For the first time, a porous and conductive Co0.85Se/graphene network (CSGN), constructed by Co0.85Se nanocrystals being tightly connected with each other and homogeneously anchored on few-layered graphene nanosheets, has been synthesized by a facile one-pot solvothermal method. Compared to unhybridized Co0.85Se, CSGN exhibits much faster kinetics and better electrocatalytic behavior for hydrogen evolution reaction (HER). The HER mechanism of CSGN is improved to Volmer–Tafel combination, instead of Volmer–Heyrovsky combination, for Co0.85Se. CSGN has a very low Tafel slope of 34.4 mV/dec, which is much lower than that of unhybridized Co0.85Se (41.8 mV/dec) and is the lowest ever reported for Co0.85Se-based electrocatalysts. CSGN delivers a current density of 55 mA/cm2 at 250 mV overpotential, much larger than that of Co0.85Se (33 mA/cm2). Furthermore, CSGN shows superior electrocatalytic stability even after 1500 cycles. The excellent HER performance of CSGN is attributed to the unique porous and conductive network, which can not only guarantee interconnected conductive paths in the whole electrode but also provide abundant catalytic active sites, thereby facilitating charge transportation between the electrocatalyst and electrolyte. This work provides insight into rational design and low-cost synthesis of nonprecious transition-metal chalcogenide-based electrocatalysts with high efficiency and excellent stability for HER.Keywords: Co0.85Se nanocrystals; electrocatalytic activity; graphene; hydrogen evolution reaction; solvothermal reaction; transition-metal chalcogenide;

Lithium–tellurium (Li–Te) batteries are attractive for energy storage owing to their high theoretical volumetric capacity of 2621 mAh cm–3. In this work, highly nanoporous cobalt and nitrogen codoped carbon polyhedra (C–Co–N) derived from a metal–organic framework (MOF) is synthesized and employed as tellurium host for Li–Te batteries. The Te@C–Co–N cathode with a high Te loading of 77.2 wt % exhibits record-breaking electrochemical performances including an ultrahigh initial capacity of 2615.2 mAh cm–3 approaching the theoretical capacity of Te (2621 mAh cm–3), a superior cycling stability with a high capacity retention of 93.6%, a ∼99% Columbic efficiency after 800 cycles as well as rate capacities of 2160, 1327.6, and 894.8 mAh cm–3 at 4, 10, and 20 C, respectively. The redox chemistry of tellurium is revealed by in operando Raman spectroscopic analysis and density functional theory simulations. The results illustrate that the performances are attributed to the highly conductive C–Co–N matrix with an advantageous structure of abundant micropores, which provides highly efficient channels for electron transfer and ionic diffusion as well as sufficient surface area to efficiently host tellurium while mitigating polytelluride dissolution and suppressing volume expansion.Keywords: cathode; in-operando Raman spectroscopy; lithium−tellurium battery; metal−organic frameworks; tellurium;

•Graphene-like few-layer WSe2 was synthesized by one-pot solvothermal method.•WSe2 nanosheets possess unique porous nanostructure with rich exposed edge sites.•Graphene-like WSe2 exhibits excellent HER performance and long-term stability.The development of efficient catalysts for electrochemical hydrogen evolution is essential for energy conversion. As a new kind of two-dimensional semiconductor, tungsten selenide (WSe2) has emerged as a promising electrocatalyst for hydrogen evolution reaction (HER). Herein, graphene-like few-layered WSe2 nanosheets are synthesized through a facile, low-cost and one-pot solvothermal reaction, which has been confirmed by XRD, Raman, XPS, SEM and TEM. Compared with previous reports of WSe2, the graphene-like WSe2 exhibits an excellent HER performance with a small Tafel slope of 78 mV dec−1, a low onset potential of ∼150 mV and a very long-term stability. The remarkable enhancement in catalytic performance of graphene-like WSe2 is attributed to its unique porous nanostructure with many exposed edge sites, which can provide abundant active reaction sites. The graphene-like WSe2 is a promising catalyst for high-performance hydrogen evolution.

As a new member of the transition metal dichalcogenides (TMDs) family, rhenium disulfide (ReS2) is attracting more and more attention because of its many distinctive characteristics, such as extremely weak interlayer coupling and anisotropic electronic, optical, and mechanical properties. The studies on synthesis method and electrochemical properties of ReS2 are still rare. For the first time, three-dimensional (3D) chrysanthemum-like microspheres composed of curly ReS2 nanosheets have been synthesized through a facile hydrothermal method. The high-resolution TEM image indicates that the ReS2 nanosheet is highly crystalline with a thickness of few monolayers. As anode for lithium-ion battery, the as-synthesized 3D chrysanthemum-like ReS2 (C-ReS2) microspheres deliver a large initial discharge capacity of 843.0 mAh g−1 and remain 421.1 mAh g−1 after 30 cycles. These values are much higher than that of commercial ReS2. The significant enhancement in electrochemical performance can be attributed to its porous and chrysanthemum-like microsphere structure constructed by few-layered curly ReS2 nanosheets. This unique architecture can allow for easy electrolyte infiltration, efficient electron transfer, and ionic diffusion. The facile synthesis approach can be extended to synthesize other two-dimensional TMDs semiconductors. The study renders ReS2 a promising future in lithium-ion batteries.

For the first time, self-assembled coral-like hierarchical architecture constructed by NiSe2 nanocrystals has been synthesized via a facile one-pot DMF-solvothermal method. Compared with hydrothermally synthesized NiSe2 (H-NiSe2), the DMF-solvothermally synthesized nanocrystalline NiSe2 (DNC-NiSe2) exhibits superior performance of hydrogen evolution reaction (HER): it has a very low onset overpotential of ∼136 mV (vs RHE), a very high cathode current density of 40 mA/cm2 at ∼200 mV (vs RHE), and an excellent long-term stability; most importantly, it delivers an ultrasmall Tafel slope of 29.4 mV dec–1, which is the lowest ever reported for NiSe2-based catalysts, and even lower than that of precious platinum (Pt) catalyst (30.8 mV dec–1). The superior HER performance of DNC-NiSe2 is attributed to the unique self-assembled coral-like network, which is a benefit to form abundant active sites and facilitates the charge transportation due to the inherent high conductivity of NiSe2 nanocrystals. The DNC-NiSe2 is promising to be a viable alternative to precious metal catalysts for hydrogen evolution.Keywords: electrocatalytic activity; hydrogen evolution reaction; nickel dichalcogenide; NiSe2 nanocrystals; solvothermal reaction; transition metal dichalcogenide; ultrasmall Tafel slope;

