Reduced graphene oxide composite Ni3S2 microspheres grown directly on nickel foam as an efficient electrocatalyst for OER

The development of cheap, high-efficiency, and stable oxygen evolution reaction (OER) electrocatalysts is a current research hotspot. In this work, reduced graphene oxide (rGO) composite Ni₃S₂ microspheres grown directly on nickel foam (Ni₃S₂-rGO/NF) were prepared by tube furnace calcination and hydrothermal method. The Ni₃S₂-rGO/NF had excellent OER catalytic activity and stability with an overpotential of 303 mV at the current density of 100 mA cm⁻², which was 100 mV lower than that of Ni₃S₂/NF, and its Tafel slope was as low as 23 mV·dec⁻¹. The main reason for enhancing OER activity of the Ni₃S₂-rGO/NF is due to synergistic effect of Ni₃S₂ microspheres and rGO, which inhibited the production of NiS and refined the micron size of Ni₃S₂. This work offers a new method for developing stable and efficient OER catalysts.     

Promoted oxygen evolution reaction efficiency by Ni3S2/WO3 nanocomposite anchored over rGO

To develop a high-efficient catalyst for oxygen evolution reaction (OER), creating high current densities at low overpotentials is highly desirable. Herein, an effective and low cost catalyst based on anchoring Ni₃S₂/WO₃ nanocomposite over the reduced graphene oxide (rGO) was hydrothermaly synthesized and characterized using spectroscopic and microscopic techniques, and its electrochemical parameters as a suitable OER electrocatalyst in alkaine media at surface of nickel foam (NF) was studied. Electrochemical measurements showed that, anchored Ni₃S₂/WO₃ on rGO increased ionic conductivity, surface area, active sites of electrocatalyst, decreased the charge transfer resistance and exhibit the overpotential of 280 mV to reach 50 mA cm^?2, with a Tafel slope of ～48 mV/dec and good stability for the OER in comparison to other tested composites. As a result, this catalyst can work at high and low current densities for a long time.     

Construction of amorphous CoFeOx(OH)y/MoS2/CP electrode for superior OER performance

Design and direct construction of oxygen evolution reaction (OER) catalyst-based electrode is an efficient route to improve the water splitting reaction. Herein, we proposed a facile route to synthesize and load the composite of amorphous CoFe oxyhydroxide (CoFeO_x(OH)_y) and MoS₂ on the carbon paper by combining a hydrothermal and an electrodeposition process. CoFeO_x(OH)_y has a special feature of long-range disorder (amorphous phase) and short-range order (crystal phase), which greatly improves the OER catalytic performance of the hybrids. In virtue of the synergistic effect of CoFeO_x(OH)_y and MoS₂, an improved electronic coupling effect occurs, which increases the oxidation state of Co and Fe, and thus enhances OER activity. As-synthesized CoFeO_x(OH)_y/MoS₂/CP (CFOMS/CP) electrode affords excellent electrocatalytic activity and good electrochemical OER stability: A small Tafel slope of 37.9 mV dec^?1 (vs. 62.1 mV dec^?1 for CoFeO_x(OH)_y/CP, 120.2 mV dec^?1 for RuO₂/CP) and low overpotential 242 mV at 10 mA cm^?2 (vs. 263 mV for CoFeO_x(OH)_y/CP, 317 mV for RuO₂/CP), as well as a stable running for 25 h.     

Phytic acid-derived Co2-xNixP2O7-C/RGO and its superior OER electrocatalytic performance

A phytic acid-derived Co_2-xNi_xP₂O₇-C/RGO composite was designed and facilely synthesized, in which phytic acid acted as both a phosphoric source and carbon source. Both carbon derived from phytic acid and reduced graphene oxide (RGO) in composite, enhanced the conductivity and thus improve its electrocatalytical capability. As-synthesized Co_1.22Ni_0.78P₂O₇-C/RGO composite exhibited excellent oxygen evolution reaction (OER) catalytic performances: At the current density of 10 mA cm⁻², only a low overpotential of 283 mV and a small Tafel slope of 51 mV dec⁻¹ were observed. Good OER catalytic performance was retained even after 10 h continuously running at a constant voltage, which is even comparable to those of first-rate noble metal catalyst RuO₂. In addition, the performances of Co_2-xNi_xP₂O₇-C/RGO catalysts were also strongly dependent on Ni content.     

