Facile Hydrothermal Synthesis Research Articles

Improved electrocatalytic activity of selenide nanoparticle for oxygen evolution reaction

Oxygen Evolution Reaction (OER) plays a vital role in water electrolysis, but its slow kinetics and expensive catalysts are obstacles to widespread use. To improve the OER activity, it is crucial to create a well-structured design for electrocatalysts based on transition metals, which may be applied to a conducting polymer substrate. This research reports a facile hydrothermal synthesis and remarkable catalytic behavior of NbSe2/g-CN as an OER catalyst in an alkaline condition. The fabricated electrocatalysts were examined utilizing numerous analytical techniques to assess their crystallinity, oxidation states and morphology. NbSe2/g-CN shows enhanced electro-catalytic behavior to OER in alkaline solution (1.0 KOH) with minor overpotential (196 mV) and Tafel slop (38 mV/dec) than pristine NbSe2 electrocatalyst was associated with the exceptional conductivity of NF and its highly porous structure, along with a greater SSA. In addition, the durability of the electrocatalyst was examined via cyclic stability and chronoamperometry study over 40 h. This study demonstrates that TMSe with specific morphology can improve electrocatalytic activity when combined with g-CN, demonstrating its potential for reliable and eco-friendly energy generation

Facile and green hydrothermal synthesis of MgAl/NiAl/ZnAl layered double hydroxide nanosheets: a physiochemical comparison

Abstract Layered double hydroxide (LDH) exhibits a remarkable trait referred to as the ‘memory effect,’ demonstrating its capacity to reconstruct its layered structure from calcined oxides through hydrothermal treatment. Its uniqueness has garnered significant interest from researchers in both industrial and academic domains. Various methods have been utilized to synthesize LDH but most LDH studies still utilize alkali precipitants which might taint the final LDH product. Thus, in this study, layered double hydroxides involving MgAl/NiAl/ZnAl were synthesized via an alkali-free hydrothermal approach in which the formed precipitates of LDH were thermally destroyed via calcination at 450 °C before undergoing a rehydration treatment at 110 °C for 24 h to restore its original structure. Particularly, the physiochemical properties of MgAl/NiAl/ZnAl LDH have been undertaken by multiple techniques such as Powder X-ray Diffraction (PXRD), thermogravimetric analysis (TGA), Brunauer-Emmett-Teller (BET), Field Emission Scanning Electron Microscope (FESEM) and Fourier-transform infrared spectroscopy (FTIR). The resultant products exhibited exceptional crystallinity, accompanied by notably larger crystallite sizes and crystallinity index, particularly post-hydrothermal treatment. Among the fresh and calcined products studied, those subjected to HTM (4:1) treatment demonstrated the highest specific surface area and crystallinity surpassing both the fresh and calcined samples. In essence, this research showcased how utilizing the hydrothermal approach resulted in the most substantial increase in crystallite size and specific surface area.

Mxene-derived Na2O7Ti3 nanoribbon as a promising electrode material for the detection of ethyl paraoxon in complex matrices

This study reports the development of MXene (Ti3C2Tx) derived sodium titanate nanoribbon-based electrochemical sensor for pesticide detection. Titanium Carbide (Ti3C2) MXene-derived sodium titanate nanoribbon (MNR) was obtained by facile hydrothermal synthesis and characterized by powder X-ray Diffraction (XRD), field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray analysis(EDS) and, high-resolution transmission electron microscopy (HR-TEM). The synthesized water-dispersed MNR was stabilized with Nafion and deposited on the surface of glassy carbon electrodes (GCE), which provide a symmetrical uniform electrode surface. Further, the electrodes were electrochemically characterized with cyclic voltammetry (CV), differential pulse voltammetry (DPV), linear sweep voltammetry(LSV), and electrochemical impedance spectroscopy (EIS). The electrochemical sensing of ethyl paraoxon was carried out in 0.1 M phosphate buffer (PB) by CV, LSV, and DPV. The developed electrochemical sensor exhibited a limit of detection (LOD) of 0.22 nM, a very wide detection range from 0.69 nM to 174.03 nM, and a reliable sensitivity of 0.707 µA/nM/cm2. Moreover, the developed sensor was also employed for the detection of ethyl paraoxon in real samples (vegetable extract spiked with the pesticide). The results suggest that the developed MNR-based sensor would be a potential approach for efficient and accurate detection of ethyl paraoxon in ambient samples, with minimal interference.

