Synthesis of Graphite Oxide/Cobalt Molybdenum Oxide Hybrid Nanosheets for Enhanced Electrochemical Performance in Supercapacitors and the Oxygen Evolution Reaction

Hydrothermally designed Ag-modified TiO2heterogeneous nanocatalysts for efficient hydrogen evolution by photo/electro/photoelectro-chemical water splitting

One compelling goal of carbon-neutrality is to advance sustainable energy applications through advanced functional nanomaterials for achieving remarkable performance in energy conversion processes, especially in green H2energy. Here, Ag-modified TiO2nanostructures with highly specific exposed surface sites have been fabricated hydrothermally, elucidating its prominence towards photocatalytic, and photo/-electrocatalytic H2production. Further, the as-synthesized nanomaterials were investigated by XRD, electron microscopy (SEM/EDAX/TEM/HRTEM), ICP-MS, PL, Raman, UV-visible DRS, and BET surface area studies. The enhanced activity was established due to the exceptional optoelectronic properties and highly exposed active sites of the Ag-modified TiO2nanocatalysts. The photocatalytic activity of 2.5% Ag-doped TiO2photocatalyst demonstrated the highest hydrogen evolution, measuring 15.66 mmolgcat-1with 17.33% apparent quantum yield. Moreover, for photo-electrolysis, 1% and 2.5% Ag-doped TiO2nanocatalysts exhibited significantly improved activity with Tafel slopes of 162.49, 87.56 mV dec-1and onset potentials of 0.77 V (at 1.55 mA cm-2), -0.96 V (at 10 mA cm-2) for oxygen evolution reaction and hydrogen evolution reaction in alkaline and acidic conditions. Experiments indicated that incorporation of Ag ions in TiO2boosted the H2evolution due to the extraordinary surface properties and the presence of defect-sides /oxygen vacancies.

Biomass-Derived-Carbon-Supported Spinel Cobalt Molybdate as High-Efficiency Electrocatalyst for Oxygen Evolution Reaction

Ananas comosus leaves were converted to a porous graphitized carbon (GPLC) material via a high-temperature pyrolysis method by employing iron salt as a catalyst. A cobalt molybdate (CoMoO4)-and-GPLC composite (CoMoO4/GPLC) was then prepared by engineering CoMoO4 nanorods in situ, grown on GPLC. N2 adsorption-desorption isothermal curves and a pore size distribution curve verify that the proposed composite possesses a porous structure and a large specific surface area, which are favorable for charge and reactant transport and the rapid escape of O2 bubbles. Consequently, the as-synthesized CoMoO4/GPLC shows low overpotentials of 289 mV and 399 mV to afford the current densities of 10 mA cm-2 and 100 mA cm-2 towards the oxygen evolution reaction (OER), which is superior to many CoMoO4-based catalysts in previous studies. In addition, the decrease in current density is particularly small, with a reduction rate of 3.2% after a continuous OER procedure for 30 h, indicating its good stability. The excellent performance of the CoMoO4/GPLC composite proves that the GPLC carrier can obviously impel the catalytic activity of CoMoO4 by improving electrical conductivity, enhancing mass transport and exposing more active sites of the composite. This work provides an effective strategy for the efficient conversion of waste ananas comosus leaves to a biomass-derived-carbon-supported Co-Mo-based OER electrocatalyst with good performance, which may represent a potential approach to the development of new catalysts for OER, as well as the treatment of waste biomass.

