Subsequent Calcination Process Research Articles

Synthesis and characterization of aluminum hydroxide-reinforced silica-zirconia ceramic membrane for thermal protection applications

In the domain of personal thermal protection, there is a growing demand for lightweight and efficient ceramic thermal insulation materials. However, conventional ceramic membranes face challenges such as brittleness, structural collapse, and pulverization, hindering their practical application. To address this issue, aluminum hydroxide-enhanced silica-zirconia ceramic membranes (SZ@ANFMs) have been successfully fabricated using electrospinning followed by subsequent calcination processes, and their properties have been comprehensively evaluated. The results demonstrate that SZ@ANFMs exhibit outstanding high-temperature resistance under an alcohol lamp, along with an extremely low thermal conductivity (only 0.041 W/m·K), excellent tensile strength (2.3 MPa), and flexible characteristics. This makes them highly promising in the domain of personal thermal protection. The study builds upon existing research in lightweight and efficient thermal insulation materials, offering improvements and robust support for the further development of personal thermal protection technology.

Enhanced Performance of Complementary Electrochromic Device with Hierarchical‐Porous NiO x Decorated ITO Glasses as the Transparent Conductive Electrodes

To pursuit advancing electrochromic technology, the preparation of a novel hierarchical‐porous NiOx‐decorated ITO transparent conductive electrode was developed through the vapor‐assisted conversion and subsequent calcination processes. The modified transparent electrode exhibited advantages in the electrodeposition of conductive polymer films, which significantly enhanced electrochromic cycling stability. Moreover, the complementary electrochromic device based on NiOx‐decorated ITO transparent electrode was fabricated, demonstrating rapid response time (1.75 s for coloration and 0.87 s for bleaching), high optical contrast (53.4%), and remarkable cycling stability (90% optical contrast retention over 2000 cycles). This finding holds prominent potential for applications in related fields.

Glucose-Assisted Synthesis of Porous, Urchin-like Co3O4 Hierarchical Structures for Low-Concentration Hydrogen Sensing Materials.

The Co3O4 is a typical p-type metal oxide semiconductor (MOS) that attracted great attention for hydrogen detection. In this work, porous, urchin-like Co3O4 was synthesized using a hydrothermal method with the assistance of glucose and a subsequent calcination process. Urchin-like Co3O4 has a large specific surface area of 81.4 m2/g. The response value of urchin-like Co3O4 to 200 ppm hydrogen at 200 °C is 36.5 (Rg/Ra), while the low-detection limit is as low as 100 ppb. The obtained Co3O4 also exhibited good reproducibility, long-term stability, and selectivity towards various gases (e.g., ammonia, hydrogen, carbon monoxide, and methane). Porous, urchin-like Co3O4 is expected to become a potential candidate for low-concentration hydrogen-sensing materials with the above advantages.

TiO2/Multi-walled carbon nanotube electrospun nanofibers mats for enhanced Cr(VI) photoreduction

Industrial processes, including metal plating and paint production, generate substantial wastewater with hexavalent chromium (Cr(VI)), necessitating the development of efficient photocatalysts for its reduction. In this study, we fabricated curly hybrid nanofiber composites (TiO2/Multi-walled carbon nanotube (MWCNT)) with varying MWCNT contents (0.1, 0.3, 0.5, 0.7, and 1.0 w/w) via electrospinning and subsequent calcination process for Cr(VI) photoreduction efficiency. Our experimental results indicated an initial rise in specific surface areas and micropore volumes with increasing the MWCNT content up to TiO2/MWCNT-7, followed by a decrease, attributed to the development of a curly structure with the introduction of MWCNTs. This improved TiO2 dispersion, reduced the band gap, and densified the composites, enhancing mass transfer properties and visible light utilization. As a result, TiO2/MWCNT-7 exhibited a significant redshift in wavelength along with a 2.93 eV band gap, resulting in 97.5% Cr(VI) photoreduction efficiency within 120 min and sustained 92% efficiency over 6 cycles. This study offers insights for catalyst design and optimization in Cr(VI) photoreduction for water treatment applications.

