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Recently, transition metal oxides have been considered for various applications due to their unique properties. We present the synthesis of a three-component catalyst consisting of zirconium oxide (ZrO2), nickel oxide (NiO), and reduced graphene oxide (rGO) in the form of ZrO2/NiO/rGO by a simple one-step hydrothermal method. X-ray powder diffraction (XRD), scanning electron microscope (SEM), and bright-field transmission electron microscopy (BF-TEM) analyses were performed to accurately characterize the catalysts. Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and linear sweep voltammetry (LSV) analyses were also carried out to investigate the methanol and ethanol alcohol electrooxidation ability of the synthesized nanocatalysts. Inspired by the good potential of metal oxides in the field of catalysts, especially in fuel-cell anodes, we investigated the capability of this catalyst in the methanol oxidation reaction (MOR) and ethanol oxidation reaction (EOR). After proving the successful synthesis and examining the surface morphology of these materials, detailed electrochemical tests were performed to show the outstanding capability of this new nanocatalyst for use in the anode of alcohol fuel cells. ZrO2/NiO/rGO indicated a current density of 26.6 mA/cm2 at a peak potential of 0.52 V and 99.5% cyclic stability in the MOR and a current density of 17.3 mA/cm2 at a peak potential of 0.52 V and 98.5% cyclic stability in the EOR (at optimal concentration/scan rate 20 mV/s), representing an attractive option for use in the anode of alcoholic fuel cells. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

A three-part nano-catalyst including ruthenium oxide, manganese cobalt oxide, and reduced graphene oxide nanosheet in form of RuO 2 -MnCo 2 O 4 /rGO is synthesized by one-step hydrothermal synthesis. The material is placed on a glassy carbon electrode (GCE) for electrochemical studies. The ability of these nano-catalysts in the oxidation process of methanol in an alkaline medium for usage in direct methanol fuel cells (DMFC) was examined with electrochemical tests of cyclic voltammetry (CV), linear sweep voltammetry (LSV), and electrochemical impedance spectroscopy (EIS). The effect of the addition of rGO to the nanocatalyst structure in the methanol oxidation reaction (MOR) process was investigated. We introduced the RuO 2 -MnCo 2 O 4 /rGO as a nanocatalyst with excellent cyclic stability of 97% after 5000 cycles in the MOR process. Besides, the study of the Tafel plots and the effect of temperature and scan rate in the MOR process showed that RuO 2 -MnCo 2 O 4 /rGO nanocatalyst has better electrochemical properties than MnCo 2 O 4 and RuO 2 -MnCo 2 O 4. This high electrocatalytic activity could be related to the synergistic effect of placement of metal oxides of ruthenium, manganese, and cobalt near each other and putting them on rGO, which enhances conductivity and surface area and improve electron transfer. The decrease in the resistance against charge transfer and the increment in the anodic current density illustrated that the reaction rate is enhanced at higher temperature. Thus RuO 2 -MnCo 2 O 4 /rGO shows robust stability and superior performance for MOR. • A ternary hybrid of RuO 2 -MnCo 2 O 4 /rGO was synthesized as a catalyst for methanol oxidation. • The synergistic effect of nanocatalyst components reduced Co poisoning of catalyst in MOR process. • RuO 2 -MnCo 2 O 4 /rGO indicates good stability. [ABSTRACT FROM AUTHOR]

Summary: Hierarchical porous ZnCo2O4 nanosheets and ZnCo2O4‐coated reduced graphene oxide (ZnCo2O4/rGO) were synthesized by the hydrothermal method followed by the annealing process. The composition of materials was proved by X‐ray electron spectroscopy and X‐ray photoelectron spectroscopy. The size and morphology of the as‐prepared samples were evaluated by scanning electron microscopy and transmission electron microscopy. The result showed ZnCo2O4 nanosheets with porous morphology and a sheet thickness of about 5 nm was well synthesized. The electrochemical tests used to prove the catalytic performance of the prepared catalysts were cyclic voltammetry and impedance spectroscopy, and the analysis was performed in alkaline environments. The electrochemical investigations on ZnCo2O4 and ZnCo2O4/rGO showed the rGO has an effective role in electrooxidation of methanol in alkaline media. In addition to the synergic effect between Zn and Co, the synergistic effect between ZnCo2O4 (make active sites for adsorption of methanol) and rGO (provide more conductivity and make more sites by preventing from the agglomeration of ZnCo2O4) has an important role for this excellent performance. The polarization curves of ZnCo2O4/rGO showed a maximum power density of 24.3 mW cm−2, which proved its potential capability for the direct methanol fuel cell. [ABSTRACT FROM AUTHOR]