Cobalt molybdate nanoflowers decorated bio-waste derived porous activated carbon nanocomposite: A high performance electrode material for supercapacitors

In this work, we report a supercapacitor electrode material based on nano-flower like cobalt molybdate decorated on porous activated carbon derived from waste onion peels (β-CoMoO4-POAC). The obtained POAC exhibits highly porous structure and after the hydrothermal treatment with salts of cobalt and molybdenum, we observed a uniform distribution of β-cobalt molybdate (β-CoMoO4) as nano-flowers on the surface of POAC. The chemical composition, morphology and porosity of the materials were thoroughly analyzed using field emission scanning electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, infrared spectroscopy and Brunauer-Emmet-Teller surface area measurement. Due to its flower like and highly porous morphology, β-CoMoO4@POAC exhibits a high specific capacitance of 1110.72 F/g at a current density of 1 mA/cm2 with superior cyclic retention of 96.03% after 2000 cycles. The best electrochemical performance exhibited by β-CoMoO4@POAC is mainly due to its high surface area and porous nature of the material which assists in active transport of ions. This study reveals the exceptional electrochemical properties of β-CoMoO4@POAC which could be considered as a potential material for advanced energy storage devices.

Modification of TiO2 nanotubes by graphene-strontium and cobalt molybdate perovskite for efficient hydrogen evolution reaction in acidic medium

Herein, we demonstrate that modification of TiO₂ nanotubes with graphene-strontium and cobalt molybdate perovskite can turn them into active electrocatalysts for hydrogen evolution reaction (HER). For this purpose, a simple method of hydrothermal synthesis of perovskites was developed directly on the TiO₂ nanotubes substrate. Moreover, the obtained hybrids were also decorated with graphene oxide (GO) during one-step hydrothermal synthesis. The obtained materials were characterized by scanning electron microscopy with energy dispersive X-ray analysis, Raman spectroscopy, and X-ray diffraction analysis. Catalytic properties were verified by electrochemical methods (linear voltammetry, chronopotentiometry). The obtained hybrids were characterized by much better catalytic properties towards hydrogen evolution reaction compared to TiO₂ and slightly worse than platinum. The optimized hybrid catalyst (decorated by GO) can drive a cathodic current density of 10 mA cm^-2 at an overpotential of 121 mV for HER with a small Tafel slope of 90 mV dec^-1 in 0.2 M H₂SO₄.

Chemical fabrication, structural characterization and photocatalytic water splitting application of Sr-doped SnO2nanoparticles

Semiconductor photocatalysis has gained considerable attention in recent years due to their enabling nature to convert solar energy into fuels of renewable hydrocarbon. However, many of them suffer from some drawbacks like the inability to visible light irradiation and wide band gaps. Herein, we have synthesized monophasic strontium (Sr) doped SnO₂nanoparticles by a cost-effective and environmental friendly hydrothermal method. As-synthesized nanoparticles showed rutile crystalline structure with irregular and rough cubical shape and no other elemental impurities. Sr-doped SnO₂nanoparticles show a constant decrease in bandgap with increasing dopant concentration, which is estimated for excellent photocatalytic activity. The photocatalytic water splitting of as-prepared Sr-doped SnO₂nanoparticles for H₂generation shows a large influence of the increasing dopant concentration related to the narrowing bandgap on H₂generation rate. Hence, the tunable bandgap with adjusted dopant concentration indicates that band gap tuning through doping for produced nanostructures may open up a new opportunities for photocatalytic and other optoelectronic applications.

3D CoMoO4 nanoflake arrays decorated disposable pencil graphite electrode for selective and sensitive enzyme-less electrochemical glucose sensors

