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The catalytic potential of single atom incorporated heterostructures holds substantial promise because of their ability to offer customizable chemical functionality and abundant active sites. In this study, a novel approach is employed to synthesize ruthenium single atoms (RuSA) implanted on bimetallic NiFe-LDH derived sulfide nanosheet heterostructures (RuSA-NiS2-FeS2) via a facile technique. Experimental findings demonstrate that RuSA-NiS2-FeS2 exhibits lower overpotential (η) for water splitting. Specifically, the hydrogen evolution reaction (HER) overpotentials at current densities of (10 and 100) mA cm−2 are measured to be (57 and 187) mV, respectively. Similarly, at (20 and 100) mA cm−2, the oxygen evolution reaction (OER) overpotentials are recorded to be (242 and 304) mV, respectively. Conspicuously, the RuSA-NiS2-FeS2 (+, −) electrolyzer requires cell potentials of (1.47 and 1.74) V at (10 and 100) mA cm−2, lower than the cell potentials of (1.57 and 1.92) V required by the RuO2@NF (+)//Pt–C@NF (−) device to achieve similar current densities. These experimental results and the Density Functional Theory (DFT) calculations unveil that our research offers a promising method for single atom implanted heterostructures that can be used for large-scale clean hydrogen production through water electrolysis. [ABSTRACT FROM AUTHOR]

The preparation of highly efficient and low-priced multi-functional electrocatalysts for the hydrogen evolution reaction (HER), oxygen reduction reaction (ORR), and oxygen evolution reaction (OER) is crucial for robust zinc–air batteries (ZABs) and water electrolyzers. Herein, we report the preparation of novel Mott–Schottky Co2P/Co heterostructures encapsulated by N,P co-doped graphene and carbon nanotubes (Co2P/Co@N-CNT/NPG) using an in situ pyrolysis strategy, achieving superior trifunctional catalyst performance for the ORR, OER, and HER. The theoretical calculation indicates that the synergistic effect of the Mott–Schottky catalyst could increase the electron transport, trigger the active sites, and enhance the performance toward the ORR/OER. The Co2P/Co@N-CNT/NPG-based ZAB displays a considerable peak power density of 145 mW cm−2, and an outstanding cycle-life of 800 h. Furthermore, the flexible ZAB delivers superior mechanical properties with high flexibility, demonstrating its potential feasibility for practical application. Additionally, the water electrolysis device constructed using Co2P/Co@N-CNT/NPG electrodes requires a small cell voltage of 1.66 V at 10 mA cm−2, indicating the impressive ability to apply the catalyst for commercial energy storage and harvesting devices. [ABSTRACT FROM AUTHOR]

Herein, an efficient bifunctional electrocatalyst based on binary metal nitride (Zn3N2–Co2N) nanorod arrays decorated with ultrathin Co3O4 nanoparticles is prepared to improve overall water splitting performance. Notably, a charge redistribution process occurs at the heterointerface between the host metal nitride and the guest Co3O4, resulting in the regulation of both their electronic structures to facilitate the reaction kinetics of hydrogen/oxygen evolution reaction (HER/OER). Using the material to catalyze the HER, current density of 10 and 50 mA cm−2 are delivered at small overpotential of 80.5 and 121.7 mV, respectively. Similarly, for OER, under the action of the material, overpotential of only 271.7 and 335.7 mV, respectively, is required to achieve 10 and 50 mA cm−2. Thus, an electrolyzer is assembled with the material as both cathode and anode, and shows high performance with a small cell voltage of 1.59 V at 10 mA cm−2, and excellent stability. [ABSTRACT FROM AUTHOR]

The development of multi-metal mixed organic-framework (MMOF)-derived phosphides as promising bifunctional electrocatalysts in energy conversion holds great potential for water splitting due to the high porosity, surface area, crystallinity and exposure of more active functional sites and super inherent catalytic efficacy they offer. Herein, we have fabricated hybrid carbon shell encapsulated nitrogen trimetallic phosphide (Ni–Fe–Mn–P) ultrathin nanosheets derived from a pristine trimetallic-organic framework (Ni–Fe–Mn-MOF) grown on nickel foam using 2-aminoterephthalic acid as the ligand. The curved edge, nitrogen and carbon co-doped trimetallic-organic framework-derived phosphide grown on nickel foam (Ni–Fe–Mn–P/NC@NF) demonstrates low overpotentials of 72 mV at 10 mA cm−2 for the hydrogen evolution reaction (HER) and 274 mV at 30 mA cm−2 for the oxygen evolution reaction (OER), with corresponding Tafel slopes of (79.8 and 56.8) mV dec−1 for the HER and OER, respectively, in 1 M KOH electrolytic solution. The efficient and highly stable electrocatalyst, when constructed as a Ni–Fe–Mn–P/NC@NF (+, −) device, exhibits a cell voltage of 1.52 V at 10 mA cm−2, lower by 0.06 V than that of the benchmark device RuO2@NF (+)//Pt–C@NF (−) at the same current density. We believe this work opens the way for Ni–Fe–Mn–P/NC@NF (+, −) to be applied in industrial overall electrocatalytic water-splitting. [ABSTRACT FROM AUTHOR]

Concerning the issues of compressed hydrogen (H2) storage, we have developed a novel H2 gas barrier coating containing a dense network structure of thermoplastic polyurethane (TPU)/epoxy semi-interpenetrating network (S-IPN) reinforced with a graphene oxide (GO)/h-boron nitride (BN) hybrid nanofiller (f-GO-BN) for nylon 6 based pressure vessels. A new strategy was adopted to synthesize f-GO-BN by first reacting the aminosilane with GO in the presence of carbodiimide followed by the addition of BN, instead of following the reverse order as reported earlier. The new method manifested homogeneous distribution of BN on the GO surface with higher grafting efficiency, as well as partial reduction of GO, which ultimately exhibited a synergistic effect in mechanical properties when the hybrid nanofiller was dispersed in the S-IPN. The long tortuous path provided by f-GO-BN in conjunction with the dense crosslinked network of the S-IPN as formed after the spray coating drastically reduced the H2 transmission rate (H2GTR) at 25 °C, and at elevated temperature (50 °C). The 10 wt% f-GO-BN filled S-IPN containing 40 wt% epoxy exhibited a 97% reduction of H2GTR at 25 °C and the permeability coefficient was extremely low (0.006 cm3 mm m−2 d−1 atm−1). Moreover, f-GO-BN improved the thermal conductivity and water contact angle, and minimized the thermal expansion of the coated layer. The epoxy chains of the S-IPN and the grafted aminosilane delineated a strong adhesion with nylon 6 at ambient, as well as cryogenic temperatures, ensuring the long-term applicability of the barrier coating. [ABSTRACT FROM AUTHOR]

