glucose oxidation and it could be envisioned for the highly sensitive detection of various target molecules for their widespread applications in clinical diagnosis and health care monitoring. [Display omitted] • Successful integration of Co 3 O 4 nanocubes on MXene anchored CFE. • Simple hydrothermal-annealing method is used to fabricate freestanding Co 3 O 4 /MXene@CFE. • The Co 3 O 4 /MXene@CFE displays enhanced electrochemical sensing performance for glucose detection. • The sensor has been successfully applied to determine glucose in human serum samples. [ABSTRACT FROM AUTHOR]

Abstract: Nearly monodisperse Co3O4 nanocubes have been prepared by a microwave-assisted solvothermal (MS) method at 180°C for 20min. The samples are characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The XRD pattern and TEM images of the products illustrated that Co3O4 nanocubes had a cubic phase with a lateral size of ∼20nm. The gas response of the Co3O4 nanocubes was studied to several typical organic gases. The Co3O4 nanocubes showed good gas sensing performance towards xylene and ethanol vapors with rapid and high responses at a low-operating temperature. The results showed that the Co3O4 nanocubes can be used to fabricate high performance gas sensors. [Copyright &y& Elsevier]

Abstract: We report here a simple approach to the synthesis of highly dispersed Co3O4 nanocubes in higher yield by aqueous precipitation method at low temperatures (70–90°C). The nanosized Co3O4 powders were directly achieved from Co(II) aqueous solution under alkaline and oxidizing conditions. TEM results indicate that the as-prepared Co3O4 has a cubic nanostructure with uniform size of about 20nm and narrow size distribution. Powder X-ray diffraction (XRD) and infrared spectrum (IR) results show that the samples are Co3O4 in spinel structure. The objective Co3O4 nanocubes can be achieved in a wide range of experimental parameters, which can be preserved as stable suspension in distilled water or ethanol for several months with no obvious change. Appropriate reaction time and temperature should be controlled to get better crystallized Co3O4 nanocubes with perfect cubic appearance and good dispersibility. It is essential to achieve cubic-like Co3O4 particles by using ammonia as precipitator. The as-prepared Co3O4 nanocubes, combined with PbO2 as electrodes, extend improved electrocatalytic activities and decreased oxygen evolution potential in electrochemical reactions, so they can be used as potential electrode materials or electrocatalytic materials. This facile method for the synthesis of Co3O4 nanocubes is a simple and general process without any seed, catalyst, or template, thus it is promising for large-scale and low-cost production of Co3O4 with high-quality. [ABSTRACT FROM AUTHOR]

Fabrication of novel metal oxide nanostructured composites is a proficient approach to develop efficient energy storage devices and development of cost-free and eco-friendly metal oxide nanostructures for supercapacitor applications received considerable attention in recent years. The Co 3 O 4 nanocubes-NiO octahedral structured composite was constructed using facile and one-step calcination process. Cyclic voltammetry, charge-discharge, and electrochemical impedance spectral techniques have been employed to analyze the specific capacitance of the synthesized nanostructures and the composites. Specific capacitance and cycling stability of the composites were evaluated with the pristine Co 3 O 4 and NiO nanostructures. The composite showed a specific capacitance of 832 F g−1 at a current density of 0.25 A g−1, which was ~1.5 and ~1.9-times higher than pristine Co 3 O 4 nanocubes and NiO octahedral structure, respectively. On the other hand, electrode showed approximately 50 % capacity retention at a higher current density (5 Ag-1) because of the uniform morphology of Co 3 O 4 and NiO. The charge-discharge stability measurements of the composite showed an admirable specific capacitance retention capability, which was 94.5 % after 2000 continuous charge-discharge cycles at a current density of 5 A g−1. The superior electrochemical performance of the nano-composite was ascribed to synergistic effects and uniform morphology. Efficient nanostructure development using facile and one-step calcination process and electrochemical performance make the synthesized composite a promising device for supercapacitor applications. [Display omitted] • Heterostructured Co 3 O 4 –NiO hybrids were synthesized through calcination process. • Physico-chemical and electrochemical energy storage super-capacitive properties investigated. • Hybrid electrode showed specific capacitance of 832 F g−1 at a current density of 0.25 A g−1 • Hybrid electrode showed capacitance retention of 94.5 % after 2000 charge-discharge cycles. • Co 3 O 4 –NiO hybrids showed energy density of 42 Wh kg−1 at power density of 183 W kg−1 [ABSTRACT FROM AUTHOR]

