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A porous Co‐based metal‐oxide foam catalyst is fabricated via the dynamic hydrogen bubble template electrodeposition method followed by calcination (6 h at 300 °C thermal treatment). Electrolysis results demonstrate excellent performance of this catalyst in the electrochemical nitrate reduction reaction (NO3−RR ${\\mathrm{NO}}_3^ - {\\mathrm{RR}}$ ), attaining near‐unity Faradaic efficiency (97.8% ± 3.6% at jNH3,lim = –59.5 ± 2.3 mA cm−2) at a low (over)potential of –0.2 V vs RHE, which represents maximum achievable performance in 0.1 mol L−1 nitrate solutions (pH 13.7) under transport‐limiting conditions in the absence of extra convection. Digital simulations show that, without forced convection, the catalyst's electrochemically active surface area changes dynamically due to rapid nitrate depletion inside the 3D foam. Electrolyte replenishment, triggered by vigorous hydrogen evolution, is shown to restore the active surface in the foam interior. This self‐convection enables high ammonia partial current densities exceeding hundreds of mA cm−2 (e.g., jNH3 = –220 ± 18 mA cm−2 at –0.6 V vs RHE, with FENH3 = 80.2% ± 2.2%). Operando XAS, XRD, Raman spectroscopy, and electrochemical analysis reveal the in situ evolution of a “tandem” composite catalyst during electrolysis, where β‐Co(OH)2 and metallic Co function both as the active phases for NO3−RR ${\\mathrm{NO}}_3^ - {\\mathrm{RR}}$ , with β‐Co(OH)2 remaining kinetically stabilized under the cathodic operating conditions. A porous cobalt‐based metal‐oxide foam catalyst is synthesized using the DHBT technique, followed by calcination. It demonstrates exceptional activity for e‐NO3RR, reaching near‐unity ammonia selectivity at low overpotentials. Dynamic surface area changes due to NO3‐ depletion are mitigated by “self‐convection” during hydrogen evolution. Operando analyses reveal the formation of highly active “tandem catalyst”— β‐Co(OH)2 and metallic Co serving as a stable active phase under reaction conditions.

The ecological benefits and concerns surrounding fossil fuels had led to increased interest in bio-based rigid polyurethane foam (RPUF). Nonetheless, due to its flammability, it had limited application in various fields. To solve this problem, a green bio-flame retardant, cobalt hydroxystannate (CoSn(OH) 6 ), was prepared and compounded with montmorillonite (MMT) and chick feather protein (CF), and applied to RPUF, which not only realized the regeneration of resources, but also provided RPUF with better thermal stability, flame retardancy and smoke suppression properties. The experimental results showed that when 3 wt% CoSn(OH) 6 was added, the RPUF (CF1/MMT3/Co3) had the greatest activation energy. In addition, the peak heat release rate (PHRR) and total heat release (THR) of CF1/MMT3/Co3 decreased by 12.73%, and 11.16% respectively, compared with no CoSn(OH) 6 . In addition, its Ds decreased by 28.9% and the light transmittance increased by 17.6% compared with the RPUF without CoSn(OH) 6 . At the same time, its peak smoke production rate (PSPR) and the total smoke release (TSR) decreased by 25% and 18%. And CF1/MMT3/Co3 also had the lowest fire risk evaluation index. This study presented possibilities for practical utilization of the RPUF substances founded on bio-based flame inhibitors.

Supercapacitors are gaining popularity due to their high-power density, long life, and little maintenance. Carbon nanotubes/nickel sulphide/cobalt sulphide (CNTs/NiS/CoS) nanocomposites for supercapacitor applications are developed due to their inexpensive cost and excellent electrochemical properties. A composite material combining carbon nanotubes on CoS, NiS, and nickel foam was employed. All electrochemical tests were carried out in a solution of 3 M KOH. The R ct and R f for the CNTs/NiS/CoS electrode were found to be 1.4 Ω cm 2 and 1.2 Ω cm 2 , respectively, which were significantly lower than the corresponding R ct (42.1 Ω cm 2 ) and R f (47.5 Ω cm 2 ) for the CNTs electrode, indicating that the CNTs/NiS/CoS has a significantly lower overall impedance, which could be one of the key factors responsible for the improved electrochemical performance of the CNTs/NiS/CoS. At current density of 1 A/g, the CNTs/NiS/CoS nanocomposite electrode had specific capacitances of 1249.88 mAh/g. At a current density of 1 A/g, the CNTs/NiS/CoS electrodes retained 97.17% of their specific capacitance after 8000 charge–discharge cycles. The energy density and power density of CNTs/NiS/CoS samples are found to be 624.44 Wh/kg and 8325.87 W/kg, respectively. The CNTs/NiS/CoS nanocomposite exhibits a high specific capacitance and a long cycle life, according to galvanostatic charge/discharge measurements. Graphical Abstract