Electrochemical water-splitting is emerging as a promising pathway to produce pure and green hydrogen. However, the sluggish kinetics of the oxygen evolution reaction (OER) and slow reaction rate of the hydrogen evolution reaction (HER) remain challenging issues. The state-of-the-art Pt and RuO2/IrO2 electrocatalysts demonstrate excellent HER and OER performance. However, the scarcity and high cost hinder their practical applications. Herein, we present a novel approach to design a WCoSe/WCo3O4 heterostructure and use it as an effective bifunctional electrocatalyst for overall water-splitting. The synergistic effect of W and Co metal cations in the heterogeneous phase of Se and O anions could increase the charge transfer and electronic modulation of the material which could improve the catalytic activities. The water electrolysis device with the WCoSe/WCo3O4 heterostructure as a bifunctional catalyst required a small cell voltage of ∼1.49 and 1.66 V at current densities of 10 and 100 mA cm−2. Furthermore, the water-splitting cell displayed an exceptional durability of 100 h, surpassing the state-of-the-art Pt/C‖RuO2 electrolyzer. This work offers a promising approach to construct novel 3D heterostructure electrocatalysts, which would be suitable for various energy conversion applications. [ABSTRACT FROM AUTHOR]

Designing an earth-abundant electrode material with high activity and durability is a major challenge for water splitting to produce clean and green hydrogen energy. In this study, we report a novel high-performance electrocatalyst derived from a unique three-dimensional hierarchical network of two-dimensional iron-doped nickel selenide nanosheets (2D Fe-doped NiSe NSs) and high-quality carbon nanotubes (CNTs) grown on a carbon paper substrate. The synergistic effects derived from Fe doping and interfering effects between 2D NSs and CNTs produce an enrichment of electroactive sites and good electrical conductivity, thereby significantly improving the electrocatalytic oxygen evolution activities. As a result, the catalyst requires an overpotential of only 282.7 mV to achieve 10 mA cm−2 in 1.0 M KOH electrolyte. An electrolyzer of Pt/C(−)//Fe-doped NiSe NSs/CNTs(+) demonstrates a cell voltage of 1.57 V and effective durability, superior to the state-of-the-art Pt/C(−)//RuO2/C(+) system (1.66 V) as well as recently reported catalysts. The achievements indicate a prospective catalyst for enhancing the OER in overall water splitting application. [ABSTRACT FROM AUTHOR]

The rational design of free-standing hierarchical core–shell nanoporous architectures is a good strategy for fabricating next-generation electrode materials for application in electrochemical energy conversion/storage systems. Herein, hierarchical core–shell 3D Co9S8@Nix:Moy–Se nanowire arrays (NWAs) are constructed by a low-cost, straightforward two-step hydrothermal method and an effective electrodeposition process. The optimal 3D Co9S8@Ni0.5Mo0.5–Se NWA electrode displays an excellent specific capacity of 460.81 mA h g−1 with a corresponding areal capacity of 0.93 mA h cm−2 at 1.5 mA cm−2. It also demonstrates superb rate capability (∼68.4% capacity retention at 20 mA cm−2) and remarkable cycling stability (∼94.3% capacity retention after 10 000 charge and discharge cycles). Additionally, an asymmetric supercapacitor (ASC) is assembled using the hierarchical 3D Co9S8@Ni0.5Mo0.5–Se NWAs as the positive electrode, and the as-obtained Fe2O3@PANNFs/N-rGO aerogel as the negative electrode. The assembled Co9S8@Ni0.5Mo0.5–Se//Fe2O3@PANNFs/N-rGO ASC shows a larger operating voltage range of 1.7 V, a high electrochemical energy storage capability (96.90 W h kg−1 at 1158 W kg−1), and excellent cycling stability (∼94.47% retention of the original capacity after 10 000 cycles). The all-solid-state ASC device that is also fabricated exhibits a high output working potential window of ∼1.8 V, and an outstanding energy density of ∼102.94 W h kg−1 at ∼1534 W kg−1, demonstrating that the hierarchical 3D Co9S8@Ni0.5Mo0.5–Se NWA electrode material is a potential candidate for high-performance energy storage devices. [ABSTRACT FROM AUTHOR]

Rechargeable zinc–air batteries (ZABs) have emerged as promising alternatives for conventional Li-ion batteries due to their high energy density and low manufacturing cost. However, Pt/C and RuO2-based conventional rechargeable ZABs are mainly constrained by the sluggish kinetics of oxygen reduction/oxygen evolution reactions (ORR/OER), limiting commercialization possibilities. Herein, a new type of oxygen vacancies enriched cobalt-doped molybdenum oxynitride quantum dot-anchored N-doped carbon nanosheets (VO-CMON@NCNs) was demonstrated as an advanced air-cathode for long-life rechargeable ZABs. Such VO-CMON@NCN catalyst has an exceptional ORR performance with a high half-wave potential of 0.857 V and tremendous OER performance with an ultrasmall overpotential of 240 mV at a current density of 10 mA cm−2, outperforming conventional Pt/C and RuO2 catalysts. As proof of concept, rechargeable ZABs with an optimal VO-CMON@NCN-800 air-cathode showed an ultrahigh specific capacity of 721.2 mA h gZn−1 at a current density of 5 mA cm−2, a tremendous peak power density of 143.7 mW cm−2, and ultralong cycling life of 500 h. These consequences suggest that the oxygen vacancies enriched VO-CMON@NCN can serve as promising bifunctional catalysts for next-generation metal–air batteries and other energy-related applications. [ABSTRACT FROM AUTHOR]

In recent years, much effort has been devoted to developing hybrid supercapacitors due to their capability to deliver both high energy and power density. The hybrid approach is advantageous in terms of reinforcing the synergic combination of the properties of different components in a hybrid composite. However, a large kinetic mismatch existing between the fast capacitive and sluggish battery-type electrodes greatly hinders its advancement. In this work, we report the fabrication of a solid-state hybrid supercapacitor (SSHSC) device using metal–organic framework (MOF)-derived cobalt-embedded N-doped carbon nanofibers (Co–N-CNFs) and Co2−xFexP–N–C micropillar arrays grown on Ni foam (Co2−xFexP–N–C/NF) as multi-component hybrid electrodes with improved charge storage kinetics. Such Co–N-CNFs (negative electrode) exhibited a remarkable specific capacitance of 280 F g−1 at a current density of 1 A g−1, while Co2−xFexP–N–C/NF (positive electrode) exhibited a high specific capacity of 345 mA h g−1 at a current density of 1 A g−1 due to the synergistic combinations of different components in a single hybrid composite. The assembled Co2−xFexP–N–C/NF(+)//Co–N-CNFs(−) SSHSC device demonstrated a high specific capacity of 104 mA h g−1 at a current density of 1 A g−1 with a maximum energy density of 84.7 W h kg−1 at a power density of 706 W kg−1. It also exhibited excellent stability and reversibility with a capacity retention of 93% and coulombic efficiency of 99.6% after 10 000 galvanostatic charge–discharge (GCD) cycles. Two SSHSC devices connected in series after being charged could easily light up a red LED bulb. These excellent performances indicate that Co–N-CNFs(−) and Co2−xFexP–N–C/NF(+) materials could be considered as potential electrodes for high energy density storage systems. [ABSTRACT FROM AUTHOR]

