Hierarchical CoMoO4 nanoneedle electrodes for advanced supercapacitors and electrocatalytic oxygen evolution

MoS2/CoMoO4 composite heterogeneous catalyst towards enhanced activation of peroxymonosulfate for the efficient degradation of tetracycline hydrochloride

In this research, a composite catalyst of MoS2-modified CoMoO4 (MoS2/CoMoO4) was effectively synthesized and utilized to activate peroxymonosulfate (PMS) for the removal of tetracycline hydrochloride (TCH) in water. It was found that the MoS2/CoMoO4/PMS system possessed a greater ability to eliminate TCH compared with CoMoO4/PMS system. The experimental results demonstrated that the 0.6-MoS2/CoMoO4/PMS system eliminated 92.1% TCH (15 mg/L) and removed 50.3% TOC within 30 min under the conditions of 40mg/L 0.6-MoS2/CoMoO4 and 0.5mM PMS. The main active substances produced by MoS2/CoMoO4 activated PMS were sulfate radicals (SO4•-), hydroxyl radicals (•OH), singlet oxygen (1O2), and superoxide radicals (O2•-), as determined by scavenging experiments and EPR analyses. Probable catalytic mechanism of 0.6-MoS2/CoMoO4 for activating PMS was proposed from two aspects: one is the synergy of Co3+/Co2+ and Mo6+/Mo4+ cycles in 0.6-MoS2/CoMoO4/PMS system; on the other hand, the low valence molybdenum and sulfur promoted the Co3+/Co2+ redox recycle during PMS activation. After four reuses, the removal performance of TCH still reached 85.1%, and the crystal structure and the element compositions of the catalyst did not alter, implying that 0.6-MoS2/CoMoO4 composite had good reusability. Thus,0.6-MoS2/CoMoO4 composite has broad application prospects in removing organic contaminants.

Decoration of Ag nanoparticles on CoMoO4 rods for efficient electrochemical reduction of CO2

Hydrothermal and photoreduction/deposition methods were used to fabricate Ag nanoparticles (NPs) decorated CoMoO4 rods. Improvement of charge transfer and transportation of ions by making heterostructure was proved by cyclic voltammetry and electrochemical impedance spectroscopy measurements. Linear sweep voltammetry results revealed a fivefold enhancement of current density by fabricating heterostructure. The lowest Tafel slope (112 mV/dec) for heterostructure compared with CoMoO4 (273 mV/dec) suggested the improvement of electrocatalytic performance. The electrochemical CO2 reduction reaction was performed on an H-type cell. The CoMoO4 electrocatalyst possessed the Faraday efficiencies (FEs) of CO and CH4 up to 56.80% and 19.80%, respectively at  - 1.3 V versus RHE. In addition, Ag NPs decorated CoMoO4 electrocatalyst showed FEs for CO, CH4, and C2H6 were 35.30%, 11.40%, and 44.20%, respectively, at the same potential. It is found that CO2 reduction products shifted from CO/CH4 to C2H6 when the Ag NPs deposited on the CoMoO4 electrocatalyst. In addition, it demonstrated excellent electrocatalytic stability after a prolonged 25 h amperometric test at  - 1.3 V versus RHE. It can be attributed to a synergistic effect between the Ag NPs and CoMoO4 rods. This study highlights the cooperation between Ag NPs on CoMoO4 components and provides new insight into the design of heterostructure as an efficient, stable catalyst towards electrocatalytic reduction of CO2 to CO, CH4, and C2H6 products.

Exploring the Effects of Various Two-Dimensional Supporting Materials on the Water Electrolysis of Co-Mo Sulfide/Oxide Heterostructure

In this study, various two-dimensional (2D) materials were used as supporting materials for the bimetallic Co and Mo sulfide/oxide (CMSO) heterostructure. The water electrolysis activity of CMSO supported on reduced graphene oxide (rGO), graphite carbon nitride (gC3N4), and siloxene (SiSh) was better than that of pristine CMSO. In particular, rGO-supported CMSO (CMSO@rGO) exhibited a large surface area and a low interface charge-transfer resistance, leading to a low overpotential and a Tafel slope of 259 mV (10 mA/cm2) and 85 mV/dec, respectively, with excellent long-term stability over 40 h of continuous operation in the oxygen evolution reaction.