Graphical abstract MoFeNiS hybridized with reduced graphene oxide (MoFeNiS/RGO) were prepared by the one-step hydrothermal method as a catalyst for hydrogen evolution reaction. MoFeNiS/RGO catalyst showed good electrochemical properties for HER in all pH media. RGO ensures good distribution of MoFeNiS and more available catalytically active sites of MoFeNiS for HER. RGO enhances the conductivity of the hybrid catalyst. Abstract MoFeNiS nanocomposites and MoFeNiS/reduced graphene oxide (rGO) hybrid materials were synthesized by a modified hydrothermal method. The catalytic activity of catalysts for the hydrogen evolution reaction (HER) was investigated at acidic, alkaline and neutral media. The MoFeNiS/rGO catalyst was found to be very active for HER, and this process is probably depended on Volmer–Heyrovsky mechanism with the desorption process as the rate-determining step. Moreover, the MoFeNiS/rGO catalyst indicated the low onset overpotential of −100 mV, Tafel slope of 48.68 mV dec−1, and the overpotential of −140 mV to reach the current density of 10 mA cm−2. The excellent HER activity of MoFeNiS/rGO hybrid catalyst is probably attributed to the high surface area and conductivity of rGO, the existence of porosity in the catalyst, and the catalytic synergistic effect between MoS 2 , NiS, and FeMo 4 S 6. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract A three-component nano-electrocatalyst, magnetite coated molybdenum disulfide hybridized with reduced graphene oxide (Fe 3 O 4 @MoS 2 /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. Fe 3 O 4 @MoS 2 /RGO showed an anodic transfer coefficient and exchange current of 0.464 and 4.80 × 10−8, respectively that are higher than Fe 3 O 4 /RGO. The presence of the porous MoS 2 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 Fe 3 O 4 and MoS 2 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. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Co 5.57 Fe 1.62 Ni 1.81 S 8 /rGO was prepared through hydrothermal method. • The HER properties for nanohybrids with different mass ratios were studied. • Co 5.57 Fe 1.62 Ni 1.81 S 8 /rGO catalyst showed good electrochemical properties for HER. Abstract Co 5.57 Fe 1.62 Ni 1.81 S 8 nanocomposite hybridized with reduced graphene oxide (Co 5.57 Fe 1.62 Ni 1.81 S 8 /rGO) was prepared through a one-step hydrothermal method. The hybrid was characterized by XRD, EDX, FESEM and HRTEM. The electrochemical hydrogen evolution behavior of nanohybrids with different mass ratios was studied as modified glassy carbon electrodes by linear sweep voltammetry, chronopotentiometry and electrochemical impedance spectroscopy. The results showed overpotential in 10 mA/cm2 (−100 mV) for Co 5.57 Fe 1.62 Ni 1.81 S 8 /rGO (1 g:0.5 g) among all nanohybrids. Also, the obtained Tafel slope (53.6 mV/dec) confirmed the Volmer-Heyrovsky mechanism for HER. The electro-catalytic properties for HER of Co 5.57 Fe 1.62 Ni 1.81 S 8 /rGO (1 g:0.5 g) were compared with some transition metal dichalcogenide based composites. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • MoCoFeS supported reduced graphene oxide (MCFS/rGO) catalyst were prepared by hydrothermal method. • MCFS/rGO catalyst showed good electrochemical properties for HER. • The content of rGO on electrochemical properties of catalyst was investigated. • The Tafel slope and onset potential of MCFS/rGO0.4 were lower than MCFS. Abstract The produce of high-efficiency materials in hydrogen evolution technology is a priority. Recent development in graphene-based material shows that it can be a good candidate for this target. Accordingly, the MoCoFeS/reduced graphene oxide (rGO) catalyst was prepared by the hydrothermal method for hydrogen evolution reaction. The catalysts were characterized and the effect of rGO on the electrochemical properties of the catalyst was examined. Our results are encouraging that, the optimized catalyst (MoCoFeS/rGO0.4) at −110 mV overpotential with a Tafel slope of 50.26 mV dec−1 can be a novel candidate for an active non-precious metal hydrogen evolution reaction catalyst. [ABSTRACT FROM AUTHOR]

