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Crystalline Bi–amorphous MoOx interfaces anchored on RGO exhibit superior electrocatalytic NRR performance by enhancing the N2 adsorption/activation while suppressing the competitive HER process.

A novel functional flexible transparent film with excellent printability, swellability, degradability, and hydroxyl groups is directly developed from natural cotton.

Layered semiconductors, represented by transition metal dichalcogenides, have attached extensive attention due to their unique and tunable electrical and optical properties. In particular, lateral layered semiconductor multijunctions, including homojunctions, heterojunctions, hybrid junctions and superlattices, present a totally new degree of freedom in research on electronic devices beyond traditional materials and their structures, providing unique opportunities for the development of new structures and operation principle-based high performance devices. However, the advances in this field are limited by the precise synthesis of high-quality junctions and greatly hampered by ambiguous device performance limits. Herein, we review the recent key breakthroughs in the design, synthesis, electronic structure and property modulation of lateral semiconductor multijunctions and focus on their application-specific devices. Specifically, the synthesis methods based on different principles, such as chemical and external source-induced methods, are introduced stepwise for the controllable fabrication of semiconductor multijunctions as the basics of device application. Subsequently, their structure and property modulation are discussed, including control of their electronic structure, exciton dynamics and optical properties before the fabrication of lateral layered semiconductor multijunction devices. Precise property control will potentially result in outstanding device performances, including high-quality diodes and FETs, scalable logic and analog circuits, highly efficient optoelectronic devices, and unique electrochemical devices. Lastly, we focus on several of the most essential but unresolved debates in this field, such as the true advantages of few-layer

Developing high-performance electrode materials for energy-storage devices with high energy-power densities, such as sodium ion hybrid capacitors (SIHCs), is of vital importance for applications in electric vehicles and portable electronics. Porous hard carbon is one of the most fascinating anode materials for SIHCs due to the rapid Na+ diffusion. Doping with heteroatoms, such as pyridinic N and thiophene S, may boost both the rate performance and specific capacity. However, it is still very challenging to modulate the content and configuration of N and S dopants efficiently. Furthermore, the trade-off for several storage mechanisms, which is vital for carbon anodes with rapid storage and release of sodium ions, is still scarce. Herein, a simple and efficient method is proposed to regulate the configuration of nitrogen dopants, increase the content of thiophene S, create micropores and adjust the structure of curved graphitic domains of hard carbon. Besides, the evolution mechanism of the structure and component is explored through ex situ XRD and XPS analysis. As-prepared NS-pHC-1.348 (N and S co-doped porous hard carbon with 1.348 g MgCl2 precursor) delivers high reversible capacity (383.9 mA h g−1 at 0.05 A g−1), excellent rate ability (183.2 mA h g−1 at 20 A g−1) and fine cycle stability (287.2 mA h g−1 at 1 A g−1 after 1000 cycles). The ratio of pseudocapacitive behaviors in NS-pHC-1.348 reaches up to 70.19% at 0.2 mV s−1, which could balance the electrochemical kinetics of the cathode and anode in SIHCs. Therefore, SIHCs, assembled from the presodiated NS-pHC-1.348 anode and NPC (N-doped porous carbon) cathode, showed superb power characteristics (92.03 kW kg−1 at 5.98 W h kg−1). This work will contribute to the design of high-performance anodes with tunable multi-active sites and the construction of high-power SIHCs.