Heteroatom-Doped Amorphous Cobalt-Molybdenum Oxides as a Promising Catalyst for Robust Hydrogen Evolution

The simultaneous manipulation of the catalytic activity and intrinsic electrical conductivity in a unified system is difficult yet meaningful to unravel the possible strategy that can enhance the hydrogen evolution reaction (HER) performance. Therefore, we propose a simple strategy to enhance the HER performance based on low-temperature redox reaction with ZIF-67@ZIF-8 as a sacrificial template to prepare zinc-doped amorphous CoMo₈O_x (denoted as Zn/aCMO). Benefiting from the excellent compositional- and amorphous-based structural advantages of more exposure active sites, optimized electron transfer as well as a stable frame structure, the as-prepared electrode can drive hydrogen evolution at current densities of 10, 50, and 100 mA cm^-2, which need ultralow overpotentials of 59, 138, and 189 mV, respectively, and the Tafel slope of the electrode was 66.2 mV dec^-1 (1 M KOH). Meanwhile, the intrinsic activity of the prepared low-cost electrocatalyst was also determined, and the turnover frequency was up to 1.49 s^-1 at an overpotential of 100 mV. In addition, after continuous testing for 160 h, there was a slight decay at the overpotential of 130 mV.

A hybrid NiCo2O4@NiMoO4 structure for overall water splitting and excellent hybrid energy storage

In this study, a two-step hydrothermal method is used to prepare NiCo2O4@NiMoO4 nanoscale materials for periodic stability supercapacitors. The synthesized product can be directly used as the electrode material of the supercapacitor, and its specific capacitance is 685.7 C g-1. The composite electrode NiCo2O4@NiMoO4 is used as the positive electrode and the hybrid capacitor is assembled. Meanwhile, at the power density of 4050 W kg-1, the energy density is 96.3 W h kg-1, and the capacitance retention is 100% after 10 000 cycles. At the same time, when the composite is used as a catalyst, it exhibits OER overvoltage (300 mV), HER overvoltage (170 mV) and a low battery voltage of 1.65 V at 10 mA cm-2. After 14 hours of long-term use, NiCo2O4@NiMoO4 maintained good stability, indicating that its structure further improved the electrochemical performance, providing a great advantage for the study of low-cost electrode materials for overall water splitting.

CoMoO4 nanobelts as efficient peroxidase mimics for the colorimetric determination of H2O2

CoMoO₄ materials were prepared through a simple hydrothermal method and developed as highly efficient peroxidase mimics for colorimetric determination of H₂O₂. Based on the different experimental conditions in the synthesis process, the CoMoO₄ materials present distinct morphologies, structures, surface properties, and peroxidase mimetic activities. Among them, CoMoO₄ nanobelts (NBs) display the best intrinsic peroxidase mimetic abilities due to the high-energy (100) facet exposed, more Co active sites at (100) facet, more negative potential, and larger specific surface area. It can efficiently catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of H₂O₂ to generate a blue oxide. In view of the excellent peroxidase mimetic catalytic activity of CoMoO₄ NBs, a rapid, convenient, and ultrasensitive method was successfully established for the visual and colorimetric determination of H₂O₂. The method exhibits good selectivity, practicability, stability, and reusability, and has a detection limit of 0.27 μM. The peroxidase mimetic catalytic mechanism of CoMoO₄ NBs was illustrated according to the kinetic and active species trapping experiments. The method has a good potential for rapid and sensitive determination of H₂O₂ for biomedical analysis. Graphical abstract Schematic presentation of the process of CoMoO₄ nanobelts catalyzing the oxidation of peroxidase substrate 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of H₂O₂ to generate a typical blue color, which can be applied in rapid and ultrasensitive detection of H₂O₂ visually.

3D Hierarchically Mesoporous Zinc-Nickel-Cobalt Ternary Oxide (Zn0.6Ni0.8Co1.6O4) Nanowires for High-Performance Asymmetric Supercapacitors

Increased efforts have been devoted recently to develop high-energy-density supercapacitors (SC) without renouncing their power efficiency. Herein, a hierarchically mesoporous nanostructure of zinc-nickel-cobalt oxide (ZNCO) nanowires (NWs) is constructed by hierarchical aggregation of ZNCO nanoparticles. It is worth noting that cobalt and nickel rich lattice imparts higher charge storage capability by enhanced reversible Faradaic reaction while zinc provides structural stability and higher conductivity. Moreover, particulate nature of ZNCO NWs allows deep diffusion of electrolyte thus enabling reversible charge storage under higher current densities. The as-prepared ZNCO NWs exhibited excellent specific capacitance of 2082.21 F g⁻¹ at the current density of 1 A g⁻¹ with high stability up to 5,000 charge-discharge cycles. Further, the asymmetric SC device was assembled using ZNCO NWs (ZNCO NWs//MWCNTs) which exhibited high energy density of 37.89 Wh kg⁻¹ and excellent capacitance retention up to 88.5% over 1,000 cycles. This work presents ways to construct multi-component high-energy-density materials for next-generation energy storage devices.

