N-doped Reduced Graphene Oxide Research Articles

Natural sunlight energy harvesting using NiAl2O4@N-rGO hetero-junction for photocatalytic degradation of crystal violet dye: Kinetic and mechanistic insights

In this study, NiAl2O4 (NA) was synthesized by the co-precipitation route and its hetero-junctions were fabricated with N-doped reduced graphene oxide (N-rGO) through the ultra-sonication method. The structural, morphological, magnetic, optical and photocatalytic properties of synthesized NA, N-rGO, and the NA@N-rGO 1–4 hetero-junctions characterized by XRD, FTIR, SEM, VSM, PL and UV–visible spectroscopy, respectively. XRD results showed that crystallite size decreases from 25.01 nm (NA) to 15.20 nm for NA@N-rGO-4 and porosity increases up to 77.7 % for NA@N-rGO-4 making it remarkable for photocatalytic applications and FTIR results confirmed the formation of N-rGO as well as its successful integration into NA matrix, resulting in the formation of hetero-junctions. Magnetic properties were investigated using a vibrating sample magnetometer (VSM), revealing distinctive S-shaped hysteresis loops at 25 °C for both NA and N-rGO, as well as the NA@N-rGO 1–4 hetero-junctions and magnetic saturation decreases with an increase in N-rGO content as for NA@N-rGO-4 Ms drops to 0.0038 emu/g. Notably, the bandgap of NA@N-rGO-4 hetero-junction was effectively reduced from 3.0 eV (in the case of NA) to 2.1 eV, resulting in a discernible decrease in photoluminescence (PL) intensity and increase in e--h+ pair separation. Under visible light, NA@N-rGO-4 exhibited a remarkable 94.68 % efficiency in crystal violet (CV) dye degradation within just 90 min, outperforming NA's 59.05 % degradation efficiency and OH. Radicals play a major contribution to the degradation of dye. The optimization of degradation capabilities was achieved through the manipulation of catalyst dosage, dye concentration and varying pH values for the degradation of CV dye. NA@N-rGO-4 hetero-junction demonstrates the considerable potential for efficient dye degradation in wastewater under visible light, owing to its exceptional catalytic performance.

Mn and N-doped RGO as a sulfur hosting accelerate electron transfer and redox reactions for Li–S batteries

The notorious polysulfides shuttling and slow redox reaction kinetics largely limit the Li–S battery commercial application as an effective energy storage system. In this report, Mn/N catalysts were co-doped on a high specific surface area reduced graphene oxide (RGO) scaffold by a simple formamide media-assisted method to develop the sulfur holding material for Li–S battery. The N-doped RGO with conductive layer structure not only facilitates the ion and electron transfer, but also provides superb reservoir space for sulfur volume expansion and intermediate polysulfides. Moreover, the introduction of Mn metal catalysts both paly the roles of chemical trappers and electrocatalysts to chemically anchor the polysulfides and accelerate the redox kinetics. It is a promising holding material to improve the reutilization of the polysulfides and suppression of the shuttle effect in lithium-sulfur batteries. As a result, the high initial discharge capacity for the Mn-NG modified Li–S battery is about 1124.7 mAh g−1 at 0.2 C, which can still reach to 914.3 mAh g−1 after 100 cycles, with a retention rate up to 81%. We believe that our method offers a significant approach to prepare multi-functional sulfur hosts for high performance Li–S batteries.