The proposal of pseudocapacitive materials breaks the barriers between batteries and capacitors, allowing for the possible achievement of a balanced energy-power performance. However, the limited reserve of lithium restricts the practical applications of pseudocapacitive materials in lithium-based systems, whereas sodium resources are abundant with the similar properties to lithium, but there is a lack of suitable pseudocapacitive materials for sodium-based systems. The exploitation of pseudocapacitive materials for Na+ storage is urgent. This study, for the first time, reports a sonochemical approach, involving intercalation and ultrasonic exfoliation processes, to prepare composite K2Mo4O13/α-MoO3 (i.e., KMO) nanorods, and the possible applications of the KMO nanorods in Li+/Na+ pseudocapacitance were evaluated. The as-synthesized KMO possessed a uniform rod-like morphology formed by assembling nanoneedles (or nanobelts) with a large apparent aspect ratio of more than 10. Both in lithium ion batteries (LIBs) and sodium ion batteries (SIBs), the KMO nanorods exhibited efficient pseudocapacitance, which was not observed in the pristine MoO3–Na system. In SIBs, the as-synthesized KMO delivered a capacity of 895 mA h g−1 at 0.02 A g−1, which was much higher than that of the pristine MoO3–Na system. Moreover, it was found that the b values of KMO (i = avb, current i and scan rate v in the CV curves) were over 0.9 at potentials ranging from 1 V to 2 V in SIBs, indicating an obvious pseudocapacitive process. Benefiting from the layered K2Mo4O13 nanorods built with edge-shared distorted MoO6 octahedra, the Na+ ions with a larger size could be intercalated into the spaces between the double MoO6 plates. This sonochemical approach based on the intercalation and exfoliation chemistry opened a new path to prepare molybdenum-based nanostructures for superior Li+/Na+ pseudocapacitance applications on a large scale in a low-carbon and environment-friendly manner.

Lithium ion capacitors (LICs), bridging the advantages of batteries and electrochemical capacitors, are regarded as one of the most promising energy storage devices. Nevertheless, it is always limited by the anodes that accompany with low capacity and poor rate performance. Here, we develop a versatile and scalable method including ball-milling and pyrolysis to synthesize exfoliated MoS2 supported by N-doped carbon matrix derived from chitosan, which is encapsulated by pitch-derived carbon shells (MoS2/CP). Because the carbon matrix with high nitrogen content can improve the electron conductivity, the robust carbon shells can suppress the volume expansion during cycles, and the sufficient exfoliation of lamellar MoS2 can reduce the ions transfer paths, the MoS2/CP electrode delivers high specific capacity (530 mA h g−1 at 100 mA g−1), remarkable rate capability (230 mA h g−1 at 10 A g−1) and superior cycle performance (73% retention after 250 cycles). Thereby, the LICs, composed of MoS2/CP as the anode and commercial activated carbon (21 KS) as the cathode, exhibit high power density of 35.81 kW kg−1 at 19.86 W h kg−1 and high energy density of 87.74 W h kg−1 at 0.253 kW kg−1.

Exploring anode materials with excellent rate performance and high initial coulombic efficiency (ICE) is crucial for lithium/sodium-ion batteries (LIBs/SIBs). However, it is still very challenging to achieve this goal in a cost-effective way, particularly for SIBs. Herein, graphite oxide, was treated in ammonia atmosphere for a balance between the oxygen- and nitrogen-contained functional groups and yielded nitrogen-doped expanded graphite oxide (NEGO). Electrochemical characterizations were systematically carried out in ether and ester-based electrolytes to shed light on the storage mechanism of NEGO in SIBs. The ICE of NEGO employed in ether-based electrolyte improves to 72.08% from that in ester-based electrolyte (24.73%). Moreover, the as-synthesized NEGO exhibits ∼125 mA h g−1 and ∼110 mA h g−1 capacities in ether and ester-based electrolytes, respectively, even under a record high current density (30 A g−1). Expanded surface area and nitrogen doping significantly increase the active sites and decrease the electrical resistivity from 140 Ω (EGO) to 40 Ω (NEGO) by removing excess oxygen. Moreover, small amounts of residual oxygen, particularly quinone and carboxyl, along with nitrogen occupied sites offer additional pseudocapacitance. Considering the advantages in scale-up and cost-effective production, NEGO is a promising low-cost anode material for SIBs. This study also provides strategies for the design of electrolyte for SIBs to realize practical applications in power-grid energy storage.