Harnessing solar power for enhanced photocatalytic degradation of coloured pollutants using novel Mg-doped-ZnFe2O4/S@g-C3N4 heterojunction: A facile hydrothermal synthesis approach.

The ability of heterogeneous photocatalysis to effectively remove organic pollutants from wastewater has shown great promise as a tool for environmental remediation. Pure zinc ferrites (ZnFe2O4) and magnesium-doped zinc ferrites (Mg@ZnFe2O4) with variable percentages of Mg (0.5, 1, 3, 5, 7, and 9 mol%) were synthesized via hydrothermal route and their photocatalytic activity was checked against methylene blue (MB) taken as a model dye. FTIR, XPS, BET, PL, XRD, TEM, and UV-Vis spectroscopy were used for the identification and morphological characterization of the prepared nanoparticles (NPs) and nanocomposites (NCs). The 7% Mg@ZnFe2O4 NPs demonstrated excellent degradation against MB under sunlight. The 7% Mg@ZnFe2O4 NPs were integrated with diverse contents (10, 50, 30, and 70 wt.%) of S@g-C3N4 to develop NCs with better activity. When the NCs were tested to degrade MB dye, it was revealed that the 7%Mg@ZnFe2O4/S@g-C3N4 NCs were more effective at utilizing solar energy than the other NPs and NCs. The synergistic effect of the interface formed between Mg@ZnFe2O4 and S@g-C3N4 was primarily responsible for the boosted photocatalytic capability of the NCs. The fabricated NCs may function as an effective new photocatalyst to remove organic dyes from wastewater.

Two-stage hydrothermal process driven visible light sensitive photocatalytic m-ZnWO4/m-WO3 heterojunction composite materials

The current study reports on the facile two-step hydrothermal synthesis of heterojunction m-ZnWO4/m-WO3 composite powders for visible light sensitive photocatalytic applications. The ZnWO4 particles start crystallizing on the surface of the WO3 powder in the second stage of the reaction in a basic medium. The phases of the composite powders were confirmed using x-ray diffraction analysis. The monoclinic cubic shaped WO3 and rod shaped ZnWO4 morphologies were disclosed from the field emission scanning electron microscope images. Strong interfacial adhesion between ZnWO4 and WO3 was unveiled from the high-resolution transmission electron microscopy study. The optimized composite 5ZW exhibits a calculated bandgap of 2.58 eV, positioning it within the visible light wavelength range (λ = 400–700 nm). Furthermore, there is a notable enhancement in the average lifetime of the electron–hole pair recombination rate, which is extended to 30.3 ns. The composite 5ZW demonstrated 96% methylene blue dye degradation efficiency within 420 min under visible light irradiation at pH 12. Due to the optimal phase fraction and strong interfacial adhesion between ZnWO4 and WO3, the heterojunction scheme seemed to be highly efficient in the 5ZW composite. Hence, it is believed that a two-step hydrothermal method can be a proficient route to prepare heterojunction composites m-ZnWO4/m-WO3 in alkali conditions with visible light active photodegradation efficiency.

Facile hydrothermal synthesis and continuously improved sonophotocatalytic performance of PO4-doped Bi2WO6 nanoplates

The doping of ionic group composed of various atoms can play a great role in regulating electronic structure, optimizing light absorption capacity, and enhancing the catalytic performance of semiconductor catalysts. Herein, we took a urea-precipitate assisting hydrothermal route for preparing PO4-doped Bi2WO6 nanoplates and discussed the effect of the ionic group doping on the sonophotocatalytic performance toward the degradation of pollutant. The result of the X-ray photoelectron spectrometer (XPS) measurements revealed that abundant oxygen vacancies were formed in PO4-doped Bi2WO6 owing to the incorporation of the ionic group, which would contribute to the regulation of electronic structure and activated carriers’ migration rate. The sonophotocatalytic activity toward the removal of tetracycline hydrochloride (TCH) was investigated under visible-light coupling with ultrasonic irradiation. The results showed that PO4-doped Bi2WO6 nanoplates possessed higher sonophotocatalytic degradation rate than pure Bi2WO6. More interestingly, the TCH removal efficiency was continuously improved over PO4-doped Bi2WO6 nanoplates with the assistance of the sulfate radical-mediated technique. Based on the comprehensive discussion and analysis, a possible enhancement mechanism of the sonophotocatalytic behavior was proposed for PO4-doped Bi2WO6 nanoplates catalyst in the presence of peroxymonosulfate.