Controlled Synthesis of Cr-Co0.85 Se Nanoarrays for Water Splitting at an Ultralow Cell Voltage of 1.43 V

Water splitting has attracted more and more attention as a promising strategy for the production of clean hydrogen fuel. In this work, a new synthesis strategy was proposed, and Co_0.85 Se was synthesized on nickel foam as the main matrix. The doping of appropriate Cr amount into the target of Co_0.85 Se and the Cr-Co_0.85 Se resulted in an excellent electrochemical performance. The doping of Cr introduces Cr³⁺ ions which substitute Co²⁺ and Co³⁺ ions in Co_0.85 Se, so that the lattice parameters of the main matrix were changed. It is worth noting that the Cr0.15-Co_0.85 Se/NF material exhibits an excellent performance in the oxygen evolution reaction (OER) test. When the current density reaches 50 mA cm^-2 for OER, the overpotential is only 240 mV. For the hydrogen evolution reaction (HER) tests, the overpotential is only 117 mV to drive 10 mA cm^-2 of current density. Moreover, when the Cr0.15-Co_0.85 Se/NF material is used as a two-electrode device for whole water splitting, the required cell voltage is only 1.43 V to reach a current density of 10 mA cm^-2 , which is among the lowest values of the published catalysts up to now. In addition, the Cr0.15-Co_0.85 Se/NF catalyst also exhibits excellent stability during a long period of water splitting. The experimental result demonstrates that the change of the lattice structure has an obvious influence on the electrocatalytic activity of the material. When an external electric field is applied, it facilitates the rapid electron transfer rate and enhances the electrocatalytic performance and stability of the material.

Synthesis of NiMoO4/3D-rGO Nanocomposite in Alkaline Environments for Supercapacitor Electrodes

Although Graphene oxide (GO)-based materials is known as a favorable candidate for supercapacitors, its conductivity needs to be increased. Therefore, this study aimed to investigate the performance of GO-based supercapicitor with new methods. In this work, an ammonia solution has been used to remove the oxygen functional groups of GO. In addition, a facile precipitation method was performed to synthesis a NiMoO4/3D-rGO electrode with purpose of using synergistic effects of rGO conductivity properties as well as NiMoO4 pseudocapacitive behavior. The phase structure, chemical bands and morphology of the synthesized powders were investigated by X-ray diffraction (XRD), Raman spectroscopy, and field emission secondary electron microscopy (FE-SEM). The electrochemical results showed that the NiMoO4/3D-rGO(II) electrode, where ammonia has been used during the synthesis, has a capacitive performance of 932 Fg−1. This is higher capacitance than NiMoO4/3D-rGO(I) without using ammonia. Furthermore, the NiMoO4/3D-rGO(II) electrode exhibited a power density of up to 17.5 kW kg−1 and an energy density of 32.36 Wh kg−1. These results showed that ammonia addition has increased the conductivity of rGO sheets, and thus it can be suggested as a new technique to improve the capacitance.

Morphology-controlled synthesis of CoMoO4 nanoarchitectures anchored on carbon cloth for high-efficiency oxygen oxidation reaction

Novel CoMoO₄ nanoarrays with different morphologies are anchored on a carbon cloth via a simple hydrothermal method by adjusting the Co/Mo atom ratio. The in situ growth and tight immobilization of the CoMoO₄ nanocomposite on the carbon cloth can facilitate the electrolyte infiltration and electrons transfer rate at the contact interface. Therefore, the free-standing electrode of CoMoO₄/carbon cloth with interconnected nanosheets shows superior electrocatalytic activity, and the overpotential of 286 mV is obtained at 15 mA cm⁻² in alkaline solution. Moreover, the catalyst also exhibits a small Tafel slope of 67 mV dec⁻¹ as well as good stability. The relationship between the active material morphology, contact interface and the electrocatalytic performance is also discussed. As the carbon cloth is commercially available, this simple but effective structural controlling method demonstrates a new large-scale practical electrode fabrication technique for high performance OER electrodes and large-scale water splitting.

Novel CoMoO₄ nanoarrays with different morphologies are anchored on a carbon cloth via a simple hydrothermal method by adjusting the Co/Mo atom ratio.