Owing to the high theoretical specific capacity (1675 mA h g−1) and low cost, lithium–sulfur (Li–S) batteries offer advantages for next-generation energy storage. However, the polysulfide dissolution and low electronic conductivity of sulfur cathodes limit the practical application of Li–S batteries. To address such issues, well-designed yolk–shelled carbon@Fe3O4 (YSC@Fe3O4) nanoboxes as highly efficient sulfur hosts for Li–S batteries are reported here. With both physical entrapment by carbon shells and strong chemical interaction with Fe3O4 cores, this unique architecture immobilizes the active material and inhibits diffusion of the polysulfide intermediates. Moreover, due to their high conductivity, the carbon shells and the polar Fe3O4 cores facilitate fast electron/ion transport and promote continuous reactivation of the active material during the charge/discharge process, resulting in improved electrochemical utilization and reversibility. With these merits, the S/YSC@Fe3O4 cathodes support high sulfur content (80 wt%) and loading (5.5 mg cm−2) and deliver high specific capacity, excellent rate capacity, and long cycling stability. This work provides a new perspective to design a carbon/metal-oxide-based yolk–shelled framework as a high sulfur-loading host for advanced Li–S batteries with superior electrochemical properties.

•Three-dimensional WS2/graphene/Ni electrocatalytic electrode has been synthesized.•The WS2/graphene/Ni electrode has a high WS2 loading of 8.9 mg cm−2.•The contact between WS2 and three-dimensional graphene/Ni backbone is robust.•The WS2/graphene/Ni electrocatalytic electrode has abundant active sites.•The WS2/graphene/Ni electrode exhibits excellent electrocatalytic performance.Tungsten disulfide (WS2) has attracted much attention as the promising electrocatalyst for hydrogen evolution reaction (HER). Herein, the three-dimensional (3D) structure electrode composed of WS2 and graphene/Ni foam has been demonstrated as the binder-free electrode for highly effective and stable HER. The overpotential of 3D WS2/graphene/Ni is 87 mV at 10 mA cm−2, and the current density is 119.1 mA cm−2 at 250 mV overpotential, indicating very high HER activity. Moreover, the current density of 3D WS2/graphene/Ni at 250 mV only decreases from 119.1 to 110.1 mA cm−2 even after 3000 cycles, indicating a good stability. The high HER performance of 3D WS2/graphene/Ni binder-free electrode is superior than mostly previously reported WS2-based catalysts, which is attributed to the unique graphene-based porous and conductive 3D structure, the high loading of WS2 catalysts and the robust contact between WS2 and 3D graphene/Ni backbones. This work is expected to be beneficial to the fundamental understanding of both the electrocatalytic mechanisms and, more significantly, the potential applications in hydrogen economy for WS2.

•Ar plasma-pretreated and N, S co-doped 3D graphene foam (3DGF-Ar-NS) is fabricated.•Ar plasma pretreatment and N, S co-doping create many more electrocatalytic active sites.•3DGF-Ar-NS delivers a relatively low Tafel slope and excellent long-term stability.•Excellent HER activity of 3DGF-Ar-NS is due to Ar plasma pretreatment and N, S co-doping.Three-dimensional graphene foam (3DGF) with high conductivity and rich porosity is an ideal carbon-based metal-free electrocatalyst for hydrogen evolution reaction (HER); however, its HER performance is still very poor due to insufficient electrocatalytic active sites. Herein, in order to create many more electrocatalytic active sites, a facile approach combining Ar plasma pretreatment and subsequent N, S co-doping is presented. As a free-standing and binder-free electrocatalyst, the Ar-plasma-pretreated and N, S co-doped 3DGF (3DGF-Ar-NS) demonstrates significantly enhanced HER performance: the Tafel slope of 3DGF-Ar-NS dramatically decreases from 182 mV/dec (3DGF) to 75 mV/dec. The excellent HER performance and long-term stability of 3DGF-Ar-NS can be attributed to the synergistic effect of the 3DGF skeleton, Ar plasma pretreatment and heteroatom doping: the conductive, porous and flexible 3D graphene skeleton provides the interconnected conductive paths and facilitates the charge transportation; the Ar plasma pretreatment and N, S co-doping effectively create many more electrocatalytic active sites, resulting in significant enhancement in HER performance. This work provides a facile strategy to tailor and enhance the electrocatalytic performances of carbon-based materials for hydrogen evolution applications.Download high-res image (258KB)Download full-size image

•The NiSe2 nanoparticles/carbon nanowires (NiSe2/C NWs) composite is prepared.•NiSe2/C NWs is constructed by NiSe2 nanoparticles embedded in carbon nanowires.•NiSe2/C NWs catalyst delivers superior HER performance and excellent stability.•Superior HER activity is due to its unique NiSe2 NPs embedded in carbon nanowires.Clean hydrogen energy through water splitting via hydrogen evolution reaction (HER) has attracted much interests. It is significant and urgent to search for low-cost non-noble metal electrocatalysts for highly efficient and stable HER. Herein, for the first time, we present a facile and cost-effective hydrothermal and selenization strategy to synthesize NiSe2 nanoparticles embedded in carbon nanowires (NiSe2/C NWs). As a HER electrocatalyst, the NiSe2/C NWs hybrid delivers outstanding catalytic performance with a very low Tafel slope of 38.7 mVdec−1, a small onset potential of ∼−144 mV (vs RHE), and a high cathode current density of 33 mA cm−2 at −250 mV (vs RHE). Moreover, it also exhibits excellent long-term stability of NiSe2/C NWs even after 2000 voltammetric sweeps. The superior HER performance of NiSe2/C NWs is attributed to its unique structure constructed by ultrafine NiSe2 nanoparticles homogenously embedded in highly conductive carbon nanowires, which can not only provide abundant HER active sites, but also enhance the conductivity between the nanoparticles. It suggests that NiSe2/C NWs hybrid is a promising candidate to replace noble metal electrocatalysts for HER.Download high-res image (167KB)Download full-size image

•Nanocrystalline Co0.85Se is synthesized by a facile DMF-solvothermal method.•Nanocrystalline Co0.85Se electrocatalyst delivers superior HER performance.•Superior HER Performance of Co0.85Se is due to its unique 3D network structure.For the first time, the nanocrystalline Co0.85Se (NC-Co0.85Se) electrocatalyst with high efficiency of hydrogen evolution reaction (HER) has been synthesized through a facile DMF-solvothermal reaction. Compared to hydrothermally synthesized Co0.85Se (H-Co0.85Se) with relatively poor HER performance, the NC-Co0.85Se catalyst exhibits superior HER performances. Electrochemical measurements show that the NC-Co0.85Se has a very low onset overpotential of ∼127 mV in 0.5 M H2SO4, a high cathode current density of 30 mA cm−2 at ∼−210 mV vs RHE, and excellent long-term stability. Most importantly, the NC-Co0.85Se exhibits an ultra-small Tafel slope of 34.1 mV dec−1, which is close to that of noble platinum (Pt) catalyst (30.1 mV dec−1). It is promising for NC-Co0.85Se as a highly efficient non-noble-metal electrocatalyst to replace precious Pt-based catalysts for hydrogen evolution.Download high-res image (157KB)Download full-size image