Rigid polyurethane foam/ammonium polyphosphate/cobalt phytate (RPUF/APP/PA-Co) composites were prepared by one-step water-blown method using ammonium polyphosphate (APP)/cobalt phytate (PA-Co) as a flame retardant system. The char residue of RPUF/APP/PA-Co increased significantly than that of RPUF, indicating that the thermal stability of composites was enhanced. Cone calorimetry and smoke density tests showed that when 40 phr APP and 10 phr PA-Co were added, the total heat release and smoke release of RPUF/APP40/PA-Co10 composite decreased significantly. TG-IR test confirmed that APP/PA-Co could significantly inhibit the release of flammable gases (hydrocarbons, esters) and toxic gases (aromatic compounds, isocyanate, CO, HCN,) of RPUF/APP/PA-Co composites and improve the fire resistance of composites. SEM-EDS, Raman spectra and FTIR were applied to investigate the char residues of composites. The results showed that APP/PA-Co loading was beneficial to the generation of dense char layer with high degree of graphitization and reducing the release of combustible substances and smoke of composites.

CoFe 2 O 4 has been widely used for electromagnetic wave absorption owing to its high Snoek limit, high anisotropy, and suitable saturation magnetization; however, its inherent shortcomings, including low dielectric loss, high density, and magnetic agglomeration, limit its application as an ideal absorbent. This study investigated a microstructure regulation strategy to mitigate the inherent disadvantages of pristine CoFe 2 O 4 synthesized via a sol–gel auto-combustion method. A series of CoFe 2 O 4 foams (S0.5, S1.0, and S1.5, corresponding to foams with citric acid (CA)-to-Fe(NO 3 ) 3 ·9H 2 O molar ratios of 0.5, 1.0, and 1.5, respectively) with two-dimensional (2D) curved surfaces were obtained through the adjustment of CA-to-Fe 3+ ratio, and the electromagnetic parameters were adjusted through morphology regulation. Owing to the appropriate impedance matching and conductance loss provided by moderate complex permittivity, the effective absorption bandwidth (EAB) of S0.5 was as high as 7.3 GHz, exceeding those of most CoFe 2 O 4 -based absorbents. Moreover, the EAB of S1.5 reached 5.0 GHz (8.9–13.9 GHz), covering most of the X band, owing to the intense polarization provided by lattice defects and the heterogeneous interface. The three-dimensional (3D) foam structure circumvented the high density and magnetic agglomeration issues of CoFe 2 O 4 nanoparticles, and the good conductivity of 2D curved surfaces could effectively elevate the complex permittivity to ameliorate the dielectric loss of pure CoFe 2 O 4 . This study provides a novel idea for the theoretical design and practical production of lightweight and broadband pure ferrites.

In recent years, research scholars have conducted in-depth research on the efficient and stable electrocatalysts for oxygen reduction reaction (ORR) and analyzed how to reduce the polymer binders in the cathode of metal–air batteries. Although some research progress has been made, there are still many challenges. On the basis of full consideration of factors such as good electrical conductivity, unique porous structure, improved performance, surface area, and synergistic effects, composite materials (m-Co3O4/3DG) of three-dimensional graphene and mesoporous Co3O4 nanowires are prepared on a Ni foam substrate. Here, a facile solution (NaBH4) reduction method is introduced, resulting in an increase in the oxygen vacancies on the surface of the mesoporous Co3O4 nanowires, thereby improving the electrocatalytic activity of m-Co3O4/3DG ORR. The reduced m-Co3O4/3DG composite exhibits a much positive half-wave potential of 0.84 V (vs. RHE) and onset potential of 0.93 V (vs. RHE), and much higher mass activity of 0.109 A mg−1 at 0.766 V (vs. RHE) compared with m-Co3O4/3DG, m-Co3O4, and 3D graphene electrocatalysts, or even superior to the Pt/C catalyst. In addition, when reduced m-Co3O4/3DG is used as the binder-free cathode of the aluminum–air battery, showing a 422.74 mAh g−1 specific capacity and a 1.53 V open-circuit voltage under the discharge current density of 1.0 mA cm−2, which are more excellent compared with the traditional Pt/C, m-Co3O4, and m-Co3O4/3DG electrodes. The 1D and 3D morphology hierarchically porous feature leads to high-efficiency surface reduction and charge and mass transportation. This research provides a solution reduction method with a simple operation to generate more defect states on electrocatalysts and supplies valuable view into the development of reduced Co3O4/3DG with excellent ORR electrocatalytic performance as binder-free cathodes in aluminum–air battery.Graphic abstract