Three-dimensional (3D) cobalt molybdate (CoMoO₄) hierarchical nanoflake arrays on pencil graphite electrode (PGE) (CoMoO₄/PGE) are actualized via one-pot hydrothermal technique. The morphological features comprehend that the CoMoO₄ nanoflake arrays expose the 3D, open, porous, and interconnected network architectures on PGE. The formation and growth mechanisms of CoMoO₄ nanostructures on PGE are supported with different structural and morphological characterizations. The constructed CoMoO₄/PGE is operated as an electrocatalytic probe in enzyme-less electrochemical glucose sensor (ELEGS), confronting the impairments of cost- and time-obsessed conventional electrode polishing and catalyst amendment progressions and obliged the employment of a non-conducting binder. The wide-opened interior and exterior architectures of CoMoO₄ nanoflake arrays escalate the glucose utilization efficacy, whilst the intertwined nanoflakes and graphitic carbon layers, respectively, of CoMoO₄ and PGE articulate the continual electron mobility and catalytically active channels of CoMoO₄/PGE. It jointly escalates the ELEGS concerts of CoMoO₄/PGE including high sensitivity (1613 μA mM^-1 cm^-2), wide linear glucose range (0.0003-10 mM), and low detection limit (0.12 µM) at a working potential of 0.65 V (vs. Ag/AgCl) together with the good recovery in human serum. Thus, the fabricated CoMoO₄/PGE extends exclusive virtues of modest electrode production, virtuous affinity, swift response, and excellent sensitivity and selectivity, exposing innovative prospects to reconnoitring the economically viable ELEGSs with binder-free, affordable cost, and expansible 3D electrocatalytic probes.

Investigation of enhanced electro-catalytic HER/OER performances of copper tungsten oxide@reduced graphene oxide nanocomposites in alkaline and acidic media

In this paper, we investigate the electro-catalytic hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) of synthesized copper tungsten oxide@reduced graphene oxide (CuWO4@rGO) nanocomposites.

Preparation of ZnCo2O4@PANI core/shell nanobelts for high-performance asymmetric supercapacitors

ZnCo2O4@PANI core/shell nanobelts with excellent sufficient material utilization efficiency and good electronic conductivity have been synthesized, and they exhibit excellent performance in supercapacitor applications.

Insights into the Antimicrobial Activity of Hydrated Cobaltmolybdate Doped with Copper

Molybdates are biocidal materials that can be useful in coating surfaces that are susceptible to contamination and the spread of microorganisms. The aim of this work was to investigate the effects of copper doping of hydrated cobalt molybdate, synthesized by the co-precipitation method, on its antibacterial activity and to elucidate the structural and morphological changes caused by the dopant in the material. The synthesized materials were characterized by PXRD, Fourier Transformed Infrared (FTIR), thermogravimetric analysis/differential scanning calorimetry (TG/DSC), and SEM-Energy Dispersive Spectroscopy (SEM-EDS). The antibacterial response of the materials was verified using the Minimum Inhibitory Concentration (MIC) employing the broth microdilution method. The size of the CoMoO₄·1.03H₂O microparticles gradually increased as the percentage of copper increased, decreasing the energy that is needed to promote the transition from the hydrated to the beta phase and changing the color of material. CoMoO₄·1.03H₂O obtained better bactericidal performance against the tested strains of Staphylococcus aureus (gram-positive) than Escherichia coli (gram-negative). However, an interesting point was that the use of copper as a doping agent for hydrated cobalt molybdate caused an increase of MIC value in the presence of E. coli and S. aureus strains. The study demonstrates the need for caution in the use of copper as a doping material in biocidal matrices, such as cobalt molybdate.

Efficient Multifunctional Catalytic and Sensing Properties of Synthesized Ruthenium Oxide Nanoparticles

Ruthenium oxide is one of the most active electrocatalyst for oxygen evolution (OER) and oxygen reduction reaction (ORR). Herein, we report simple wet chemical route to synthesize RuO2 nanoparticles at controlled temperature. The structural, morphological and surface area studies of the synthesized nanoparticles were conducted with X-ray diffraction, electron microscopy and BETsurface area studies. The bifunctional electrocatalytic performance of RuO2 nanoparticles was studied under different atmospheric conditions for OER and ORR, respectively, versus reversible hydrogen electrode (RHE) in alkaline medium. Low Tafel slopes of RuO2 nanoparticles were found to be ~47 and ~49 mV/dec for OER and ORR, respectively, in oxygen saturated 0.5 M KOH system. Moreover, the catalytic activity of RuO2 nanoparticles was examined against the Horseradish peroxidase enzyme (HRP) at high temperature, and the nanoparticles were applied as a sensor for the detection of H2O2 in the solution.