MnCo2O4/NiCo2O4/rGO as a Catalyst Based on Binary Transition Metal Oxide for the Methanol Oxidation Reaction.

The demands for alternative energy have led researchers to find effective electrocatalysts in fuel cells and increase the efficiency of existing materials. This study presents new nanocatalysts based on two binary transition metal oxides (BTMOs) and their hybrid with reduced graphene oxide for methanol oxidation. Characterization of the introduced three-component composite, including cobalt manganese oxide (MnCo2O4), nickel cobalt oxide (NiCo2O4), and reduced graphene oxide (rGO) in the form of MnCo2O4/NiCo2O4/rGO (MNR), was investigated by X-ray diffraction (XRD), scanning electron microscope (SEM), and energy-dispersive X-ray (EDX) analyses. The alcohol oxidation capability of MnCo2O4/NiCo2O4 (MN) and MNR was evaluated in the methanol oxidation reaction (MOR) process. The crucial role of rGO in improving the electrocatalytic properties of catalysts stems from its large active surface area and high electrical conductivity. The alcohol oxidation tests of MN and MNR showed an adequate ability to oxidize methanol. The better performance of MNR was due to the synergistic effect of MnCo2O4/NiCo2O4 and rGO. MN and MNR nanocatalysts, with a maximum current density of 14.58 and 24.76 mA/cm2 and overvoltage of 0.6 and 0.58 V, as well as cyclic stability of 98.3% and 99.7% (at optimal methanol concentration/scan rate of 20 mV/S), respectively, can be promising and inexpensive options in the field of efficient nanocatalysts for use in methanol fuel cell anodes.

Binary mixed molybdenum cobalt sulfide nanosheets decorated on rGO as a high-performance supercapacitor electrode.

This work represents the production of MoS2/CoS2 hybridized with rGO as a material for high-performance supercapacitors. The hydrothermal method is used for the synthesis. The as-prepared material is characterized by x-ray diffraction spectroscopy, x-ray photoelectron spectroscopy, and electron microscopy. The size of the nanoparticles is estimated at 80 nm, and their uniform dispersion on rGO is observed from electron microscopy images. A high-specific capacitance of 190 mF cm-2 obtains for MoS2/CoS2/rGO at the current density of 0.5 mA cm-2 in 2 M KOH. The cyclic stability over 5000 cycles at a scan rate of 100 mV s-1 shows that the MoS2/CoS2/rGO electrode is stable, and 88.6% of its initial capacitance sustains at the end of 5000 cycles. This excellent performance is assigned to the synergistic effect of rGO and MoS2/CoS2. This electrode with excellent stability and capacitance could be a potential candidate for supercapacitor electrode materials.

Fe3O4@MoS2/RGO as an effective nano-electrocatalyst toward electrochemical hydrogen evolution reaction and methanol oxidation in two settings for fuel cell application.

A three-component nano-electrocatalyst, magnetite coated molybdenum disulfide hybridized with reduced graphene oxide (Fe3O4@MoS2/RGO), is synthesized by a two-step hydrothermal method. This catalyst is applied as an effective substitution for the platinum catalyst in methanol oxidation and hydrogen evolution reactions. Cyclic voltammetry, chronoamperometry, and linear sweep voltammetry are used to evaluate the performance of the electrocatalyst in acidic and basic media. The results of methanol oxidation reaction on the hybridized nano-electrocatalyst showed good electrocatalytic properties with considerable diffusion currents. This fact is confirmed by the Tafel plots and the calculated kinetic parameters of electron transfer. Fe3O4@MoS2/RGO showed an anodic transfer coefficient and exchange current of 0.464 and 4.80 × 10-8, respectively that are higher than Fe3O4/RGO. The presence of the porous MoS2 in catalyst has a key effect on supplying electroactive sites for electron transfer. Also, the high actual surface area obtained for the hybridized nano-electrocatalyst (A = 0.0295 cm2). The maximum power density of 35.03 mW cm-2 obtained for a single cell containing the prepared hybridized catalyst as the anode which shows a competitive feature of the synthetic catalyst compared to other reports. Furthermore, the synthetic catalyst shows the low-value overpotential of 108 mV and Tafel slope of 48 mV dec-1 during the hydrogen evolution process in acidic media. This is attributed to the synergistic effect between Fe3O4 and MoS2 and also increase the electron transfer rate due to adding conductive RGO to the catalyst. The results show that the synthetic nanocatalyst can have promising applications for hydrogen evolution and methanol oxidation reactions.

Synthesis and microwave absorption characterization of SiO2 coated Fe3O4-MWCNT composites.

This study investigated the microwave absorption properties of core-shell composites containing; iron oxide decorated carbon nanotubes (CNTs) and silica (SiO2@Fe3O4-MWCNTs) with various thicknesses of silica shells (7, 20 and 50 nm). Transmission electron microscopy (TEM) and X-ray diffraction results confirmed the formation of these core-shell structures. Microwave absorption characterization of the samples at the ranging band under consideration (the X-band) showed increased absorption and shifting of the peaks to lower frequencies compared to the uncoated sample (Fe3O4-MWCNTs). The minimum reflection loss decreased with increasing SiO2 thickness. The minimum reflection loss of the composite with an optimized thickness of the silica shell (7 nm) exceeded -41 dB at 8.7-9 GHz.