Ternary Ni2P/reduced graphene oxide/g-C3N4 nanotubes for visible light-driven photocatalytic H2 production

Developing low cost co-catalysts is crucial for both fundamental research and practical application of g-C₃N₄. In this work, we prepared ternary Ni₂P/rGO/g-C₃N₄ nanotubes with different Ni₂P contents for visible-light-driven photocatalytic H₂ generation from triethanolamine aqueous solution. The optimal Ni₂P/rGO/g-C₃N₄ produced H₂ at a rate of 2921.9 μmol h⁻¹ g⁻¹, which is about 35, 16 and 9 times as large as that of g-C₃N₄, binary rGO/g-C₃N₄ and Ni₂P/g-C₃N₄, respectively. The apparent quantum efficiency of optimal Ni₂P/rGO/g-C₃N₄ was 5.6% at λ = 420 nm. We believe that the improved photocatalytic performance of Ni₂P/rGO/g-C₃N₄ originates from the synergistic effect of rGO as electron transfer medium and Ni₂P as reaction site, which is supported by photoelectrochemical and photoluminescence measurements. Cyclic experiment demonstrated an excellent stability of Ni₂P/rGO/g-C₃N₄. Moreover, we further studied the effect of other nickel-based compounds by replacing Ni₂P with NiS, Ni₃C, and Ni₃N, respectively. The order of the H₂-generation rate is Ni₂P/rGO/CNNT > NiS/rGO/CNNT > Ni₃C/rGO/CNNT > Ni₃N/rGO/CNNT, which could be reasonably explained based on Mott–Schottky plots. Our work reveals that Ni₂P can be used as a promising cocatalyst for photocatalytic H₂ evolution.     

Co2FeO4@rGO composite: Towards trifunctional water splitting in alkaline media

Development of efficient, low cost and multifunctional electrocatalysts for water splitting to harvest hydrogen fuels is a challenging task, but the combination of carbon materials with transition metal-based compounds is providing a unique and attractive strategy. Herein, composite systems based on cobalt ferrite oxide-reduced graphene oxide (Co₂FeO₄) @(rGO) using simultaneous hydrothermal and chemical reduction methods have been prepared. The proposed study eliminates one step associated with the conversion of GO into rGO as it uses direct GO during the synthesis of cobalt ferrite oxide, consequently rGO based hybrid system is achieved in-situ significantly, the optimized Co₂FeO₄@rGO composite has revealed an outstanding multifunctional applications related to both oxygen evolution reaction (OER) and hydrogen counterpart (HER). Various metal oxidation states and oxygen vacancies at the surface of Co₂FeO₄@rGO composites guided the multifunctional surface properties. The optimized Co₂FeO₄@rGO composite presents excellent multifunctional properties with onset potential of 0.60 V for ORR, an overpotential of 240 mV at a 20 mAcm^?2 for OER and 320 mV at a 10 mAcm^?2 for HER respectively. Results revealed that these multifunctional properties of the optimized Co₂FeO₄@ rGO composite are associated with high electrical conductivity, high density of active sites, crystal defects, oxygen vacancies, and favorable electronic structure arisinng from the substitution of Fe for Co atoms in binary spinel oxide phase. These surface features synergistically uplifted the electrocatalytic properties of Co₂FeO₄@rGO composites. The multifunctional properties of the Co₂FeO₄@ rGO composite could be of high interest for its use in a wide range of applications in sustainable and renewable energy fields.     