Effectiveness of green-synthesized nickel-doped calcium ferrite nanoparticles in the X-ray/gamma radiation shielding applications

Nanoparticles comprising calcium ferrite doped with Nickel within a concentration range of 10 to 50 mol% were successfully produced using a solution combustion technique, employing neem leaf extract as a reducing agent. The subsequent calcination process at 500 °C validated the formation of orthorhombic calcium ferrite, featuring distinct Bragg reflections indicative of Nickel doping. An analysis via scanning electron microscopy (SEM) affirmed the presence of irregularly shaped nanoparticles with pores and voids within their structure. The optical energy band gap, determined through Wood and Tauc’s relation, ranged from 2.89 to 2.97 eV. Notably, an increase in Nickel substitution was found to correlate with an increase in the energy band gap and a reduction in crystallite size. The research extensively evaluated the nanoparticles’ efficacy in radiation protection, encompassing parameters such as mass attenuation coefficient, mean free path, half-value layer, and effective atomic number. The mass attenuation coefficient is found to be 0.05353 cm2g−1 for 40 mol% at 1332 KeV. EABF is found to be large for 40 mol% at 0.89 MeV energy. Likewise, 50 mol% has a high Neutron absorption cross section (σab) which is 1.5(barn). Also, the bremsstrahlung dose rate is found to be 1.35 (R/h)*103, at 1.511 MeV.Additionally, the study comprehensively explored variations in the energy-absorbing buildup factor across diverse energy ranges, taking into account the Nickel concentration within the calcium ferrite nanoparticles. This aspect holds significant importance in the field of radiation dosimetry, particularly in applications related to neutron shielding and bremsstrahlung radiation.

Electrospun Mo2C-embedded carbon nanofibers: A promising material for supercapacitors with enhanced electrochemical performance

Recently there has been a growing fascination with two-dimensional (2D) materials, driven by their remarkable and distinctive characteristics. This paper introduces a straightforward, efficient, and affordable approach for producing Mo2C@CNF nanocomposite electrodes by using the Electrospinning (E-Spun) technique and subsequent calcination process. The Mo2C@CNF-1 and Mo2C@CNF-2 are E-spun, iodized, and notably Mo2C@CNF-2 is carried out by the ageing process. The purpose of the iodization and ageing process before carbonization is to create a stronger C=C backbone and to reduce carbon loss during the formation of carbon nanofiber. The physical properties of the sample were characterized using XRD, HRSEM, EDAX, HRTEM, XPS, and BET. Further, their electrochemical performance is comparatively studied for supercapacitor applications in three-electrode setups. The Mo2C@CNF-2 exhibits a high specific capacitance of 873 F g−1 with a coulombic efficiency of 88.4 % at 1 A g-1 current density. Further studies on the electrochemical performance of symmetric Mo2C@CNF-2 devices show 126 F g−1 capacitance indicating its good electrochemical performance at 0.1 A g−1. Furthermore, the charge storage kinetics studied for the Mo2C@CNF-2 device, shed light on the insertion/de-insertion process of electrolytic ions being responsible for its excellent performance.

Highly (002)-oriented ZnO in ZnO-N-C microflakes coating layer for stable zinc anode in zinc-air batteries

Rechargeable alkaline zinc–air batteries (ZABs) are widely used in small electronic devices with high theoretical energy density, low cost, and environmentally friendly. However, Zn anode will emerge dendrite growth and corrosion problems during cycling and seriously affect the cycle life of the batteries. Thereby, a new ZnO-N-C microflake was synthesized as a protection layer for Zn anode by hydrothermal methods and subsequent calcination processes in this work. The ZnO with more preferred crystal plane (002) in the ZnO-N-C-600 microflakes can provide uniform charge distribution to induce the uniform deposition of Zn2+. And the strong interaction among each component in the ZnO-N-C can accelerate the electron transport to inhibit the violent growth of dendrites and further improve reversibility of Zn2+ plating/stripping. The Zn@ZnO-N-C-600 assembled symmetric battery achieves a stable 800 h cycling with a low polarization voltage (70 mV) at 0.5 mA cm−2, while the bare zinc symmetric battery has a cycle life of less than 170 h. Zn@ZnO-N-C -600 used as anode in alkaline zinc–air batteries shows comparable electrochemical performance. This work provides a broad application prospect for the development of a stable Zn anode for rechargeable zinc–air batteries.