Fluorescent Carbonized Polymer Dots Derived from o-phenylenediamine and its Photonic Application.

Optimizing the optoelectronic characteristics of low-dimensional carbon dots (CDs) through surface modifications and doping has proven instrumental in tailoring them for diverse applications. This study explores a facile and economical hydrothermal synthesis method for generating Carbonized Polymer Dots using o-phenylenediamine at different temperatures. The resulting materials exhibit structural and morphological variations linked to the synthesis temperature. A transition from carbon dots (CDs) embedded in reduced graphene oxide (rGO)-like sheet structures at low temperatures to the core-shell structure at the highest temperature is observed in HR-TEM, implying the formation of CPDs. X-ray photoelectron spectroscopy (XPS) corroborates these findings, showing an augmented degree of graphitization in alignment with HR-TEM results. The photoluminescence spectra of CPDs synthesized at the lowest temperature exhibit multiple emission peaks, resulting in a yellowish-orange color. Utilizing these CPDs to fabricate light-emitting diodes (LEDs) produces a vivid bright-green emission with CIE coordinates (0.378, 0.522). Moreover, the CPDs demonstrate solvatochromism across diverse solvents of varying polarity, covering the entire visible spectrum. This intriguing solvatochromic effect positions the CPDs as promising materials for polarity probing applications.

Impressive efficiency of zinc oxide-manganese oxide/MAX composite in two-electrode system for photovoltaic-electrolyzer water splitting

The improvement and use of affordable and efficient electrocatalysts for complete water splitting are crucial for the future of energy supply. Here, a hybrid zinc oxide (ZnO)–manganese oxide (Mn3O4)/Ti3AlC2 (MAX) composite produced by a facile hydrothermal synthesis is utilized as a dual-function electrocatalyst for the hydrogen and oxygen evolution reactions (HER and OER, respectively). Its well-organized surfaces and bulky porous framework provide numerous catalytically active sites during electrochemical reactions, leading to significant improvement in the HER and OER activities. In particular, the ZnO and Mn3O4 phases increase the catalytic activity of the electrode, while the MAX phase enhances the conductivity and promotes low overpotential Ni sites through charge transfer effects. Consequently, the optimized ZnO-Mn3O4/MAX/Ni foam electrode exhibits relatively low overpotentials (η) of 244 and 340 mV at 20 mA cm−2 for the HER and OER at 1.0 M KOH, respectively. The electrodes also demonstrate exceptional long-term stability during cycling for both the HER and OER. A fully homemade water splitter, using these electrodes as anode and cathode, achieves a current density of 10 mA cm−2 at a cell voltage of only 1.62 V. When integrated with commercially available silicon-based solar cells, combined PV-EC water splitting devices enable increased hydrogen generation from stimulated sunlight. This study presents a typical demonstrated and proven strategy for real large-scale solar hydrogen generation using cost-effective PV-EC technology.

Self-Supported Mn-Ni3Se2 Electrocatalysts for Water and Urea Electrolysis for Energy-Saving Hydrogen Production.

