Enhanced oxygen evolution reaction activity of NiFe layered double hydroxide on nickel foam- reduced graphene oxide interfaces

Herein, we prepared a novel nickel iron-layered double hydroxide/reduced graphene oxide/nickel foam (NiFe-LDH/RGO/NF) electrodes by two step electrodeposition processes for oxygen evolution reaction (OER). The modification of NF by RGO increased the interface conductivity and electrochemical active surface areas (ECSA) of the electrode. The NiFe-LDH/RGO/NF electrode has shown higher catalytic activity with a lower overpotential of 150 mV at the current density of 10 mA cm⁻². The NiFe-LDH/RGO/NF electrode has also shown a small Tafel slope of 35 mV per decade due to the synergy effect between the larger ECSA and the conductive RGO interface. Furthermore, the electrodes exhibits almost 10 h stability under a general current density of 10 mA cm⁻².     

Synergistic coupling of CoFe-layered double hydroxide nanosheet arrays with reduced graphene oxide modified Ni foam for highly efficient oxygen evolution reaction and hydrogen evolution reaction

Novel CoFe-LDH (layered double hydroxide) nanosheet arrays in situ grown on rGO (reduced graphene oxide) uniformly modified Ni foam were synthesized by a citric acid-assisted aqueous phase coprecipitation strategy. Systematic characterizations indicates that the series of Co_xFe₁-LDH/rGO/NF (x = 4, 3, 2) all show Co_xFe₁-LDH nanosheets (150–180 × 15 nm) grown vertically on the surface of rGO/NF. Especially, the Co₃Fe₁-LDH/rGO/NF exhibits the best performance with overpotentials of 250 and 110 mV at 10 mA cm^?2 in 1 M KOH for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), respectively. When it is used as cathode and anode simultaneously for overall water splitting, they require 1.65 and 1.84 V at 10 and 100 mA cm^?2, respectively. Excellent performance of Co₃Fe₁-LDH/rGO/NF is due to the nanosheet arrays structure with open channels, synergistic coupling between Co₃Fe₁-LDH and rGO enhancing electrical conductivity, and in-situ growth of Co₃Fe₁-LDH on rGO/NF enhancing stability.     

Novel route of NiCr-layered double hydroxide nanosheets synthesis on nickel foam as a bifunctional electrocatalyst for water splitting process

In this study, we present a novel direct synthetic route for producing NiCr-layered double hydroxide (LDH) nanosheets on a nickel foam surface using the Successive Ionic Layer Deposition (SILD) method. The morphology of the nanolayers was characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). Additionally, the electrocatalytic properties of the nanolayers were examined using electrochemical techniques. The NiCr-layered double hydroxide nanolayers produced through SILD using sodium hexahydroxochromate (III) anion precursor were found to be ultrathin “nanosheets” with a hydrotalcite-like structure and low crystallinity. The efficacy of electrodes based on these nanolayers as cathode and anode materials in electrocatalytic cells for hydrogen production through electrolytic water splitting in alkaline media were investigated. Our results showed that the electrode based on NiCr-LDH nanolayers exhibited good kinetics in both the cathode and anode areas.     

Facile synthesis of nanometer-sized NiFe layered double hydroxide/nitrogen-doped graphite foam hybrids for enhanced electrocatalytic oxygen evolution reactions

We report a self-standing NiFe layered double hydroxide/nitrogen doped graphite foam (NiFe LDH/NGF) electrode for the oxygen evolution reaction (OER) prepared via a facile electrodeposition method. The electrode showed high electrocatalytic activity towards OER, exhibiting a low onset overpotential of 0.239 V and a small Tafel slope of 57.9 mV dec^?1 in basic electrolytes, as well as a good stability during the long-term cycling test. The outstanding electrocatalytic activity is mainly attributed to the synergy between the abundant catalytically active sites through good dispersion of NiFe LDH across NGF and fluent electron transport arising from NGF.     

