Co3O4 Layer Research Articles

(Invited) Structure and Reactivity of Cobalt-Containing Nanocomposites for Electrocatalytic Oxygen Evolution in Acid Medium

Electrochemical water splitting involves two heterogeneous multi-step half-reactions, which are referred to as the cathodic hydrogen evolution reaction (HER) and the anodic oxygen evolution reaction (OER). It should be noted that the OER under acidic conditions has the following two advantages compared to the process in neutral and alkaline solutions. The kinetics of the OER in acidic media could be much faster due to the higher proton transfer rate between anode and cathode. The proton exchange membrane (PEM) is an acidic solid polymer electrolyte membrane characterized by good proton conductivity, excellent electrochemical durability, and high mechanical strength.Polynuclear iron(III) hexacyanoferrate(II), or Prussian blue, and its analogues possess unique open framework structures with the general chemical formula of AxMy[Fe-(CN)6]z·nH2O (where A = alkali metal cation, M = transition metal cation). The possibility to accommodate different transition metal cations within the coordination framework renders them with appealing electrochemical, ion-exchange, sensing, or photomagnetic properties, which have been the subject of intense research for decades. Despite their rigid structure, these mixed-metal coordination polymers are usually nonstoichiometric. This chemical variety makes them a versatile type of molecule-based materials. Prussian Blue type cobalt hexacyanoferrates seem to activate water molecules during photoelectrochemical oxidations. Here we report the water oxidation catalytic activity found in Prussian blue-type cobalt hexacyanoferrate modified electrodes both under conventional electrochermcal and photoelectrochemical conditions (using WO3 n-type semiconductor) in acid medium. It is noteworthy that some of the hybrid cobalt-ruthenium hexacyanoferrate compositions showed remarkable catalytic ability towards the oxygen evolution reaction in acid electrolyte. The enhanced catalytic activities of the as-synthesized electrodes should also be attributed to such features as high population of hydroxyl groups and high Broensted acidity (due to presence of Ru or W oxo sites) and related fast electron transfers coupled to unimpeded proton displacements. The possibility of metal-metal interactions between nanosized metals (Co and Ru or Co and W) cannot be excludedFor comparison, we also show that mixed-metal oxide nanocomposites combining the favorable catalytic properties of Co3O4 and CeO2, nanocomposites (with different phase distribution and Co3O4 loading) can modify the cobalt-oxo-species and enhance its intrinsic oxygen evolution reaction activity. Synthesis of Co3O4-modified CeO2, which was addressed through three different sol-gel based routes, each with 10.4 wt% Co3O4 loading, yielded three different nanocomposite morphologies: CeO2-supported Co3O4 layers, intermixed oxides, and homogeneously dispersed Co. It is reasonable to expect that the local bonding environment of Co3O4 can be modified after the introduction of nanocrystalline CeO2, which allows the CoIII species to be easily oxidized into catalytically active CoIV species, thus avoiding the undesirable surface reconstruction process. Here, ceria is likely to regulate the surface oxygen concentration, due to its oxygen buffer (storage/release) capacity, associated with the fast CeIV/CeIII redox transition. Our research addresses the problems related to the fabrication of efficient earth-abundant catalysts for oxygen evolution reaction, and it provides strategies for designing more active and stable catalytic systems.

Investigation the Structure and Linear/Nonlinear Spectroscopic Performance of Fe:Co3O4/TiO2 Nanostructured Heterojunctions

Abstract The structure and linear/nonlinear spectroscopic performance of Fe:Co3O4/TiO2 (FCTO) nanostructured heterojunctions (HJs) were investigated. Pure TiO2 nanostructures and FCTO nanostructured HJs were synthesized by spray pyrolysis technique. The surfaces morphology of the samples was examined utilizing a scanning electron microscope. Energy-dispersive X-ray measurements were performed to confirm the content of the prepared FCTO HJs. The structures’ variations and bonding were explored with Fourier transform infrared spectroscopy. X-ray diffraction measurements were carried out to study the crystallinity, structures, and lattice parameters, revealing that the pure TiO2 nanostructures have a tetragonal crystalline structure with an anatase phase, while the Fe:Co3O4 layer possesses a cubic crystalline structure. XRD analysis also showed that the crystallite size increases from 15.9 nm (pure TiO2) to 25.4 nm (FCTO HJ). Optical performance was studied via UV-visible-NIR measurements. The optical parameters of the FCTO HJs were investigated and the nonlinear optical performance of the prepared samples was assessed. Great enhancement of the linear/nonlinear optical performance of the FCTO HJs was achieved compared with the pure TiO2 nanostructures. The results reveal that the Fe:Co3O4/TiO2 nanostructured HJs are recommended for many visible spectrum applications.