•CoSe2 nanoparticles have been prepared by in-situ selenization of Co-based MOFs.•The CoSe2 nanoparticles were anchored into the MOFs architecture with N-doped carbon.•The MOF-CoSe2 exhibits excellent catalytic performance for HER.Metal-organic frameworks (MOFs) derived cobalt diselenide (MOF-CoSe2) constructed with CoSe2 nanoparticles anchored into nitrogen-doped (N-doped) graphitic carbon has been synthesized through in-situ selenization of Co-based MOFs. The obtained MOF-CoSe2 exhibits excellent hydrogen evolution reaction (HER) performance: it shows a small Tafel slope of 42 mV dec−1, a low onset potential of 150 mV; it delivers a high current density and excellent long-term stability. Such enhancement can be attributed to the unique N-doped MOFs derived architecture with high conductivity, which can not only provide abundant active reaction sites, but also ensure robust contact between the CoSe2 nanoparticles and N-doped carbon matrix, leading to outstanding electrocatalytic activity for HER. This study provides a route to prepared non-noble-metal catalyst with high efficiency and excellent electrocatalytic activity for HER.Download high-res image (252KB)Download full-size image

•A hybrid structure (NCH) composed of NiSe2 nanoparticles embedded in a CNT network is prepared.•NCH is synthesized by scalable and low-cost spray drying and selenization.•The NCH electrocatalyst delivers excellent HER performance and stability.•The excellent HER behavior is due to the unique structure of the electrocatalyst.For the first time, NiSe2 nanoparticles embedded in CNT networks have been synthesized via spray-drying followed by a selenization process. The NiSe2/CNTs hybrid (NCH) delivers superior electrocatalytic performance for HER. It has a low onset potential of ~ 159 mV and a cathode current density of 35.6 mA cm− 2 at − 250 mV vs RHE; more importantly, the Tafel slope has a very low value of 29 mV dec− 1, which is comparable to a platinum (Pt) catalyst; in addition, it is stable even after 1000 cycles. The superior HER performance of NCH is attributed to its unique structure, which is composed of ultrathin NiSe2 nanoparticles homogenously embedded in highly conductive and porous CNT networks. This not only provides abundant HER active sites, but also guarantees robust contact between the NiSe2 nanoparticles and the CNT networks. The present study provides new insights into the large-scale and low-cost synthesis of a highly effective and stable NiSe2-based electrocatalyst which could be extended to large-scale production of other non-precious metal hybrid catalysts with low cost, high efficiency and excellent stability.Download high-res image (126KB)Download full-size image

•The ReS2/rGO composites have been synthesized by a facile one-pot method.•The ReS2/rGO composites exhibit hierarchical architecture.•The ReS2/rGO composites deliver better electrochemical performances than ReS2.•The enhanced performance is due to porous and conductive structure of ReS2/rGO.Rhenium disulfide (ReS2), a two-dimensional (2D) semiconductor, has attracted more and more attention due to its unique anisotropic electronic, optical, mechanical properties. However, the facile synthesis and electrochemical property of ReS2 and its composite are still necessary to be researched. In this study, for the first time, the ReS2/reduced graphene oxide (rGO) composites have been synthesized through a facile and one-pot hydrothermal method. The ReS2/rGO composites exhibit a hierarchical, interconnected, and porous architecture constructed by nanosheets. As anode for lithium-ion batteries, the as-synthesized ReS2/rGO composites deliver a large initial capacity of 918 mAh g−1 at 0.2 C. In addition, the ReS2/rGO composites exhibit much better electrochemical cycling stability and rate capability than that of bare ReS2. The significant enhancement in electrochemical property can be attributed to its unique architecture constructed by nanosheets and porous structure, which can allow for easy electrolyte infiltration, efficient electron transfer, and ionic diffusion. Furthermore, the graphene with high electronic conductivity can provide good conductive passageways. The facile synthesis approach can be extended to prepare other 2D transition metal dichalcogenides semiconductors for energy storage and catalytic application.Download high-res image (282KB)Download full-size image

Heteroatom doping can effectively tune the structure and properties of graphene. Theoretical calculations indicate that sulfur doping can effectively modify the band structure and further modulate the carrier transport properties of graphene. However, it is still a big challenge to synthesize large-area sulfur-doped graphene (SG) films with a high sulfur doping concentration and reasonable electrical properties since sulfur has a much larger atomic radius than carbon. In this study, the solid organic source thianthrene (C12H8S2) is employed as both a carbon source and sulfur dopant to grow large-area, few-layered SG films via chemical vapor deposition (CVD). The results show that the doping concentration, doping configuration and electrical properties can be effectively tuned via the hydrogen flux. The sulfur doping concentration is as high as 4.01 at% and the maximal mobility of SG can reach up to 270 cm2 V−1 s−1, which are the highest ever reported for sulfur-doped graphene.

•We present a low-cost scalable synthesis method of RGO@CoSe2-SnSe2 nanoboxes (RCSB).•RCSB is synthesized by a facile aqueous reaction, spray drying and selenization.•RCSB delivers superior electrocatalyic performance and excellent stability.•Superior HER behavior of RCSB is due to its unique RGO wrapped hollow structure.For the first time, a novel electrocatalyst constructed by reduced graphene oxide (RGO)-wrapped CoSe2-SnSe2 hollow nanoboxes (RCSB) has been synthesized by aqueous reaction, spray drying and selenization, which is facile, low-cost and easy to realize scalable production. Compared to bare CoSe2-SnSe2 nanoboxes (CSB), RCSB exhibits better electrocatalytic behavior for hydrogen evolution reaction (HER): the HER mechanism of RCSB is improved from Volmer-Heyrovsky combination (CSB) to Volmer-Tafel combination; the Tafel slope of RSCB dramatically decreases from 70.3 mV dec−1 (CSB) down to 36.7 mV dec−1, which nearly approaches to that of commercial Pt/C catalyst; RCSB delivers a very large current density of 36.7 mA cm−2 at 250 mV, which is over 60 times larger than that of CSB (0.6 mA cm−2); moreover, RCSB shows excellent electrocatalytic stability even after 1500 cycles. The superior HER performance of RCSB can be attributed to the unique conductive hollow nanobox structure, which can not only guarantee interconnected conductive paths in the whole electrode, but also provide abundant catalytic active sites and facilitate the charge transportation between the electrocatalyst and electrolyte. This work provides insight into rational design and low-cost synthesis of non-precious transition-metal chalcogenide-based electrocatalysts with high efficiency and excellent stability for HER.Download high-res image (210KB)Download full-size image

