Direct pyrolysis and ultrasound assisted preparation of N,S co-doped graphene/Fe3C nanocomposite as an efficient electrocatalyst for oxygen reduction and oxygen evolution reactions

Bifunctional electrocatalysts to enable efficient oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are essential for fabricating high performance metal–air batteries and fuel cells. Here, a defect rich nitrogen and sulfur co-doped graphene/iron carbide (NS-GR/Fe₃C) nanocomposite as an electrocatalyst for ORR and OER is demonstrated. An ink of NS-GR/Fe₃C is developed by homogeneously dispersing the catalyst in a Nafion containing solvent mixture using an ultrasonication bath (Model-DC150H; power − 150 W; frequency − 40 kHz). The ultrasonically prepared ink is used for preparing the electrode for electrochemical studies. In the case of ORR, the positive half-wave potential displayed by NS-GR/Fe₃C is 0.859 V (vs. RHE) and for the OER, onset potential is 1.489 V (vs. RHE) with enhanced current density. The optimized NS–GR/Fe₃C electrode exhibited excellent ORR/OER bifunctional activities, high methanol tolerance and excellent long-term cycling stability in an alkaline medium. The observed onset potential for NS–GR/Fe₃C electrocatalyst is comparable with the commercial noble metal catalyst, thereby revealing one of the best low-cost alternative air–cathode catalysts for the energy conversion and storage application.     

Laser-Induced Graphitic Carbon with Ultrasmall Nickel Nanoparticles for Efficient Overall Water Splitting

Metal nanoparticles encapsulated in graphitic carbon can show high catalytic efficiency and stability, yet the production method remains improved. Herein, it is demonstrated that a Ni-based metal–organic framework [EG-MOF-74(Ni)] can be rapidly transformed into ultrasmall Ni-nanoparticles with different sizes (4–11 nm) encapsulated in graphitic carbon via the laser-scribing method. The synthesized sample shows the best electrocatalytic performances with excellent stability in alkaline electrolyte for oxygen/hydrogen evolution reactions with overpotentials of 0.35/0.18 V at a current density of 10 mA cm⁻² when the Ni particle size is ≈6 nm. This is because of its well-developed micro/mesoporous structure, high electronic transport, and large electrochemical active surface area. An electrolyzer with Ni-nanoparticles encapsulated in the graphitic carbon shows a current density of 10 mA cm⁻² at a voltage of 1.6 V, which is comparable to the Pt/C and RuO₂ counterparts. The laser-based synthesis can serve as a powerful tool for the size-controlled synthesis of various catalysts out of MOFs.     

A sonochemical assisted synthesis of hollow sphere structured tin (IV) oxide on graphene oxide sheets for the low-level detection of environmental pollutant mercury in biological samples and foodstuffs

In modern approaches for nanomaterials synthesis, ultrasonication plays an important role in providing the larger surface area and smaller crystalline size properties that are favorable to electrochemical techniques. Herein, we report the tin (IV) oxide on graphene oxide nanoparticles were synthesized (SnO₂@GO NPs) by ultrasonic methodology (UZ SONOPULS HD 3400 Ultrasonic homogenizer) with the total power of 400 W and the (frequency of 20 kHz; 140 W/dm³). The formation of as-prepared SnO₂@GO NPs and its surface morphology were scrutinized over XRD, XPS, TEM, and FESEM. Besides, the sonochemically prepared SnO₂@GO NPs were employed for the determination of environmental hazardous mercury (Hg). As a result, the modified electrode acquired a very low-level detection limit of 1.2 nM with a wider range of 0.01–10.41-µM and 14.52–225.4-µM for the detection of Hg. Finally, the practical applicability of SnO₂@GO NPs in spiked human blood serum and tuna fish samples shows appreciable found and recovery values..     

