•CoO@Co/ZnO/graphene quaternary composite is synthesized.•The diameter of yolk-shell CoO@Co nanoparticles is merely 12.0 nm.•The composite exhibits excellent electromagnetic wave absorption properties.•RL is less than −20 dB at the absorber thickness ranging from 2.0 to 5.0 mm.•The addition amount of the composite into paraffin matrix is merely 20 wt%.A facile and efficient strategy is developed to incorporate yolk-shell CoO@Co nanoparticles (NPs) and ZnO NPs with graphene sheets. The diameter and the space between CoO shell and Co yolk are merely 12.0 nm and 1.0 nm, respectively, while the diameter of ZnO NPs is in the range of 4.0–10.0 nm. Due to the small size of NPs and the special structural feature, the resultant graphene-based composite exhibits excellent electromagnetic wave (EMW) absorption properties. Typically, the minimal reflection loss (RL) value reaches to −51.1 dB at 11.3 GHz at the absorber thickness of 2.6 mm, and less than −20 dB at the absorber thickness ranging from 2.0 to 5.0 mm. Moreover, the absorption bandwidths corresponding to the RL values below −10 dB (90% of EMW wave energy consumption) is up to 4.7 GHz (from 9.5 to 14.2 GHz) at a thickness of 2.6 mm. Furthermore, the addition amount of the composite into paraffin matrix is merely 20 wt%, less than that of most EMW absorber reported previously. Therefore, such novel hybrid materials can be used as a kind of candidate for lightweight EMW absorbing material.Download high-res image (276KB)Download full-size image

•3D self-supported Ni1-x-FexOOH/carbon fiber cloth (CFC) electrodes are synthesized.•The electrodes exhibit remarkably enhanced OER activities as x = 0.30.•The self-supported electrode requires an overpotential of 205 mV at 200 mA cm−2.•The electrode can operate stably at >350 mA cm−2 over 100 hours.•The OER performance of the electrode outperforms the commercial IrO2 catalyst.Design of low-cost and highly efficient electrodes for oxygen evolution is highly desirable for bulk water electrolysis associated with several conversion and storage of the renewable energies. Mixed Ni–Fe catalysts have showed excellent activities towards oxygen evolution reaction (OER), however, the long-term stability at high current densities has not been well-documented. Here we fabricate three-dimensional (3D) self-supported Ni1-x-FexOOH/carbon fiber cloth (CFC) electrodes for highly efficient oxygen evolution through in situ electrochemical activation of the corresponding 3D Ni1-x-FexS/CFC precursors. The activated Ni–Fe electrodes exhibit remarkably enhanced OER activities compared to the pure Ni and Fe catalysts and the highest OER activity is achieved as x = 0.30. To drive current densities of 100 and 200 mA cm−2, the 3D Ni0.70Fe0.30OOH/CFC electrode in 1.0 M KOH only requires overpotentials of 200 and 205 mV, respectively, outperforming the commercial IrO2 catalyst and all previously reported Ni–Fe catalysts. Furthermore, the Ni0.70Fe0.30OOH/CFC electrode can continuously operate at >350 mA cm−2 over 100 hours with a negligible current loss in 1.0 M KOH. Such excellent activity and robust long-term stability at high current density demonstrate that the 3D Ni–Fe catalysts can applied in industry for large-scale oxygen production.Download high-res image (132KB)Download full-size image

Designing low-cost, highly active and stable electrocatalysts is very important to various renewable energy storage and conversion devices. Herein we develop a facile method to fabricate bimetallic Ni–Mo nitride nanotubes, which can serve as highly active and stable bifunctional electrocatalysts for full water splitting. To drive a current density of 10 mA cm−2, the bimetallic Ni–Mo nitride nanotubes require an overpotential of 295 mV for the OER and 89 mV for the HER. The alkaline water electrolyzer with the nanotubes as cathode and anode catalysts requires a cell voltage of ca. 1.596 V to achieve a current density of 10 mA cm−2. Furthermore, the nanotubes for full water splitting show excellent stability even at a high current density of 370 mA cm−2, superior to the integrated performance of commercial Pt and IrO2. Our experimental results show that the NiOOH and NH groups formed at the catalyst surface during the OER process are active species for the OER, while the Ni(OH)2, NH and Mo species at the catalyst surface play a key role in the HER. The present strategy may open an avenue for fabrication of low-cost, highly active and stable electrocatalysts for large-scale water splitting.