Thermal cycling behavior of Srx(Zr0.9Y0.05Yb0.05)O1.95+x thermal barrier coatings by suspension plasma spraying

AbstractThe thermal barrier coatings (TBCs) consisting of Srx(Zr0.9Y0.05Yb0.05)O1.95+x were prepared using the suspension plasma spraying (SPS) method. Precursor suspensions were prepared via co‐precipitation for this purpose. Detailed microstructural, phase composition, and phase content analyses were conducted on these coatings, designated as SZYY‐1 (x = 1.0), SZYY‐2 (x = 0.9), and SZYY‐3 (x = 0.8). Additionally, the coatings underwent a thermal cycling test at 1121°C for 1 h. To assess the morphology of thermally grown oxide (TGO) in a real coating, a finite element model was employed. SPS‐SZYY‐2 with columnar crystal structure was found to have the highest number of thermal cycling, up to 345 times. The thermophysical high‐temperature properties of the coating can be effectively improved through suitable second‐phase content. Microstructural and finite element analyses revealed that stress, primarily caused by the continuous growth of the Co3O4, NiO and Spinel (CNS) layer within TGO, was the predominant factor leading to coating failure. At elevated temperatures, transverse cracks formed at the interface between the bond coating and ceramic top coating due to mismatched thermal expansion and sintering effects, ultimately leading to coating degradation. Therefore, reducing the generation rate of large stresses in the coating, especially shear stresses, can effectively prevent the generation and propagation of transverse cracks and increase the thermal cycling life of TBCs.

Active Thermochemical Barrier Coatings Using Metal Oxides: First Experimental Results.

A new concept of active thermal coating based on the use of reversible thermochemical reactions is presented in this paper. The new active thermal barrier coating uses redox reactions to buffer the temperature changes that a metallic component may suffer at high temperatures. The heat is stored when the temperature is equal/above the reduction temperature of the active coating (endothermic reaction) and the heat is released when the temperature is equal/below the oxidation temperature (exothermic reaction). The paper describes the development and testing of a reactive thermal barrier coating based on the redox reaction of Co3O4 and its cyclability. Co3O4 was chosen as a reference material due to the high enthalpy of reaction (844 kJ/kg) and redox reversibility. The activity of coatings with 1, 2, and 3 Co3O4 layers was demonstrated by simultaneous thermal analysis, showing good stability for 5 five cycles.

Improvement of Thermal Stability and Photoelectric Performance of Cs2PbI2Cl2/CsPbI2.5Br0.5 Perovskite Solar Cells by Triple-Layer Inorganic Hole Transport Materials.

Conventional hole transport layer (HTL) Spiro-OMeTAD requires the addition of hygroscopic dopants due to its low conductivity and hole mobility, resulting in a high preparation cost and poor device stability. Cuprous thiocyanate (CuSCN) is a cost-effective alternative with a suitable energy structure and high hole mobility. However, CuSCN-based perovskite solar cells (PSCs) are affected by environmental factors, and the solvents of an HTL can potentially corrode the perovskite layer. In this study, a Co3O4/CuSCN/Co3O4 sandwich structure was proposed as an HTL for inorganic Cs2PbI2Cl2/CsPbI2.5Br0.5 PSCs to address these issues. The Co3O4 layers can serve as buffer and encapsulation layers, protecting the perovskite layer from solvent-induced corrosion and enhancing hole mobility at the interface. Based on this sandwich structure, the photovoltaic performances of the Cs2PbI2Cl2/CsPbI2.5Br0.5 PSCs are significantly improved, with the power conversion efficiency (PCE) increasing from 9.87% (without Co3O4) to 11.06%. Furthermore, the thermal stability of the devices is also significantly enhanced, retaining 80% of its initial PCE after 40 h of continuous aging at 60 °C. These results indicate that the Co3O4/CuSCN/Co3O4 sandwich structure can effectively mitigate the corrosion of the perovskite layer by solvents of an HTL and significantly improves the photovoltaic performance and thermal stability of devices.