Transparent and flexible energy-storage devices have currently gained a lot of attention as wearable and portable electronics. Herein, we develop a one-step electrodeposited MoS2 nanosheet@Ni-mesh core–shell network nanostructure as a transparent negative electrode for the flexible and transparent asymmetric solid-state supercapacitor (FT-ASSc). In the fabricated core–shell nanosheet network architecture, the junctionless interconnected Ni-mesh network with excellent conductivity contributes to superior electron transport pathways, and the nanostructure of the MoS2 over the Ni-mesh provides effective interface contact between the active material and current collector. As a result, the MoS2@Ni-mesh network negative electrode provides an areal capacitance of 7.31 mF cm−2 at the scan rate of 10 mV s−1 with an 80% capacity retention rate after 5000 GCD cycles. Moreover, the fabricated FT-ASSc with a transmittance of 51% can operate up to a maximum working potential window of 1.6 V and also provide a maximum volumetric capacitance of 48.32 mF cm−3 at 0.4 mA cm−3 current density. This work might provide a new strategy for improving the electrochemical performance of transparent and flexible energy-storage devices for next-generation integrated electronic gadgets. [ABSTRACT FROM AUTHOR]

Innovating efficient and robust electrocatalysts with economical production cost for the oxygen reduction reaction (ORR) is of utmost significance for enhancing the energy efficiency of fuel cells and metal–air batteries. Herein, a single-step doping/annealing strategy has been developed for fabricating an Fe–N–C/Fe3C/C–S–C nanohybrid with a high N-doping level, well-defined mesoporous/microporous architecture, and high density of efficient active sites. The importance of tuning the S-doping into the electrocatalyst carbon framework has been fully elaborated for the first time. Under alkaline conditions, the nanohybrid displayed an exceptional onset potential (E0) and half-wave potential (E1/2) of 1.078 and 0.929 V vs. reversible hydrogen electrode (RHE). Furthermore, it manifests a dominant four-electron transfer reaction, marvelous selectivity for the ORR in the presence of methanol, and excellent durability after 15 000 potential cycles with almost zero degradation in performance under both acidic and alkaline conditions. The superb performance is due to the high density of active sites, like FeNx, FeSx, Fe3C, pyridinic-N, graphitic-N, C–S–C, and C–SOx–C, that efficiently catalyze the ORR. In addition, the high graphitization degree boosts the electron conductivity and corrosion resistance; meanwhile, the high surface area and ideal mesoporosity enhance the mass transfer and facilitate the maximum exposure of the active sites to the electrolyte and reactants. [ABSTRACT FROM AUTHOR]

The electrocatalytic water-splitting performance of MoS2 nanostructures can be improved by increasing the edge density, activating basal planes, expanding the interlayer spacing and stabilizing the 1T-phase. In this work, for the first time, we have studied the synchronous involvement of all these driving factors to achieve the highest bifunctional performance of MoS2 for water-splitting following doping and intercalation of nickel (Ni) and phosphorus (P) in a single-step reaction. Two nanostructures, nanoflowers (1T-Ni0.2Mo0.8S1.8P0.2 NFs, powder) for large scale synthesis and freestanding nanosheets on carbon-cloth (1T-Ni0.2Mo0.8S1.8P0.2 NS/CC) as binder-free electrodes, are fabricated. Co-doping of Ni and P enriches the 1T-phase, expands the interlayer spacing by 24%, activates basal planes significantly and increases the edge density of MoS2 in the 2D-nanostructures. The 1T-Ni0.2Mo0.8S1.8P0.2 NS/CC and 1T-Ni0.2Mo0.8S1.8P0.2 NFs exhibit significantly low overpotentials of 55 and 99 mV at the current density of 10 mA cm−2 for the hydrogen evolution reaction (HER) and 286 and 305 mV at 40 mA cm−2 for the oxygen evolution reaction (OER), respectively. Further, 1T-Ni0.2Mo0.8S1.8P0.2-NS/CC (±) and 1T-Ni0.2Mo0.8S1.8P0.2-NF (±) alkaline electrolyzers require only 1.52 and 1.53 V, respectively, to generate a current density of 20 mA cm−2 with robust stability, and are much superior to recently reported electrocatalysts, indicating the immense potential of the employed strategy for developing highly efficient and low-cost electrocatalysts for water-splitting. [ABSTRACT FROM AUTHOR]

The development of highly efficient electrocatalysts for simultaneous evolution of hydrogen and oxygen is a vital concern in water splitting. In this study, a novel catalyst derived from a porous interconnected network of nickel cobalt oxysulfide interfacial assembled Cu@Cu2S nanowires was rationally designed. It was recognized that the formation of multi-integrated active centers and a higher number of active sites, together with an adjusted adsorption energy towards reactants caused by the modulated surface and crystalline distortion of the NiCo oxide layer due to S insertion synergistically promoted both HER and OER. In addition, such 3D innovative core–shell structure effectively fine-tuned conductive properties and maximized interfacial contact to improve charge/mass transfer, thereby boosting catalytic activity and durability towards hydrogen and oxygen evolution. The catalyst only required an overpotential of 203 mV to achieve a current response of 20 mA cm−2 for the HER and 295 mV to reach 50 mA cm−2 for the OER in 1.0 M KOH medium. A developed electrolyzer enabled a small cell voltage of 1.61 V at 20 mA cm−2 without performance decay upon long-term operation. This result suggested an exciting prospect for developing new bifunctional electrocatalysts, which could effectively accelerate both hydrogen and oxygen evolution for water splitting applications. [ABSTRACT FROM AUTHOR]