Stable Cycling of BiSbSe1.5Te1.5 Conversion-Alloying Anodes

Conversion-alloying anodes based on metal-selenides/tellurides have been explored extensively during the past decade for usage in lithium-ion batteries (LIBs), in order to increase cell energy density.1,2 Due to the large expansion and contraction during (de)lithiation, however, deterioration due to pulverization is a main hurdle to overcome for stable cycling. Strategies such as nano-structuring and composites have been applied to improve the mechanical stability, but no silver-bullet has yet been found.Here we present proof-of-concept for a conversion-alloying based anode BiSbSe1.5Te1.5, a medium high-entropy alloy (MHEA). The main idea is that the increased entropy can enhance the mechanical properties via solid solution strengthening. The MHEA was synthesized using high-energy ball milling to get a single phase (R3m), which was subsequently used as the anode active material, and this without compositing with any carbon material, in contrast to previously reported Se/Te-based alloys.3,4 As a result, our half-cells (Li//MHEA) were able to attain stable cycling with high capacity (420 mAh g-1), agreeable capacity retention (84%), and coulombic efficiency (>99%) for 100 cycles at C/5 rate (Figure 1).5 The formation of a stable solid electrolyte interphase (SEI) was inferred by electrochemical impedance spectroscopy (EIS) data, showing reduced charge transfer resistance with cycling. Furthermore, operando XRD showed reversibility of the initial phases during (de)lithiation. We furthermore believe that moving from MHEAs to “proper” HEAs might further enhance the mechanical properties and stabilize the structure for even longer duration.Figure 1: a) Charge-discharge curves and b) galvanostatic cycling of Li//BiSbSe1.5Te1.5. References Li, L., Zhao, J., Zhao, H. & Mao, J. Bi2Se0.5Te2.5/S, N-doped reduced graphene oxide as anode materials for high-performance lithium ion batteries. J. Alloys Compd. 920, 166003 (2022).Fan, H. et al. Recent advances of metal telluride anodes for high-performance lithium/sodium-ion batteries. Mater. Horizons 9, 524–546 (2022).Zhang, Z., Zhao, X. & Li, J. SnSe/carbon nanocomposite synthesized by high energy ball milling as an anode material for sodium-ion and lithium-ion batteries. Electrochim. Acta 176, 1296–1301 (2015).Wei, Y. et al. Wrapping Sb2Te3 with a Graphite Layer toward High Volumetric Energy and Long Cycle Li-Ion Batteries. ACS Appl. Mater. Interfaces 12, 16264–16275 (2020).Alvi, S. et al. To be submitted. (2023). Figure 1

Synthesis, characterization and insights into the supercapacitive and electrocatalytic (OER) bi-functional properties of nitrogen-doped reduced graphene oxide using dicyandiamide precursor

A facile methodology to synthesize the nitrogen-doped reduced graphene oxide (NG) via a solvothermal process exhibiting a substantial content of either pyrrolic-N or pyridinic N, is demonstrated. In the synthesis of NG, different amounts of dicyandiamide (DCDA) with a constant (1 g) amount of graphene oxide have been taken in DMF (solvent). This approach produced the nanosheets of N-doped graphene (NG-2) which possess optimum defect density and 10.58 % total nitrogen. Nitrogen within this NG material predominantly manifests in four distinct bonding configurations, with the most prevalent being pyrrolic-N. The solvothermally synthesized N-doped reduced graphene oxide exhibited good charge storage characteristics. Three electrode testing of NG-2 shows high specific capacitance (865.82 F/g at a particular current density of 0.5 A/g) and a high energy density (76.96 Wh/kg) in acidic conditions. This sample showed poor electrocatalytic activity for oxygen evolution reaction (OER). However, the material prepared with very high amount of DCDA (NG-4) showed a total N-content of 29 % with high contribution of pyridinic N, demonstrated good electrocatalytic activity for OER following the four-electron path. The Tafel slope of NG-4 sample is around 140 mV/dec which implies the facile conversion of OH− into O2, at relatively low overpotential within an alkaline system. Consequently, the synthesized dual-functional N-doped reduced graphene oxide material holds characteristics for the advancement of carbon-based energy storage materials, and simultaneously be utilized as catalyst for OER.