Efficient Photothermal Catalytic Oxidation Enabled by Three-Dimensional Nanochannel Substrates.

Photothermal catalysis exhibits promising prospects to overcome the shortcomings of high-energy consumption of traditional thermal catalysis and the low efficiency of photocatalysis. However, there is still a challenge to develop catalysts with outstanding light absorption capability and photothermal conversion efficiency for the degradation of atmospheric pollutants. Herein, we introduced the Co3O4 layer and Pt nanoclusters into the three-dimensional (3D) porous membrane through the atomic layer deposition (ALD) technique, leading to a Pt/Co3O4/AAO monolithic catalyst. The 3D ordered nanochannel structure can significantly enhance the solar absorption capacity through the light-trapping effect. Therefore, the embedded Pt/Co3O4 catalyst can be rapidly heated and the O2 adsorbed on the Pt clusters can be activated to generate sufficient O2- species, exhibiting outstanding activity for the diverse VOCs (toluene, acetone, and formaldehyde) degradation. Optical characterization and simulation calculation confirmed that Pt/Co3O4/AAO exhibited state-of-the-art light absorption and a notable localized surface plasmon resonance (LSPR) effect. In situ diffuse reflectance infrared Fourier transform spectrometry (in situ DRIFTS) studies demonstrated that light irradiation can accelerate the conversion of intermediates during toluene and acetone oxidation, thereby inhibiting byproduct accumulation. Our finding extends the application of AAO's optical properties in photothermal catalytic degradation of air pollutants.

Broadband photodetector based on Co3O4/ZnO/Si double heterojunctions: A morphological and optoelectronic study

The growing demand for efficient and cost-effective optoelectronic devices has motivated extensive research into advanced photodetector architectures. This work realizes a robust platform for broadband photodetection via architectural engineering of Co3O4/ZnO/Si double heterojunctions using facile chemical spray pyrolysis. Comprehensive materials and device characterization provides fundamental insights into the role of tailored morphology, band alignment engineering, and defect landscape in dictating device behavior. Aligned ZnO nanorods and fine-grained Co3O4 layers enable efficient light harvesting and charge transport. A triple bandgap structure stemming from the synergistic combination of the two oxides facilitates broadband spectral response from 400 to 1000 nm. Based on the optical properties, triple energy bandgap ranges have been observed, ZnO exhibits an energy bandgap ranging from 2.35 eV to 3.15 eV, while Co3O4 shows energy bandgaps in the range of 1.85 eV–2.23 eV and 1.35 eV–1.5 eV. The responsivity measurements show that Co3O4/ZnO/Si double-heterojunction device has the highest responsivity over a wide range, with distinct peaks at 480 nm and 950 nm, reaching values of 3.5 A/W and 4.5 A/W, respectively. Analysis of electrical transport characteristics and energy band diagrams elucidates the photogenerated carrier dynamics and photocurrent generation governed by strategic heterointerfaces. These fundamental insights into nanoscale interface and architecture engineering lay the foundation for custom-designing high performance metal oxide heterojunction photodetectors through facile and scalable spray pyrolysis technique.

Understanding the role of TiO2 coating for stabilizing 4.6V high-voltage LiCoO2 cathode materials

TiO2 surface coating is considered to be an effective strategy for improving the cycling performance of commercially available high voltage LiCoO2 (HV-LCO) batteries. However, the mechanism underlying the TiO2 coating remains ambiguous due to the synergy of solid-state coating and annealing processes. In this work, the effects of TiO2 were systematically studied for 4.6 V HV-LCO batteries. The results showed that the coated TiO2 can be transformed into LiTiO2-rich layer, which can reduce surface residual lithium (SRL), lower the formation of Co3O4 and LiF-rich cathode electrolyte interphase (CEI) layer. Moreover, the annealed sample delivered improved surface texture, reduced specific surface area, and lower SRL, which was beneficial to improve the rate capability and cyclic performance. However, the LCO after annealing and coating exhibited weak static oxygen stability at high voltage due to the change in bulk Li/Co stoichiometry, leading to higher gas production. This work provides new insights into the effects of metal oxide coating and sheds light on the commercial process for HV-LCO.