A new type of electrodes with attractive nanostructures is garnering extensive attention for application in energy storage technologies owing to the ultrahigh charge storage properties of these electrodes. Transition metal dichalcogenides (TMDs), especially ternary metal selenide-based TMDs, exhibit excellent electrical conductivity and a lower band gap. However, to date, only few studies have been reported on the application of Se-based nanostructures. To achieve high electrochemical performance, herein, we established a novel flexible electrode consisting of tin nickel selenide (SnxNi1−xSe2) vertically grown on carbon fiber cloth (CFC) with tunable composition and attractive nanostructures, which enhanced the electrical conductivity, provided more electroactive surface area, and shortened the electron/ion transport pathways. Due to the hierarchical nanostructures and superior electrical conductivity, the optimal Sn0.33Ni0.67Se2 electrode showed significantly improved electrochemical performance, which included an ultrahigh specific capacity of ∼346 mA h g−1 at a current density of 1.0 mA cm−2, extraordinary rate capability, and outstanding durability. Remarkably, a flexible supercapacitor was assembled using Sn0.33Ni0.67Se2 as the positive electrode and Fe2O3@NG as the negative electrode, resulting in an ultrahigh energy density (∼90.3 W h kg−1 at 0.631 kW kg−1), tremendous power density (20.14 kW kg−1 at 67.2 W h kg−1), and super-high cycling life (∼96.41% capacity retention after 10 000 charge–discharge cycles at a high current density of 30 mA cm−2). These results clearly indicate that the hierarchical Sn0.33Ni0.67Se2 nanosheets have substantial potential for next-generation energy conversion and storage technologies. [ABSTRACT FROM AUTHOR]

A porous, efficient, and durable nonprecious electrocatalyst for the oxygen reduction reaction (ORR) under both alkaline and acidic conditions is synthesized by a green, solvent-free, one-pot, economical, scalable, and template-free strategy. In situ formed graphitic carbon nitride (g-C3N4) is utilized as a sacrificial template for constructing the core–shell Fe3C@NSC electrocatalyst with a highly porous substructure and nanosheet-like morphology. The presence of glucose facilitates the homogeneous distribution of nanoparticles and establishes the nanosheet structure, otherwise agglomeration and formation of nanotubes occur in the Fe3C@NSC electrocatalyst. Optimizing the synthetic conditions generates a highly active ORR electrocatalyst with a unique mesoporous architecture, large surface area, high nitrogen doping level, encapsulated Fe3C nanoparticles in NS co-doped carbon layers and multiple exposed edge active centers. The best performing electrocatalyst displays outstanding ORR performance under alkaline conditions with onset potential and half-wave potential (E1/2) values of 1.059 and 0.938 V vs. the reversible hydrogen electrode (RHE), much higher than those of the state-of-the-art commercial Pt/C (20%), and admirable performance in acidic media. In addition, it exhibits 4e− selectivity, tolerance toward methanol, and superb durability with zero degradation after 12 000 potential cycles under both alkaline and acidic conditions. These exceptional characteristics make the as-synthesized electrocatalyst one of the top-level non-precious ORR electrocatalysts reported to date. [ABSTRACT FROM AUTHOR]

Metal oxides have attracted great attention as active materials for supercapacitor devices because of their high energy densities. However, their application for transparent supercapacitors is limited due to their opaqueness. The challenge remains to fabricate flexible transparent metal oxide supercapacitor electrodes. Here, in this paper, we report a novel technique to fabricate flexible transparent core–shell MnO2@AuNF network electrodes for flexible transparent supercapacitors. A high electro-optical performance AuNF network electrode (sheet resistance 9.58 Ω sq−1 and optical transparency ∼93.13%) was fabricated using a scalable electrospinning process and thermal vacuum deposition technique. With the AuNF network electrode as a current collector, a hierarchal MnO2 nanosheet was electrodeposited over the AuNF network, yielding a highly interconnected core–shell MnO2@AuNF network electrode structure with high transparency (∼86%). The fabricated MnO2@AuNF network electrode exhibited a high areal capacitance of 8.26 mF cm−2 at 5 mV s−1, along with high rate capability, long-term cycling stability, and excellent mechanical flexibility. Furthermore, the assembled flexible transparent supercapacitor device also showed high transparency (∼79%), a high energy density of 0.14 μW h cm−2 at a power density of 4 μW cm−2, along with excellent mechanical flexibility. [ABSTRACT FROM AUTHOR]

Metal–organic framework derived nanostructures have unique properties, such as large specific surface area, exclusive porous networks, numerous active sites, and exceptional electrochemical properties, when compared to traditional nanostructures. Herein, a novel strategy is proposed to design and fabricate hierarchical copper cobalt sulfide nanosheet (CuCo2S4 NS) arrays from a metal–organic framework. The hierarchical CuCo2S4 NS arrays can provide enriched electroactive sites, as well as shorten the ion/electron diffusion pathways. When evaluated as electrodes for supercapacitors (SCs), the CuCo2S4 NS electrode exhibited remarkable electrochemical properties with an ultra-high specific capacity of ∼409.2 mA h g−1 and an areal capacity of ∼0.96 mA h cm−2 at a current density of 3 mA cm−2, exceptional rate capability (∼77.9% capacity retention at a higher current density of 50 mA cm−2), and outstanding cycling stability (∼94.2% capacity retention after 10 000 cycles). Most importantly, the assembled CuCo2S4 NS//Fe2O3/NG solid-state asymmetric SC displayed a wide operating potential window of 1.6 V with an ultra-high volumetric capacity of ∼2.1 mA h cm−3 at a current density of 3 mA cm−2, an excellent energy density of ∼89.6 W h kg−1 at a power density of ∼663 W kg−1, and an ultra-long cycle life (∼91.5% capacity retention after 10 000 cycles). This proposed method provides a general protocol to design and fabricate metal sulfide nanosheet arrays with superior electrochemical energy storage properties and exceptional cycling stability, holding limitless potential for future energy storage devices in commercial aspects. [ABSTRACT FROM AUTHOR]

To develop supercapacitors (SCs) with high energy and power densities, a new type of electrode material with unique properties is strongly required. Metal sulfides (MSs) have been recently studied as promising electrode materials for high-performance SCs because they have excellent redox properties, outstanding electrical conductivity, exceptional catalytic activity, and ultra-high specific capacity. However, their large volume changes and poor rate performances seriously hinder their commercial applications. Herein, a novel nitrogen-doped graphene encapsulated cobalt iron sulfide core–shell (Co8FeS8@NG) hybrid was successfully synthesized through a facile, scalable, and single-step in situ hydrothermal technique. The hierarchical core–shell Co8FeS8@NG hybrid was employed as an advanced electrode material for high-performance solid-state asymmetric SCs (ASCs). The Co8FeS8@NG electrode delivers an ultra-high specific capacitance of ∼1374 F g−1 at a current density of 2 A g−1, with tremendous rate capability (∼71.69% of capacitance retention at 40 A g−1) and excellent cycling stability (∼96.1% of capacitance retention after 10 000 cycles). Furthermore, the assembled Co8FeS8@NG//FeS@NG ASC device exhibits an ultra-high energy density of ∼70.4 W h kg−1 at a power density of 0.598 kW kg−1, exceptional power density (∼22.55 kW h kg−1 at 49.5 W h kg−1), and outstanding cycling stability (∼93.7% of initial capacitance after 10 000 cycles). Therefore, these results demonstrate a simple and cost-effective route for the development of new types of NG encapsulated ternary MSs for future electronics. [ABSTRACT FROM AUTHOR]