Petaloid N-doped reduced graphene oxide supported zero-valent iron as catalyst activated peroxydisulfate for effective oxidation of β-hexachlorocyclohexane

Developing an efficient heteroatom-doped Fe-carbon catalyst is of great significance for the remediation of contaminated water and soil. In this study, a three-dimensional petaloid N-doped reduced graphene oxide (N-rGO)-supported nanoscale zero-valent iron (nZVI) composite (nZVI@N-rGO) was successfully prepared and applied to activate peroxydisulfate (PDS) to remove typical organochlorine pesticides (OCPs) from contaminated water and soil. The results indicated that N doping not only restructured the surface morphology of rGO and generated a petaloid nanosheet structure but also introduced additional defect sites for the loading of nZVI. nZVI@N-rGO effectively activated PDS to degrade β-hexachlorocyclohexane (β-HCH) in aqueous solution and contaminated soil. Characterization of the reaction process revealed that SO4∙-, •OH, 1O2 and O2∙- were the reactive species involved in β-HCH degradation and that the abundant N-doped sites and high conductivity of nZVI@N-rGO promoted the generation of reactive species and mediated direct electron transfer. Furthermore, the petaloid structure of N-rGO allowed for greater contact of PDS and β-HCH with nZVI, which improved the mass transfer of reactants. nZVI@N-rGO has good adaptability to different anions, humic acid concentrations and pH conditions in water. This work provides the necessary inspiration and guidance for the practical application of Fe-Carbon catalysts in the remediation of water and soil contaminated by OCPs.

Nitrogen-doped reduced graphene oxide enfolded zinc cobaltite micro flowers as efficient triiodide reduction for a platinum-free counter electrode in dye-sensitized solar cell applications

Diverse varieties of organic and inorganic materials have been employed as counter electrodes (CEs) in dye-sensitized solar cell applications (DSSCs) to replace platinum (Pt). Interestingly, the influence of N-doped reduced graphene oxide on ZnCo2O4 with high surface area, superior electrical activity, and chemical stability has been addressed in this work. Pure ZnCo2O4 (ZCO), ZnCo2O4/reduced graphene oxide (rGO) (ZCOG), and ZnCo2O4/nitrogen-doped reduced graphene oxide (N-rGO) (ZCONG) had synthesized using a facile hydrothermal technique, and their performance as a CE material in DSSC application was further investigated. The formation of the material free of impurities is depicted by X-Ray Diffraction (XRD) and Raman analysis. The analysis utilizing Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) confirmed the existence of ZnCo2O4 micro flowers made of rods and sheets as well as the thin sheet-like shape of graphene oxide (GO) and N-rGO. The X-ray photoelectron spectroscopy (XPS) analysis technique was employed to determine the chemical composition and purity of the prepared samples. Further, the BET analysis confirms the higher specific surface area (1198.431 m2/g) of the ZCONG sample. The electrochemical property of the coated CEs was investigated using cyclic voltammetry (CV) analysis with the iodine-based electrolyte in a three-electrode system showing superior catalytic properties of the ZCONG CE than the other ZCO and ZCOG CEs. The as-fabricated CEs were utilized to assemble the DSSC device, and the ZCONG CE reached a photovoltaic power conversion efficiency (PCE) of 5.84 ± 0.06%, surpassing ZCO (3.51 ± 0.15 %) and ZCOG (4.81 ± 0.08 %) CEs.

Single-Atomic Dispersion of Fe and Co Supported on Reduced Graphene Oxide for High-Performance Lithium-Sulfur Batteries.

High theoretical energy density and low cost make lithium-sulfur (LSB) batteries a promising system for next-generation energy storage. LSB performance largely depends on efficient reversible conversion of elemental sulfur to Li2S. Here, well-designed sulfur host materials including Fe or Co single atoms embedded on N-doped reduced graphene oxide (MNC/G with M = Fe or Co) are proposed to tackle the LSB challenges and enhance the electrochemical performance. Using a combination of Mössbauer spectroscopy and high-resolution scanning electron microscopy, the atomic dispersion of Co and Fe was revealed up to relatively high mass loadings. After optimization of the electrolyte/sulfur (E/S) ratio, FeNC/G shows the most promising cycle performance combining a constant high discharge capacity at low E/S values with the lowest polarization. In particular, the material FeNC/G@S with a high sulfur loading (9.4 mg cm-2) delivers a high area capacity of 7.7 mAh cm-2 under lean electrolyte conditions (6 mL g-1).