Role of Re additions on hot corrosion behaviors of a Co–Al–W superalloys

The hot corrosion behaviors of Co–Al–W superalloys with Re additions were investigated at 900 °C. The results showed that the addition of Re improved the hot corrosion resistance significantly. The alloys developed multi-layer oxidation and corrosion products, which located from surface to substrate were: the CoO and Co3O4 layer, the CoWO4 and CoAl2O4 layer, the Al2O3 layer, and the Co3W layer. The addition of Re promotes the formation of the α-Al2O3 scale, which is stable and dense. The thickness the α-Al2O3 scale in 1Re alloy is 1.9 μm, which is much thicker than that of the base alloy. The well-developed α-Al2O3 scale leads to the improvements in hot corrosion resistance.

Operando Surface X-Ray Diffraction Studies of Co Oxide Catalyst Films for Electrochemical Water Splitting

The need for environmental friendly and sustainable energy conversion has triggered renewed interest into the electrochemical and photoelectrochemical splitting of water. A key challenge in this field is the development of economically viable electrocatalyst materials for the oxygen evolution reaction (OER). Transition-metal oxide catalysts, in particular the cobalt (hydr)oxide materials, have been found as promising candidates, since they are earth-abundant, efficient and scalable over a wide range of electrochemical conditions [1]. They present good catalytic properties and stability in alkaline solution under ambient conditions. Although a wide variety of different catalysts with rather diverse nanoscale morphologies have been synthesized and studied, the atomic scale surface structure usually is still unknown or poorly defined. This makes it difficult to compare their electrocatalytic activity and correlate it with ab initio theoretical studies, which hinders the development of clear structure-reactivity relationships and unambiguous determination of the OER reaction mechanism.We presentsystematic comparative studiesof structurally well-defined, 18-35nm thick Co3O4 films, prepared by electrodeposition or physical vapor deposition (PVD) on Au(111), Au(100) and Ir(100) single crystals. In all cases a well ordered epitaxial Co3O4(111) arrangement results, but the film morphology differs substantially, as shown by AFM and surface X-ray diffraction (SXRD). In order to elucidate the quantitative relationship between the catalyst surface structure and the OER reactivity, synchrotron-based operando SXRD and electrochemical measurements were performed simultaneously under reaction conditions, using a dedicated operando cell which allows massive gas evolution and current densities of up to 150 mA/cm2 [2,3].We find that the Co3O4(111) layers prepared by PVD on Ir(100) stay perfectly stable in the pre-OER and OER potential regime, whereas all electrodeposited films exhibit reversible changes in the oxide structure and oxidation state, in agreement with a previous study of Co3O4 catalysts [2]. Specifically, we observe the reverse formation of an ultrathin X-ray-amorphous CoOx(OH)y skin layer above 1 V vs. RHE and the gradual buildup of tensile lattice strain in the underneath, remaining Co3O4 layer with increasing potential. These structural changes occur for all electrodeposited samples, albeit to a different extent, depending on the film morphology [3]. Studying the relationship between the effective thickness of this skin layer and the OER reactivity, we found clear evidence that the entire skin layer is a three dimensional OER zone, which strongly exceeds one monolayer.Our results suggest that even subtle changes of the surface morphology have large influence on the OER activity of the Co3O4 catalyst, which may be expected also for other spinel-type transition metal oxides. On the one hand, this reveals that great care as to be taken in comparing the OER activity of differently prepared catalysts. On the other hand, these observations may provide a base for targeted preparation of highly reactive oxide catalysts.[1] C. C. L. McCrory et al., Journal of the American Chemical Society 2015, 137, 4347.[2] F. Reikowski, et al., ACS Catalysis, 2019, 9, 3811.[3] T. Wiegmann, et al., ACS Catalysis, 2022, 12, 256.