•Few-layered ReS2 grown on CNTs was synthesized by hydrothermal reaction.•The ReS2/CNTs delivers much better electrochemical performances than ReS2.•The enhanced performance is due to porous and conductive structure of ReS2/CNTs.•The synthesis approach can be extended to other 2D-semiconductor-based composite.Rhenium disulfide (ReS2) two-dimensional (2D) semiconductor, has attracted more and more attention due to its unique anisotropic electronic, optical, mechanical properties. However, the facile synthesis and electrochemical performance of ReS2 and corresponding composite are still necessary to be explored. In this study, for the first time, few-layered ReS2 nanosheets directly nucleated and grown on the tube walls of carbon nanotubes (CNTs) have been synthesized through a facile and one-pot hydrothermal method. Compared with bare ReS2, the ReS2/CNTs composite anode delivers remarkably enhanced electrochemical performance. It exhibits a very high capacity with 1048 mAh g−1 at 0.2 C and high capacity retention of 93.6% after 100 cycles at 0.5 C, which are much larger than that of bare ReS2. The significant enhancement in electrochemical performance is mainly attributed to its unique architecture: the CNTs not only guarantee to construct a high conductive and porous internetwork, but also ensure a compact contact with ReS2, which allow for easy electrolyte infiltration, efficient electron transfer and ionic diffusion. The presented synthesis approach can be extended to synthesize other 2D-semiconductor-based composite for energy storage and catalytic devices.Download high-res image (130KB)Download full-size image

•The CNT/WSe2 composite has been synthesized via a facile solvothermal reaction.•The adding of CNTs can provide a highly conductive underlying skeleton for WSe2.•The CNT/WSe2 composite has abundant exposed active edges.•The CNT/WSe2 composite exhibits superior photocatalytic activity.Flowerlike WSe2 and multi-walled carbon nanotubes modified WSe2 (CNT/WSe2) composite has been successfully synthesized via a facile one-pot solvothermal reaction. The morphologies, structures and photocatalytic activities were characterized by scanning electron microscopy, transmission electron microscope, X-ray diffraction, and UV–vis absorption spectroscopy, respectively. Compared to bare WSe2, the characterization results show that the CNT/WSe2 composite exhibits enhanced photocatalytic activity in photocatalytic degradation of organic dye methyl orange (MO) under visible light irradiation. The enhanced photocatalytic activity is attributed to the CNTs can reduce electron-hole pair recombination and efficiently inhibit the aggregation of WSe2 for fully exposing the active edges. In addition, a possible mechanism of CNT/WSe2 composite for degradation of MO molecules is proposed and discussed.Download high-res image (195KB)Download full-size image

•N-doped graphitic C-Co scaffold (C-Co-N) derived from MOF is synthesized.•Se is immobilized with C-Co-N via physical/chemical molecular interaction.•In-situ Raman spectroscopy and density functional theory simulation are employed.•C-Co-N/Se cathode with 76.5 wt% Se delivers superior electrochemical performances.Three-dimensional, porous graphitic carbon co-doped with cobalt and nitrogen (C-Co-N) is prepared with metal-organic framework (MOF) and employed as Lewis base matrix to host selenium. Owing to the unique structure with abundant micro/meso-pores, the highly-conductive C-Co-N matrix provides highly-efficient channels for electron transfer and ionic diffusion, and sufficient surface area for loading of selenium nanoparticles while mitigating dissolution of polyselenides and suppressing volume expansion. The homogenous distribution of cobalt nanoparticles and nitrogen-group in C-Co-N composite immobilize polyselenides through strong chemical interaction in the operation of Li-Se batteries. With a very high Se loading of 76.5 wt%, the C-Co-N/Se cathode delivers superior electrochemical performance with an ultrahigh reversible capacity of 672.3 mAh g−1 (99.6% of the theoretical value) and a capacity of 574.2 mAh g−1 after 200 cycles, giving a capacity fading of only 0.07% per cycle and a nearly 100% Columbic efficiency. In-situ Raman spectroscopy and density functional theory simulations are employed to investigate the Se (de)lithiation mechanism at the electrolyte/cathode interface, and confirm that the structure and composition of C-Co-N scaffold give rise to efficient cathode host for high-performance Se-based cathodes with dramatically reduced capacity fading.

•Flexible 3D Li2S/graphene cathode is synthesized with an infiltration method.•3D Graphene increases the surface area and conductivity of the cathode.•The cathode exhibits a high discharge capacity of 894.7 mAh g−1 at 0.1 C.•The cyclic performance is record-breaking compared to the previous reports.•The high-rate capacity up to 4 C reaches 598.6 mAh g−1.Three-dimensional Li2S/graphene hierarchical architecture (3DLG) is synthesized with a facile infiltration method. Highly-crystalline Li2S nanoparticles are deposited homogenously into three-dimensional graphene foam (3DGF) network grown by chemical vapor deposition (CVD), resulting in 3DLG with high surface area, porosity, flexibility and conductivity. The 3DLG is employed as flexible, free-standing and binder-free cathode without metallic current collectors or conducting additives. Due to the unique structure, the 3DLG exhibits a high discharge capacity of 894.7 mAh g−1 at 0.1 C, a high capacity retention of 87.7% after 300 cycles at 0.2 C, and the high-rate capacity up to 4 C reaches 598.6 mAh g−1. The cyclic performance is record-breaking compared to the previous reports on free-standing graphene-Li2S cathodes. Flexible lithium-sulfur batteries based on the high-capacity 3DLG cathode have promising application potentials in flexible electronics, electrical vehicles, etc.

•An interwoven WSe2/CNTs hybrid network has been synthesized.•The contact between the WSe2 nanosheets and the CNTs is robust.•The WSe2/CNTs hybrid has abundant exposed active sites.•The WSe2/CNTs hybrid exhibits superior electrocatalytic properties.A WSe2/CNTs hybrid network (WCHN) composed of a few layers of WSe2 nanosheets interwoven with carbon nanotubes (CNTs) has been synthesized through a facile one-pot solvothermal method. The WCHN is shown to be a highly effective and stable electrocatalyst for hydrogen evolution. Compared with bare WSe2, which has relatively poor performance for the hydrogen evolution reaction (HER), the WCHN exhibits superior HER performance with a small Tafel slope of 59.7 mV/decade, a remarkably low onset potential of ~ 120 mV, a high current density and excellent long-term stability. The significant enhancement in HER performance of the WCHN is attributed to the unique network structure produced by two-dimensional WSe2 nanosheets interwoven with one-dimensional highly conductive CNTs, which not only provides abundant active reaction sites, but also guarantees robust contact between the WSe2 nanosheets and the CNTs.