Customized design of nZVI supported on an N-doped reduced graphene oxide aerogel for microwave-assisted superefficient degradation of imidacloprid in wastewater

High-performance and energy-saving microwave (MW)-assisted catalysts are of great significance for MW-assisted treatments of wastewater. Herein, a novel nitrogen-doped reduced graphene oxide aerogel with supported nanoscale zero-valent iron (nZVI@N-rGOA) was successfully synthesized and used in the MW-assisted removal of imidacloprid (IMI) from wastewater. The resulting nZVI@N-rGOA had an open pomegranate-like multicompartment structure consisting of wrinkled flaky reticular N-rGOA walls and embedded nZVI particles, and the nZVI@N-rGOA/MW system rapidly eliminated nearly 100% of the IMI in a 10 mg/L solution within 2 min. The highly efficient MW-assisted catalytic degradation of IMI resulted from synergistic effects, including the nZVI active centres, pyridinic N sites and open pomegranate-like multicompartment structures, which facilitated MW harvesting, mass transfer of the reactants and generation of heat, electrons, holes and •OH radicals. Accordingly, the localized surface plasmon resonance and electron transfer processes enabled catalytic oxidations/reductions, respectively. This work provides a novel paradigm for designing MW-assisted catalysts for wastewater treatment.

Favoring the Selective H2O2 Generation of a Self-Antibiofouling Dissolved Oxygen Sensor for Real-Time Online Monitoring via Surface-Engineered N-Doped Reduced Graphene Oxide.

Dissolved oxygen (DO) is a key parameter in assessing water quality, particularly in aquatic ecosystems. The oxygen reduction reaction (ORR) has notable prevalence in energy conversion and biological processes, including biosensing. Nevertheless, the long-term usage of the submersible DO sensors leads to undesirable biofilm formation on the electrode surface, deteriorating their sensitivity and stability. Recently, the reactive oxygen species (ROS), such as the two-electron pathway ORR byproduct, H2O2, had been known for its biofilm-degradation activity. Herein, for the first time, we reported N-doped reduced graphene oxide (N-rGO) for H2O2 selectivity as the self-antibiofouling DO sensor. Introducing foreign atom doping could reorient the electron network of graphene by the electronegativity gap, which facilitated highly selective and efficient two electron pathway of ORR. Mitigating the N content of N-rGO had enhanced the H2O2 selectivity (57.5%) and electron transfer number (n = 2.84) in neutral medium. Moreover, the N-rGO could be integrated to a wireless DO monitoring device that might realize an applicable device in the aquatic fish farming.

In situ-growth ultrathin hexagonal boron nitride /N-doped reduced graphene oxide composite aerogel for high performance of thermal insulation and electromagnetic wave absorption

Owing to widely used various electronic devices in the rapidly developing 5G era, electromagnetic wave pollution could not be avoided. Security risks which caused by electromagnetic wave pollution have gotten serious attention. Especially in combat environment, applied electromagnetic wave absorption materials and reduced the surface temperature of combat equipment key parts would effectively reduce the risks of radar and infrared recognition. Herein, we designed hexagonal boron nitride (h-BN)/N-doped reduced graphene oxide (rGO) composite aerogels with 3D parallel porous network hetero-structure for electromagnetic wave absorption and thermal insulation. The results showed that attributed to structure design, dielectric loss and optimized impedance match, h-BN/rGO composite aerogels exhibited excellent electromagnetic wave absorption and thermal insulation performance. When the matching thickness was 3.1 mm, the effective absorption bandwidth was achieved up to 10.13 GHz in 7.9–18 GHz, and the minimum reflection loss was −21.49 dB. The TGA results exhibited that the thermal decomposition temperature of rGO was 560 °C, h-BN/rGO was 674 °C, which increased by 114 °C. Infrared imaging analysis showed that the surface temperature of 10 mm thick h-BN/rGO aerogel was only 44.45 °C in external thermal environment of 200 °C, which could effectively isolate the heat to 155.55 °C. The excellent electromagnetic wave absorption performance and effective heat isolation performance not only enabled the application of h-BN/rGO aerogel in the stealth materials, but also had application prospects in the thermal management field.