Fabrication of robust CoP/Ni2P/CC composite for efficient hydrogen evolution reaction and the reduction of graphene oxide

Developing the novel catalysts with an excellent performance of hydrogen generation is essential to facilitate the application of hydrogen evolution reaction (HER). Herein, a heterostructured cobalt phosphide/nickel phosphide/carbon cloth (CoP/Ni₂P/CC) composite was fabricated via an interfacial engineering strategy to achieve the modification of CoP nanoleaf on Ni₂P nanosheet skeleton supported by carbon cloth. By virtue of the unique heterostructure, abundant exposing active sites and the synergistic coupling effect of CoP and Ni₂P nanoparticles, the elaborated CoP/Ni₂P/CC composite exhibits a robust catalytic property. Among fabricated composites, the optimal CoP/Ni₂P/CC-4 catalyst behaves an excellent HER performance at a wide pH range (overpotentials of 67, 71 and 95 mV to afford 10 mA cm^?2 in 0.5 M H₂SO₄, 1 M KOH and 1 M PBS, respectively). The HER current density of this composite shows a negligible degradation after continuous test for 24 h. Charmingly, the HER process of this catalyst was innovatively applied to reduce graphene oxide, and thus exploiting the fabrication route of reduced graphene oxide (rGO). We are sure that this work will provide a firm guideline for the exploitation of pH-universal HER catalysts and the exploration of HER application.     

Three dimension (3D) hierarchical electrode (Au/rGO/CoPt3) for electrooxidation of ethanol in fuel cells

A highly efficient electrode for ethanol electrooxidation was successfully fabricated with the assistance of Nanoimprint Lithography (creation of 3D structure) and facile preparation method-electrodeposition. Scanning Electron Microscope (SEM), Transmission Electron Microscope (TEM), X-ray Diffraction (XRD) and Raman spectroscopy were used to characterize the electrodes obtained, which were further evaluated by Cyclic Voltammetry Potentiostat. It concludes that the electrocatalytic activity of the electrodes towards ethanol oxidation is promoted in the sequence of Au < Au/rGO < Au/rGO/CoPt₃. The synergy effect of reduced GO and CoPt3 nanoparticle along with highly active gold thin layer forming 3D structure is responsible for the significant improvement of the catalysis.     

Co(OH)2 nanoparticles deposited on reduced graphene oxide nanoflake as a suitable electrode material for supercapacitor and oxygen evolution reaction in alkaline media

In this work, cobalt hydroxide nanoparticles are simply synthesized (size is about 50 nm) and deposited on the reduced graphene oxide nanoflake by the hydrothermal method. Then, the ability of glassy carbon electrode modified with this low-cost nanocomposite is examined as a supercapacitor and oxygen evolution electrocatalysts in 2.0 mol L^?1 KOH by a three-electrode system. The modified electrode as a pseudocapacitor with potential windows of 0.35 V, exhibits a powerful specific capacitance (235.20 F g^?1 at 0.1 A g^?1 current density), energy density, stability (about 90% of the initial capacitance value maintain after 2000 cycles at 1.0 A g^?1) and fast charge/discharge ability. Furthermore, the modified electrode displays a good electrocatalytic activity for oxygen evolution reaction with a current density of 10.0 mA cm^?2 at 1.647 V, small Tafel slope of 56.5 mV dec^?1, good onset potential of 1.521 V vs. RHE and suitable durability.     

Electrochemical layer-by-layer fabrication of a novel three-dimensional Pt/graphene/carbon fiber electrode and its improved catalytic performance for methanol electrooxidation in alkaline medium

Here, we report a novel method for assembling reduced graphene oxide (RGO) and Pt nanoparticles on a carbon fiber (CF) electrode successively to form a stable Pt nanoparticle-RGO-Pt nanoparticle-RGO/CF multiple junction for electrocatalysis application. As the SEM imaging exhibited, Pt nanoparticles are uniformly deposited on the surface of each RGO sheet, performing an alternative covering structure of RGO and Pt nanoparticle multi-layer on the CF electrode. Thus, a novel three-dimensional (3D) multi-layered Pt/RGO modified CF electrode (N–Pt/RGO/CF) is obtained. Experimental results demonstrate that the prepared N–Pt/RGO/CF electrode shows good electrochemical properties and enhanced electrocatalytic activity toward methanol electrooxidation in alkaline medium as compared with the Pt/RGO/CF electrode without layer-by-layer structure or the Pt/CF electrode without RGO. It is due to the unique 3D pore structure of N–Pt/RGO/CF and the good electron transport property of RGO in the composite electrode.     