•3D VS4/graphene hierarchical architecture was synthesized by a facile one-pot hydrothermal method.•VS4 particles was uniformly wrapped by graphene nanosheets.•3D VS4/graphene exhibits high capacity and good C-rate performance.•The excellent electrochemical performance should be owed to the unique porous and conductive 3D network structure.Graphene-based three-dimensional hierarchical architecture is one of the most desirable templates to modify the electrochemical performance of the cathode or anode material with low conductivity for lithium-ion batteries (LIBs). Herein, three-dimensional VS4/reduced graphene oxide (3DVG) hierarchical architecture with VS4 particles homogenously wrapped by the graphene nanosheets has been synthesized via a facile one-pot hydrothermal process. The 3DVG composite anode demonstrates excellent electrochemical performance: it exhibits a large specific capacity of 1044.2 mAh g−1 (close to its theoretical capacity of 1196 mAh g−1) and remains 890.8 mAh g−1 after 80 cycles at 0.2 A g−1; it also has a large rate capacity of 479.2 mAh g−1 even at 4 A g−1. This superior performance of the 3D composite for LIBs is attributed to the porous 3D architecture with the conductive graphene interconnected network to guarantee the high conductivity and enable fast electron transport between graphene and VS4. Moreover, the 3DVG provides a hierarchical template to accommodate the volume change of VS4 particles during the electrochemical cycling. The 3DVG was proved as a high capacity anode material for LIBs.

Heteroatom-doping of graphene is of fundamental importance to enable a wide range of optoelectronic and energy storage devices while exploring their basic material properties. Herein, a facile and low-cost method is presented to synthesize the silicon-doped reduced graphene oxide (Si-rGO) via annealing treatment of triphenylsilane and graphene oxide. Compared to the pristine reduced graphene oxide (rGO), Si-rGO exhibits significant enhancement in electrocatalytic and electrochemical properties: when Si-rGO is used as a metal-free electrocatalyst in counter electrodes in dye-sensitized solar cells (DSSCs), the conversion efficiency is increased by 29.6%; when Si-rGO is used as an active electrode in a supercapacitor, the specific capacity is increased by 48.5%. This suggests that silicon doping can effectively improve the electrocatalytic ability and electrochemical performance. It is promising for Si-rGO to be used as a metal-free catalytic and active material.

•Large-area few-layer ReS2 film was synthesized via physical vapour deposition.•The centimeter-size ReS2 film is few-layer, continuous and homogenous.•The few-layer ReS2 film has highly crystalline quality.•PVD is facile and controllable to grow ReS2 and other 2D semiconductors.As a new two-dimensional semiconductor, rhenium disulfide (ReS2), has lots of distinctive features and exhibits great potential for future novel device applications due to its unusual structure and unique anisotropic properties. In this study, for the first time, large-area few-layer ReS2 has been grown on the SiO2/Si substrate by physical vapour deposition (PVD) using ReS2 powder as source material. XPS and Raman data confirm the composition and bonding configurations of ReS2. Clear lattice fringes of the high-resolution TEM images reveal that the ReS2 is few-layer with highly crystalline quality. It suggests that PVD is promising to synthesize wafer-scale ReS2 film to realize its applications in electronics, optoelectronics, valleytronics and spintronics. The PVD method can be extended to grow other two-dimensional semiconductors with few-layer thickness and high quality.

Owing to the high theoretical specific capacity (1166 mAh g–1), lithium sulfide (Li2S) has been considered as a promising cathode material for Li–S batteries. However, the polysulfide dissolution and low electronic conductivity of Li2S limit its further application in next-generation Li–S batteries. In this report, a nanoporous Li2S@C–Co–N cathode is synthesized by liquid infiltration–evaporation of ultrafine Li2S nanoparticles into graphitic carbon co-doped with cobalt and nitrogen (C–Co–N) derived from metal–organic frameworks. The obtained Li2S@C–Co–N architecture remarkably immobilizes Li2S within the cathode structure through physical and chemical molecular interactions. Owing to the synergistic interactions between C–Co–N and Li2S nanoparticles, the Li2S@C–Co–N composite delivers a reversible capacity of 1155.3 (99.1% of theoretical value) at the initial cycle and 929.6 mAh g–1 after 300 cycles, with nearly 100% Coulombic efficiency and a capacity fading of 0.06% per cycle. It exhibits excellent rate capacities of 950.6, 898.8, and 604.1 mAh g–1 at 1C, 2C, and 4C, respectively. Such a cathode structure is promising for practical applications in high-performance Li–S batteries.Keywords: cathode; lithium sulfide; lithium−sulfur battery; metal−organic frameworks;

Three-dimensional aerogel with ultrathin tellurium nanowires (TeNWs) wrapped homogeneously by reduced graphene oxide (rGO) is realized via a facile hydrothermal method. Featured with high conductivity and large flexibility, the rGO constructs a conductive three-dimensional (3D) backbone with rich porosity and leads to a free-standing, binder-free cathode for lithium–tellurium (Li–Te) batteries with excellent electrochemical performances. The cathode shows a high initial capacity of 2611 mAh cm–3 at 0.2 C, a high retention of 88% after 200 cycles, and a high-rate capacity of 1083 mAh cm–3 at 10 C. In particular, the 3D aerogel cathode delivers a capacity of 1685 mAh cm–3 at 1 C after 500 cycles, showing pronounced long-cycle performance at high current density. The performances are attributed to the well-defined flexible 3D architecture with high porosity and conductivity network, which offers highly efficient channels for electron transfer and ionic diffusion while compromising volume expansion of Te in charge/discharge. Owing to such advantageous properties, the reported 3D rGO/tellurium nanowire (3DGT) aerogel presents promising application potentials as a high-performance cathode for Li–Te batteries.Keywords: free-standing cathode; lithium batteries; reduced graphene oxide; tellurium; three-dimensional aerogel

A three-dimensional (3D) graphene-CNT@Se (3DG-CNT@Se) aerogel with carbon nanotube/selenium sandwiched between graphene nanosheets is realized through a facile solvothermal method. Without polymetric binders, conductive additives, or metallic current collectors, the freestanding cathode demonstrates an initial capacity of 632.7 mA h g–1, a value close to 95% of the theoretical capacity of 675 mA h g–1. At 1, 4, and 10 C, the cathode owns reversible specific capacities of 558.3, 436.4, and 192.9 mA h g–1, respectively. Such record-breaking values, as compared to earlier Li–Se batteries, are attributed to the unique 3D mesoporous, conductive network offering highly efficient channels for electron transfer and ionic diffusion, as well as the hierarchical structure preventing fast dissolution of polyselenides and suppressing volume expansion of Se in charge/discharge. The work is expected to open up promising opportunities to realize the application of Li–Se batteries in portable electronics, electrical vehicles, and so forth.