The design and development of innovative heterostructures with multifunctional properties are technically very important for efficient practical energy storage and conversion applications. Herein, we report the synthesis of a nitrogen-doped carbon (N–C) layer sandwiched between MnCo2O4 and MnO2 (MnCo2O4@N–C@MnO2) as a core@sandwich@shell type heterostructure on Ni foam. The thin layer of sandwiched N–C acts as a “superhighway” for good electron/ion transport and protects the MnCo2O4 and MnO2 from destructive morphological changes during repeated charge–discharge processes. The MnCo2O4@N–C@MnO2 material is well characterized by standard techniques, and its energy storage performance is studied in a three-electrode system and solid-state asymmetric capacitor device. The resultant electrochemical performance is compared with those of MnCo2O4 and MnCo2O4@N–C. The MnCo2O4@N–C@MnO2 electrode exhibits an excellent areal/gravimetric capacity of 0.75 mA h cm−2/312 mA h g−1 at 3 mA cm−2 with ca. 89.6% capacitance retention after 10 000 cycles. A solid-state asymmetric supercapacitor device assembled with MnCo2O4@N–C@MnO2 as a cathode and nitrogen-doped graphene hydrogel as an anode exhibits a high energy density of 68.2 W h kg−1 at 749.2 W kg−1 power density without compromising long cycle life (ca. 91.1% retention after 10 000 cycles). The highly efficient energy storage performance of this new class of heterostructures synthesized with earth-abundant materials enables commercial applications. [ABSTRACT FROM AUTHOR]

A hydroxylated boron nitride (BN(OH)x) functionalized p-phenylenediamine modified reduced graphene oxide (rGO) filler (BN(OH)x–PrGO) is synthesized for the first time using a facile and novel strategy. BN(OH)x–PrGO/polyurethane (PU) composite films are prepared using different filler loadings via a solution casting technique. BN(OH)x–rGO/PU and BN(OH)x/PU composite films are also prepared in order to compare the reinforcing effects of different fillers. FESEM and TEM analyses show the excellent dispersion and compatibility of BN(OH)x–PrGO sheets in the PU matrix. The tensile strength and modulus of the composite film show 62% and 95% enhancement, respectively, following the inclusion of 3 wt% BN(OH)x–PrGO compared to those of the pure PU film. The BN(OH)x–PrGO/PU composite films exhibit outstanding oxygen gas barrier properties, ideal dielectric properties, and excellent anti-corrosion performances. In particular, the 3BN(OH)x–PrGO/PU film shows nearly 91% reduction in the O2 transmission rate compared to the PU film. The permeability of O2 through the composite film is correlated with the diffusivity, solubility and Bharadwaj model. The dielectric constant (at 103 Hz) increases from 6.8 for the pure PU film to 13.1 for the 3BN(OH)x–PrGO/PU composite, and the dielectric loss also remains low for the composite. The potentiodynamic polarization curve shows a substantial shift of the corrosion potential of 3BN(OH)x–PrGO/PU-coated steel towards the anodic direction compared to the PU film, and it exhibits an ultralow corrosion rate (6.14 × 10−5 mm per year) and excellent corrosion inhibition efficiency (99.96%) in saline solution. [ABSTRACT FROM AUTHOR]

High-performance all-solid-state supercapacitors (SCs) have potential applications in modern electronics, such as portable and flexible electronics; however, their low specific capacity and operating voltage window limit their industrial applications. Herein, we developed a new type of zinc nickel phosphide nanosheet (Zn–Ni–P NS) arrays via a simple, scalable, and cost-effective hydrothermal and subsequent effective phosphorization technique to enhance the electrochemical performance of SCs. The hierarchical Zn–Ni–P NS array electrode exhibits an ultra-high specific capacity of ∼384 mA h g−1 at a current density of 2 mA cm−2 with excellent rate capability (79.43% of capacity retention at 50 mA cm−2), and outstanding cycling stability (∼96.45% of capacity retention after 10 000 cycles). Furthermore, the Zn–Ni–P NS//Fe2O3@NG all-solid-state asymmetric SC (ASC) delivers an ultra-high volumetric capacity of ∼1.99 mA h cm−3, excellent energy density of ∼90.12 W h kg−1 at a power density of 611 W kg−1, and extraordinary cycling stability (93.05% of initial capacity after 20 000 cycles at a high current density of 15 mA cm−2). Such enhanced electrochemical performances are ascribed to the 3D hierarchical nanostructures, porous nanonetworks, improved conductivity, and synergistic interaction between the active components of Zn–Ni–P NS arrays. [ABSTRACT FROM AUTHOR]

Recently, graphene-based three-dimensional (3D) architectures have attracted a lot of attention because of their multifunctional properties. In this paper, we report on hierarchical nanohoneycomb-like CoMoO4–MnO2 core–shell and Fe2O3 nanosheet arrays on 3D graphene foam (GF) and explore their use as a binder-free electrode in supercapacitor applications. The GF was prepared by solution casting on a Ni foam scaffold. The nanohoneycomb-like CoMoO4–MnO2 core–shell nanosheet arrays were prepared by a hydrothermal method under optimized conditions. The unique core–shell network provides efficient space and a short diffusion length for faradaic reactions. The as-synthesized CoMoO4–MnO2@GF hybrid electrode exhibits excellent areal and specific capacitances of 8.01 F cm−2 and 2666.7 F g−1, respectively, at a current density of 3 mA cm−2. In addition, Fe2O3@GF was also prepared using a hydrothermal process followed by hydrogen treatment. Under optimized conditions Fe2O3@GF exhibits a high areal capacitance of 1.26 (572.7 F g−1) F cm−2. The asymmetric supercapacitor (ASC) assembled from CoMoO4–MnO2@GF as the positive electrode and Fe2O3@GF as the negative electrode delivers an excellent specific capacitance of 237 F g−1 and a high rate capability of 61%. Moreover, the as-fabricated ASC also exhibits an ultra-high energy density of 84.4 W h kg−1 and an outstanding power density of 16 122 W kg−1 as well as an exceptional capacitance retention of 92.1% after 10 000 cycles. [ABSTRACT FROM AUTHOR]