Sm2O3 promoted Pd/rGO electrocatalyst for formic acid oxidation

Herein, we report the synthesis of Sm₂O₃ incorporated palladium based electrocatalyst, supported over reduced graphene oxide (rGO). Pd_xSm_y nanoparticles (20 wt %) are distributed over rGO surface by using sodium borohydride reduction technique. Different physicochemical analyses are used to characterize the Pd_xSm_y/rGO electro-catalysts (x = 2,4,6 and y = 8,6,4). The synthesized materials (Pd_xSm_y/rGOs) are investigated for their catalytic capabilities toward electro-oxidation of formic acid. The results show that adding Sm₂O₃ to the Pd/rGO electrocatalyst boosts electrochemical activities of the materials toward formic acid oxidation. The optimized catalyst (Pd₆Sm₄/rGO) shows excellent activity towards formic acid oxidation with current density of 46.70 mA/cm² compared to reference catalysts i.e., Pd/rGO (28.78 mA/cm²) and Pd/C (22.22 mA/cm²). The optimized catalyst also demonstrates high CO tolerance and great stability during formic acid oxidation reaction. The enhanced activity and stability are attributed to the synergistic interaction between Sm₂O_3, and palladium nanoparticles supported over reduced graphene oxide.     

Effect of slurry preparation process on electrochemical performances of LiCoO2 composite electrode

The slurries comprising LiCoO₂ powder, carbon, and polymeric binder are prepared by two different mixing processes, and their rheological properties are compared. In the multi-step process, the solvent is added into solid mixture in stepwise, whereas the total amount at once in the one-step process. The former process gives the slurry that is more suitable for electrode preparation with fluid-like behavior and more uniform dispersion of solid ingredients as compared to those prepared from the letter. In the composite electrode prepared from the former, the LiCoO₂ and carbon particles are homogeneously distributed without agglomeration. Indebted to this favorable feature, this electrode exhibits a better electrochemical performance for cyclability and rate capability. It is very likely that the contact resistance and charge transfer resistance for lithiation/de-lithiation are smaller in the former electrode due to the homogeneous distribution of LiCoO₂ and carbon particles, which leads to a less significant electrode polarization.     

Exploration of 1D-2D LaFeO3/RGO S-scheme heterojunction for photocatalytic water splitting

Sustainable energy innovation is spearheading the way to achieve decarbonisation through commercially viable and highly competitive renewable technologies for green hydrogen. Photocatalytic water splitting has received global attention, as it promotes the direct conversion of solar energy to chemical energy and hydrogen production. Lanthanum orthoferrite (LaFeO₃) has been selected due to its narrow bandgap perovskite-oxides (ABO₃) type nature, low cost and high chemical stability but it is limited with fast charge recombination. To circumvent its constraint of fast charge recombination, an efficient graphene-based nanocomposite has been prepared by employing reduced graphene oxide (RGO) nanosheets as charge separators for visible light driven photocatalytic water splitting. Here, we present a thorough physical and spectroscopic characterization of the Lanthanum orthoferrite/Reduced Graphene oxide (LaFeO₃/RGO) nanocomposites, and investigate its photocatalytic and photoelectrochemical performance. The photocurrent density of the nanocomposites demonstrated ∼21 times higher in comparison to pure LaFeO₃. The as-prepared nanocomposites have been successfully used as photocatalysts for H₂ generation through water reduction under visible light. A significant enhancement in H₂ generation has been recorded for nanocomposites (∼82 mmol g⁻¹ h⁻¹) as compared to that of bare LaFeO₃ (∼9 mmol g⁻¹ h⁻¹) which is among the highest values obtained using noble-metal-free graphene-based photocatalytic nanocomposites. This work offers a facile approach for fabricating highly efficient 1D-2D heterostructure for photocatalysis application.     