Recently, there has been a huge research interest in developing robust, efficient, low-cost, and earth-abundant materials for water and urea electrolysis for hydrogen (H2) generation. Herein, we demonstrate the facile hydrothermal synthesis of self-supported Mn-Ni3Se2 on Ni foam for overall water splitting under wide pH conditions. With the optimized concentration of Mn in Ni3Se2, the overpotential for hydrogen evolution, oxygen evolution, and urea oxidation is significantly reduced by an enhanced electrochemical active surface area. Different electronic states of metal elements also produce a synergistic effect, which accelerates the rate of electrochemical reaction for water and urea electrolysis. Owing to the chemical robustness, Mn-doped Ni3Se2 shows excellent stability for long time duration, which is important for its practical applications. A two-electrode electrolyzer exhibits low cell voltages of 2.02 and 1.77 V for water and urea electrolysis, respectively, to generate a current density of 100 mA/cm2. Finally, the prepared nanostructured Mn-Ni3Se2@NF acts as an electrocatalyst for overall water splitting under wide pH conditions and urea electrolysis for energy-saving hydrogen production and wastewater treatment.

Ni/WS2/WC Composite Nanosheets as an Efficient Catalyst for Photoelectrochemical Hydrogen Peroxide Sensing and Hydrogen Evolution.

It is highly attractive to develop a photoelectrochemical (PEC) sensing platform based on a non-noble-metal nano array architecture. In this paper, a PEC hydrogen peroxide (H2O2) biosensor based on Ni/WS2/WC heterostructures was synthesized by a facile hydrothermal synthesis method and melamine carbonization process. The morphology, structural and composition and light absorption properties of the Ni/WS2/WC catalyst were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and UV-visible spectrophotometer. The average size of the Ni/WS2/WC nanosheets was about 200 nm. Additionally, the electrochemical properties toward H2O2 were studied using an electrochemical workstation. Benefiting from the Ni and C atoms, the optimized Ni/WS2/WC catalyst showed superior H2O2 sensing performance and a large photocurrent response. It was found that the detection sensitivity of the Ni/WS2/WC catalyst was 25.7 μA/cm2/mM, and the detection limit was 0.3 mmol/L in the linear range of 1-10 mM. Simultaneously, the synthesized Ni/WS2/WC electrode displayed excellent electrocatalytic properties in hydrogen evolution reaction (HER), with a relatively small overpotential of 126 mV at 10 mA/cm2 in 0.5 M H2SO4. This novel Ni/WS2/WC electrode may provide new insights into preparing other efficient hybrid photoelectrodes for PEC applications.

Hydrothermal-assisted synthesis of Sr-doped SnS nanoflower catalysts for photodegradation of metronidazole antibiotic pollutant in wastewater promoted by natural sunlight irradiation.

In this study, we report a facile hydrothermal synthesis of strontium-doped SnS nanoflowers that were used as a catalyst for the degradation of antibiotic molecules in water. The prepared sample was characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), and ultraviolet-visible absorption spectroscopy (UV-Vis). The photocatalytic ability of the strontium-doped SnS nanoflowers was evaluated by studying the degradation of metronidazole in an aqueous solution under photocatalytic conditions. The degradation study was conducted for a reaction period of 300 min at neutral pH, and it was found that the degradation of metronidazole reached 91%, indicating the excellent photocatalytic performance of the catalyst. The influence of experimental parameters such as catalyst dosage, initial metronidazole concentration, initial reaction pH, and light source nature was optimized with respect to metronidazole degradation over time. The reusability of the strontium-doped SnS nanoflowers catalyst was investigated, and its photocatalytic efficiency remained unchanged even after four cycles of use.

Silk‐Based Functional Inks with Color‐Tunable Light Upconversion for Printing on Arbitrary Surfaces

AbstractA biocompatible and versatile silk‐based functional ink with hydrophilic upconversion nanoparticles (UCNPs) that can be printed or painted on arbitrary substrates, including biological surfaces is demonstrated. Hydrophilic UCNPs, ready to be dispersed in aqueous silk fibroin solution, are synthesized in large quantities via facile hydrothermal synthesis using citric acid. Based on a systematic study of dopant control to achieve robust red emission from citrate‐capped UCNPs, three primary colors are obtained, which serve as the basis for the expansion of the color palette. The synthesized UCNPs are homogeneously dispersed in regenerated silk fibroin solutions derived from Bombyx mori cocoons to produce water‐based functional inks. Cyan, magenta, and yellow (CMY) inks are created by combining red, green, and blue (RGB) inks. Demonstrator devices, where a variety of colorful patterns and codes are revealed only under near‐infrared irradiation, are realized through stencil printing or brush painting on flexible polymer films, fruit, leaves, silkworm cocoons, and pig skin. The patterns and codes are highly heat resistant (≈230 °C) and can be easily washed off with water after use. The printable/paintable inks and functions proposed here will provide new opportunities for applications where sustainability, biocompatibility, and intentional luminescence are simultaneously required.