Three-dimensional (3D) CNT/graphene-Li2S (3DCG–Li2S) cathodes with 81.4 wt % record Li2S loading have been realized through solvothermal reaction and a subsequent liquid-infiltration-evaporation coating method. The highly flexible, conductive 3D mesoporous interconnected network based on two-dimensional (2D) graphene nanosheets and one-dimensional (1D) carbon nanotubes (CNTs) provides highly efficient channels for electron transfer and ionic diffusion, and leads to a low solubility of polysulfides in electrolytes in charges/discharges. Without polymeric binders or conductive additives, the freestanding 3DCG–Li2S cathode exhibits record electrochemical performances including reversible discharge capacities of 1123.6 mAh g–1 and 914.6 mAh g–1, 0.02% long-term capacity decay per cycle and a high-rate capacity of 514 mAh g–1 at 4 C. The reported 3DCG–Li2S aerogel with ultrahigh Li2S content presents promising application potentials in high-performance Li–S batteries.

Theoretical calculations have predicted that silicon doping modifies the electronic structure of graphene; however, it is difficult to synthesize high-quality silicon-doped graphene (SiG), thus the electrical properties of SiG have still remained unexplored. In this study, a monolayer SiG film was synthesized by chemical vapour deposition using triphenylsilane (C18H15Si) as a sole solid source, which provides both carbon and silicon atoms. The silicon doping content is ∼2.63 at%, and silicon atoms are incorporated into the graphene lattice with pure Si–C bonds. Furthermore, electrical studies reveal that the as-synthesized SiG film shows a typical p-type doping behaviour with a considerably high carrier mobility of about 660 cm2 V−1 s−1 at room temperature. In addition, due to the single doping structure of Si–C bonds, the SiG film can be expected to be used as an excellent platform for studying silicon doping effects on the physical and chemical properties of graphene.

A facile method is presented to synthesize three-dimensional carbon nanotube/graphene–sulfur (3DCGS) sponge with a high sulfur loading of 80.1%. In the well-designed 3D architecture, the two-dimensional graphene nanosheets function as the 3D porous backbone and the one-dimensional (1D) highly conductive carbon nanotubes (CNTs) can not only significantly enhance the conductivity, but also effectively tune the mesoporous structure. Compared to the three-dimensional graphene–sulfur (3DGS) sponge without CNTs, the conductivity of 3DCGS is enhanced by 324.7%; most importantly, compared to the monomodal mesopores (with a size of 3.5 nm) formed in the 3DG, bimodal mesopores (with sizes of 3.5 and 32.1 nm) were formed in 3DCG; the bimodal mesopores, especially the newly formed 32.1 nm mesopores, provide abundant electrochemical nanoreactors, accommodate plenty of sulfur and polysulfides, and facilitate charge transportation and electrolyte penetration. The significantly enhanced conductivity and the unique bimodal-mesopore structure in 3DCGS result in its superior electrochemical performance. The reversible discharge capacity for sulfur is 1217 mA h g−1; the corresponding capacity for the whole electrode (including the 3DCGS, the conductive additive and the binder) is 877.4 mA h ge−1, which is the highest ever reported. In addition, the capacity decay is as low as 0.08% per cycle, and the high-rate capacity up to 4C is as large as 653.4 mA h g−1. The 3DCGS sponge with high sulfur loading is promising as a superior-capacity cathode for lithium–sulfur batteries.

A facile method with ethanol assisted dispersion combined with a magnetic stirrer to prepare reduced graphene oxide (RGO) wrapped LiMn2O4 nanorods (LNs) is presented. The results show that compared to LNs, a LNs/RGO cathode for lithium-ion batteries (LIBs) exhibits much smaller impedance and much better electrochemical performance. After coating with RGO, the initial discharge capacity can be increased from 118.9 to 143.5 mA h g−1 at 0.2C which can retain 139.2 mA h g−1 after 50 cycles; the rate discharge capacities of LNs/RGO can reach 99.5, 82.1, 56 mA h g−1 at 10, 20, 30C, respectively. The significant performance enhancement can be attributed to the synergetic effect of the LiMn2O4 nanorods matrix and the conductive graphene wrapping layers. The excellent electrochemical properties make LNs/RGO a promising cathode material for high-performance LIBs. In addition, the facile synthesis route enables mass production and can be extended to prepare other graphene wrapped anode or cathode electrodes for LIBs.

For the first time, a three-dimensional hierarchical architecture of CoS2/reduced graphene oxide (3DCG) with CoS2 particles uniformly anchored on the graphene network has been synthesized by a facile hydrothermal method. The 3DCG anode exhibits superior electrochemical performances: it delivers a high reversible specific capacity of 1499 mA h g−1 and remains 1245 mA h g−1 after 150 cycles at a current density of 100 mA g−1, which is the highest ever reported for CoS2-based materials; the rate capability remains 306 mA h g−1 even at 4000 mA g−1. The excellent performance can be attributed to the unique 3D porous structure, in which the reduced graphene oxide (RGO) network can guarantee the high conductivity of the composite, accommodate the volume change of CoS2 particles during cycling, and shorten the diffusion lengths for lithium ions. The 3DCG composite can be a promising anode candidate for high-performance lithium-ion batteries.

•Large-area MoS2 thin layers were synthesized by the thermolysis of (NH4)2MoS4 film.•The structure and growth mechanism of MoS2 thin layers has been investigated.•MoO3 can be easily formed which will dramatically degrade the quality of MoS2 film.•Unexpected Mo oxidation can be completely prevented when H2 flux reaches 100 sccm.Large-area MoS2 thin layers have been synthesized onto the SiO2/Si substrate by the thermolysis of (NH4)2MoS4 film. The structure and growth mechanism of MoS2 thin layers have been investigated. The results reveal that MoO3 can be easily formed during the growth process of MoS2 film, which will dramatically degrade the quality of MoS2 film. Further studies show that with increasing hydrogen fluxes, the content of MoO3 will decrease, and when the hydrogen flux reaches 100 sccm, pure MoS2 film can be obtained. It means that hydrogen plays a critical factor for synthesis of high-quality MoS2 thin layers without unexpected Mo oxidation. This work is beneficial for not only the fundamental understanding of growth mechanism, but also the potential applications of MoS2 film in electronics.