Reduced graphene oxide-supported nickel oxide catalyst with improved CO tolerance for formic acid electrooxidation

The superior catalytic activity along with improved CO tolerance for formic acid electrooxidation has been demonstrated on a NiO-decorated reduced graphene oxide (rGO) catalyst. The cyclic voltammetry response of rGO–NiO/Pt catalyst elucidates improved CO tolerance and follows direct oxidation pathway. It is probably due to the bene?cial effect of residual oxygen groups on rGO support which is supported by FT-IR spectrum. A strong interaction of rGO support with NiO nanoparticles facilitates the removal of CO from the catalyst surface. The chronoamperometric response indicates a higher catalytic activity and stability of rGO–NiO/Pt catalyst than the NiO/Pt and unmodified Pt electrode catalyst for a prolonged time of continuous oxidation of formic acid.     

A non-noble metal oxide Ti2O3/rGO composite as efficient and highly stable electrocatalyst for oxygen reduction

Developing low-cost and high-performance non-precious metal catalysts for oxygen reduction reaction (ORR) is highly desirable. Herein, the Ti₂O₃/reduced graphene oxide (Ti₂O₃/rGO) composite was successfully prepared by solid state synthesis. The electrochemical experiments indicated that the Ti₂O₃/rGO composite presents an excellent electrocatalytic activity and high selectivity for ORR via a four - electron pathway. Moreover, this composite also has outstanding durability and superior methanol tolerance compared with a commercial Pt/C catalyst in the alkaline (0.1M KOH) media. The superior ORR performance of Ti₂O₃/rGO composite may be ascribed to the low valence Ti, and the synergetic chemical coupling effects between Ti₂O₃ and rGO.     

Construction of ternary hybrid layered reduced graphene oxide supported g-C3N4-TiO2 nanocomposite and its photocatalytic hydrogen production activity

Reduced graphene oxide (rGO) supported g-C₃N₄-TiO₂ ternary hybrid layered photocatalyst was prepared via ultrasound assisted simple wet impregnation method with different mass ratios of g-C₃N₄ to TiO₂. The synthesized composite was investigated by various characterization techniques, such as XRD, FTIR, Raman Spectra, FE-SEM, HR-TEM, UV vis DRS Spectra, XPS Spectra and PL Spectra. The optical band gap of g-C₃N₄-TiO₂/rGO nanocomposite was found to be red shifted to 2.56 eV from 2.70 eV for bare g-C₃N₄. It was found that g-C₃N₄ and TiO₂ in a mass ratio of 70:30 in the g-C₃N₄-TiO₂/rGO nanocomposite, exhibits the highest hydrogen production activity of 23,143 μmol g^?1h^?1 through photocatalytic water splitting. The observed hydrogen production rate from glycerol-water mixture using g-C₃N₄-TiO₂/rGO was found to be 78 and 2.5 times higher than g-C₃N₄ (296 μmol g^?1 h^?1) and TiO₂ (11,954 μmol g^?1 h^?1), respectively. A direct contact between TiO₂ and rGO in the g-C₃N₄-TiO₂/rGO nanocomposite produces an additional 10,500 μmol g^?1h^?1 of hydrogen in 4 h of photocatalytic reaction than the direct contact between g-C₃N₄ and rGO. The enhanced photocatalytic hydrogen production activity of the resultant nanocomposite can be ascribed to the increased visible light absorption and an effective separation of photogenerated electron-hole pairs at the interface of g-C₃N₄-TiO₂/rGO nanocomposite. The effective separation and transportation of photogenerated charge carriers in the presence of rGO sheet was further confirmed by a significant quenching of photoluminescence intensity of the g-C₃N₄-TiO₂/rGO nanocomposite. The photocatalytic hydrogen production rate reported in this work is significantly higher than the previously reported work on g-C₃N₄ and TiO₂ based photocatalysts.     