Synthesis of Bitter gourd-shaped Cu-doped ZnO nanostructures and their investigation for the detection of NO2 gas at low concentrations

Nitrogen dioxide (NO2) exposure can have several adverse health impacts on people, especially the respiratory system. Low selectivity, a lack of long-term stability, and structural and morphological optimization are some challenges associated with using ZnO for NO2 gas sensing. Therefore, we intended copper (Cu) doping in ZnO to alter its shape and gas-sensing characteristics. This study explores the synthesis, properties, and gas-sensing capabilities of bitter gourd-shaped Cu-doped zinc oxide (ZnO) nanostructures for the detection of nitrogen dioxide (NO2). A facile hydrothermal synthesis method was employed to synthesize bitter gourd-shaped Cu-doped ZnO nanostructures and comprehensively characterized by several techniques. Comprehensive characterizations of our produced Cu-doped ZnO nanomaterial demonstrated by X-ray diffraction (XRD), Scanning electron microscope (SEM), Energy-dispersive X-ray spectroscopy (EDS), and different energy spectrum. The material was annealed at 400 °C in a controlled dry air environment to improve its suitability for gas sensor applications. A series of temperature-ranging experiments were conducted to get gas-sensing readings from 25 °C to 300 °C. The resulting sensor, founded upon the distinctive morphology of Cu-doped ZnO structures reminiscent of the intricate shape of bitter gourd, unveiled good selectivity with a pronounced affinity for detecting NO2 gas. Notably, the zenith of its performance was attained at an operating temperature of 200 °C, where its selectivity and sensitivity were most pronounced. Even at a low concentration of 1 ppm, the sensors displayed a maximum response of 3.7, highlighting their high sensitivity. The sensors demonstrated excellent reproducibility, selectivity, and a low detection limit. These findings position bitter gourd-shaped Cu-doped ZnO nanostructures as promising candidates for NO2 sensing applications across diverse environments.

Facile Microwave-Assisted Hydrothermal Synthesis of Copper Oxide Nanoneedle Arrays for Practical Biomedical Applications.

Copper oxide nanoneedle arrays (CuO NAs) have been widely used as antibacterial agents and in therapeutic applications because of their unique physicochemical features, low cytotoxicity, low cost, exceptional antibacterial action, and significant interest in biomedicine. Various analytical techniques were used to assess the related phase constitution, optical characteristics, elemental content, and surface morphology. The X-ray diffraction (XRD) patterns and field-emission scanning electron microscopy (FE-SEM) micrographs revealed that the CuO NAs had a monoclinic phase with a nanoneedle-like shape. Our findings may cover the progress of innovative and effective anti-bacterial capabilities based on CuO NAs, which have been shown to be effective against various pathogens, making them ideal options for fighting bacterial infections. Objective: This research aimed to synthesize CuO NAs using microwave-solvothermal (MW-ST) technology, explore their effectiveness, and assess their biological activity. The CuO NAs were synthesized using the MW-ST process, and their properties were assessed using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FE-SEM), energy dispersive analysis (EDS), field emission transmission microscopy (FE-TEM), and ultraviolet-visible (UV-Vis) techniques. The biocompatibility of CuO NAs was determined through hemolytic assays, and their bioactivities like antioxidant and anti-inflammatory assays were also determined. The CuO NAs were successfully developed,and various analytical tools were used to characterize and validate their morphology, size, crystallinity, and elemental compositions. It has been shown in in-vitro investigations that a strong anti-inflammatory impact is demonstrated by the inhibition of protein denaturation with low hemolytic potential. As a result, CuO NAs have the potential to be an excellent choice for anti-inflammatory solicitations. CuO NAs were synthesized and characterized with various advanced techniques, revealing the formation of nanoneedles-like morphology. Based on the experimental findings, CuO NAs have the potential for anti-microbial, anti-oxidant, anti-inflammatory, and anti-hemolytic activities. However, additional in-vivo testing is essential to properly evaluate their efficiency and safety.