Electrospun carbon fiber films have high contact resistance at the fiber junctions, which causes poor cycling stability and limits their further improvement in energy storage performances. To eliminate the contact resistance of the film, we provide a new strategy to fuse the fiber junctions by introducing MoO2 in the fibers, which replaces the C–C interface by a more active C–MoO2–C interface at the fiber junction to promote mass transfer. MoO2 reacts with C matrix to generate Mo2C and form self-fused junctions during the carbonization process. Due to much lower charge transfer and sodium diffusion resistance, the C–Mo2C fiber film with self-fused junctions shows much better cyclability with capacity retention of 90% after 2000 cycles at a constant current density of 1 A g−1. Moreover, the Mo2C particles provide many electrochemically active sites, leading to additional improvement in sodium storage. The C–Mo2C fiber film has a capacity of 134 mA h g−1 at 1 A g−1 and a high capacity of 99 mA h g−1 even at 5 A g−1.

There has been intensive concentration and effort on addressing the notorious challenges of Li–S batteries with respect to polysulphide utilization and lithium dendrite inhibition. However, the search for and optimisation of a Li-metal-free full cell design remain relatively premature in terms of the generic synchronous approach to improve the anode/cathode stability while balancing the anode/cathode capacity. We hereby report a parallel interface engineering (PIE) strategy to enhance the full-cell performance of the Li-ion polysulphide battery. Very importantly, this PIE strategy allows the use of a Li-metal-free anode and a LiNO3-free electrolyte. The cell-level improvement is attributable to more efficient and uniform lithium sulphide deposition on the chemically uniform surfaces of the carbon cathode and suppressed growth of dendritic species on the Li–Al alloy anode with an implantable solid–electrolyte interphase. Quantitative electrochemical alloying for anode fabrication allows increased lithium utilization relative to the total anode capacity. The PIE strategy represents a facile approach to address the troublesome issues of Li–S batteries at the full cell level.

Lack of visible light response and low quantum yield hinder the practical application of TiO2 as a high-performance photocatalyst. Herein, we present a rational design of TiO2 nanorod arrays (NRAs) decorated with Ag/Ag2S nanoparticles (NPs) synthesized through successive ion layer adsorption and reaction (SILAR) and covered by graphene oxide (GO) at room temperature. Ag/Ag2S NPs with uniform sizes are well-dispersed on the TiO2 nanorods (NRs) as evidenced by electron microscopic analyses. The photocatalyst GO/Ag/Ag2S decorated TiO2 NRAs shows much higher visible light absorption response, which leads to remarkably enhanced photocatalytic activities on both dye degradation and photoelectrochemical (PEC) performance. Its photocatalytic reaction efficiency is 600% higher than that of pure TiO2 sample under visible light. This remarkable enhancement can be attributed to a synergy of electron-sink function and surface plasmon resonance (SPR) of Ag NPs, band matching of Ag2S NPs, and rapid charge carrier transport by GO, which significantly improves charge separation of the photoexcited TiO2. The photocurrent density of GO/Ag/Ag2S–TiO2 NRAs reached to maximum (i.e. 6.77 mA cm−2 vs. 0 V). Our study proves that the rational design of composite nanostructures enhances the photocatalytic activity under visible light, and efficiently utilizes the complete solar spectrum for pollutant degradation.

Efficient absorption in the S-band (2–4 GHz) has been a very challenging task for developing high-performance microwave absorption materials. Three-dimensional reduced graphene oxide (3D-rGO) powders were prepared by using a hydrothermal method and subsequent thermal treatment. It is found that as-prepared 3D-rGO could significantly enhance the electromagnetic wave attenuation in 2–4 GHz. When the content in the paraffin matrix is 4%, the 3D-rGO shows the strongest absorption in S-band, and the absorption will get stronger with the increase of coating thickness. When the thickness is 5 mm, the bandwidth of reflection loss less than −5 dB is in the range of 2.3 to 4.1 GHz, that is, it can almost cover the whole S-band. The excellent microwave absorption could be attributed to the honeycomb-like structures and the strong polarization of 3D-rGO powders. Considering the low density and good corrosion resistance, 3D-rGO powders may serve as an excellent component for the design of lightweight electromagnetic wave absorption coatings.