Synthesis of high performing Cu0.31Ni0.69O/rGO hybrid for oxygen reduction reaction in alkaline medium

In this feature article, Cu_0.31Ni_0.69O nanoparticles were assembled on reduced graphene nanosheets (Cu_0.31Ni_0.69O/rGO) by a simple hydrothermal method. The structural characterizations confirm that the synthesized nanoparticles with an average size around 9 nm are densely and uniformly assembled on the reduced graphene oxide (rGO) nanosheets. The electrochemical measurements demonstrate that the as-synthesized Cu_0.31Ni_0.69O/rGO catalyst exhibits excellent catalytic performance for oxygen reduction reaction with high cathodic current density (2.08 × 10⁻⁴ mA/cm²), positive onset potential (−0.21 V), low H₂O₂ yielding rate (less than 2.5%) and long-term running stability. The rotating disk and rotating ring-disk electrode measurements proved that the oxygen reduction reaction occurs on Cu_0.31Ni_0.69O/rGO through a high efficient four-electron pathway. The Cu_0.31Ni_0.69O/rGO nanoparticles shows great potential to be promising noble metal-free catalyst for cathodes of alkaline fuel cells.     

Electrochemical conversion of CO2 to methanol using a glassy carbon electrode,modified by Pt@histamine-reduced graphene oxide

The electrochemical reduction of CO₂ to value-added products is one of the useful approaches to reducing the effects of global climate change. Herein, a novel electrocatalyst consisting of platinum nanoparticles on histamine-reduced graphene oxide plates (Pt@His-rGO) supported by a glassy carbon (GC) substrate for the electrochemical conversion of CO₂ to methanol has been developed. The nanocomposite was optimized in terms of pH, applied potential, CO₂ purging time and platinum loading for the highest current densities and faradaic efficiencies toward methanol production. The best results were obtained in a solution containing KNO₃ 0.1 mol L⁻¹ at the pH of 2.0, the applied potential of −0.3 V vs Ag/AgCl (KCl_sat), CO₂ purging duration of 30 min and Pt loading of 5.17 × 10⁻⁷ mol cm⁻². The faradaic efficiency of 37% was obtained for methanol production. The prepared nanocomposite requires a lower applied potential and serves as an intermediate stabilizer through the production of methanol.     

A hybrid PEMFC/supercapacitor device with high energy and power densities based on reduced graphene oxide/Nafion/Pt electrode

Proton exchange membrane fuel cells (PEMFCs) possess high energy and low power densities, while supercapacitors are characterized by high power and low energy densities. A hybrid PEMFC/supercapacitor device (HPSD) with high energy and power densities was proposed and fabricated for the first time using a reduced graphene oxide/Nafion/Pt electrode in this study. The reduced graphene oxide (rGO) was a capacitive material, and Pt was used as the electrocatalyst. Nafion ionomers adsorbed onto the rGO sheets surface and connected the rGO sheets and the electrolyte (Nafion membrane), thus increasing the utilization rate and specific capacitance of rGO. During the half-cell tests, the rGO/Nafion/Pt electrode exhibited better pulse discharge and galvanostatic discharge performance than the conventional Nafion/Pt electrode. Due to the unique synergy of electrochemical reaction current and capacitance current during the discharge process, the HPSD exhibited a higher power density (26.2 kW kg⁻¹) than the PEMFC (23.9 kW kg⁻¹). The energy density (12.7 kWh kg⁻¹) exhibited by HPSD was close to that of the PEMFC (13.5 kWh kg⁻¹). Therefore, the concept of HPSD is to create a new method for developing next-generation electrochemical devices with high energy and power densities.