The development of non-precious, earth-abundant and efficient water oxidation catalysts is very important for water splitting systems associated with the conversion and storage of renewable energy. Here, we report a facile method to fabricate amorphous iron oxide nanosheet arrays on carbon fiber cloth (CFC) as a three-dimensional (3D) self-supported electrode for efficient water oxidation. FeSOy nanosheets with a lateral size of 400 nm and a thickness of 20 nm were first grown on a CFC substrate by a hydrothermal method, and were then converted to FeOx nanosheets without an obvious change in the morphology and size through a rapid and in situ electrochemical oxidation desulfurization process. After the electrochemical activation process, the 3D self-supported electrodes exhibited superior OER activity to previously reported iron oxide films, and were even comparable to some state-of-the-art OER catalysts such as cobalt oxides. Furthermore, the 3D self-supported electrodes showed excellent stability toward the OER process even at a high current density. Surprisingly, the activity of the 3D self-supported electrode was enhanced significantly after the long-term OER process. In addition, the direct growth of the active catalysts on the CFC substrate can avoid the use of other conductive agents and binders, which ensures good electrical connection and improves the electrical conductivity of the electrode. The superior activity and long-term stability as well as the facile fabrication process demonstrated that the 3D self-supported electrode has promising application in large-scale water splitting.

H2S gas in the environment, even at a concentration as low as 20 ppb, is very harmful to the health of human beings. Therefore, the design and fabrication of sensors for detecting trace H2S gas in the environment are highly desirable. However, it remains a challenge to develop gas sensors that can detect H2S at ppb concentration levels and at a relatively low temperature. Herein we developed a facile method to fabricate porous two-dimensional net-like SnO2/ZnO heteronanostructures. Both the SnO2 and ZnO nanoparticles were significantly smaller in the net-like heteronanostructures than in net-like SnO2 and ZnO homonanostructures. Heterojunctions formed at the interfaces between SnO2 and ZnO—and, as a result, the net-like SnO2/ZnO heteronanostructures—exhibited better H2S-sensing properties, including higher sensor response, better selectivity and long-term stability, than did the net-like SnO2 and ZnO homonanostructures, and other types of metal oxide-based nanocomposites. Importantly, the SnO2/ZnO heteronanostructures could detect 10 ppb H2S even at a working temperature of 100 °C. Therefore, the net-like SnO2/ZnO heteronanostructures have very promising applications in high-performance H2S sensors. In addition, the fabrication method presented here is facile, repeatable and operable, and may thus be extended to synthesize other types of metal oxide-based heteronanostructures for applications in various fields.

We developed a strategy for coupling hollow Fe3O4–Fe nanoparticles with graphene sheets for high-performance electromagnetic wave absorbing material. The hollow Fe3O4–Fe nanoparticles with average diameter and shell thickness of 20 and 8 nm, respectively, were uniformly anchored on the graphene sheets without obvious aggregation. The minimal reflection loss RL values of the composite could reach −30 dB at the absorber thickness ranging from 2.0 to 5.0 mm, greatly superior to the solid Fe3O4–Fe/G composite and most magnetic EM wave absorbing materials recently reported. Moreover, the addition amount of the composite into paraffin matrix was only 18 wt %.Keywords: absorption property; composite; electromagnetic wave; graphene; hollow nanoparticles

Hollow structures with hierarchical architecture and multi-composition have attracted extensive interest because of their fascinating physicochemical properties as well as wide applications. Herein we report the designed synthesis of hierarchical nanosheet-based CoMoO4–NiMoO4 nanotubes by a hydrothermal treatment and a subsequent calcination method. The walls of the hierarchical nanotubes are composed of interconnected NiMoO4 nanosheets and CoMoO4 nanoparticles anchored on the surface of the nanosheets. The diameter of the hollow interior, the thickness of NiMoO4 nanosheets and the diameter of CoMoO4 nanoparticles are around 180 nm, less than 6 nm and 3 nm, respectively, providing the hierarchical nanotubes with a high surface area and a large pore volume. When evaluated as electrodes for pseudocapacitors, the hierarchical nanotubes with an appropriate amount of CoMoO4 show a high specific capacitance of 1079 F g−1 at a current density of 5 A g−1 and excellent stability with 98.4% capacitance retention after 1000 cycles. Furthermore, an asymmetric capacitor, consisting of active carbon and hierarchical nanosheet-based CoMoO4–NiMoO4 nanotubes as negative and positive electrodes, respectively, delivers an energy density of 33 W h kg−1 at a power density of 375 W kg−1, and 16.3 W h kg−1 even at a high power density of 6000 W kg−1. The supercapacitive properties are much higher than those of single-phase NiMoO4 nanotubes, and most of the other metal molybdates and metal oxides reported previously. Besides, the hierarchical nanotubes also exhibit much better electrocatalytic activity for the oxygen evolution reaction than single-phase NiMoO4 nanotubes, and most of the other metal molybdates and metal oxides. Our results demonstrate the importance of rational design of complex hollow structures with enhanced properties for a wide range of practical applications.