A novel “On-Off” colorimetric sensor for ascorbic acid and hydrogen peroxide based on peroxidase activity of CeO2/Co3O4 hollow nanocubes

The development of artificial nanostructured enzymes has garnered significant interest in the field of nanobiotechnology due to the distinct advantages. In this work, CeO2/Co3O4 hollow nanocubes (named as CeO2/Co3O4 HNs) with exceptional peroxidase-like activity have been prepared employing ion exchange and subsequent calcination process. In the presence of hydrogen peroxide (H2O2), the CeO2/Co3O4 HNs display high peroxidase-like activity, catalyzing the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) and resulting in a color change from transparent to blue. The oxidized TMB (ox-TMB) is subsequently reduced to TMB due to the reducibility of ascorbic acid (AA), restoring the original color of solution. Consequently, a straightforward and efficient "On-Off" colorimetric sensor has been established for the accurate detection of H2O2 and AA, with detection limits (LOD) of 3.56 and 0.179 μM, respectively. In summary, the prepared colorimetric sensor offers numerous advantages, including ease of operation, cost-effectiveness, rapid response, and effective visual monitoring, which holds substantial promise for applications in detection of hydrogen peroxide and ascorbic acid.

Hydrothermal synthesis of ZnGa2O4 nanophosphors with high internal quantum efficiency for near-infrared pc-LEDs.

NIR luminescent materials have garnered widespread attention because of their exceptional properties, with high tissue penetration, low absorption and high signal-to-noise ratio in the field of optical imaging. However, producing nanophosphors with high quantum yields of emitting infrared light with wavelengths above 1000 nm remains a significant challenge. Here, we prepared a nanoscale ZnGa2O4:xCr3+,yNi2+ phosphor with good luminescence performance in near-infrared emission, which was synthesized via a hydrothermal method and subsequent calcination process. By co-doping with Cr3+ and Ni2+, the ZnGa2O4 phosphor shows a strong broadband emission of 1100-1600 nm in the second near-infrared (NIR-II) region, owing to the energy transfer from Cr3+ to Ni2+ with an efficiency up to 90%. Meanwhile, a near-infrared phosphor-conversion LED (NIR pc-LED) device is fabricated based on the ZnGa2O4:0.8%Cr3+,0.4%Ni2+ nanophosphor, which has under 100 mA input current, an output power of 23.99 mW, and a photoelectric conversion efficiency of 7.53%, and can be effectively applied in imaging and non-destructive testing. Additionally, the intensity ratio of INi/ICr of ZnGa2O4:0.8% Cr3+,0.4%Ni2+ with its high sensitivity value of 4.21% K-1 at 453 K under 410 nm excitation, indicates its potential for thermometry application.

Facial Construction of Hydroxyl Functional Modified Ultrafine BiPO4 with Variation of Dipole Moment Induced by –OH Group

The hydroxyl groups generated by hydrolysis are grafted onto the surface of BiPO4, and a stable surface hydroxylation structure is formed during the subsequent calcination process. This would facilitate the formation of a new hydroxyl functional structure on the surface of the parent photocatalyst without damaging its intrinsic structure. Synchronous illumination X‐Ray photoelectron spectroscopy shows that the hydroxyl functional ultrafine BiPO4 can realize the conversion of defective oxygen to lattice oxygen, which is more conducive in improving the photocatalytic efficiency. The process of filling hydroxyl oxygen vacancies and forming a stable structure is explored using in‐ situ infrared spectroscopy. The induced dipole moment promotes the separation of photogenerated electron–hole pairs, which is beneficial for the enhancement of photocatalytic activity. The dipole moment of the hydroxyl functional‐modified ultrafine BiPO4 is −1.409 D compared to −1.385 D for ordinary BiPO4. The results of this study indicate that hydroxyl functional structure and reduced sample granularity are effective strategies to improve the photocatalytic performance of BiPO4.

MIL-101-derived porous WO3/FeWO4 hierarchical structures with efficient heterojunction interfaces for excellent room temperature n-butanol-sensing performance

This study originally reports the in-situ construction of porous WO3/FeWO4 ribbon-like hierarchical composites with unique and intense heterojunction interface behavior and the enhanced adsorption and carrier transport capability for effectively detecting n-butanol at room temperature. The introduction of different adding amounts of MIL-101 plays the key role of the morphological evolution of WO3-based microstructures with the well-distributed nanoparticles in situ growth on the surface by a facile electrospinning and subsequent calcination process. Compared with pristine WO3, a sharp and useful reduction of the optimal operating temperature from 220 to 25 °C can be observed as the Fe component increasing, mainly owing to the inverted p-type gas sensitive response caused by the controllable variable of FeWO4 phase in the multiple effective WO3-FeWO4 heterojunctions. The optimal WO3/FeWO4 composites can display the highest response of 12.3 and a relatively short response/recovery times of 110/140 s to 100 ppm n-butanol at 25 °C, together with the superior gas selectivity, repeatability, humidity and long-term stability. Density functional theory (DFT) simulation is employed for verifying the significant adsorption interaction and charge transfer between n-butanol molecule and WO3/FeWO4. Regular distribution of WO3-FeWO4 heterojunction interfaces can not only determine the collaborative modulation of electronic structures, but also provide the efficient surface/interface transport mechanism for MIL-101 induced one-dimensional (1D) hierarchical ribbons. Actually, the integrated gas-sensitive components based on WO3/FeWO4 composites exhibit the rapid response characteristic under room temperature condition and provide a friendly strategy of optimizing the practical detection of ppm-level n-butanol for other inorganic heterogeneous sensors.