•A facile method to prepare PVDF-HFP/PMMA/TiO2 (0–7 wt.%) composite polymer electrolyte (CPE) is presented.•The CPE has reticular porous fabric with suitable pore size.•The CPE exhibits much higher ionic conductivity and wider electrochemical window.•LiCoO2/Li cells with CPE exhibit much better cyclic stability and C-rate performance.(Poly(vinylidene fluoride-co-hexafluoropropylene)/poly(methyl methacrylate)) PVDF-HFP/PMMA based gel polymer electrolyte comprising 0–7 wt.% TiO2 nanoparticles has been synthesized. After introducing TiO2 nanoparticles, the thermal properties of the PVDF-HFP/PMMA/TiO2 composite polymer electrolyte (CPE) are remarkably improved: when the working temperature is up to 90 °C, the weight loss of CPE with 7% TiO2 is only 12.8% of that without TiO2, suggesting much higher thermal stability; the shrinkage of the CPE at 130 °C can also obviously decrease from 23.4% down to 14.4% after introducing TiO2 nanoparticles. In addition, the CPE exhibits much higher ionic conductivity and better electrochemical stability. Furthermore, the LiCoO2/Li cells with CPE exhibit good cyclic stability and C-rate performance: the capacity maintains 92.1% of the initial capacity after 50 cycles; the capacity can reach as large as ~ 80 mAhg− 1 even at 5 C. It is promising for PVDF-HFP/PMMA/TiO2 CPE to meet the practical demands of high-performance and thermal safety for lithium ion batteries.

Here we propose, for the first time, a new and green ethanol-thermal reaction method to synthesize high-quality and pure thiophene–sulfur doped reduced graphene oxide (rGO), which establishes an excellent platform for studying sulfur (S) doping effects on the physical/chemical properties of this material. We have quantitatively demonstrated that the conductivity enhancement of thiophene–S doped rGO is not only caused by the more effective reduction induced by S doping, but also by the doped S atoms, themselves. Furthermore, we demonstrate that the S doping is more effective in enhancing conductivity of rGO than nitrogen (N) doping due to its stronger electron donor ability. Finally, the dye-sensitized solar cell (DSCC) employing the S-doped rGO/TiO2 photoanode exhibits much better performance than undoped rGO/TiO2, N-doped rGO/TiO2 and TiO2 photoanodes. It therefore seems promising for thiophene–S doped rGO to be widely used in electronic and optoelectronic devices.

Nitrogen doping is a promising method to modulate the electrical properties of graphene. However, the reported nitrogen-doped graphene (NG) films usually show low electron concentration and low carrier mobility. In this study, we have demonstrated the chemical vapour deposition of NG films, where melamine was used as the sole source of both carbon and nitrogen. The studies show that the nitrogen content and configurations are strongly dependent on the growth temperature. At a growth temperature of 990 °C, the total N content and graphitic-N/total N simultaneously reached the maximum values of ∼5.6 at% and ∼40%, respectively. Further, the electrical studies reveal that the NG film displays typical n-type behaviour in air. The Dirac point and mobility were determined to be ∼−25 V and ∼74 cm2 V−1 s−1, respectively, which indicate that the as-synthesized NG film has high electron concentration and high carrier mobility. This can be attributed to the significant increase in the ratio of graphitic-N to total N, because graphitic-N has a higher electron donor ability and shows lower carrier scattering than do pyridinic-N and pyrrolic-N. This study is beneficial for not only the carrier transport mechanism, but also potential applications of NG film.

•Phosphorus (P)-doped rGO was synthesized with two bonding states of P–C and P–O.•For the first time, P-doped rGO is employed as the counter electrode (CE) in DSSC.•P doping can effectively enhance the electrocatalytic activity of rGO.•P–C structures have higher electrocatalytic activity than P–O ones.•P-doped rGO shows comparable electrocatalytic activity to Pt as CE.In this study, phosphorus (P) atoms were doped into reduced graphene oxide (rGO) with two bonding states of P–C and P–O by using annealing treatment. For the first time, the P-doped rGO (PrGO) was employed as the counter electrode (CE) for dye-sensitized solar cell (DSSC). The electrochemical studies reveal that the P doping can effectively enhance the electrocatalytic activity of rGO, and P–C structures have higher electrocatalytic activity than P–O ones for I−/I3− redox reaction. More significantly, PrGO shows comparable electrocatalytic ability to Pt as CEs. It therefore seems promising for PrGO to be widely used in metal-free DSSCs with low cost and high efficiency.

High-quality, reduced graphene oxide (RGO) homogeneously coated LiCo1/3Ni1/3Mn1/3O2 (NCM) was synthesized by ultrasonically mixing/stirring GO and NCM in water and then thermal reduction of GO to RGO. The composite NCM cathode shows much higher specific capacity, better cycling stability and high rate performance after being wrapped by RGO, which is attributed to the much lower electrochemical impedance for the electrode due to the presence of RGO. It is promising for RGO modified NCM to be used as an excellent cathode.

●A modified argon-assisted method was proposed to grow high-quality epitaxial graphene.●Several pinholes punched on top of the chamber ensure homogenous temperature and gas flow.●Graphene grown by modified method has much larger domain size and lower growth rate.We present a modified argon-assisted (MAA) epitaxial method to grow epitaxial graphene in a relative closed sample chamber with several pinholes punched on the top of the chamber to ensure more homogeneous distributions of temperature and gas flow. The morphology and structure of modified argon-assisted epitaxial graphene (MAA-EG) films grown on 6H–SiC (0001) substrates were investigated. The results reveal that the domain size of MAA-EG is much larger and the corresponding terraces are much more regular than those of EG by conventional argon-assisted epitaxial graphene (AA-EG). Moreover, it demonstrates that the growth of MAA-EG is much more controllable and the corresponding growth rate is much lower, compared to those of AA-EG. It is promising to use MAA to grow EG with large domain size and high crystalline quality.Comparison of morphologies and thicknesses of epitaxial graphene grown by conventional argon-assisted (AA) method and modified argon-assisted method.