Sonochemical synthesis and fabrication of perovskite type calcium titanate interfacial nanostructure supported on graphene oxide sheets as a highly efficient electrocatalyst for electrochemical detection of chemotherapeutic drug

In green approaches for electrocatalyst synthesis, sonochemical methods play a powerful role in delivering the abundant surface areas and nano-crystalline properties that are advantageous to electrocatalytic detection. In this article, we proposed the sphere-like and perovskite type of bimetal oxides which are synthesized through an uncomplicated sonochemical procedure. As a yield, the novel calcium titanate (orthorhombic nature) nanoparticles (CaTiO₃ NPs) decorated graphene oxide sheets (GOS) were obtained through simple ultrasonic irradiation by a high-intensity ultrasonic probe (Titanium horn; 50 kHz and 60 W). The GOS/CaTiO₃ NC were characterized morphologically and chemically through the analytical methods (SEM, XRD, and EDS). Besides, as-prepared nanocomposites were modified on a GCE (glassy carbon electrode) and applied towards electrocatalytic and electrochemical sensing of chemotherapeutic drug flutamide (FD). Notably, FD is a crucial anticancer drug and also a non-steroidal anti-androgen chemical. Mainly, the designed and modified sensor has shown a wide linear range (0.015–1184 µM). A limit of detection was calculated as nanomolar level (5.7 nM) and sensitivity of the electrode is 1.073 μA μM⁻¹ cm⁻². The GOS/CaTiO₃ modified electrodes have been tested in human blood and urine samples towards anticancer drug detection.     

Ultrasonic assisted synthesis of Ni3(VO4)2-reduced graphene oxide nanocomposite for potential use in electrochemical energy storage

In the present study, Ni₃(VO₄)₂-reduced graphene oxide (NV/RGO) nanocomposite was synthesized for energy storage purpose. To this end, a mixture containing RGO nanosheets, Ni (CH₃COOH)₂ and Na₃VO₄ mixture was prepared under probe-type ultrasonic irradiation with frequency of 20 KHz and the optimized power of 100 W. The Raman and energy-dispersive X-ray spectroscopies confirmed the presence of RGO nanosheets, nickel and vanadium elements in the NV/RGO, respectively. In addition, field emission-scanning electron microscopy (FESEM) data showed the formation of the NV nanoparticles on the RGO nanosheets. NV/RGO nanocomposite was pasted on nickel foam (NF) and its performance was investigated in energy storage using a three-electrode cell containing 6 M KOH. In cyclic voltammogram of NV/RGO/NF, redox peaks for Ni (II)/Ni (III) with intensities higher than that for NV/NF were observed which confirms the synergistic effect of RGO on the performance of NV. Chronopotentiometry data revealed that the NV/RGO/NF electrode exhibits high capacity of 117.22 mA h g⁻¹ at 2 A g⁻¹. Electrochemical impedance spectroscopy also demonstrated an improvement in the electrical conductivity and electrochemical behavior of NV/RGO/NF nanocomposite compared to the RGO/NF and NV/NF. Furthermore, NV/RGO/NF electrode reserved about 88% of its initial capacity after 1000th potential cycle at 50 mV s⁻¹. Overall, the results of our study suggest that the NV/RGO nanocomposite prepared in the presence of ultrasonic irradiation might be regarded as a suitable active material for energy storage systems.     

Ultrasonic-assisted electrodeposition of Ni/diamond composite coatings and its structure and electrochemical properties

Ni/diamond composite coatings have been synthesized by ultrasonic-assisted electrodeposition in a Ni electroplating bath containing diamond nanoparticles. The influences of current density and ultrasonic agitation on the coating composition, morphology, topography, phase structure, and electrochemical characteristics of the electrodeposits were evaluated. Ultrasonic agitation was provided using an external ultrasonic bath at a frequency of 40 kHz and acoustic power of 300 W. Coating samples were also prepared under magnetic stirring for comparison with the ultrasonic-assisted deposits. This work reveals that the diamonds have been incorporated and evenly distributed in the composites. The coatings exhibit dense, granular like morphology with pyramid-like grains. As current density increases, the diamond amount of ultrasonic-assisted electrodeposits first increased to maximum of 11.4 wt% at 3 A dm⁻² and then decreases to 9.9 wt% at 5 A dm⁻², and the RTC of the preferred orientation (2 0 0) plane increases from 76.3% up to 93.4%. The crystallite size was 60–80 nm and the R_a of the magnetic and ultrasonic agitations were 116 nm, 110 nm, respectively. The maximum R_p of 39.9, 50.3 kΩ cm² was obtained at 4 A dm⁻² when respectively immersed 30 min and 7 days, illustrating the best corrosion resistance of the coatings of 4 A dm⁻². The effects of mechanical and ultrasonic agitations on the mechanism of the co-electrodeposition process were both proposed. The incorporation of diamond particles enhances the hardness and wear-resisting property of the electrodeposits. The ultrasonic-assisted electrodeposited Ni/diamond coating has better corrosion resistance than that prepared under mechanical stirring conditions.     