Due to the low density of nanostructured materials, it is still a big challenge to realize high volumetric performance instead of high specific gravimetric capacity with many state-of-the-art electrodes for compact electrochemical energy storage. Moreover, developing high-performance flexible and binder-free electrode materials is also crucial for their future applications in diverse fields, such as portable electronics and wearable devices. In this work, we designed and synthesized a Ni3V2O8/carbon cloth (CC) hierarchical structure as a flexible anode for sodium-ion batteries. Morphology-controllable growth of different Ni3V2O8/CC hierarchical structures is achieved by optimizing the synthesis parameters (e.g. the growth temperatures). The high mass loading (4 mg cm−2), ultra-high areal specific capacity (2.6 mA h cm−2 at a current density of 500 mA g−1), no addition of binders or other additives and good flexibility facilitate their application in sodium-ion batteries.

Vertically aligned α-Fe2O3 nanopillar arrays (NPAs) were fabricated by thermally oxidizing Fe NPAs on Si, quartz and F-doped SnO2 (FTO) substrates prepared by glancing angle e-beam deposition (GLAD). The photocatalytic activity of these NPAs was evaluated by measuring the photodegradation of crystal violet (CV) and methyl orange (MO) in the presence of H2O2 under visible light irradiation. Moreover, the photoelectrochemical (PEC) performance was also studied. Typically the sample oxidized at 400 °C exhibits both the highest degradation efficiency and photocurrent density compared with those oxidized at other temperatures (e.g. 300 °C, 350 °C, 450 °C, 500 °C). This phenomenon might be attributed to a trade-off between two opposite effects. On the one hand, with the increase of the oxidation temperature, the improvement of NPAs' crystallinity will enhance the photocatalytic performance accordingly. On the other hand, increasing oxidation temperature may cause the reduction of oxygen vacancies on the NPAs' surface, which are regarded as the photoreaction active sites. This will thus degrade the photocatalytic performance.

Air-cathodes are a critical component for microbial fuel cells (MFCs) and need to have high catalytic performance for the oxygen reduction reaction (ORR). As an important two-dimensional material, graphene has been explored in various applications including ORR catalysts for MFCs. However, the reported graphene for MFC cathodes was usually small flakes/powders, which cannot be directly coated onto metal meshes without binders. Here, we report a binder-free nitrogen-doped graphene (NG) sheet in situ grown on nickel mesh as an efficient catalyst layer for MFC air-cathodes. By optimizing the growth parameters of NG, the maximum power density of MFCs based on NG can be boosted up to 1470 ± 80 mW m−2, which is 32% higher than that of the conventional Pt/C air-cathode. The optimized NG air-cathode has a low internal resistance (21 ± 3 Ω), only 20% of that of the Pt/C air-cathode. These results provide a proof-of-concept for the binder-free NG air-cathode as an alternative to the costly Pt cathode for MFCs.

The traditional fabrication of graphene-based devices requires polymer-assisted transfer of graphene and a removal procedure of polymer coatings. Here, we propose to turn this process on its head and demonstrate a novel strategy of polymer-coated graphene as an optically antireflective and transparent electrode used in a graphene/silicon (G/Si) solar cell. No additional polymer removal and antireflection coatings (e.g. TiO2 colloids) are needed in our strategy. By engineering the thickness of polymer protective coatings, the light absorption and short-circuit current density of graphene solar cells can be greatly enhanced. We also showed that retaining the polymer coatings avoided the degradation of electrical conductivity of graphene films. With HNO3 doping applied on PMMA-coated G/Si solar cells, the PCEs can reach up to 13.34%. The long-term stabilities of HNO3 doped G/Si solar cells are also improved by using fluoropolymer (CYTOP) coatings on graphene. Our approach provides a novel fabrication method of transparent graphene electrodes for graphene-based optoelectronic devices with excellent light absorption.