Lotus-root-like multichannel nanotubes of IrO2–ZnO for electrocatalysis of pH-universal oxygen evolution reaction: A simple strategy to control the structure and crystallinity

A series of IrO2-ZnO composite oxide nanomaterials (IrO2-ZnO-x) were synthesized by electrospinning and subsequent calcination process using an electrospinning solution composed of Ir/Zn metal precursors and blended polymers of PVP/PVDF at different mixing ratios (PVDF wt% out of total polymer is denoted as x = 0, 17, 33, 50, 100). The fine structure and crystallinity of the produced IrO2-ZnO-x materials were tuned simply depending on the polymer mixing ratio: As PVDF content increased in a polymer blend, IrO2-ZnO-x (x = 0, 17, 33, 50) changed the structure from wire-in-tubes to nanofibers and then to lotus-root-like multichannel nanotubes with a greater degree of amorphization via better alloying between Ir and Zn elements. IrO2-ZnO-33, exhibiting a lotus-root-like multichannel nanotubular structure with very porous surface morphology and low crystallinity, showed the best OER activity and long-term durable stability for 24 h in a wide range of pH solutions among a series of IrO2-ZnO-x, outperforming commercial Ir/C and a counterpart containing only Ir element. IrO2-ZnO-33 synthesized with an optimal polymer-blending ratio boosted up the electrocatalytic activity toward OER, which was ascribed to (1) enlarged surface area from its unique structure, (2) increased defects along with the greater amount of oxygen vacancies in the amorphous phase, and (3) the synergistic effect between Ir and Zn. This study presents a straightforward strategy to control the structure and crystallinity of nanocatalysts using a blend of properly selected two different polymers.

Exploring the photo-catalytic degradation of methyl orange dye using Strontium doped Bismuth oxide nanoparticles

Low dimensional metal oxide Nps have garnered significant attention due to their distinctive characteristics and diverse application domains. This investigation can provide further elucidation regarding the synthesis of Strontium doped-Bi2O3 efficacious photocatalysts operating under visible light, thereby potentially addressing environmental quandaries. The photoactivity of Strontium doped-Bi2O3 Nps exhibits a significantly greater magnitude when compared to that of Bi2O3 nanoparticles lacking Strontium doping. The hydrothermal method shall be employed for the synthesis of Strontium-doped Bismuth oxide in the course of preparation. A solution of NH4OH will be introduced to Bismuth nitrate and Strontium chloride. The resulting mixtures shall be subjected to vigorous stirring for a duration of 1 hour, after which they will be transferred into 100 mL autoclaves made of stainless steel and equipped with Teflon liners. These autoclaves shall then be heated to a temperature of 180 °C for a period of 6 h. The prepared samples shall subsequently undergo collection and undergo multiple washes utilising de-ionized water. In order to synthesise Strontium doped-Bi2O3 is imperative to subject the resulting compound to a subsequent calcination process at a temperature of 450° C. Infra-Red spectroscopy (FT-IR), UV-Visible, scanning electron microscopy (SEM), X-ray diffraction (XRD), techniques shall be employed for the investigation of the crystalline structures and morphologies of the powder. The resultant specimen shall subsequently serve as a catalyst for the photolytic degradation of organic dye methyl orange under diverse illumination circumstances. UV-Visible spectroscopy shall subsequently be employed to monitor the extent of photocatalytic efficacy.

One-Pot Synthesis of Ultra-Small Pt Nanoparticles-Loaded Nitrogen-Doped Mesoporous Carbon Nanotube for Efficient Catalytic Reaction.