Fabrication of samarium doped MOF-808 as an efficient photocatalyst for the removal of the drug cefaclor from water.

MOFs are emerging photocatalysts designed by tuning organic ligands and metal centers for optimal efficiency. In this study, a samarium decorated MOF-808(Ce) metal organic framework was fabricated by facile hydrothermal synthesis. The synthesized samarium decorated MOF-808(Ce) was characterized by using analytical techniques such as SEM, EDX, XRD and TGA to study its morphological, thermal and structural properties. SEM images showed that MOF-808(Ce) comprised of truncated octahedrons. The morphology of the material was changed upon Sm incorporation. Sm/MOF-808(Ce) exhibited better UV-vis light absorption properties than MOF-808(Ce) as evidenced by its slightly higher band gap value. This material was exploited for the degradation of the drug cefaclor from water. Cefaclor removal followed double a first order in parallel model (DFOP). Under UV light, 97.7% of the cefaclor was removed in only 20 minutes and after 60 minutes this removal efficiency was increased to 99.25%. These features exhibited that samarium decorated MOF has immense potential for the photocatalytic degradation of cefaclor as it generates e- and h+ to enhance the photocatalytic efficiency and it is a promising candidate to treat wastewater without formation of harmful byproducts.

Facile hydrothermal synthesis of a tri-metallic Cu-Mn-Ni oxide-based electrochemical pseudo capacitor.

Transition metal oxide nanocomposites with heterostructures have gained a lot of attention for use in supercapacitors owing to their low cost, high surface area, fast transport of ions and electrons and high specific capacitance due to efficacious interplay between the electrode and the electrolytes. In this study, we fabricated tri-metallic Cu, Mn, Ni(CMNO), bi-metallic Mn, Ni(MNO) and mono-metallic Ni(NO) oxides through a facile hydrothermal route. All the fabricated materials were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and energy dispersive spectroscopy (EDX), and their electrochemical properties were studied using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic charge-discharge (GCD). The CMNO material showed remarkable electrochemical performance with a specific capacitance of 790.63 F g-1 at a current density of 1 A g-1, surpassing the performance of MNO (438.4 F g-1) and NO (290.82 F g-1). Furthermore, CMNO showed high cycling stability with a retention of 96.7% specific capacitance after 8000 cycles. Based on remarkable and unique properties, the CMNO material is regarded as a promising material for new-generation pseudo-capacitor applications.

Titanium carbide (Ti3C2Tx) decorated molybdenum diselenide (MoSe2) nanoflower composite enhanced photo-electrocatalytic activity in hydrogen evolution

Two-dimensional titanium carbides (Ti3C2Tx) are part of the novel family of transition metal carbides/nitrides known as MXenes, which exhibit a broad range of photo-electrocatalytic applications. In this study, we present a facile hydrothermal synthesis method for Ti3C2Tx decorated on molybdenum diselenide (MoSe2) nanoflower composites, serving as an enhanced catalyst for hydrogen (H2) evolution. Ti3C2Tx, acting as a 2D conductive substrate, facilitates electron transfer, preventing MoSe2 agglomeration, while MoSe2 offers abundant active sites. The characterizations of surface analysis, optical properties, morphological nanostructure, and elemental composition performance of Ti3C2Tx nanosheets, MoSe2 nanoflowers, and Ti3C2Tx/MoSe2 nanoflower composites was conducted using FTIR, XRD, UV–Visible spectroscopy, SEM, EDS Mapping, TEM, and XPS techniques. The catalyst with optimal performance, the Ti3C2Tx/MoSe2 nanoflower composite demonstrates excellent functional properties in the H2 evolution, showing a lower overpotential of 135 mV and smaller Tafel slope of 72 mV/dec at 10 mA/cm2 compared to Ti3C2Tx nanosheets and MoSe2 nanoflowers. The Ti3C2Tx/MoSe2 nanoflower composite forms heterojunctions to inhibit the rapid recombination rate of photo-induced electrons and holes. In comparison to MoSe2 nanoflowers and Ti3C2Tx catalysts (where Tx = F, and O surface terminations), the optimized Ti3C2Tx/MoSe2 nanoflower composite exhibits significantly enhanced photocatalytic activity in H2 production, with a H2 production rate of 2146 μmolg−1h−1 superior than the Ti3C2Tx nanosheets (1367 μmolg−1h−1) and MoSe2 nanoflowers (986 μmolg−1h−1), respectively. Through this design, effective separation of photogenerated charge carriers is achieved, improving the activity of photocatalytic H2 production and demonstrating the promise of the cocatalyst strategy for photocatalysis.