A 3D hierarchical spherical honeycomb-like composite electrode materialof neodymium oxide (Nd2O3), cobalt tetraoxide (Co3O4), and reduced graphene oxide (rGO) on nickel foam (named as Nd2O3/Co3O4/rGO/NF) were successfully fabricated by combining the hydrothermal synthesis method and the annealing process. Nickel foam with a three-dimensional spatial structure was used as the growth substrate without the use of any adhesives. The Nd2O3/Co3O4/rGO/NF composite has outstanding electrochemical performance and can be used directly as an electrode material for supercapacitors (SCs). By taking advantage of the large specific surface area of the electrode material, it effectively slows down the volume expansion of the active material caused by repeated charging and discharging processes, improves the electrode performance in terms of electrical conductivity, and significantly shortens the electron and ion transport paths. At a 1 A/g current density, the specific capacitance reaches a maximum value of 3359.6 F/g. A specific capacitance of 440.4 F/g with a current density of 0.5A/g is still possible from the built symmetric SCs. The capacitance retention rate is still 95.7% after 30,000 cycles of testing at a high current density of 10 A/g, and the energy density is 88.1 Wh/kg at a power density of 300 W/kg. The outcomes of the experiment demonstrate the significant potential and opportunity for this composite material to be used as an electrode material for SCs.

In order to improve the microwave absorption performance of absorbing materials, the composite foam absorbing materials with different multi-walled carbon nanotube (MWCNT) contents were prepared using polyurethane foam as the substrate and MWCNTs and flaked carbonyl iron powder as absorbers. The electromagnetic properties of the materials were characterized and analyzed. Then, CST electromagnetic simulation software was used to simulate the electromagnetic shielding effect of absorbing materials on mechatronics products under a strong electromagnetic irradiation environment, and, finally, it was verified by irradiation experiment. The results show that the materials have good microwave absorption properties, in which the composites containing 1.5 wt.% MWCNTs exhibit good microwave absorption properties. The minimum reflectivity reaches −29 dB when the thickness is 3 mm and −15.6 dB when the thickness is 1.5 mm, with a bandwidth of 5.7 GHz for reflectivity less than −10 dB. The good microwave absorption performance of the material is due to the synergistic effect of MWCNTs particles and good impedance matching. The simulation and experimental results show that the mechatronics product with absorbing materials can protect against strong electromagnetic interference and ensure the normal operation of the mechatronics product circuits.

This study utilizes mechanical interlocking as a method to improve the adhesion between the 3D carbon felt foam (CFs) and the epoxy matrix (EP). Hydrothermally, Co 3 O 4 nanoarrays in nanostrips, nanowires, nanoprisms, and nanostars were added to CFs surfaces. Pure 3D carbon fiber-epoxy composites had 62.7% higher storage modulus and 7.8% higher glass transition temperature than pure epoxy. The 3D carbon fiber/epoxy composite with Co 3 O 4 nanowires has a storage modulus of 5297 MPa and a Tg of 148.4 °C, which is higher than that of pure 3D CFs and other nanocomposites. Compared to pure 3D CFs/ EP, Co 3 O 4 nanowires boost flexural strength by 75.0%. Nano-strip, nano-prismatic, and nanostar composites improve 53.6%, 21.4%, and 11.43%, respectively. Pure 3D CFs boost epoxy matrix impact strength to 174.6%. The impact strength of the Co 3 O 4 nano-wire@CFs/EP composite is 45.6% higher than that of the 3D CFs/EP composite. Nano-strip, nano-prismatic, and nano-star modifications are 31.2%, 19.5%, and 2.5%. 3D CFs/EP composites have a 69 MPa initial tensile strength. However, Co 3 O 4 nano-wires increase tensile strength by 73% to 130 MPa. Nano-strip, nano-prismatic, and nanostar composites outperform 3D CFs/EP by 68%, 33%, and 7%, respectively. In 3D CFs/EP composites, Co 3 O 4 nanowires reduce wear by 50.0% and friction by 27.9%.

The oxygen evolution reaction (OER) holds pivotal importance in sustainable energy conversion, as it forms the critical half-reaction in various electrochemical processes, including water splitting for hydrogen production and rechargeable metal-air batteries. Here, a CoFe 2 O 4 @Co 3 O 4 nano-composite was synthesized using a facile hydrothermal process and deposited onto the surface of nickel foam through electrophoresis. Characterization using XRD, Raman spectroscopy, and XPS confirmed the successful synthesis of the composite, exhibiting characteristic peaks of both Co 3 O 4 and CoFe 2 O 4 . The nano-composite exhibited a more amorphous phase than pure oxides, benefiting electrocatalytic activity. Scanning and transmission electron microscopy highlighted the composite’s morphological characteristics, showcasing a Co 3 O 4 island distribution on the CoFe 2 O 4 surface. Electrochemical evaluations revealed the superior oxygen evolution reaction (OER) performance of CoFe 2 O 4 @Co 3 O 4 , with low overpotentials, faster kinetics, and enhanced stability compared to pure oxides and the benchmark RuO 2 catalyst. A comprehensive analysis was carried out to investigate the dynamic behavior during electrocatalytic oxygen evolution reaction. This study unveils the intricate charge and electron transfer mechanisms between cobalt and iron atoms, providing insights into their collaborative role throughout the OER process. Graphical Abstract