Pt-Ni alloy nanoparticles supported on CNF as catalyst for direct ethanol fuel cells

Carbon nanofiber (CNF) network supported Pt and Pt-Ni alloy nano particle catalysts were prepared by electrochemical deposition at different deposition cycles. Structure, composition and surface morphology of the Pt/CNF and Pt-Ni/CNF were analyzed using X-ray diffraction, Energy dispersive X-ray spectroscopy and field emission scanning electron microscopy. Structural analysis by XRD revealed a face centered cubic crystal structure for Pt and its alloy. SEM images have shown that the Pt-Ni nanoparticles distributed evenly on the CNF network. The electrocatalytic activity of the Pt/CNF and Pt-Ni/CNF electrodes was verified using an electrochemical linear voltammetrty (ELV), cyclic voltammetry (ECV) and electrochemical impedance spectroscopy (EIS) in an alkaline solution containing 1 M C₂H₅OH + 1 M KOH. The results show increased catalytic activity with enhancement of the Pt-Ni alloy formation.     

Facile sonochemical synthesis of rutile-type titanium dioxide microspheres decorated graphene oxide composite for efficient electrochemical sensor

In this reports the facile and green synthesis of rutile-type titanium dioxide nanoparticles decorated graphene oxide nanocomposite via the ultrasonication process (frequency: 50 kHz, Power: 100 W/cm² and Ultrasonic type: Ti-horn). Because, the sonochemical synthesis method is simple, non-explosive and harmless method than other conventional technique. Furthermore, the synthesized material was characterized by various analytical techniques including FESEM, EDX, XRD, EIS and electrochemical methods. Then, the synthesized TiO₂ MPs@GOS composite was applied for the electrocatalytic detection of theophylline (TPL) using CV and amperometric (current-time) techniques. Captivatingly, the modified sensor has excellent electrocatalytic performance with the wider linear range from 0.02 to 209.6 µM towards the determination of theophylline and the LOD and sensitivity of the modified sensor was calculated as 13.26 nM and 1.183 μA·µM⁻¹·cm⁻², respectively. In addition, a selectivity, reproducibility and stability of the TiO₂ MPs@GOS modified GCE were analyzed towards the determination of theophylline molecule. Finally, the real time application of TiO₂ MPs@GOS modified theophylline sensor was established in serum and drug samples.     

Facile synthesis of copper ferrite nanoparticles with chitosan composite for high-performance electrochemical sensor

Herein, the synthesis of copper ferrite nanoparticles (CuFe₂O₄ NPs)/chitosan have been prepared by sonochemical route under ultrasonic irradiation bath at 40 kHz and 50 W. A high sensitive and stable modified electrochemical sensor was developed using a composition of copper ferrite nanoparticles coordinated with biopolymer through a facile ultrasound approach. Besides, power and frequency parameters are highly important for sonochemical synthesis and specifically structure, and size of the nanomaterials development during the ultrasonic irradiation time. In this work, ultrasonic bath was used to synthesis of CuFe₂O₄ nanomaterial at 40 kHz with 1 h. CuFe₂O₄/chitosan was characterized by FESEM, EDX, XRD and electrochemical methods. Furthermore, 8-hydroxyguanine is one of biomarker by oxidative stress. The concentrations of 8-hydroxyguanine within a cell are a measurement of oxidative stress in human body. Consequently, the measurement of 8-hydroxyguanine in blood serum samples with high specificity is of greatest importance. The CuFe₂O₄/chitosan modified electrode is displayed a low detection limit of 8.6 nM and long linear range (0.025–697.175 µM).     