Polysulfide functionalized reduced graphene oxide for electrocatalytic hydrogen evolution reaction and supercapacitor applications

Functionalized carbon based 2D materials are promising candidates for low cost and environment friendly electrocatalyst for hydrogen evolution reaction (HER) and supercapacitor applications. To overcome the limitations posed by the noble metals and transition metal based composites, we have successfully synthesized metal free polysulfide functionalized reduced graphene oxide (GPS) in a simple chemical route. Structure and morphology of the material are characterized via XRD, FTIR, Raman, TEM, XPS measurements. The material behaves as an efficient HER electrocatalyst in acidic medium as well as energy storage device. It shows an onset potential of 97 mV and overpotential of 254 mV to reach a high current density of 10 mA/cm². DFT calculations are carried out to understand the structural stability and identification of active sites of the material. Boosting catalytic activity via increasing the number of active sites is an elegant approach. In this material we have used the S atoms of polysulfide polymer to facilitate hydrogen adsorption and desorption, thus improving the hydrogen evolution ability. The supecapacitor attains the high specific capacitance 347 F/g at the current density of 1 A/g. The origin of such performances is due to synergistic effect of both the graphene network and the polysulfide functionalizations.     

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.     

A novel co-electrodeposited Co/MoSe2/reduced graphene oxide nanocomposite as electrocatalyst for hydrogen evolution

In this study, a simple and fast electrochemical method was employed to synthesis molybdenum diselenide thin film. The morphology, structure and chemical composition of the nanocomposites were investigated by field emission scanning electron microscopy, X-ray diffraction, energy dispersive X-ray spectroscopy, Raman spectroscopy and X-ray photoelectron spectroscopy. The progressive effects of transition metal ions including Ni, Cu, and Co were surveyed on the hydrogen evolution activity of MoSe₂ thin films. Co/MoSe₂ nanocomposite thin films has significant electrocatalytic activity as compared to other samples, In order to achieve higher performance, preparing Co/MoSe₂/RGO nanocomposite thin film, two strategies including layer by layer electrodeposition and co-electrodeposition has been employed. The presence of reduced graphene oxide leading to the onset potential shifts to more positive values and increase the current density. Also, results showed that the Co/MoSe₂/RGO nanocomposite prepared by co-electrodeposition exhibits the best electrochemical hydrogen evolution at onset potential of −0.18 with an overpotential of −0.45 V.     

Synthesis of Co(OH)2/graphene/Ni foam nano-electrodes with excellent pseudocapacitive behavior and high cycling stability for supercapacitors

Vertically aligned graphene nanosheets have been synthesized by radio-frequency plasma-enhanced chemical vapor deposition on nickel-foam current collectors and that have been used as substrates for cathodic electrodeposition of cobalt hydroxide nanosheets in Co(NO₃)₂ aqueous solution. Raman spectrum exhibits that high-quality graphene nanosheets have been synthesized. The composites have been characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, cyclic voltammetry and galvanostatic charge/discharge. It indicates that hexagonal Co(OH)₂ has a network microstructure, consisting of interlaced sheets with the thickness of 12 nm coated on the graphene nanosheets. The binder-free nano-electrode exhibits excellent pseudocapacitive behavior with pseudocapacitances of 693.8 and 506.2 Fg⁻¹ at current density of 2 and 32 Ag⁻¹, respectively, in a potential range of −0.1–0.45 V. The capacitance can retain about 91.9% after 3000 charge–discharge cycles at 40 Ag⁻¹, which is higher than that of Co(OH)₂/Ni foam (after 2000 cycles, 75.5% of initial capacitance remains). The introduction of graphene between Co(OH)₂ and Ni foam demonstrates an enhancement of electrochemical stability of the nano-electrodes.     

Improved electrochemical performance of nickel-cobalt hydroxides by electrodeposition of interlayered reduced graphene oxide

Efficient, economical, and eco-friendly water splitting catalysts are in priority to replace the fossil fuels. In the presented work, reduced graphene oxide is formed through electrochemical reduction and applied as an effective interlayer between nickel foam substrate and nickel-cobalt hydroxide catalyst to augment its activity toward hydrogen evolution reaction. Through subsequent cyclic voltammetry deposition of nickel-cobalt hydroxide over the surface of supported interlayer, the prepared electrocatalyst exhibited remarkable performance by reaching a current density of 10 mA cm⁻² at a small overpotential of 60 mV in 1.0 M KOH electrolyte, much lower than that of the same electrocatalyst without interlayer (78 mV). The proposed strategy made the active metallic catalyst phase acquiring a small Tafel slope and superior durability for hydrogen production in alkaline medium. By utilizing the reduce graphene oxide interlayer, the electrical conductivity of the final nickel-cobalt hydroxide electrode was boosted. Furthermore, a clear transition from ordered reticulated arrays of nanosheets to roughened and disordered nanosheet-comprised nanospheres is demonstrated for surface morphology of nickel-cobalt electrocatalyst that indeed prompts the increase in its electrochemically active surface area.     