It is quite desirable but challenging to prepare highly active materials for various energy storage applications at low cost. Here, an efficient strategy to produce nitrogen-enriched hierarchical porous carbon (N-HPC) is reported by facile pyrolysis of magnesium citrate and subsequent NH3 treatment. As-prepared N-HPC presents a developed hierarchical micro- and trimodal meso-porosity with a high specific surface area of 1290 m2 g−1 and pore volume of 3.04 cm3 g−1. It also shows an abundant nitrogen doping of 3.6%. When used for electrochemical electrodes in supercapacitors and lithium–sulfur (Li–S) batteries, significantly enhanced performances have been obtained compared with commercially available activated carbon. In supercapacitor testing, the N-HPC electrode shows a specific capacitance of 101 F g−1 in a nonaqueous electrolyte. And the capacitance retains 67% even at a 200-fold charge/discharge rate. Moreover, its performance in Li–S batteries is more outstanding. It enables a very high sulfur loading (76.2% by weight) and the resulting N-HPC/S cathode shows high discharge capacities of 1153 mA h g−1sulfur (or 702 mA h g−1electrode) at 0.2C and 671 mA h g−1 even at 4C. And it still remains 600 mA h g−1 over 300 charge/discharge cycles at 1C with an average coulombic efficiency of 99.0%.

Magnesium citrate and potassium citrate are two commonly used food additives in our daily life. Herein, we prepared nitrogen-doped hierarchical porous carbon nanosheets (N-HPCNSs) through direct pyrolysis of their mixtures and subsequent NH3 treatment. The as-prepared N-HPCNS shows hierarchical porosity (specific surface area of 1735 m2 g−1 and pore volume of 1.71 cm3 g−1), and a moderate nitrogen doping of 1.7%. Moreover, it can be effectively applied in various energy storage/conversion systems. When used as supercapacitor electrodes, it shows a high specific capacitance of 128 F g−1 in organic electrolytes and retains 45% of the original capacitance even at an ultrahigh current density of 100 A g−1. It can also serve as an effective sulfur carrier in lithium–sulfur batteries. The N-HPCNS/sulfur cathode shows high discharge capacities of 1209 mA h g−1 at 0.2C and 493 mA h g−1 even at 4C. Over 500 charge/discharge cycles at 1C, it still retains a high discharge capacity of 486 mA h g−1 with an ultralow capacity loss of 0.051% per cycle and a high average coulombic efficiency of 99.4%.

Nitrogen-enriched porous carbon nanofiber networks (NPCNFs) were successfully prepared by using low-cost melamine and polyacrylonitrile as precursors via electrospinning followed by carbonization and NH3 treatments. The NPCNFs exhibited inter-connected nanofibrous morphology with a large specific surface area, well-developed microporous structure, relatively high-level nitrogen doping and great amount of pyridinic nitrogen. As free-standing new anode materials in lithium-ion batteries (LIBs), the NPCNFs showed ultrahigh capacity, good cycle performance and superior rate capability with a reversible capacity of as high as 1323 mA h g−1 at a current density of 50 mA g−1. These attractive characteristics make the NPCNFs materials very promising anode candidates for high-performance LIBs and, as free-standing electrode materials to be used in other energy conversion and storage devices.

Graphene (G) films were grown on copper foils by chemical vapor deposition and transferred onto n-type silicon (Si) to form G/Si Schottky heterojunction solar cells. The power conversion efficiencies (PCEs) of the G/Si solar cells were in the range of 1.94–2.66%. Four volatile oxidants HNO3, HCl, H2O2 and SOCl2 were employed to treat the graphene films in the G/Si solar cells, and the PCEs could be greatly enhanced after being treated by all the volatile oxidants and SOCl2 doping showed the best improvement. A solar cell with an initial PCE of 2.45% could be increased to 5.95% upon SOCl2 doping treatment. The PCE stability of the volatile oxidant-treated cells was also investigated. The PCEs decreased with time, while SOCl2 and HCl showed much better PCE stability than HNO3 and H2O2.

Hybrid graphene/amorphous carbon (G/a-C) films with tadpole-like agglomerates were prepared by chemical vapor deposition using ethanol as the precursor. The agglomerates have a quasi 1-D nanostructure with a height of 30–100 nm, width of ∼50 nm and length of ∼1 μm. A Schottky junction solar cell was assembled by transferring as-synthesized G/a-C films onto n-Si, showing a power conversion efficiency of 3.66%. The remarkable cell efficiency can be attributed to the tadpole-like agglomerates, which could act as a direct path for charge transport. The cell efficiency could be further enhanced to 6.07% by HNO3 treatment of the G/a-C films, demonstrating their potential applications in carbon-based photovoltaic devices.