In this study, Pt nanoparticles-loaded nitrogen-doped mesoporous carbon nanotube (Pt/NMCT) was successfully synthesized through a polydopamine-mediated "one-pot" co-deposition strategy. The Pt source was introduced during the co-deposition of polydopamine and silica on the surface of SiO2 nanowire (SiO2 NW), and Pt atoms were fixed in the skeleton by the chelation of polydopamine. Thus, in the subsequent calcination process in nitrogen atmosphere, the growth and agglomeration of Pt nanoparticles were effectively restricted, achieving the in situ loading of uniformly dispersed, ultra-small (~2 nm) Pt nanoparticles. The method is mild, convenient, and does not require additional surfactants, reducing agents, or stabilizers. At the same time, the use of the dual silica templates (SiO2 NW and the co-deposited silica nanoclusters) brought about a hierarchical pore structure with a high specific surface area (620 m2 g-1) and a large pore volume (1.46 cm3 g-1). The loading process of Pt was studied by analyzing the electron microscope and X-ray photoelectron spectroscopy of the intermediate products. The catalytic performance of Pt/NMCT was investigated in the reduction of 4-nitrophenol. The Pt/NMCT with a hierarchical pore structure had an apparent reaction rate constant of 0.184 min-1, significantly higher than that of the sample, without the removal of the silica templates to generate the hierarchical porosity (0.017 min-1). This work provides an outstanding contribution to the design of supported noble metal catalysts and also highlights the importance of the hierarchical pore structure for catalytic activity.

Simultaneous degradation of binary fluoroquinolone antibiotics by B and N in-situ self-doped guar gum hydrogel

Using guar gum (GG) as the raw material and borax (B) as the cross-linker, zeolitic imidazolate framework-8 (ZIF-8) was in-situ loaded into the 3D network of GG hydrogel, forming a highly efficient catalytic material GG-B-ZIF-8 combined with a subsequent low-temperature calcination process. In GG-B-ZIF-8 activated peroxymonosulfate (PMS) system, binary norfloxacin (NOR) and ciprofloxacin (CIP) could be removed simultaneously, with the degradation efficiency of >99.9% within 1 h. This system was adaptable to a wide pH range of 3.0–9.0, and was also highly resistant to 5–20 mM Cl− and 10–40 mg/L humic acid. The degradation process was dominated by free radical O2•-, non-radical 1O2 and electron transfer, with eleven degradation products identified for NOR and nine for CIP via eight possible degradation pathways. Finally, the potential eco-toxicity of NOR, CIP and degradation intermediates was evaluated using the ECOSAR method.

Construction of hexagonal hollow rod-shaped NiCo2O4–In2O3 p-n heterojunction for low concentration formaldehyde detection

The construction of p-n heterostructures using n-type and p-type semiconductor is a very important way to enhance gas sensing performance. In this work, hexagonal rod-shaped NiCo2O4/In2O3 with larger surface area was prepared via a simple water bath approach and subsequent calcination process. The microscopic morphology characterization results show that the NiCo2O4/In2O3 composite has a hexagonal hollow rod-shaped structure, where NiCo2O4 grows in situ on the surface of In2O3, forming p-n heterojunctions. Notably, the NiCo2O4/In2O3 composites formed with 6% NiCo2O4 addition (In-NC6) at 200 °C showed the best gas sensing performance for 1 ppm formaldehyde with a response value of 9.11 and a theoretical detection limit as low as 10.83 ppb. The rich oxygen vacancies, active site and p-n heterojunction are conducive to the adsorption of formaldehyde and electron transfer. This in situ growth approach provides novel ideas and promising prospects to synthesize other p-n heterojunction materials for applying to toxic gas detection.

Improved Electrochemical Performance of Li-Rich Cathode Materials via Spinel Li2MoO4 Coating.

Li-rich manganese-based cathode materials (LRMs) are considered one of the most promising cathode materials for the next generation of lithium-ion batteries (LIBs) because of their high energy density. However, there are problems such as a capacity decay, poor rate performance, and continuous voltage drop, which seriously limit their large-scale commercial applications. In this work, Li1.2Mn0.54Co0.13Ni0.13O2 coated with Li2MoO4 with a unique spinel structure was prepared with the wet chemistry method and the subsequent calcination process. The Li2MoO4 coating layer with a spinel structure could provide a 3D Li+ transport channel, which is beneficial for improving rate performance, while protecting LRMs from electrolyte corrosion, suppressing interface side reactions, and improving cycling stability. The capacity retention rate of LRMs coated with 3 wt% Li2MoO4 increased from 69.25% to 81.85% after 100 cycles at 1 C, and the voltage attenuation decreased from 7.06 to 4.98 mV per cycle. The lower Rct also exhibited an improved rate performance. The results indicate that the Li2MoO4 coating effectively improves the cyclic stability and electrochemical performance of LRMs.