Tungsten-molybdenum oxide nanowires/reduced graphene oxide nanocomposite with enhanced and durable performance for electrocatalytic hydrogen evolution reaction

Hydrogen has attracted huge interest globally as a durable, environmentally safe and renewable fuel. Electrocatalytic hydrogen evolution reaction (HER) is one of the most promising methods for large scale hydrogen production, but the high cost of Pt-based materials which exhibit the highest activity for HER forced researchers to find alternative electro-catalyst. In this study, we report noble metal free a 3D hybrid composite of tungsten-molybdenum oxide and reduced graphene oxide (GO) prepared by a simple one step hydrothermal method for HER. Benefitting from the synergistic effect between tungsten-molybdenum oxide nanowires and reduced graphene oxide, the obtained W-Mo-O/rGO nanocomposite showed excellent electro-catalytic activity for HER with onset potential 50 mV, a Tafel slope of 46 mV decade^?1 and a large cathodic current, while the tungsten-molybdenum oxide nanowires itself is not as efficient HER catalyst. Additionally, W-Mo-O/rGO composite also demonstrated good durability up to 2000 cycles in acidic medium. The enhanced and durable hydrogen evolution reaction activity stemmed from the synergistic effect broadens noble metal free catalysts for HER and provides an insight into the design and synthesis of low-cost and environment friendly catalysts in electrochemical hydrogen production.     

Facile scalable manufacture of improved electrodes using structured surface coatings of nickel oxide as cathode and reduced graphene oxide as anode for evaluation in a prototype development on microbial fuel cells

Improvement of the microbial fuel cell performance is highly required in energy production associated with domestic sewage treatment. For this objective, metal electrodes coated with specific materials for anode and cathode were manufactured. Materials such as reduced graphene oxide (rGO) as an anode, with high electrical conductivity, and structured nickel oxide (sNiO), which act as air cathode, could be the key to obtaining substantial improvements in the production of energy and treatment of domestic sewage. In this work, simple methods were developed to coat the stainless steel meshes with rGO and sNiO, used in MFC prototypes. The results show that the methodologies developed for the coating of the electrodes aid to improve the performance of the MFC in the delivery of potential, current density and power density up to 220%, 140% and 700% respectively, compared to the blank stainless steel electrodes; while the COD levels in the water purified by the MFC with covered electrodes reached a decrease of 36% compared to the same system without covered electrodes. Additionally, the built MFCs prototypes were tested as a power supply for a digital clock and an LED light.     

Spatially confined growth of ultrathin NiFe layered double hydroxide nanosheets within carbon nanofibers network for highly efficient water oxidation

The rational design of catalysts with low cost, high efficient and robust stability toward oxygen evolution reaction (OER) is greatly desired but remains a formidable challenge. In this work, a one-pot, spatially confined strategy was reported to fabricate ultrathin NiFe layered double hydroxide (NiFe-LDH) nanosheets interconnected by ultrafine, strong carbon nanofibers (CNFs) network. The as-fabricated NiFe-LDH/CNFs catalyst exhibits enhanced OER catalytic activity in terms of low overpotential of 230 mV to obtain an OER current density of 10 mA cm^?2 and very small Tafel slope of 34 mV dec^?1, outperforming pure NiFe-LDH nanosheets assembly, commercial RuO₂, and most non-noble metal catalysts ever reported. It also delivers an excellent structural and electrocatalytic stability upon the long-term OER operation at a large current of 30 mA cm^?2 for 40 h. Furthermore, the cell assembled by using NiFe-LDH/CNFs and commercial Pt/C as anode (+) and cathode (?) ((+)NiFe-LDH/CNFs||Pt/C(?)) only requires a potential of 1.50 V to deliver the water splitting current of 10 mA cm^?2, 130 mV lower than that of (+)RuO₂||Pt/C(?) couple, demonstrating great potential for applications in cost-efficient water splitting devices.     