Efficient aerobic oxidative desulfurization over Co–Mo–O bimetallic oxide catalysts

Co–Mo–O bimetallic oxides were prepared as efficient catalysts for aerobic oxidative desulfurization with oxygen in air as the oxidant.

Humid atmospheric pressure plasma jets exposed micro-defects on CoMoO4 nanosheets with enhanced OER performance

A novel humid APPJs method was adopted to treat CoMoO₄ nanosheet arrays resulting in micro-defects and more reaction intermediates that led to an enhanced OER property.

Oxygen vacancy-confined CoMoO4@CoNiO2 nanorod arrays for oxygen evolution with improved performance

Experimental and DFT calculation results show that the presence of oxygen vacancies can decrease the adsorption energy of intermediates at active sites and facilitate the adsorption of intermediates, thus improving the catalytic properties.

Hierarchically Designed Ag@Ce6Mo10O39 Marigold Flower-Like Architectures: An Efficient Electrode Material for Hybrid Supercapacitors

We facilely prepared silver nanoparticle-decorated Ce₆Mo₁₀O₃₉ marigold flower-like structures (Ag NPs@CM MFs) for use as an effective positive material in hybrid supercapacitors (HSCs). With the aid of ethylenediaminetetraacetic acid (EDTA) as a chelating agent, self-assembled CM MFs were synthesized by a single-step hydrothermal method. When the electrochemical properties were tested in an aqueous alkaline electrolyte, the synthesized CM MFs with 0.15 g of EDTA exhibited a relatively high charge storage property (55.3 μA h/cm² at 2 mA/cm²) with a battery-type redox behavior. The high capacity performance is mainly because of the large surface area of the CM MFs, and the hierarchically connected nanoflakes provide wide open wells for rapid accessibility of electrolyte ions and enable fast transportation of electrons. A further improvement in electrochemical performance was achieved (62 μA h/cm² at 2 mA/cm²) by decorating Ag NPs on the surface of the CM MFs (i.e., Ag NPs@CM MFs), which is attributed to the increased electric conductivity. Considering the synergistic effect and the high electrochemical activity, Ag NPs@CM MFs were further employed as an effective positive electrode for the fabrication of pouch-type HSC with porous carbon (negative electrode) in an alkaline electrolyte. The HSC exhibited a high cell potential (1.5 V) with maximum energy and power densities of 0.0183 mW h/cm² and 10.237 mW/cm², respectively. The potency of HSC in practical applications was also demonstrated by energizing red and yellow light-emitting diodes as well as a three-point pattern torch light.

Heteroatom-doped porous carbons derived from moxa floss of different storage years for supercapacitors

Two novel carbons (MCs) derived from moxa floss of different storage years have been prepared by two low-cost and facile approaches, which are hydrothermal carbonization at a low temperature (200 °C) and direct pyrolysis at a moderate temperature (500 °C) followed by potassium hydroxide (KOH) activation strategy at a high temperature (800 °C), respectively. The physicochemical properties of MCs are investigated by Raman spectra, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and nitrogen adsorption-desorption isotherms. Results show that MCs derived from moxa floss of different storage years by two facile approaches possess different morphologies: MCs by hydrothermal carbonization (denoted as MC-1, MC-2 and MC-3) exhibit porous nanosheet structures, the highest specific surface area is about 1788.6 m2 g-1, and the largest total pore volumes is around 0.8170 cm3 g-1, while MCs by direct pyrolysis (denoted as MC-4, MC-5 and MC-6) have basically blocky and rod-like morphologies, the highest specific surface area is about 1628.0 m2 g-1, and the largest total pore volume is around 0.7058 cm3 g-1. However, despite the different morphologies, all MCs possess a similar hierarchical porous structure, numerous heteroatom groups and good electrical conductivity. Therefore, these low-cost, biomass-derived porous carbons with promising capacitive performance are used for supercapacitors application with high performance, for example, the as-assembled supercapacitor based on MC-5 exhibits a high specific capacitance of 288.3 F g-1 at 0.25 A g-1, an excellent rate performance of 243.5 F g-1 even at 30 A g-1 with 84.5% capacitance retention of its initial specific capacitance, and an outstanding long-term cycling stability with 98.7% capacitance retention after 10 000 cycles at 5 A g-1. Furthermore, the maximum energy density for these supercapacitors with an aqueous electrolyte in a two-electrode system is about 10.0 W h kg-1 at a power density of 70.3 W kg-1. Therefore, this work opens up a whole new field for the applications of moxa floss and this novel concept of moxa floss use is an extremely promising strategy for developing high-performance carbons with porous structures and heteroatom-doping from renewable sources.