A Comparative Study of NiCo2O4, NiO, and Co3O4 Electrocatalysts Synthesized by a Facile Spray Pyrolysis For Electrochemical Water Oxidation

AbstractExploiting low‐cost, highly active, and robust oxygen evolution reaction (OER) electrocatalysts based on earth‐abundant elements by a simple synthesis approach holds paramount importance for green hydrogen production through water electrolysis. In this work, the NiO, Co3O4 and NiCo2O4 nanoparticle layers with identical surface morphologies are prepared under same deposition conditions by a simple spray pyrolysis method and their OER activities are comparatively investigated. Among all these three electrocatalysts, NiCo2O4 shows the lowest overpotential of 420 mV to drive benchmark current density of 10 mA cm−2 and the smallest Tafel slope (84.1 mV dec−1), which are comparable to the OER performance of the benchmark commercial RuO2 electrocatalyst. The high OER activity of NiCo2O4 is attributed to the synergy effect and the modulation of electronic properties between Co and Ni atoms, which drastically reduces the overpotential required to drive OER activities. Therefore, it is believed that the NiCo2O4 synthesized by this simple method would be a competitive candidate as an industrial electrocatalyst with high‐efficiency and low cost for large‐scale green hydrogen production via water electrolysis.

Gas sensing properties of AACVD-derived ZnO/Co3O4 bilayer thin film nanocomposites

ZnO/Co3O4 nanocomposites with different Co3O4 concentrations and layer thicknesses were obtained by two-stage aerosol vapor deposition (AACVD). In pure oxide films ZnO particles have a mean size of 64 ± 11 nm, and Co3O4 particles 55 ± 10 nm. It was shown based on EDX data that cobalt oxide content in the films with its deposition time being 10, 20 and 30 min is 4.7, 7.2 and 12.4 mol.% respectively. Coating thickness was estimated using AFM as 144 ± 59, 173 ± 36 and 207 ± 71 nm for these samples. The film thickness of ZnO and Co3O4 was 115 ± 34, 149 ± 26 respectively. Gas-sensitive properties to a wide range of analyte gases: CO, NH3, H2, CH4, C6H6, ethanol, acetone and NO2 at 125–300 °C were measured. It was found that the individual ZnO film showed a high and selective response to 0.3–100 ppm NO2, and the Co3O4 and sample with Co3O4 deposition time of 10 min (ZCo10) had response to 4–100 ppm acetone and ethanol at moderate temperatures. ZnO and ZCo10 films were shown to exhibit minimal drop in response at elevated humidity.

Surface-Modified Carbon Nanotubes with Ultrathin Co3O4 Layer for Enhanced Oxygen Evolution Reaction.

Alkaline water electrolysis is a vital technology for sustainable and efficient hydrogen production. However, the oxygen evolution reaction (OER) at the anode suffers from sluggish kinetics, requiring overpotential. Precious metal-based electrocatalysts are commonly used but face limitations in cost and availability. Carbon nanostructures, such as carbon nanotubes (CNTs), offer promising alternatives due to their abundant active sites and efficient charge-transfer properties. Surface modification of CNTs through techniques such as pulsed laser ablation in liquid media (PLAL) can enhance their catalytic performance. In this study, we investigate the role of surface-modified carbon (SMC) as a support to increase the active sites of transition metal-based electrocatalysts and its impact on electrocatalytic performance for the OER. We focus on Co3O4@SMC heterostructures, where an ultrathin layer of Co3O4 is deposited onto SMCs using a combination of PLAL and atomic layer deposition. A comparative analysis with aggregated Co3O4 and Co3O4@pristine CNTs reveals the superior OER performance of Co3O4@SMC. The optimized Co3O4@SMC exhibits a 25.6% reduction in overpotential, a lower Tafel slope, and a significantly higher turnover frequency (TOF) in alkaline water splitting. The experimental results, combined with density functional theory (DFT) calculations, indicate that these improvements can be attributed to the high electrocatalytic activity of Co3O4 as active sites achieved through the homogeneous distribution on SMCs. The experimental methodology, morphology, composition, and their correlation with activity and stability of Co3O4@SMC for the OER in alkaline media are discussed in detail. This study contributes to the understanding of SMC-based heterostructures and their potential for enhancing electrocatalytic performance in alkaline water electrolysis.