(Invited) Synthesis, Characterization and Quality Control of Heteroatom-Doped Graphene

Heteroatom doped graphene materials have gained attention as promising candidates for a variety of energy-related applications. Addition of heteroatoms in the graphene lattice is a powerful tool to modify their electronic, electrochemical, and catalytic properties. This presentation focusses on N-doped reduced graphene oxide and summarizes strategies to engineer the structure and properties of the material through control of the synthetic conditions. The produced N-doped graphene materials are characterized to determine their chemical composition, nitrogen content, degree of graphitization, surface area, electronic and electro-chemical properties. The scalability and manufacturability of the N-doped graphene materials are assessed and various examples of their current and future applications in batteries and supercapacitors are discussed.

N-doped reduced graphene oxide supported Pd-doped lanthanum vanadate constructs an electrochemical sensing platform for simultaneous detection of carbendazim and methyl parathion in food

The abuse of pesticides is apt to cause residue issues. In this study, an electrochemical sensing platform was developed using N-doped reduced graphene oxide (N-rGO) loaded with the Pd-doped lanthanum vanadate (Pd-LaV) to simultaneously detect two pesticides: carbendazim (CBZ) and parathion methyl (MP). The results demonstrated that N-doping can not only enhance the electron transport and catalytic ability of rGO, but also avoid the aggregation of Pd-LaV. Moreover, Pd compensated for the insufficient conductivity of LaV, fulfilling the catalytic performance of LaV better played out. N-rGO/Pd-LaV possessed abundant active groups, reaction sites, and effective interaction, which served its charge transfer rate and electrocatalytic ability as superior. In individual detection, LODs of CBZ and MP were 2.42 nmol/L and 1.85 nmol/L, respectively. In simultaneous detection, LODs of CBZ and MP were 1.94 nmol/L and 1.71 nmol/L, respectively. Finally, the sensing platform was applied to water and vegetable juice samples.

A simple one-pot method for growing metal (Co, Ni, Cu) oxide naoparticles on N-doped reduced graphene oxide and their application in lithium-ion storage

A simple one-pot method for growing metal (Co, Ni, Cu) oxide naoparticles on N-doped reduced graphene oxide and their application in lithium-ion storage

Bimetallic-based CuxCo3−xO4 nanoparticle-embedded N-doped reduced graphene oxide toward efficient oxygen evolution reaction and hydrogen evolution reaction for bifunctional catalysis

The fabrication of efficient electrocatalysts for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is essential for hydrogen production to obtain sustainable renewable energy. Owing to the increase in chemical complexity, multimetallic catalysts provide flexibility to alter their electronic structure to attain high intrinsic catalytic activity via synergistic effects. In this study, bimetallic copper-cobalt oxide nanoparticles (CuxCo3−xO4 NPs) embedded on nitrogen-doped reduced graphene oxide (N-RGO) substrates are fabricated as catalysts for the OER and HER via a facile solution-hydrothermal synthesis. In the fabricated N-RGO-supported Cu-doped Co3-xO4 nanoparticle (CuxCo3−xO4 NPs@N-RGO) hybrid catalyst, the RGO sheet acts as a conductive network to promote electron transfer, thereby increasing the electrical conductivity of the catalyst. Additional active sites acting as bridged sites from the Cu and N dopants improve the catalytic activity, resulting in outstanding electrochemical activity for OER and HER. The optimal Cu0.35Co2.65O4 NPs@N-RGO catalyst exhibits an overpotential of 170 mV at 10 mA cm−2 for HER and a low overpotential of 270 mV for the OER in basic media, which are comparable to those of Pt/C and IrO2. The synthesized catalyst is a promising bifunctional catalyst for overall water splitting.