Highly efficient and durable phosphine reduced iron-doped tungsten oxide/reduced graphene oxide nanocomposites for the hydrogen evolution reaction

The design and development of inexpensive and highly efficient electrocatalysts for hydrogen production from water splitting are highly crucial for green energy and the hydrogen economy. Herein, we report phosphine reduced an iron-doped tungsten oxide nanoplate/reduced graphene oxide nanocomposite (Fe-WOxP/rGO) as an excellent electrocatalyst for the hydrogen evolution reaction. This electrocatalyst was synthesized using a hydrothermal method, followed by reduction with phosphine (PH₃), which was generated from sodium hypophosphite. The catalyst onset potential, Tafel slope, and stability were investigated. Accordingly, Fe-WOxP/rGO exhibited impressively high electrocatalytic activity with a low overpotential of 54.60 mV, which is required to achieve a current density of 10 mAcm^?2. The Tafel slope of 41.99 mV dec^?1and the linear sweep voltammetry curve is almost the same as 2000 cycles and electrolysis under static overpotential (54.60 mV) is remain for more than 24 h in 0.5 M H₂SO₄. The catalytic activity and conductivity of Fe-WOxP/rGO were higher than WO_XP, Fe-WOxP and WOxP/rGO. Such an outstanding performance of the Fe-WOxP/rGO nanocomposite is attributed to the coupled synergic effect between high oxygen vacancies formation on tungsten oxide in the nanoplate-like structure of Fe-WOxP and rGO nanosheet, making it as an excellent electrocatalyst for hydrogen evolution reaction.     

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.     

Effect of reduced graphene oxide addition on cathode functional layer performance in solid oxide fuel cells

Solid oxide fuel cells (SOFCs) operating at high temperatures are highly efficient electrochemical devices since they convert the chemical energy of a fuel directly into heat and electrical energy. The electrochemical performance of an SOFC is significantly influenced by the materials and microstructure of the electrodes since the electrochemical reactions in SOFCs take place at three/triple phase boundaries (TPBs) within the electrodes. In this study, graphene in the form of reduced graphene oxide (rGO) is added to cathode functional layer (CFL) to improve the cell performance by utilizing the high electrical properties of graphene. Various cells are prepared by varying the rGO content in CFL slurry (1–5 wt %), the number of screen printing (1–3) and the cathode sintering temperature (900–1100 °C). The electrochemical behavior of the cells is evaluated by electrochemical performance and impedance tests. It is observed that there is a ∼26% increase in the peak performance of the cell coated with single layer CFL having 1 wt % graphene and 1050 °C sintering temperature, compared to that of the reference cell.     

One step electrodeposition of V2O5/polypyrrole/graphene oxide ternary nanocomposite for preparation of a high performance supercapacitor

A new ternary nanocomposite based on graphene oxide (GO), polypyrrole (PPy) and vanadium pentoxide (V₂O₅) is obtained via one-step electrochemical deposition process. Electrochemical deposition of V₂O₅, PPy and GO on a stainless steel (SS) substrate is conducted from an aqueous solution containing vanadyl acetate, pyrrole and GO to get V₂O₅/PPy/GO nanocomposite. Characterization of the electrode material is carried out by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and atomic force microscopy (AFM). The electrochemical performance of the as-prepared nanocomposite is evaluated by different electrochemical methods including cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy (EIS) in 0.5 M Na₂SO₄ solution. Remarkably, V₂O₅/PPy/GO nanocomposite shows a specific capacitance of 750 F g^?1 at a current density of 5 A g^?1, which is far better than PPy (59.5 F g^?1), V₂O₅/PPy (81.5 F g^?1) and PPy/GO (344.5 F g^?1). Furthermore, V₂O₅/PPy/GO maintains 83% of its initial value after 3000 cycles, which demonstrates good electrochemical stability of the electrode during repeated cycling. These results demonstrate that the combination of electrical double layer capacitance of GO and pseudocapacitive behavior of the PPy and V₂O₅ can effectively increase the specific capacitance and cycling stability of the prepared electrode. Also, a symmetric supercapacitor device assembled by V₂O₅/PPy/GO nanocomposite yielded a maximum energy density of 27.6 W h kg^?1 at a power density of 3600 W kg^?1, and a maximum power density of 13680 W kg^?1 at an energy density of 22.8 W h kg^?1.     