A feasible sonochemical approach to synthesize CuO@CeO2 nanomaterial and their enhanced non-enzymatic sensor performance towards neurotransmitter

A nanostructured and high conductive cupric oxide (CuO NPs) with hierarchical CeO₂ sheets-like structure was synthesized by a facile sonochemical approach. Furthermore, CuO/CeO₂ nanostructure is synthesized by high-intensity ultrasonic probe (Ti-horn, 50 kHz and 100 W) at ambient air. Moreover, the synthesized CuO/CeO₂ material was characterized by various analytical techniques including FESEM, EDX, XRD and electrochemical methods. Then, the synthesized CuO/CeO₂ composite was applied for the electrocatalytic detection of dopamine using CV and DPV techniques. In addition, the CuO/CeO₂ modified electrode has good electrocatalytic performance with high linear range from 0.025 to 98.5 µM towards the determination of dopamine drug and high sensitivity of the CuO/CeO₂ modified drug sensor was calculated as 16.34 nM and 4.823 μA·µM⁻¹·cm⁻², respectively. Moreover, a repeatability, reproducibility and stability of the CuO@CeO₂ mixture modified electrode were analyzed towards the determination of dopamine biomolecule. Interestingly, the real time application of CuO@CeO₂ modified electrode was established in different serum and drug samples.     

Ultrasonically assisted synthesis of barium stannate incorporated graphitic carbon nitride nanocomposite and its analytical performance in electrochemical sensing of 4-nitrophenol

We describe the ultrasonic assisted preparation of barium stannate-graphitic carbon nitride nanocomposite (BSO-gCN) by a simple method and its application in electrochemical detection of 4-nitrophenol via electro-oxidation. A bath type ultrasonic cleaner with ultrasonic power and ultrasonic frequency of 100 W and 50 Hz, respectively, was used for the synthesis of BSO-gCN nanocomposite material. The prepared BSO-gCN nanocomposite was characterized by employing several spectroscopic and microscopic techniques such as X-ray diffraction, X-ray photoelectron spectroscopy, fourier transform infra-red, field emission scanning electron microscopy, and high resolution transmission electron microscopy, to unravel the structural and electronic features of the prepared nanocomposite. The BSO-gCN was drop-casted on a pre-treated glassy carbon electrode (GCE), and their sensor electrode was utilized for electrochemical sensing of 4-nitrophenol (4-NP). The BSO-gCN modified GCE exhibited better electrochemical sensing behavior than the bare GCE and other investigated electrodes. The electroanalytical parameters such as charge transfer coefficient (α = 0.5), the rate constant for electron transfer (k_s = 1.16 s⁻¹) and number of electron transferred were calculated. Linear sweep voltammetry (LSV) exhibited increase in peak current linearly with 4-NP concentration in the range between 1.6 and 50 μM. The lowest detection limit (LoD) was calculated to be 1 μM and sensitivity of 0.81 μA μM⁻¹ cm⁻²_. A 100-fold excess of various ions, such as Ca²⁺, Na⁺, K⁺, Cl⁻, I⁻, CO₃²⁻, NO₃, NH₄⁺ and SO₄²⁻ did not able to interfere with the determination of 4-NP and high sensitivity for detecting 4-NP in real samples was achieved. This newly developed BSO-gCN could be a potential candidate for electrochemical sensor applications.     

Removal of Congo red dye from aqueous solution with nickel-based metal-organic framework/graphene oxide composites prepared by ultrasonic wave-assisted ball milling

Metal-organic frameworks (MOFs) were successfully synthesized by ultrasonic wave-assisted ball milling. In the absence of organic solvent, the coupling effect of ultrasonic wave and mechanical force played an significant role in the synthesis of MOFs. Adsorption of Congo red (CR) was studied in view of adsorption kinetic, isotherm and thermodynamics. The adsorbent was carried out using X-ray diffraction (XRD), thermogravimetric analysis (TGA), N₂ adsorption-desorption isotherms, Raman spectroscopy and scanning electron microscope (SEM) methods. It was found that pseudo-second-order kinetic model and Freundlich adsorption isotherm matched well for the adsorption of CR onto nickel-based metal-organic framework/graphene oxide composites (Ni-MOF/GO). The results of the adsorption thermodynamics indicated that the adsorption process was a spontaneous and endothermic process. The adsorption capacity of graphene oxide/metal-organic frameworks (GO/MOFs) for CR reached 2489 mg/g, much higher than previous reports. It was demonstrated that an increase in the number of active metal sites can dramatically improve the adsorption capacity of dye. A suitable dry temperature is beneficial for the improvement of adsorption capacity for dye. In this paper, the adsorption results indicated that ultrasonic wave-assisted ball milling has a good prospect for synthesis of MOFs with excellent adsorption performance.     