Influence of molybdenum on Co3O4 coupled N-doped reduced graphene oxide composite for improved electrocatalytic alkaline oxygen evolution reaction: Stability and mechanism insights

The development of stable electrocatalysts for the catalysis of the electrochemical water-splitting process has become an area of particular interest in recent years. In this study, a simple interfacial method is proposed to fabricate a novel molybdenum (Mo)-substituted Co3O4 with N-doped reduced graphene oxide (N-rGO) composite for application as a high-performance oxygen evolution reaction (OER) electrocatalyst in a typical alkaline solution. Various efficient characterization methods are used to examine its structure, morphology, elemental composition, and surface area. The optimized 20MoCo/NRG composite exhibits improved electrocatalytic performance with robust electronic interfacial bonding, improved intrinsic activity, and high ECSA values. Furthermore, it exhibits remarkable electrocatalytic OER activity with a lower overpotential of 378 mV and minor Tafel slope value of 143 mV dec−1 at a current density of 10 mA cm−2 in a 1 M KOH solution compared with the other as-synthesized catalysts. Notably, the 20MoCo/NRG composite catalyst demonstrates exceptional durability for 15 h. Consequently, this effective interfacial nanostructure provides novel insights into the development of high-performance, long-lasting electrocatalysts for the water oxidation process.

Tailoring Metal-Organic Frameworks and Derived Materials for High-Performance Zinc-Air and Alkaline Batteries.

Developing multifunctional materials from earth-abundant elements is urgently needed to satisfy the demand for sustainable energy. Herein, we demonstrate a facile approach for the preparation of a metal-organic framework (MOF)-derived Fe2O3/C, composited with N-doped reduced graphene oxide (MO-rGO). MO-rGO exhibits excellent bifunctional electrocatalytic activities toward the oxygen evolution reaction (ηj=10 = 273 mV) and the oxygen reduction reaction (half-wave potential = 0.77 V vs reversible hydrogen electrode) with a low ΔEOER-ORR of 0.88 V in alkaline solutions. A Zn-air battery based on the MO-rGO cathode displays a high specific energy of over 903 W h kgZn-1 (∼290 mW h cm-2), an excellent power density of 148 mW cm-2, and an open-circuit voltage of 1.430 V, outperforming the benchmark Pt/C + RuO2 catalyst. We also hydrothermally synthesized a Ni-MOF that was partially transformed into a Ni-Co-layered double hydroxide (MOF-LDH). A MO-rGO||MOF-LDH alkaline battery exhibits a specific energy of 42.6 W h kgtotalmass-1 (106.5 μW h cm-2) and an outstanding specific power of 9.8 kW kgtotalmass-1 (24.5 mW cm-2). This work demonstrates the potential of MOFs and MOF-derived compounds for designing innovative multifunctional materials for catalysis, electrochemical energy storage, and beyond.

Facile synthesis of N-doped reduced graphene oxide matrix-covered porous Fe2VO4 hybrid composite nanostructures as anode material for lithium-ion batteries

For iron vanadium-based lithium (Li)-ion batteries (LIBs), enhancing solidity as well as exploring storage mechanism is important. Herein, a facile hydrothermal method is employed to fabricate N-doped reduced graphene oxide-wrapped porous iron vanadate (FVO@N-rGO) hybrid composite nanostructures (HCNSs), followed by the calcination under the N2 atmosphere. The as-prepared FVO@N-rGO HCNSs are used as an anode material for LIBs. The FVO@N-rGO HCNSs electrode delivers a high reversible specific capacity of 711 mA h g−1 at 100 mA g−1 and durable cycling life (226 mA h g−1 at 3000 mA g−1). The Li+ intercalation kinetics (from cyclic voltammetry analysis) reveal that the Li storage capacity of FVO@N-rGO HCNSs is normally dominated via a pseudo-capacitive behavior. A full cell using commercial LiNi0.3Mn0.3Co0.3O2 (NMC111) as a cathode and pristine FVO nanospheres and FVO@N-rGO HCNSs as an anode is also fabricated. The obtained good reversible capacity, stability, and rate capability may be due to the synergetic result of three-dimensional HCNSs construction and porous morphology with a large surface area, which offers void space to shield size expansion/contraction along with reducing the diffusion coefficient for Li ions/electrons in the cycling process. Thus, this study gives a deep understanding of improving the cell performance of iron vanadium-based LIBs.