Effect of graphene on the performance of nickel foam-based CoNi nanosheet anode catalyzed direct urea-hydrogen peroxide fuel cell

The highly porous electrode of a crisscrossed CoNi nanosheets array grown on reduced graphene oxide decorated Ni foam (CoNi/rGO@Ni foam) is fabricated through a facile dip and dry method followed by electroreduction and electrodeposition methods. The phase composition and morphology of the electrode are characterized by XRD, SEM, TEM, and EDS. In single electrode tests, CoNi/rGO@Ni foam electrode displays an excellent catalytic performance (330 mA cm⁻² at 0.6 V) and stability towards urea electrooxidation when comparing to Ni foam and CoNi nanosheets modified Ni foam (CoNi@Ni foam) electrode. Besides, a low initial oxidation potential of urea electro-oxidation to 0.14 V is achieved on the CoNi/rGO@Ni foam electrode. The introducing of rGO to the electrode greatly reduced the reaction activation energy from 14.47 to 10.35 kJ mol⁻¹. Besides, large active surface area (261.67 cm²) is also obtained from the electrode. The CoNi/rGO@Ni foam anode exhibits a maximum power density of 12.58 mW cm⁻² in direct urea-hydrogen peroxide fuel cell tests. Excellent performance shows in single electrode tests and fuel cell tests suggest that addition of rGO to the electrode is an easy and feasible method to enhance the performance of the catalyst.     

Hollow Pt skim-sandwiched Cu spheres supported on reduced graphene oxide-carbon nanotube architecture for efficient methanol electrooxidation

The disadvantages of high cost, easy poisoning and insufficient durability hinder platinum (Pt) application in direct methanol fuel cells. In this study, a hybrid of reduced graphene oxide/carbon nanotubes-supported hollow copper spheres (Cu/rGO@CNTs) is prepared by a one-step electrodeposition method. Then, the internal and external surfaces of hollow Cu spheres are coated with Pt skims to obtain a hollow bimetallic electrocatalyst (Pt/Cu/rGO@CNTs) through a simple galvanic replacement reaction by immersing Cu/rGO@CNTs in a chloroplatinic acid (H₂PtCl₆) solution. The three dimensional rGO@CNTs network structure benefit mass transport and electron transfer. Pt skims expose abundant active sites for electrocatalytic methanol oxidation reactions (MORs). Cu cores synergize Pt skims to enhance anti-poison ability. As a result, Pt/Cu/rGO@CNTs shows an excellent electrocatalytic activity for MORs with a robust tolerance of catalyst poisoning.     

A simple spray assisted method to fabricate high performance layered graphene/silicon hybrid anodes for lithium-ion batteries

Incorporating silicon (Si) in anodes has shown great promise for the development of high capacity Li-ion batteries (LIBs). Moreover, it is a safe and environmentally benign material, and hence suitable for large-scale manufacturing. However, volumetric expansion of Si particles upon lithiation causes irreversible damage to the anode structure and promotes an unstable solid electrolyte interface (SEI), that cause a rapid capacity drop. The architecture of successful Si-based anodes, therefore, needs to cater to the large volumetric expansion such that the high specific capacity of Si can be taken advantage of without having to worry about the detrimental effects of expansion. In this study, we introduce a simple and cost-effective spray-drying method to fabricate a layered (sandwich-like) anode structure using synthesized Si nanoparticles (NPs) and thermally reduced graphene oxide (rGO). The Si NPs are obtained by the magnesiothermic reduction of SiO₂ nanoparticles. Using an original, scalable, and simplistic spraying/drying method, we embedded Si NPs between two coats of strong yet flexible rGO sheets. The sandwich-like structure, which successfully contains the expansion of Si particles, protects the anode from detrimental conditions. With this new and uncomplicated production technique, the rGO-Si-rGO anode after 50 cycles, shows a high specific capacity of 1089 mAhg⁻¹ at 1C with 97% coulombic efficiency and a stable cycling performance at current densities up to 5C.     

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.