Mn-doped activated carbon aerogel as electrode material for pseudo-capacitive supercapacitor: Effect of activation agent

Carbon aerogel (CA) was prepared by a sol-gel polymerization of resorcinol and formaldehyde, and a series of activated carbon aerogels (ACA-X, X = H₃PO₄, K₂CO₃, KOH, and ZnCl₂) were then prepared by a chemical activation using different activation agent (X represented an activation agent). Specific capacitances of activated carbon aerogels were measured by cyclic voltammetry and galvanostatic charge/discharge methods in 6 M KOH electrolyte. Among the samples prepared, ACA-K₂CO₃ showed the highest specific capacitance (152 F/g). In order to combine excellent electrochemical performance of activated carbon aerogel with pseudo-capacitive property of manganese oxide, 7 wt% manganese oxide was doped on activated carbon aerogels (Mn/ACA-X) by an incipient wetness impregnation method. Capacitance measurements revealed that Mn/ACA-K₂CO₃ showed the highest specific capacitance (189 F/g). The enhanced capacitance of Mn/ACA-K₂CO₃ was attributed to the fine pore structure and outstanding electric properties of activated carbon aerogel as well as the faradaic redox reactions of manganese oxide.     

The role of passive potential in ultrasonic cavitation erosion of titanium in 1 M HCl solution

The influence of the applied passive potential on the ultrasonic cavitation erosion of Ti specimen in 1 M HCl solution was investigated by mass loss experiment, scanning electron microscopy (SEM), electrochemical impedance spectra (EIS) and Mott–Schottky plot. The results showed that Ti was in the passive state within the potential region from −0.3 V_SCE to 1.5 V_SCE under ultrasonic cavitation erosion. The applied passive potential can obviously decrease the mass loss of Ti caused by ultrasonic cavitation erosion in 1 M HCl solution. The resistance of the passive film increased, the flat band potential moved to positive direction, and the donor density of the passive film decreased with increasing the passive potential. Finally, a physical model was provided to explain the experimental results based on energy band and semi-conductive theories.     

Effect of dc bias on the compositional ratio of WNX thin films prepared by rf-dc coupled magnetron sputtering

The effect of the dc bias on the compositional ratio, resistivity, and deposition rate for tungsten nitride (WN_X) films prepared by rf-dc coupled magnetron sputtering have been investigated in detail. The value of the film compositional ratio (N/W) is significantly decreased from 0.8 to 0.2 with increasing the target dc bias voltage. The increase of the target dc bias voltage from −100 to −500 V results in a dramatical decrease in the resistivity of WN_X films. It is shown that the N/W ratio and the resistivity of WN_X thin films deposited at the target dc bias voltage of −200 V are about 0.5 and 370 μΩ cm, respectively.     

Study on ultrasound-assisted precipitation for preparing Ni/Al2O3 catalyst

With the rapid development of oil hydrogenation industry, the development of oil hydrogenation catalyst has also become a research hotspot. In this paper, ultrasound-assisted precipitation technique is used to prepare Ni/Al₂O₃ catalyst. The effect of ultrasonic output power on catalyst performance is investigated. The prepared catalyst is applied to the hydrogenation reaction of castor oil. It is found that the prepared catalyst shows the best hydrogenation performance when ultrasonic output power, frequency and ultrasonic treatment time are 80 W, 40 kHz and 600 min respectively. It also indicates that ultrasound-assisted precipitation technique can reduce the particle size and increase the specific surface area of Ni/Al₂O₃ catalyst so that its activity is improved. In addition, six important elements that should be considered in the development of industrial oil refining catalysts are discussed, and the effects of these factors on the catalyst performance are discussed. Finally, new way for improving catalyst performance is given, and the application of some new materials and methods in oil refining is introduced.     