Co 3 O 4 nano materials have attracted tremendous attention as effective catalysts for sodium oxygen batteries (SOBs). However, their electrochemical processes and fundamental catalytic mechanism remain unclear till now. Herein, in-situ environmental transmission electron microscopy technique was used to study the catalysis mechanism of the Co 3 O 4 nanocubes in SOBs during discharge and charge processes. It is found that during the 1st discharge and charge processes, Na 2 O 2 formed and decomposed, respectively, around the Co 3 O 4 nanocubes, but the following discharge and charge processes were very difficult. In order to promote the charge kinetics, we increased the charging temperature up to 500 °C, when the decomposition of Na 2 O 2 became facile. Aberration corrected high-angle annular dark field imaging indicated that a thin layer of CoO grew epitaxially on the surface of Co 3 O 4 nanocubes after the first discharge. Density functional theory calculations indicate that the CoO surface is energetically more favorable than Co 3 O 4 for the nucleation of Na 2 O 2. This study provides not only new fundamental understandings to the electrochemical reaction mechanisms of SOBs, but also strategies to improve the cycling performance of solid state SOBs. This study reported a real time study of a Na-O 2 battery by using in-situ environmental transmission electron microscopy (ETEM) technique. The catalysis mechanism of the Co 3 O 4 nano cubes (NCs) during oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) was revealed. We discovered that the surface of Co 3 O 4 was converted to CoO, and it is the latter that catalyzed the ORR reaction. Furthermore, increasing the charging temperature promotes the OER reaction. These results provide new understanding of the electrocatalysis in Na-O 2 batteries, which may guide the design of high performance Na-O 2 batteries for large scale energy storage applications. Image 1 • In-situ ETEM was conducted to study the electrocatalysis mechanism of the Co 3 O 4 nanocubes in sodium oxygen batteries. • It is CoO but not Co 3 O 4 that catalyzes the oxygen reduction reaction, clearing the long standing debate in the literature. • By using a novel MEMS heating device, the oxygen evolution reaction was greatly promoted at high temperatures. [ABSTRACT FROM AUTHOR]

Detection and control of air quality are major concerns in recent years for environmental monitoring and healthcare. In this work, we developed an integrated sensor architecture comprised of nanostructured composite sensing layers and a flexible heating substrate for portable and real-time detection of nitrogen dioxide (NO 2 ). As sensing layers, PdO-infiltrated Co 3 O 4 hollow nanocubes (PdO-Co 3 O 4 HNCs) were prepared by calcination of Pd-embedded Co-based metal-organic framework polyhedron particles. Single-walled carbon nanotubes (SWCNTs) were functionalized with PdO-Co 3 O 4 HNCs to control conductivity of sensing layers. As a flexible heating substrate, the Ni mesh electrode covered with a 40 nm thick Au layer (i.e., Ni(core)/Au(shell) mesh) was embedded in a colorless polyimide (cPI) film. As a result, SWCNT-functionalized PdO-Co 3 O 4 HNCs sensor exhibited improved NO 2 detection property at 100 °C, with high sensitivity (S) of 44.11% at 20 ppm and a low detection limit of 1 ppm. The accelerated reaction and recovery kinetics toward NO 2 of SWCNT-functionalized PdO-Co 3 O 4 HNCs were achieved by generating heat on the Ni(core)/Au(shell) mesh-embedded cPI substrate. The SWCNT-functionalized porous metal oxide sensing layers integrated on the mechanically stable Ni(core)/Au(shell) mesh heating substrate can be envisioned as an essential sensing platform for realization of low-temperature operation wearable chemical sensor.