Sulfite activation by N-doped reduced graphene oxide for As(III) oxidation: Synthesis, efficiency, and mechanisms

As a metal-free alternative, graphene-based catalysts have attracted increasing attention for minimizing the risk of heavy metal exposure. In this study, a nitrogen–doped reduced graphene oxide (N-rGO) material was synthesized by a one–pot hydrothermal method using dicyandiamide as the precursor. N-rGO has been adopted for sulfite activation for the first time, to our knowledge. The established N–rGO/sulfite system could effectively remove As(III) in water, and the solution pH and dissolved oxygen were the most important factors affecting the removal. The results of density functional theory calculations indicated that sulfite activation was more likely to occur on C atoms adjacent to the N dopant. It was inferred that the generated hydroxyl radical (HO•) played a vital role in As(III) oxidation. In addition, the conversion of pyridinic nitrogen to pyrrolic nitrogen was responsible for the poor long–term stability of N-rGO. These results demonstrated that N-rGO was a promising catalyst for water treatment.

Electrochemical Co-reduction of N2 and CO2 to Urea Using Bi2S3 Nanorods Anchored to N-Doped Reduced Graphene Oxide

Producing "green urea" using renewable energy, N2, and CO2 is a long-considered challenge. Herein, an electrocatalyst, Bi2S3/N-reduced graphene oxide (RGO), was synthesized by loading the Bi2S3 nanorods onto the N-RGO via a hydrothermal method. The Bi2S3/N-RGO composites exhibit the highest yield of urea (4.4 mmol g-1 h-1), which is 12.6 and 3.1 times higher than that of Bi2S3 (0.35 mmol g-1 h-1) and that of N-RGO (1.4 mmol g-1 h-1), respectively. N-RGO, because of its porous and open-layer structure, improves the mass transfer efficiency and stability, while the basic groups (-OH and -NH2) promote the adsorption and activation of CO2. Bi2S3 promotes the absorption and activation of inert N2. Finally, the defect sites and the synergistic effect on the Bi2S3/N-RGO composites work simultaneously to form urea from N2 and CO2. This study provides new insights into urea synthesis under ambient conditions and a strategy for the design and development of a new material for green urea synthesis.

Iron-doped nickel sulfide nanoparticles grown on N-doped reduced graphene oxide as efficient electrocatalysts for oxygen evolution reaction

Transition metal sulfide electrocatalysts have attracted substantial attention because of their outstanding activity in the oxygen evolution reaction (OER). Herein, the highly efficient iron-doped nickel sulfide catalyst supported on functionalized N-doped reduction graphene oxide (Fe-NiS/NrGO) was successfully prepared via a combination of hydrothermal and vulcanization methods. The doped Fe modifies the electronic structure of NiS, which accelerates the kinetics of OER. The NrGO, with a large specific surface area and high conductivity, facilitates the homogeneous dispersion of Fe-NiS nanoparticles, increasing the active catalytic area and accelerating the charge transfer rate. The Fe-NiS(2)/NrGO exhibits superior OER performance with an overpotential of 344 mV to achieve a current density of 100 mA cm−2 in 1.0 M KOH, and the Tafel slope is as low as 47 mV dec−1. The OER performance of Fe-NiS(2)/NrGO is better than that of commercial RuO2. This work will eventually help to rationally design efficient transition-metal catalysts in future technologies for OER.