Ultrasonic-assisted hydrothermal synthesis of cobalt oxide/nitrogen-doped graphene oxide hybrid as oxygen reduction reaction catalyst for Al-air battery

A persistent ultrasound-assisted hydrothermal method has been developed to prepare cobalt oxide incorporated nitrogen-doped graphene (Co₃O₄/N-GO) hybrids. The electrochemical behaviors and catalytic activity of the prepared hybrids have been systematically investigated as cathode materials for Al-air battery. The results show that ultrasonication can promote the yield ratio of Co₃O₄ from 63.1% to 70.6%. The prepared Co₃O₄/N-GO hybrid with ultrasonication exhibits better ORR activity over that without ultrasonication. The assembled Al-air battery using the ultrasonicated Co₃O₄/N-GO hybrid exhibited an average working voltage of 1.02 V in 4 M KOH electrolyte at 60 mA∙cm⁻², approximately 60 mV higher than that using hybrid without ultrasonication. This should be attributed to large number density of fine Co₃O₄ particles growing on the dispersed GO sheets under the persistent ultrasonication. The related ultrasonic mechanism has been discussed in details.     

Layered nanocomposite of zinc sulfide covered reduced graphene oxide and their implications for electrocatalytic applications

Herein, we have synthesized zinc sulfide nanospheres (ZnS NPs) encapsulated on reduced graphene oxide (RGO) hybrid by an ultrasonic bath (50 kHz/60 W). The physical and structural properties of ZnS NPs@RGO hybrid were analyzed by TEM, XRD, EIS and EDS. As-prepared ZnS NPs@RGO hybrid was applied towards the electrochemical determination of caffeic acid (CA) in various food samples. The ZnS NPs@RGO hybrid modified electrode (GCE) exhibited an excellent electrocatalytic performance towards caffeic acid detection and determination, when compared to other modified electrodes. Therefore, the electrochemical sensing performance of the fabricated and nanocomposite modified electrode was significantly improved owing to the synergistic effect of ZnS NPs and RGO catalyst. Furthermore, the hybrid materials provide highly active electro-sites as well as rapid electron transport pathways. The proposed electrochemical caffeic acid sensor produces a wide linear range of 0.015–671.7 µM with a nanomolar level detection limit (3.29 nM). In addition, the real sample analysis of the proposed sensor has applied to the determination of caffeic acid in various food samples.     

Electrochemical characterization of mixed conducting and composite SOFC cathodes

The electrochemical performance of La_0.58Sr_0.4Co_0.2Fe_0.8O_3−δ (L58SCF), La_0.9Sr_1.1FeO_4−δ (LS2F) and LSM (La_0.65Sr_0.3MnO_3−δ)/LSM–YSZ (50 wt.% LSM–50 wt.% ZrO₂ (8 mol% Y₂O₃)) cathode electrodes interfaced to a double layer Ce_0.8Gd_0.2O_2−δ (CGO)/YSZ electrolyte was studied in the temperature range of 600 to 850 °C and under flow of 21% O₂/He mixture, using impedance spectroscopy and current density–overpotential measurements. The L58SCF cathode exhibited the highest electrocatalytic activity for oxygen reduction, according to the order: LS2F/CGO/YSZ ≤ LSM/LSM–YSZ/CGO/YSZ < L58SCF/CGO/YSZ.     

Preparation of carbon supported Pt-P catalysts and its electrocatalytic performance for oxygen reduction

The carbon supported PtP (PtP/C) catalysts were synthesized from Pt(NO₃)₂ and phosphorus yellow at the room temperature. The content of P in the PtP/C catalysts prepared with this method is high and the average size of the PtP particles is decreased with increasing the content of P. The electrocatalytic performances of the PtP/C catalysts prepared with this method for the oxygen reduction reaction (ORR) are better than that of the commercial Pt/C catalyst. The promotion action of P for enhancing the electrocatalytic performance of the PtP/C catalyst for ORR is mainly due to that Pt and P form the alloy and then the electron density of Pt is decreased.