Facile hydrothermal synthesis of NiMoO4·xH2O nanorods-like structures as bifunctional oxygen electrocatalysts for rechargeable zinc-air batteries

Developing highly active and low-cost bifunctional catalyst materials to replace precious metal species is of utmost importance for the commercialization of clean and sustainable energy systems. In this report, homogenous NiMoO4·xH2O nanorods (NRs)-like structured materials were synthesized by an annealing-free hydrothermal method. The synthesized electrode electrochemical properties were determined by linear sweep voltammetry using a rotating ring disk electrode to determine the characteristics of oxygen reduction reaction in an O2-saturated electrolyte solution. For the oxygen evolution reaction, the NiMoO4·xH2O NRs electrocatalyst showed lower overpotential of 185 mV to obtain 10 mA cm−2. Furthermore, the NiMoO4·xH2O NRs electrocatalyst-based zinc (Zn)-air battery exhibited lower voltage gaps and smaller electrochemical impedance spectroscopy values than the Pt/C catalyst. Importantly, the NiMoO4·xH2O NRs-based battery (60 cycles (∼1100 min)) revealed excellent cycling stability results when compared with the Pt/C-based battery (30 cycles (∼550 min)). The NR structured electrode provided good steady potential after being subjected to a fixed current density of 10 mA cm−2 for 100 h. Therefore, these results demonstrate that the synthesized NiMoO4·xH2O NRs material is promising as a bifunctional electrocatalyst for rechargeable Zn-air batteries.

Halloysite nanotubes decorated with Co(OH)F nanorods as a novel binary composite for the enhanced electrocatalytic water oxidation

Oxygen evolution reaction is central to several emerging electrochemical energy conversion and storage technologies. This study reports the synthesis, characterization, and OER electrocatalytic performance of binary nanocomposites composed of halloysite nanotubes (HNTs) and Co(OH)F. Five Co(OH)F/HNT with different compositions were fabricated by a facile hydrothermal synthesis. The crystalline phase and microstructure of the as-prepared materials were examined by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The synthesized Co(OH)F (pristine or mixed with HNTs in the nanocomposites) revealed an orthorhombic crystal system with a nanorod morphology. The nanocomposite with ∼19 wt% of Co (designated as Co(OH)F/HNT_3) was found to possess an appreciably improved activity in OER compared to the pristine HNTs, Co(OH)F, and other Co(OH)F/HNT nanocomposites. Co(OH)F/HNT_3 displayed an overpotential of 252 mV (at the current density of 10 mA cm−2), a Tafel slope of 51.1 mV dec−1, and a robust operational performance under harsh alkaline conditions. Furthermore, nitrogen adsorption–desorption isotherms indicated a much higher specific surface area for this nanocomposite than its components. Overall, the versatile synthesis and outstanding catalytic performance of Co(OH)F/HNT_3 make it an auspicious earth-abundant transition metal-based electrocatalyst for OER in an alkaline medium.