Enhanced Oxygen Storage Capacity of Porous CeO2 by Rare Earth Doping.

CeO2 is an important rare earth (RE) oxide and has served as a typical oxygen storage material in practical applications. In the present study, the oxygen storage capacity (OSC) of CeO2 was enhanced by doping with other rare earth ions (RE, RE = Yb, Y, Sm and La). A series of Undoped and RE-doped CeO2 with different doping levels were synthesized using a solvothermal method following a subsequent calcination process, in which just Ce(NO3)3∙6H2O, RE(NO3)3∙nH2O, ethylene glycol and water were used as raw materials. Surprisingly, the Undoped CeO2 was proved to be a porous material with a multilayered special morphology without any additional templates in this work. The lattice parameters of CeO2 were refined by the least-squares method with highly pure NaCl as the internal standard for peak position calibrations, and the solubility limits of RE ions into CeO2 were determined; the amounts of reducible-reoxidizable Cen+ ions were estimated by fitting the Ce 3d core-levels XPS spectra; the non-stoichiometric oxygen vacancy (VO) defects of CeO2 were analyzed qualitatively and quantitatively by O 1s XPS fitting and Raman scattering; and the OSC was quantified by the amount of H2 consumption per gram of CeO2 based on hydrogen temperature programmed reduction (H2-TPR) measurements. The maximum [OSC] of CeO2 appeared at 5 mol.% Yb-, 4 mol.% Y-, 4 mol.% Sm- and 7 mol.% La-doping with the values of 0.444, 0.387, 0.352 and 0.380 mmol H2/g by an increase of 93.04, 68.26, 53.04 and 65.22%. Moreover, the dominant factor for promoting the OSC of RE-doped CeO2 was analyzed.

Multifunctional SiC aerogel reinforced with nanofibers and nanowires for high-efficiency electromagnetic wave absorption

Ceramic aerogels with recoverable compressibility, super-insulation capacity, and remarkable thermal and chemical stability are fascinating for use in the field of high-level electromagnetic wave (EMW) absorption. However, integrating multiple functions into a monolithic ceramic aerogel using presently available fabrication techniques remains a challenge. Therefore, we employed a novel strategy to successfully synthesize a multifunctional and monolithic SiC ceramic aerogel using a simple freeze casting technique with a subsequent carbonation and calcination process. The as-synthesized SiC aerogel-2 exhibits ultralow density, fire resistance, high-temperature chemical and thermal stability, and excellent insulating properties. Notably, the one-dimensional SiC nanofibers and nanowires inside the SiC aerogel-2 act as a reinforcement to ensure the presence of a stable porous structure. The sample exhibits excellent mechanical performance and also achieves ideal impedance matching to present high-efficiency EMW-absorbing properties, including a minimum reflection loss (RLmin) of − 61.56 dB and a maximum effective absorption bandwidth (EABmax) of 9.82 GHz. Thus, the successful fabrication of multifunctional SiC aerogels will pave the way for the development and widespread application of high-level EMW absorption materials in aviation and aerospace fields.

Novel self-assembled porous yolk-shell NiO nanospheres with excellent electrochromic performance for smart windows

With the rapid development of optoelectronics, electrochromic (EC) materials (ECMs) with the advantages of low power consumption, easy viewing, high contrast ratio, etc. have attached more and more attention from the fields of smart windows, electronic billboards, emerging wearable and portable electronics, and other next-generation displays. Nickel oxide (NiO) is a promising candidate for high-performance ECMs because of its neutral-colored states and low cost. However, NiO-based ECMs still face the problem of slow switching speed due to their low electrical conductivity and small lattice spacing. Metal-organic frameworks (MOFs) are promising candidates to fabricate hollow and porous transition metal oxides (TMOs) with high ion transport efficiency, excellent specific capacitance, and electrochemical activities. In this work, porous yolk-shell NiO nanospheres (PYS–NiO NSs) were synthesized via a solvothermal and subsequent calcination process of Ni-MOF, which exhibited outstanding EC performance. Because the large specific surface areas and hollow porous nanostructures were conducive to ionic transport, PYS-NiO NSs exhibited a fast coloring/bleaching speed (3.6/3.9 s per one coloring/bleaching cycle) and excellent cycling stability (82% of capacity retention after 3000 cycles). These superior EC properties indicated that the PYS-NiO NSs was a promising candidate for high-performance EC devices. This work provides a new and feasible strategy for the efficient preparation of TMOs ECMs with good EC performance, especially fast switching speed.