Novel supercapacitor electrodes comprising hierarchical architectures with high specific surface areas, unique porosities, excellent conductivities, and admirable mechanical stabilities are necessary for developing high-performance solid-state supercapacitors. Herein, a novel ultra-thin copper nickel sulfide (Cu1−xNixS) nanosheet array supercapacitor electrode was constructed on a 3D Ni backbone through a powerful anion exchange technique and it demonstrated a unique architecture with a substantial degree of porosity. Accordingly, Cu1−xNixS plays an imperative role in the electrochemical energy storage characteristics of the electrode by accomplishing an ultra-high areal capacitance of 5.88 F cm−2 and a specific capacitance of 2672 F g−1 at a current density of 2 mA cm−2 with an excellent rate capability (71.26% capacitance retention at 20 mA cm−2) and a superior cycling performance (97.33% capacitance retention after 10 000 cycles). To design asymmetric supercapacitors (ASCs), Cu1−xNixS and N, S co-doped graphene nanosheets (NSGNSs) are employed as positive and negative electrodes, respectively. Remarkably, the fabricated ASC exhibits a potential window of ∼1.8 V, which demonstrates an ultra-high energy density of ∼94.05 W h kg−1 at 1.09 kW kg−1 as well as an excellent life cycle (95.86% capacitance retention after 10 000 cycles). Owing to this fact, this investigation offers a simple, scalable, and cost-effective approach for the fabrication of other ternary transition metal sulfides (TMSs), emphasizing great prospects in next-generation energy storage applications. [ABSTRACT FROM AUTHOR]

A novel hybrid of 2D Ni–Mo–S nanosheet integrated nitrogen doped graphene (NG) is successfully developed via a simple, scalable, and cost-effective hydrothermal process, and its application towards energy conversion devices is explored. The presence of exclusive mesoporous structures combined with an excellent conducting NG network in the Ni–Mo–S/NG hybrid exhibits superior electrocatalytic activities as a counter electrode (CE) for dye-sensitized solar cells (DSSCs) and the oxygen reduction reaction (ORR) in alkaline electrolytes. SEM and TEM studies demonstrate the uniform anchoring of ultra-thin Ni–Mo–S nanosheets on NG networks. The hierarchical Ni–Mo–S/NG hybrid outperformed Ni–Mo–S, NG, and Pt when used as a CE in DSSCs and showed excellent ORR activity. The power conversion efficiency (PCE) of DSSCs with the Ni–Mo–S/NG hybrid as the CE achieved 9.89%, outperforming conventional Pt CEs (8.73%). Furthermore, Ni–Mo–S/NG showed high catalytic activity for the ORR with an onset of 0.98 VRHE and outstanding durability compared to commercial Pt/C. The present study demonstrates the unique role of integrated Ni–Mo–S nanosheets anchored NG towards I3− reduction and the ORR, and demonstrates an efficient strategy for designing highly catalytically active and cost-effective electrocatalysts for DSSC and fuel cell applications. [ABSTRACT FROM AUTHOR]

Flexible transparent conducting electrodes (TCEs) in replacement of brittle indium tin oxide (ITO) films are of ultimate importance in the production of flexible and stretchable displays, lighting devices, and solar panels with the ability to resist harsh weather conditions. Herein, the fabrication of an ultra-smooth, highly flexible transparent conducting electrode with a fully embedded structure of the silver coated electrospun polyvinyl alcohol (PVA) nanofiber (PVA@Ag NF) network is reported. These electrodes are fabricated using a scalable electrospinning and thermal evaporation process. The embedded PVA@Ag NF (E-PVA@Ag NF) network TCE structure provides several advantages, including a smooth surface, mechanical stability under high bending stress, and strong adhesion to the substrate with excellent flexibility, without sacrificing the electrical–optical properties. Ultrahigh aspect ratios with fused crossing at the junction points of the PVA@Ag NF network result in a high transmittance (∼90%) at a low sheet resistance (∼2.56 Ω□−1). The E-PVA@Ag NF network TCE structure shows a smooth surface topology (RRMS∼ 2.0 nm) with excellent bending stability; the sheet resistance of the TCE remains almost constant after 10 000 bending cycles with a 1.0 mm bending radius. Finally, a flexible transparent heater is fabricated and its performance at low operating voltage is reported. [ABSTRACT FROM AUTHOR]

Vanadium pentoxide (V2O5) nanorod decorated graphene polypyrrole nanocomposites have been synthesized successfully by a facile hydrothermal process for supercapacitor (SC) applications. The morphological study revealed the successful decoration of V2O5 nanorods and polypyrrole (PPy) within the intergallery of graphitic materials due to their high degree of propensity for intercalation which leads to the formation of mesoporous 3D nanostructures. These mesoporous structures can efficiently allow fast diffusion and ion transport at the electrode–electrolyte interface towards high electrochemical utilization and superior performance. Here, decoration of V2O5 within a polymer matrix along with a graphitic material renders different electrical profiles by virtue of their electron hopping within nanocomposites. Galvanostatic charging discharging revealed that VGP was found to be superior with a maximum specific capacitance of 787 F g−1 at a current density of 1 A g−1 using KCl as an electrolyte. These observations were also confirmed by electrochemical measurements through CV and EIS studies. Furthermore, cyclic stability performed for 5000 consecutive cycles also substantiate their high durability and high power delivery uptake. Thus, considering all such key features, V2O5 based nanocomposites can be suitable for SC applications. [ABSTRACT FROM AUTHOR]

A unique morphology, high specific surface area, extraordinary porosity, and excellent conductive networks are typical favorable properties of pseudocapacitors; however, fully comprehending and interpreting this substantive topic still remains a great challenge. Herein, we present a new strategy for the direct growth of a cobalt monoxide@manganese oxide core–shell nanostructure on 3D Ni foam (CoO@MnO2/Ni foam). This is accomplished by simple, scalable, in situ fabrication methods to produce a material that can be employed as an advanced electrode material for high-energy solid state asymmetric supercapacitors (ASCs). The cost-effective, binder-free 3D CoO@MnO2 core–shell nanostructure delivers excellent electrochemical properties with an ultra-high specific capacitance (1835 F g−1 at a current density of 1 A g−1), tremendous rate capabilities with an extraordinary capacitance of 1198 F g−1 at a current density of 20 A g−1, and outstanding stability (97.7% capacitance retention after 10 000 cycles). ASCs with a maximum potential window of 1.8 V are fabricated by using a 3D CoO@MnO2 core–shell nanohybrid as the positive electrode and N-doped graphene (NG) as the negative electrode in order to validate the outstanding performance for practical energy storage devices. Impressively, the ASCs delivered a high specific capacitance (191 F g−1 at 1 A g−1), excellent energy density (∼85.9 W h kg−1), an ultra-high power density (∼16 769 W kg−1 at 51.7 W h kg−1), and remarkable cycle stability (86.8% capacitance retention after 10 000 cycles). These findings provide a new method to design 3D CoO@MnO2 core–shell nanostructures that are cost-effective and binder-free electrode materials for the development of high-performance energy storage devices. [ABSTRACT FROM AUTHOR]