Co-WO3 composite coating on ferritic stainless steel interconnects

In order to apply Co-WO3 composite coating to SUS 430 steel interconnects for solid oxide fuel cell (SOFC) interconnects, a combination of electrophoresis and electroplating is used, followed by thermal energy exposure to ambient temperature at 800 ℃ for up to 5 weeks. The thermal growth of the oxide scale displays a tri-layer structure with a Cr2O3 layer in the inner part, a CoWO4 layer in the middle and (Co,Fe)3O4 and Co3O4 layer in the outer part. Co-WO3 coating produces an oxide layer that not only prevents Cr2O3 development and outward transport of Cr species but also enhances the electrical behavior of the surface scale.

Electrochemical denitrification by a recyclable cobalt oxide cathode: Rapid recovery and selective catalysis

Cathodic aging and fouling have presented significant challenges in the realm of electrochemical denitrification for engineering applications. This study focused on the development of an economical and recyclable nanoporous Co3O4/Co cathode through anodization for nitrate reduction. What distinguished our cathode was its exceptional sustainability. Cobalt from the inactive catalyst could be reclaimed onto the substrate, enabling the regeneration of a new Co3O4 layer. This innovative approach resulted in an exceptionally low Co catalyst consumption, a mere 1.936 g/1 kg N, making it the most cost-effective choice among all Co-based cathodes. The Co3O4 catalyst exhibited a truncated octahedron structure, primarily composed of surface Co2+ ions. Density functional theory calculations confirmed that the bonding between the O atom in NO3- ions and the Co atom in Co3O4 was thermodynamically favorable, with a free energy of − 0.89 eV. Co2+ ions acted as "electron porters" facilitating electron transfer through a redox circle Co2+–Co3+–Co2+. However, the presence of two energy barriers (*NH2NO to *N2 and *N2 to N2) with respective heights of 0.83 eV and 1.17 eV resulted in a N2 selectivity of 9.84% and an NH3 selectivity of 90.02%. In actual wastewater treatment, approximately 78% of TN and 93% of NO3- were successfully removed after 3 h, consistent with the prediction kinetic model. This anodization-based strategy offers a significant advantage in terms of long-term cost and presents a new paradigm for electrode sustainability.

Enhanced CO oxidation performance over hierarchical flower-like Co3O4 based nanosheets via optimizing oxygen activation and CO chemisorption

Enhancing low-temperature activity is a focus for carbon monoxide (CO) elimination by catalytic oxidation. In this work, the hierarchical flower-like silver (Ag) modified cobalt oxides (Co3O4) nanosheets were prepared by solvothermal method and applied into catalytic CO oxidation. The doped Ag species in the form of AgCoO2 induced the prolongated surface Co–O bond and weaker bond intensity. Consequently, the oxygen activation/migration ability and redox capacity of Ag0.02Co were enhanced with more oxygen vacancies. The chemisorbed CO was preferentially converted to CO2 but not carbonates. The inhibited carbonates accumulation could avoid the coverage of active sites. According to Density functional theory (DFT) calculations, the electron transfer from AgCoO2 to Co3O4 promote electron donation ability of Co3O4 layer, benefiting for oxygen activation. Moreover, the longer Co–C and C–O bond length suggest the weakened chemisorption strength and higher active of CO molecule. The Ag modified Co3O4 exhibited more satisfactory activity at lower temperature. Typically, it realized 100% CO conversion at 90 °C, and displayed 6.3-fold higher reaction rate than pristine Co3O4 at 40 °C. Moreover, the Ag0.02Co exhibited outstanding long-term stability and water resistance. In summary, the optimized oxygen activation, CO chemisorption and interfacial electron transfer synergistically boosted the CO oxidation activity on Ag modified Co3O4.

Photo-switching of magnetoresistance in p-Co3O4/n-WS2 heterojunction

Tuning and controlling magnetic states by light is of great interest for applications such as magneto-optical recording and sensing devices. In this research, the change of sign and adjustability of magnetoresistance by light is shown experimentally. In a simple device, a p-n junction is created at the interface of a thin layer of n-type WS2 and p-type Co3O4. The device displays positive magnetoresistance in the dark, while under light illumination, it displays negative magnetoresistance. We suggest that this effect may be due to the suppression of photogenerated electron-hole recombination under the Zeeman effect. The findings of this research can lead to the development of practical fields such as light sensor systems or magnetoresistance memory devices of the new generation.