A ternary transition metal chalcogenide, containing MoS 2 , NiS, and Co 3 S 4 (MCNS), and MCNS/reduced graphene oxide (MCNS/rGO) composite were prepared as anode catalysts by a simple hydrothermal process for Urea electro-oxidation. It's expected that rGO with high specific surface area provides superior catalytic performance for MCNS/rGO than MCNS. Also, the synergic effect of Mo, Ni, and Co in the composite accelerates the urea oxidation and enhances the performance of the catalyst. The composites were characterized by field emission electron microscopy, transition electron microscopy, and X-ray diffraction spectroscopy. Electrochemical properties of composites were evaluated by cyclic voltammetry. The MCNS/rGO demonstrated superior electrocatalytic performance than the MCNS catalyst. The incorporating of rGO into MCNS creates a high electrochemical surface area for urea electro-oxidation that resulted in a higher current density (18 mA cm−2) than MCNS (3.7 mA cm−2) at the presence of 0.6 M urea and the scan rate of 20 mV s−1. The maximum current density obtained 43 mA cm−2 for MCNS/rGO at the scan rate of 70 mV s−1 in room temperature. Also, single cells based on MCNS and MCNS/rGO supplied a maximum power density of 7.7 mW cm−2 and 21.0 mW cm−2 at room temperature, respectively. Hence, MCNS/rGO can be a favorable electrocatalyst for application in the direct urea fuel cell. Image 10547 • A ternary transition metal chaclogenide was embedded in reduced graphene oxide as electrocatalyst for urea oxidation. • The performance of the catalyst in urea oxidation was evaluated. • MCNS/rGO indicated excellent electrocatalytic performance for urea oxidation. • Single-cell studies showed the potential of the as-prepared hybrid catalyst for urea fuel cell. [ABSTRACT FROM AUTHOR]

A non-noble dual metal electrocatalyst based on CoS 2 /MoS 2 embedded in reduced graphene oxide (rGO) was synthesized as an electrocatalyst for direct methanol fuel cells and hydrogen generation applications. In the methanol oxidation reaction, the CoS 2 /MoS 2 /rGO catalyst exhibited a maximum current density of 1.68 mA cm−2 at 290 K and 2.71 mA cm−2 at 310 K. In the hydrogen evolution reaction, Tafel slopes of 48 and 86 mV dec−1 and onset overpotentials of 90 and 160 mV were obtained for CoS 2 /MoS 2 /rGO and CoS 2 /MoS 2 , respectively. Furthermore, CoS 2 /MoS 2 /rGO as an anode catalyst in a single cell showed a maximum power density of 19 mW cm−2 at 60 °C. The excellent performance of the catalyst suggests its potential for energy production. The specific surface area and edge sites of the catalyst and the presence of rGO as a conductive material have a collective effect on the catalyst performance. Image 1 • A non-noble dual metal electrocatalyst based on CoS 2 /MoS 2 was embedded in reduced graphene oxide (rGO). • The performance of the CoS 2 /MoS 2 /rGO catalyst in the hydrogen evolution and the methanol oxidation was evaluated. • CoS 2 /MoS 2 /rGO exhibited excellent electrocatalytic hydrogen evolution reaction performance and long-term stability. • Single-cell studies showed the potential of the as-prepared hybrid catalyst for use in direct methanol fuel cells. [ABSTRACT FROM AUTHOR]

The structures containing iron and nickel can provide a unique platform for supercapacitor electrodes. In this research, the synthesis of iron and nickel nanoparticles and their hybrid with reduced graphene oxide (rGO) were performed. The samples were characterized with XRD analysis, SEM microscopy along with the EDS mapping, and TEM microscopy. The several electrochemical tests, i.e. cyclic voltammetry (CV), galvanostatic charge/discharge (GCD), and electrochemical impedance spectroscopy (EIS) were performed to probe the applicability of materials as the supercapacitor electrode. The obtained results showed a fairly good capability of the NiFe/rGO hybrid for supercapacitor applications with a specific capacitance of 1224 F/g and discharge time of 351 s. Moreover, the cyclic stability of the electrode composed of both NiFe and rGO was enhanced up to 7%. • NiFe/rGO hybrid composite was evaluated as supercapacitor materials. •An excellent specific capacity of 1224.2 F/g at a scan rate of 10 mV s−1. •Capacity retention of 89% for NiFe/rGO after 2000 cycles. [ABSTRACT FROM AUTHOR]