•Wrinkled sulfur@graphene microspheres (WSGM) was synthesized by spray drying route.•WSGM cathode with 82.3 wt% sulfur delivers superior electrochemical performance.•Excellent performance is attributed to N-doping and unique wrinkled architecture.For the first time, wrinkled sulfur@graphene microspheres (WSGM) with very high mass (82.3 wt%) and areal (2.0 mg cm−2) sulfur loading, constructed with sulfur nanoparticles wrapped by N-doped graphene nanosheets, have been synthesized through a facile spray drying route. When WSGM is used as the cathode for lithium-sulfur (LiS) cells, it delivers superior electrochemical performance: the reversible specific capacity at 0.1C is as large as 1165.7 mAh g−1; even after 200 cycles, the specific capacity at 0.2C remains 954.5 mAh g−1 with a high capacity retention of 82.9%; the C-rate capacities at 1, 2, and 4C are 735.1, 605, and 440.3 mAh g−1, respectively. The excellent performance is attributed to its unique wrinkled architecture: the N-doped graphene matrix guarantees its high conductivity for better electron and ion kinetics; the unique porous, wrinkled and flexible microsphere structure can not only provide abundant active sites to host sulfur and enhance the adsorption of soluble lithium polysulfides intermediates, but also effectively accommodate the volume variation of sulfur during lithiation. The spray drying strategy is facile, effective, and easily realized the large-scale and low-cost industrial production for graphene-sulfur composite cathode, which can be extended to produce other high-capacity electrode materials.Download high-res image (199KB)Download full-size image

For the first time, self-assembled cauliflower-like FeS2 anchored into three-dimensional graphene foams (3DGF-FeS2) are synthesized by one-pot hydrothermal method. Without polymeric binders, conductive additives, or metallic current collectors, the 3DGF-FeS2 composite can be directly used as freestanding and binder-free anode for lithium-ion batteries (LIBs), which demonstrates pronounced electrochemical performance: it exhibits a large initial capacity of 1251.3 mAh g−1 and remains 1080.3 mAh g−1 after 100 cycles at 0.2 C, which is much higher than the theoretical capacity (890 mAh g−1) of bare FeS2 bulk material; it delivers excellent high-rate performance with a capacity of 615.1 mAh g−1 even at 5 A g−1. The pronounced enhancement in electrochemical performance is mainly attributed to the synergistic effect of 3DGF matrix and the unique self-assembly architecture. The porous and conductive 3DGF network offers efficient channels for electron transfer and ionic diffusion and the self-assembled cauliflower-like architecture restrains the aggregation of FeS2 and enhance the stability of 3DGF-FeS2 by suppressing the volume expansion during cycling processes. The 3DGF-FeS2 is promising as superior-capacity free-standing and binder-free anode for LIBs.

Highly active, durable and inexpensive HER catalyst for electrochemical hydrogen evolution is a significant solution to cope with the energy crisis. Herein, self-assembled CoSe2 nanocrystals embedded into carbon nanowires (CoSe2@CNWs) have been synthesized by a facile hydrothermal reaction and subsequent selenylation process. Compared to bare CoSe2 NWs, the CoSe2@CNWs show outstanding performance of hydrogen evolution reaction (HER) with a small Tafel slope of 41.3 mV dec−1 and a low onset potential of ∼130 mV vs RHE. Moreover, the CoSe2@CNWs also demonstrate good long-term stability in acidic electrolyte with a high current retention of 94.1% after 1500 cycles. The excellent HER performance of CoSe2@CNWs is attributed to the unique architecture constructed by CoSe2 nanocrystals embedded into highly conductive carbon nanowires, which guarantees rich active reaction sites and facilitates the charge transportation in HER process.

Theoretical calculations have predicted that silicon doping modifies the electronic structure of graphene; however, it is difficult to synthesize high-quality silicon-doped graphene (SiG), thus the electrical properties of SiG have still remained unexplored. In this study, a monolayer SiG film was synthesized by chemical vapour deposition using triphenylsilane (C18H15Si) as a sole solid source, which provides both carbon and silicon atoms. The silicon doping content is ∼2.63 at%, and silicon atoms are incorporated into the graphene lattice with pure Si–C bonds. Furthermore, electrical studies reveal that the as-synthesized SiG film shows a typical p-type doping behaviour with a considerably high carrier mobility of about 660 cm2 V−1 s−1 at room temperature. In addition, due to the single doping structure of Si–C bonds, the SiG film can be expected to be used as an excellent platform for studying silicon doping effects on the physical and chemical properties of graphene.

A facile method is presented to synthesize three-dimensional carbon nanotube/graphene–sulfur (3DCGS) sponge with a high sulfur loading of 80.1%. In the well-designed 3D architecture, the two-dimensional graphene nanosheets function as the 3D porous backbone and the one-dimensional (1D) highly conductive carbon nanotubes (CNTs) can not only significantly enhance the conductivity, but also effectively tune the mesoporous structure. Compared to the three-dimensional graphene–sulfur (3DGS) sponge without CNTs, the conductivity of 3DCGS is enhanced by 324.7%; most importantly, compared to the monomodal mesopores (with a size of 3.5 nm) formed in the 3DG, bimodal mesopores (with sizes of 3.5 and 32.1 nm) were formed in 3DCG; the bimodal mesopores, especially the newly formed 32.1 nm mesopores, provide abundant electrochemical nanoreactors, accommodate plenty of sulfur and polysulfides, and facilitate charge transportation and electrolyte penetration. The significantly enhanced conductivity and the unique bimodal-mesopore structure in 3DCGS result in its superior electrochemical performance. The reversible discharge capacity for sulfur is 1217 mA h g−1; the corresponding capacity for the whole electrode (including the 3DCGS, the conductive additive and the binder) is 877.4 mA h ge−1, which is the highest ever reported. In addition, the capacity decay is as low as 0.08% per cycle, and the high-rate capacity up to 4C is as large as 653.4 mA h g−1. The 3DCGS sponge with high sulfur loading is promising as a superior-capacity cathode for lithium–sulfur batteries.

Nitrogen doping is a promising method to modulate the electrical properties of graphene. However, the reported nitrogen-doped graphene (NG) films usually show low electron concentration and low carrier mobility. In this study, we have demonstrated the chemical vapour deposition of NG films, where melamine was used as the sole source of both carbon and nitrogen. The studies show that the nitrogen content and configurations are strongly dependent on the growth temperature. At a growth temperature of 990 °C, the total N content and graphitic-N/total N simultaneously reached the maximum values of ∼5.6 at% and ∼40%, respectively. Further, the electrical studies reveal that the NG film displays typical n-type behaviour in air. The Dirac point and mobility were determined to be ∼−25 V and ∼74 cm2 V−1 s−1, respectively, which indicate that the as-synthesized NG film has high electron concentration and high carrier mobility. This can be attributed to the significant increase in the ratio of graphitic-N to total N, because graphitic-N has a higher electron donor ability and shows lower carrier scattering than do pyridinic-N and pyrrolic-N. This study is beneficial for not only the carrier transport mechanism, but also potential applications of NG film.