Development of Co3O4 nanomaterials on flexible carbon cloth substrates for hydrogen and oxygen evolution reactions

In this work, cobalt oxide decorated on carbon cloth (Co3O4/CC) is fabricated by the electrodeposition method by optimizing two factors: (i) the electrodeposition time; (ii) the volume ratio between ethylene glycol (EG) and deionized water (DI) in deposition solution. Results indicate that 5 min of electrodeposition is the most effective interval to acquire the sample with the most homogeneous in size and distribution. Furthermore, the addition of EG has a significant effect on the surface morphology of Co3O4/CC, causing the formation of the mesoporous Co3O4 layers on the substrate's surface. Due to the porous and rough structure of Co3O4/CC, its specific surface area reaches 111.3 m2g-1 as opposed to pure CC (37.2 m2g-1). Additionally, the coverage of Co3O4 on the cloth helps to enhance the electrochemical surface area up to 10 times and improve strongly the conductivity of the whole system. In the electrochemical water splitting (EWS) application, the Co3O4/CC sample prepared in precisely 5 min with the existence of EG at 40 %vol. possesses the best electrocatalytic performance with the lowest overpotentials for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), with 291 mV and 357 mV at a current density of 10 mA cm−2 for each. This material also exhibits good stability to maintain a stable voltage at 10 mA cm−2 for 30 h.

Efficient Mo–Co(OH)2/Co3O4/Ni foam electrocatalyst for overall water splitting

Bifunctional catalysts for water splitting based on 3d transition metals are well-documented. Herein, a Co3O4 layer was introduced between tremella-like Mo–Co(OH)2 and nickel foam through electrodeposition(1st)-pyrolysis-electrodeposition(2nd) strategy as the conductive secondary substate. The secondary electrodeposition particularly led to introduce the Mo species into the surface layer of Co(OH)2. The as-prepared Mo–Co(OH)2/Co3O4/NF-x(x represents the deposition time) was further applied as the catalyst for HER, OER and the overall water-splitting reactions. Notably, the Mo–Co(OH)2/Co3O4/NF-800 catalyst exhibited outstanding activity to achieve a current density of 10 ​mA ​cm-2, with overpotentials of 116 ​mV and 234 ​mV for HER and OER in 1 ​M KOH, respectively. Moreover, a cell voltage of 1.62V was only required to achieve the current density of 10 ​mA ​cm-2, when the catalyst was assembled as the anode and cathode simultaneously. Several characterizations were performed, including HRTEM, XRD, SEM and XPS analysis, to explore the structure-activity relationship of the Mo–Co(OH)2/Co3O4/NF catalyst. Notably, the existence of the Co3O4 nanosheet middle layer enhanced the electro-chemical active surface area of the whole Mo–Co(OH)2/Co3O4/NF catalyst, which boosted the conductivity of the catalyst. Moreover, the XPS analysis revealed that the doped Mo6+ can attract the electrons from Co2+, increasing the active sites that are favorable for the OER and HER. The unique synthetic strategy adapted in this work will open up a new approach for the construction of heteroatom-doped multilayered heterostructure to achieve effective catalytic activity for overall water-splitting.

Microstructure and diffusion behavior of Co-Ni-W conversion coating for metallic interconnect of solid oxide fuel cell

To improve the oxidation resistance and electrical conductivity of the interconnects, a new Co-Ni-W alloy layer containing 5.0 at.% W electroplated on the surface of SUS 430 stainless steel and oxidized at 800°C in air for 1000 h was studied. It was confirmed that the oxide layer structure eventually evolves into six oxide layers after oxidation, namely Co3O4, CoFe2O4, NiCo2O4/CoWO4, (Co,Fe,Ni)3O4, (Cr,Fe,Co)3O4, and Cr2O3 layer by scanning electron microscope, transmission electron microscope and X-ray diffraction. The four Cr-free oxide layers completely prevented the outward diffusion of Cr. Furthermore, the Co-Ni-W coating significantly reduced the area specific resistance of sample.