MoSe2 nanosheets with ultrathin thickness and rich defects were grown on the surface of carbon fiber cloth by a facile solvent-thermal method. The active area and conductivity of the MoSe2 catalyst were increased simultaneously because of the NH4F etching effect and its incorporation with carbon fiber cloth. As a result, the MoSe2-based catalysts exhibited excellent HER activity including small onset potential, large exchange current density and small Tafel slope, which is superior to most of MoSe2-based catalysts reported previously.Keywords: carbon fiber cloth; catalysts; hydrogen evolution; MoSe2 nanosheets; NH4F etching effect;

In situ solid and subsequent hydrothermal reactions were developed to grow ultrathin MoS2 nanosheets on Mo2C-embedded N-doped carbon nanotubes. As applied as electrocatalysts for hydrogen evolution, the hybrid nanotubes exhibited excellent catalytic activity.

In the paper, we developed an in situ diffusion growth method to fabricate porous Fe2(MoO4)3 nanorods. The average diameter and the length of the porous nanorods were 200 nm and 1.2–4 μm, respectively. Moreover, many micropores existed along axial direction of the Fe2(MoO4)3 nanorods. In terms of nitrogen adsorption–desorption isotherms, calculated pore size was in the range of 4–115 nm, agreeing well with the transmission electron microscope observations. Because of the uniquely porous characteristics and catalytic ability at low temperatures, the porous Fe2(MoO4)3 nanorods exhibited very good H2S sensing properties, including high sensitivity at a low working temperature (80 °C), relatively fast response and recovery times, good selectivity, and long-term stability. Thus, the porous Fe2(MoO4)3 nanorods are very promising for the fabrication of high-performance H2S gas sensors. Furthermore, the strategy presented here could be expended as a general method to synthesize other hollow/porous-type transition metal molybdate nanostructures by rational designation in nanoscale.Keywords: diffusion growth; gas sensor; Iron molybdate; low-temperature sensing; porous nanostructure;

The porous Fe3O4/carbon core/shell nanorods were fabricated via a three-step process. α-Fe2O3 nanorods were first obtained, and α-Fe2O3/carbon core/shell nanorods were subsequently fabricated using glucose as a carbon source by a hydrothermal method, in which the thickness of the carbon coating was about 3.5 nm. Fe3O4/carbon core/shell nanorods were synthesized after an annealing treatment of the product above under a mixture of Ar/H2 flow. After the H2 deoxidation process, the Fe3O4 core exhibited a character of porosity; the thickness of the carbon shell was decreased to about 2.5 nm, and its degree of graphitization was enhanced. The interesting core/shell nanostructures are ferromagnetic at room temperature, and the Verwey temperature was about 120 K. Electromagnetic properties of the core/shell nanorod–wax composite were investigated in detail. The maximum reflection loss was about −27.9 dB at 14.96 GHz for the composite with a thickness of 2.0 mm, and the absorption bandwidth with the reflection loss below −18 dB was up to 10.5 GHz for the absorber with the thickness of 2–5 mm. The excellent electromagnetic wave absorption properties of the porous Fe3O4/carbon core/shell nanorods were attributed to effective complementarities between the dielectric loss and the magnetic loss.

Designing low-cost, highly active and stable electrocatalysts is very important to various renewable energy storage and conversion devices. Herein we develop a facile method to fabricate bimetallic Ni–Mo nitride nanotubes, which can serve as highly active and stable bifunctional electrocatalysts for full water splitting. To drive a current density of 10 mA cm−2, the bimetallic Ni–Mo nitride nanotubes require an overpotential of 295 mV for the OER and 89 mV for the HER. The alkaline water electrolyzer with the nanotubes as cathode and anode catalysts requires a cell voltage of ca. 1.596 V to achieve a current density of 10 mA cm−2. Furthermore, the nanotubes for full water splitting show excellent stability even at a high current density of 370 mA cm−2, superior to the integrated performance of commercial Pt and IrO2. Our experimental results show that the NiOOH and NH groups formed at the catalyst surface during the OER process are active species for the OER, while the Ni(OH)2, NH and Mo species at the catalyst surface play a key role in the HER. The present strategy may open an avenue for fabrication of low-cost, highly active and stable electrocatalysts for large-scale water splitting.