A novel strategy for the synthesis of high-quality ternary cobalt copper sulfide nanoparticles (NPs) anchored on nitrogen doped graphene nanosheets (Co2CuS4/NG) was developed via a one-pot solvothermal method. FE-SEM and TEM images showed that the Co2CuS4 NPs with an average size of ∼21 nm were anchored to NG nanosheets. The NG nanosheets provide a large surface area to reduce self-aggregation and confine the shape of the Co2CuS4 NPs for a highly conductive network to boost the charge transport properties of energy storage devices. Impressively, the synergetic Co2CuS4/NG composite showed a high specific capacitance of ∼1005 F g−1 at 1 A g−1, excellent rate capability (770 F g−1 at 50 A g−1), and outstanding stability (96.3% capacitance retention after 5000 cycles). The electrochemical performance of the Co2CuS4/NG composite was superior to that of monometallic CoS/NG, Cu2S/NG composite, pure Co2CuS4, and NG. An asymmetric supercapacitor device fabricated using the Co2CuS4/NG composite as the positive electrode material and NG as the negative electrode material illustrates the outstanding performance for practical energy storage devices. The asymmetric supercapacitor device delivers superb energy density (53.3 W h kg−1), high power density (∼10 936 W kg−1 at 38.4 W h kg−1), and a long-cycle life (∼4000 times). [ABSTRACT FROM AUTHOR]

A novel three-dimensional (3D) hierarchical hybrid architecture, consisting of in situ designed cobalt-encapsulated nitrogen doped carbon nanotubes (Co–NCNTs) grown on nitrogen doped graphene (NG), is fabricated for asymmetric supercapacitors. When evaluated as an electrode material for supercapacitors, the 3D hybrid has an excellent energy density, outstanding rate capability and long-cycle life compared with commercial electrode materials. The decent electrochemical performance is comparable to most of the earlier reported results and the synergistic effect boosts the pseudocapacitive performance. The constructed hybrid exhibits excellent energy storage characteristics, which result in an ultra-high specific capacitance of 2568 F g−1 at 2 A g−1 and excellent rate capability with an extraordinary capacitance of 1594 F g−1 at 100 A g−1 (96.64% capacitance retention after 20 000 cycles). The improvement in the outstanding electrochemical performance can be attributed to the unique morphology, extraordinary porosity, excellent conductive networks, and the intense networking of Co–NCNT and NG nanosheets in the 3D hybrid. An asymmetric supercapacitor fabricated using the 3D NG/Co–NCNT hybrid as the positive electrode and NG as the negative electrode demonstrates exceptional performance for practical energy storage devices. The assembled asymmetric supercapacitors provide a greater energy density (∼88.44 W h kg−1), an ultra-high power density (∼17 991 W kg−1 at 56.97 W h kg−1), and outstanding cyclability (∼10 000 times). [ABSTRACT FROM AUTHOR]

A simple, additive-free, cost-effective and scalable successive ionic layer adsorption and reaction (SILAR) method is reported to prepare nickel–cobalt binary hydroxide (Ni–Co–BH) on a reduced graphene oxide (RGO) directing template over a macro-porous conductive nickel foam substrate. This green technique is not only considered as fundamental research interest, but also describes the commercial applications of supercapacitors to reduce the electrode fabrication cost. Three different Ni–Co–BH–G (Ni–Co–BH/RGO) composites are synthesised by tailoring the nickel–cobalt ratios. The flower-like 3D framework of Ni–Co–BH–G provides a porous nano-structure to facilitate the charge transfer and ion diffusion. The cathodic peak current density vs. square root of the scan rate slope values of cyclic voltammetry are consistent with specific capacitance (SC) retention (vs. current density) from charge–discharge curves and the diffusion time constant of the Nyquist plot of the Ni–Co–BH–G composites. Taking the advantage of 3D conductive mesoporous open framework, the Ni–Co–BH–G has provided an excellent SC of 2130 F g−1 at 2 A g−1. An asymmetric supercapacitor device is designed with the optimized Ni–Co–BH–G as the positive electrode and concentrated HNO3 treated conducting carbon cloth (CCN) as the negative electrode. An excellent energy density of ∼92 W h kg−1 and a high power density of ∼7.0 kW kg−1 with lifetime stability up to 10 000 charge–discharge cycles (capacitance retention ∼ 80%) are provided by the asymmetric device. Four asymmetric devices have been assembled in series, which provided ∼5.6 V charge–discharge potential. The assembled system has powered a 5 V light-emitting diode (LED) successfully. [ABSTRACT FROM AUTHOR]

Layer-structured graphene oxide (GO)/polyvinyl alcohol (PVA) nanocomposite coated polyethylene terephthalate films have been fabricated by spray coating. GO/PVA nanocomposite solution was prepared by decreasing the volume of GO solution via vacuum filtration and mixing with PVA. The obtained composite films show dramatic enhancement of hydrogen gas barrier properties. [ABSTRACT FROM AUTHOR]

3-Aminopropyltriethoxysilane (APTES) surface-modified silica nanoparticles were attached to graphene oxide (GO) using isocyanate group-terminated flexible chains in order to synthesize silica nanoparticles with GO attached (SATPGO). The SATPGOs of various compositions were used as reinforcing fillers to prepare epoxy composites. Fourier transform infrared (FT-IR) spectroscopy and X-ray photoelectron spectroscopy analyses confirmed the surface modification of silica nanoparticles after surface grafting with the silane coupling agent, 1,2,4-benzenetricarboxylic anhydride, followed by crosslinking of the surface-modified silica nanoparticles to GO. X-ray diffraction analysis confirmed the attachment of silica nanoparticles to fully exfoliated GO sheets. Transmission electron microscopy images revealed that the silica nanoparticles were introduced uniformly onto the GO sheets. The mechanical properties (impact and tensile properties) of the SATPGO/epoxy composites were dramatically enhanced with the addition of small amounts of SATPGO. The storage modulus of the SATPGO filled epoxy composites was higher than that of pure epoxy. The impact strength of the SATPGO (0.5 wt%)/epoxy composite improved by 154% at room temperature and by 92% at 77 K without any sacrifice of the tensile properties. Moreover, the tensile strength and modulus of the epoxy resin improved with SATPGO loading. The improvements of the thermal stability and mechanical properties were attributed to the synergistic effects of the silica nanoparticles, flexible polymer chains, and GO ternary system. [ABSTRACT FROM AUTHOR]