Selectivity of Control of Oxygen Reduction Reaction over Mesoporous Transition Metal Oxides Catalysts for Electrified Purification Technologies

Introduction: The use of abundant feedstocks, such as water and air, in manufacturing of value-added products is important in achieving the UN’s Sustainable Development Goals.1 In this context, electrified direct synthesis of chemicals from oxygen in the air is of special interest since it avoids greenhouse gas emissions if the electricity used to drive the synthesis comes from sustainable sources such as solar- and wind-power. The controlling of oxygen reduction path over catalysts incorporation with oxygen evolution reaction as auxiliary reaction enables the electrosynthesis of value-added chemicals, oxygen and hydroxyl radical. The development of cheap materials e.g., mesoporous transition metal oxides, is urged to replace the expensive and scarce of platinum group metal (PGM)-based catalysts, with the ability to provide competitive reaction rate in alkaline media.2 Experimental: A template-free hydrothermal method is developed for the synthesis of mesoporous NiO and NiCo2O4. The materials’ physicochemical properties are characterized by X-ray diffraction, physisorption, electron microscopy, selected electron area diffraction, and X-ray photoelectron spectroscopy. The electrochemical properties and electrocatalytic oxygen activity are evaluated via cyclic voltammetry and electrochemical impedance spectra in alkaline electrolyte using a standard three electrodes electrochemical working station equipped with (ring) rotating disk electrode (RDE/RRDE) techniques.The catalysts coated on carbon fiber paper (CFP) are used as electrode assembled with anion exchange membrane in two-electrodes-electrochemical cell for device test. NiO- and NiCo2O4-modified CFP are used as cathode and anode, respectively, for constructing electrochemical generator of hydroxyl radical. 50 mL min-1 O2 flow was maintained in catholyte to enable oxygen saturation. 20 mg L-1 rhodamine B (RhB)was fed into cathode. Off-line UV-vis measurements were used for RhB quantification. In Electrochemical oxygen purifier, NiCo2O4-modified CFP are used as electrodes. 0.1 - 3 M KOH aqueous solutions were used as anolyte and air-saturated catholyte. The volume of produced oxygen on the anode after 2 h was collected and measured by a water displacement method. Results and Discussion: A facile template-free hydrothermal synthesis is developed for bifunctional oxygen electrocatalysts (OER and ORR) of NiO and NiCo2O4. Physicochemical characterization shows that both NiO and NiCo2O4 are mesoporous with the pore size within a range of 2 - 8 nm and specific surface areas of 60 and 120 m2 g-1, respectively. In addition, NiO and NiCo2O4 possess cubic crystal structures with the corresponding crystal sizes of ~6.0 and 9.3 nm.Electrochemical analysis shows that mesoporous NiCo2O4 has about two times larger capacitance and eight times smaller charge transfer resistance compared to NiO. NiCo2O4 shows higher electrocatalytic activity in OER and selectivity to water as the terminal product of ORR. On the contrary, ORR over NiO yielded hydroxyl radicals, as a product of a Fenton-like reaction of H2O2. The product selectivity in ORR is used to construct two electrolyzers of electrified purification of oxygen and generation of hydroxyl radicals. The optimization of configuration of hydroxyl radical generator enables the degradation of RhB up to 90% after 1 hour, and the electrochemical oxygen purifier shows high efficiency of about 100%. Significance: It is demonstrated that the synthesized mesoporous transition metal oxides via a simple template-free hydrothermal route, and the materials can be used as alternatives to PGM-based electrocatalysts for driving electrochemical cell towards to various products. The work also clearly shows how the composition and structure of catalysts affect the oxygen reactions, and the selectivity of ORR used for producing value-added chemicals coupling with OER. It is shown that the established electrochemical oxygen purifier and hydroxyl radical generator have a high conversion efficiency. Schematic 1. (a) Scheme of operation of the hydroxyl radical generator, (b) the degradation efficiency and rate constants as function of current densities; (c) Scheme of the oxygen purifier, and (d) the generated oxygen volume as a function of working power of the electrochemical cell with different anolyte concentrations. Acknowledgements: This work was supported by the competence center FunMat-II funded by the Swedish Agency for Innovation Systems (Vinnova, grant no 2016-05156), the Swedish Energy Agency (project no 42022-1), and Swedish Research Council (VR 2019-05577, Flexible metal-air primary batteries). Reference: 1 United Nations. Transforming our world: The 2030 agenda for sustainable developement. (UN General Assembly, New York, 2015).2 Yang, Y. et al. Electrocatalysis in Alkaline Media and Alkaline Membrane-Based Energy Technologies. Chem. Rev. 6, 6117–6321 (2022). Figure 1