The development of non-precious, earth-abundant and efficient water oxidation catalysts is very important for water splitting systems associated with the conversion and storage of renewable energy. Here, we report a facile method to fabricate amorphous iron oxide nanosheet arrays on carbon fiber cloth (CFC) as a three-dimensional (3D) self-supported electrode for efficient water oxidation. FeSOy nanosheets with a lateral size of 400 nm and a thickness of 20 nm were first grown on a CFC substrate by a hydrothermal method, and were then converted to FeOx nanosheets without an obvious change in the morphology and size through a rapid and in situ electrochemical oxidation desulfurization process. After the electrochemical activation process, the 3D self-supported electrodes exhibited superior OER activity to previously reported iron oxide films, and were even comparable to some state-of-the-art OER catalysts such as cobalt oxides. Furthermore, the 3D self-supported electrodes showed excellent stability toward the OER process even at a high current density. Surprisingly, the activity of the 3D self-supported electrode was enhanced significantly after the long-term OER process. In addition, the direct growth of the active catalysts on the CFC substrate can avoid the use of other conductive agents and binders, which ensures good electrical connection and improves the electrical conductivity of the electrode. The superior activity and long-term stability as well as the facile fabrication process demonstrated that the 3D self-supported electrode has promising application in large-scale water splitting.

Hollow structures with hierarchical architecture and multi-composition have attracted extensive interest because of their fascinating physicochemical properties as well as wide applications. Herein we report the designed synthesis of hierarchical nanosheet-based CoMoO4–NiMoO4 nanotubes by a hydrothermal treatment and a subsequent calcination method. The walls of the hierarchical nanotubes are composed of interconnected NiMoO4 nanosheets and CoMoO4 nanoparticles anchored on the surface of the nanosheets. The diameter of the hollow interior, the thickness of NiMoO4 nanosheets and the diameter of CoMoO4 nanoparticles are around 180 nm, less than 6 nm and 3 nm, respectively, providing the hierarchical nanotubes with a high surface area and a large pore volume. When evaluated as electrodes for pseudocapacitors, the hierarchical nanotubes with an appropriate amount of CoMoO4 show a high specific capacitance of 1079 F g−1 at a current density of 5 A g−1 and excellent stability with 98.4% capacitance retention after 1000 cycles. Furthermore, an asymmetric capacitor, consisting of active carbon and hierarchical nanosheet-based CoMoO4–NiMoO4 nanotubes as negative and positive electrodes, respectively, delivers an energy density of 33 W h kg−1 at a power density of 375 W kg−1, and 16.3 W h kg−1 even at a high power density of 6000 W kg−1. The supercapacitive properties are much higher than those of single-phase NiMoO4 nanotubes, and most of the other metal molybdates and metal oxides reported previously. Besides, the hierarchical nanotubes also exhibit much better electrocatalytic activity for the oxygen evolution reaction than single-phase NiMoO4 nanotubes, and most of the other metal molybdates and metal oxides. Our results demonstrate the importance of rational design of complex hollow structures with enhanced properties for a wide range of practical applications.

In situ solid and subsequent hydrothermal reactions were developed to grow ultrathin MoS2 nanosheets on Mo2C-embedded N-doped carbon nanotubes. As applied as electrocatalysts for hydrogen evolution, the hybrid nanotubes exhibited excellent catalytic activity.

H2S gas in the environment, even at a concentration as low as 20 ppb, is very harmful to the health of human beings. Therefore, the design and fabrication of sensors for detecting trace H2S gas in the environment are highly desirable. However, it remains a challenge to develop gas sensors that can detect H2S at ppb concentration levels and at a relatively low temperature. Herein we developed a facile method to fabricate porous two-dimensional net-like SnO2/ZnO heteronanostructures. Both the SnO2 and ZnO nanoparticles were significantly smaller in the net-like heteronanostructures than in net-like SnO2 and ZnO homonanostructures. Heterojunctions formed at the interfaces between SnO2 and ZnO—and, as a result, the net-like SnO2/ZnO heteronanostructures—exhibited better H2S-sensing properties, including higher sensor response, better selectivity and long-term stability, than did the net-like SnO2 and ZnO homonanostructures, and other types of metal oxide-based nanocomposites. Importantly, the SnO2/ZnO heteronanostructures could detect 10 ppb H2S even at a working temperature of 100 °C. Therefore, the net-like SnO2/ZnO heteronanostructures have very promising applications in high-performance H2S sensors. In addition, the fabrication method presented here is facile, repeatable and operable, and may thus be extended to synthesize other types of metal oxide-based heteronanostructures for applications in various fields.