A synergetic effect of multiwall carbon nanotube (MWCNT) attached pre-stitched graphene oxide (GO) on the mechanical properties of its linear low density polyethylene (LLDPE) composite was demonstrated. The reduction, functionalization and stitching of GO occurred simultaneously with the amine (–NH2) functionalities of ethylenediamine through nucleophilic addition and condensation reaction. The structural features of MWCNT attached pre-stitched GO with ethylenediamine (EtGO) (EtGO–MWCNT) hybrids were confirmed by X-ray diffraction, Fourier transform infrared and Raman spectroscopy. The EtGO–MWCNT hybrid filled LLDPE composite was prepared by solution mixing. The tensile strength of the EtGO–MWCNT/LLDPE composite with 1 wt% loading was enhanced by 148.7% compared to that of the neat LLDPE, which is much higher than those of O-MWCNTs, GO and EtGO filled composites. The enhanced properties of the EtGO–MWCNT/LLDPE composites were attributed to the homogeneous dispersion and the enhanced interfacial interaction with the matrix due to the multi-dimensional structure of EtGO–MWCNT. The EtGO–MWCNT/LLDPE composite also showed better dimensional stability than those of O-MWCNTs, GO, and EtGO filled composites. [ABSTRACT FROM AUTHOR]

Synthesis of reduced graphene oxide (RGO) from graphite oxide (GO) usually involves the use of some harmful reducing agents. Here, we report a simple approach for the reduction of GO at room temperature using a mixture of potassium iodide and hydrochloric acid. The reduction of GO involves (a) iodide mediated epoxide ring-opening, resulting in hydroxyl groups and dehydration to the corresponding olefins, (b) hydroxyl group substitution by iodide ions, and (c) elimination of iodide ions on the surface. The as-synthesized RGO has an electrical conductivity of 1251 S m−1 and an excellent electrocatalytic activity. The electrocatalytic activity of RGO towards the electrochemical reduction of oxygen and the oxidation of hydrazine was investigated. The RGO-based electrode showed pronounced electrocatalytic activity towards the reduction of oxygen and the oxidation of hydrazine in 0.1 M KOH. At alkaline pH, the reduction of oxygen and oxidation of hydrazine were observed at −0.35 and 0.5 V, respectively. In comparison with the bare glassy carbon (GC) electrode, a spectacular decrease in the overpotential and considerable increase in the oxidation peak current for hydrazine were observed on the RGO-based electrode without using any redox mediator. The RGO-based platform is highly sensitive towards the electrochemical oxidation of hydrazine and reproducible results were obtained. Moreover, the RGO-based electrode showed excellent operational and long time storage stabilities. The sensitivity of the electrode was calculated to be 0.137 ± 0.02 μA mM−1. [ABSTRACT FROM AUTHOR]

A green and facile approach for the reduction of graphene oxide (GO) to graphene has been reported using Tin (Sn) powder and dilute hydrochloric acid. Reduction has been performed by varying time from 0.5 to 3 h at room temperature (RT) and 50 °C to determine the best conditions for high quality crystalline graphene. The as-prepared Sn-reduced GO (SR-GO) has been characterized by Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy and Transmission electron microscopy. The efficiency of the reduction increases with increasing reduction time at RT and at 50 °C as evidenced by the electrical conductivity study. However, the electrical conductivity of SR-GO obtained at RT is significantly greater than that of SR-GO obtained at 50 °C. This is attributed to the presence of unreacted Sn particles that increase the electrical conductivity of graphene sheets, as evidenced by XPS elemental analysis. The electrochemical performances of SR-GOs were analyzed by cyclic voltammetry, charge–discharge and electrochemical impedance spectroscopy analysis. A maximum specific capacitance of 152 F g−1 at a current density of 1.5 A g−1 was recorded for graphene prepared at 50 °C for 3 h. The retention in specific capacitance was 92% after 1500 charge–discharge cycles, indicating good electrochemical cyclic stability of SR-GO and its suitability as an energy storage electrode material. [ABSTRACT FROM AUTHOR]

Ceria (CeO2) nanoparticles were grown on reduced graphene oxide (RGO) via the in situ reduction of graphene oxide (GO) in the presence of cerium nitrate and CTAB, followed by a one step hydrothermal treatment. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), ultraviolet-visible spectroscopy (UV-Vis), Raman spectroscopy (RS), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) were employed to characterize the samples. The characterization suggests that the ammonia-assisted hydrothermal method is a facile and advantageous route to synthesize CeO2–RGO nanocomposites compared to the widely used method utilising hydrazine hydrate as the reducing reagent. TEM investigations revealed that the CeO2 nanoparticles with an average size of ∼14 nm were dispersed on the layers of RGO. The catalytic activity of the CeO2–RGO nanocomposites towards the electrooxidation of hydrazine was further investigated by cyclic voltammetry measurements. The results obtained suggest that compared to bare CeO2 nanoparticles, the CeO2–RGO nanocomposite exhibits remarkably enhanced electrocatalytic activity, due to the synergistic effects between the CeO2 nanoparticles and RGO. [ABSTRACT FROM AUTHOR]

An environmentally friendly method for the one-step electrochemical synthesis of water dispersible graphene directly from graphite is reported. Sulfonated poly(ether-ether-ketone) (SPEEK) dissolved in deionised water was used as an electrolyte and a surface modifying agent for graphene. The effects of sodium hydroxide (NaOH) on the production yield and electrochemical performance of graphene were investigated in detail. The production yield of few-layer graphene increased to above 40%, as compared to the 6% in the absence of NaOH. Fourier transform infrared and X-ray photoelectron spectroscopy (XPS) analyses suggested that the oxygen functionalities (hydroxyl and carboxyl) generated during the electrochemical exfoliation of graphite in the absence of NaOH were decreased significantly during the electrolysis experiment in an alkaline solution of SPEEK. This is attributed to the NaOH induced reduction of oxygen functionalities present on the surface of graphene sheets. XPS elemental analysis also confirmed the removal of oxygen functionalities in an alkaline medium during the graphite exfoliation experiment. Transmission electron microscopy and atomic force microscopy analyses confirmed the formation of single layer functionalized graphene. A charge–discharge experiment showed that the specific capacitance of the as-prepared graphene in the absence of NaOH was 18 F g−1 at a current density of 2.2 A g−1. In contrast, the specific capacitance was increased to 244 F g−1 for graphene prepared under alkaline condition indicating its suitability as an energy storage electrode material. The high electrochemical performance may be due to the large surface area of graphene (433 m2 g−1) prepared under alkaline condition as observed by the Brunauer–Emmett–Teller surface area analysis. [ABSTRACT FROM AUTHOR]