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A self-powered wearable brain-machine-interface system with pulse detection and brain stimulation for ceasing action has been realized. The system is composed of (1) a power supply unit that employs a piezoelectric generator and converts the mechanical energy of human daily activities into electricity; (2) a neck pulse biosensor that allows continuous measurements of carotid pulse by using a piezoelectric polyvinylidene fluoride film; (3) a data analysis module that enables a coordinated brain-machine-interface system to output brain stimulation signals; and (4) brain stimulating electrodes linked to the brain that implement behavioral intervention. Demonstration of the system with stimulating electrodes implanted in the periaqueductal gray (PAG) in running mice reveals the great effect of forced ceasing action. The mice stop their running within several seconds when the stimulation signals are sent into the PAG brain region (inducing fear). This self-powered scheme for neural stimulation realizes specific behavioral intervention without any external power supply, thus providing a new concept for future behavior intervention.

As a new nanotechnology of mechanical energy harvesting and self-powered sensing, triboelectric nanogenerators (TENGs) have been explored as a new path of using various low-frequency disordered mechanical energies in the surrounding environment to provide power and/or sensing. However, the research of TENGs that provide full flexibility and environmental friendliness is still limited. Herein, a flexible single-electrode TENG (S-TENG) based on polyester conductive cloth as the working electrode is developed to harvest human motion energy for powering light emitting diodes (LEDs) and portable electronics. The flat conductive cloth was wrapped in a flexible elastomer. Defatted cowhide was firstly selected as a friction positive charge material for TENGs. When the size of the fabricated S-TENG is 40 × 100 mm2, high output performance has been achieved and it can generate an open-circuit voltage of 534 V and a power density of 230 mW m−2 at an operation frequency of 3.0 Hz. After integrating with a rectifier, the S-TENG can power 240 LEDs, charge various capacitors, and drive an electronic watch or a calculator. Moreover, the S-TENG can harvest the biomechanical energy of wrist movement, hand tapping, and human walking. Meanwhile, the S-TENG as a self-powered sensor can be employed to monitor subtle signals of human physiological activities, such as finger motion, facial masseter activity, and diaphragmatic breathing. Additionally, the S-TENG can be attached to clothes (such as wool coats, polyamide sweaters) to harvest the energy of cuff movement. Therefore, this work provides new insights for clean power sources of skin-mounted electronics and promotes the development of a sustainable energy supply for wearable and portable electronics.

In this study, a combined system of microneedles and a triboelectric nanogenerator (TENG) has been developed for drug delivery. A triboelectric device, which converts mechanical energy into alternating current (AC), was chosen to replace the electrophoresis (EP) effect. To directly generate triboelectricity from salmon deoxyribonucleic acid (SDNA)-based microneedles, a triboelectric series of SDNA film and chargeable polymers (polyimide and Teflon) was studied. The electrical output of the two charged polymers was compared to find a material that could be highly charged with SDNA. The electrical output was also compared as a function of the concentration of a drug embedded in the SDNA film, and the results confirmed that drug intercalation affected the carrier diffusion. The mechanical strength of the microneedles was assessed by histological analysis of their penetration into porcine cadaver skin. Furthermore, the output voltage of a system incorporating microneedles and TENG in cadaver skin, and in vitro drug release into gelatin were evaluated to examine potential application as an electrically active drug delivery system. The electrical output voltage of this system was ∼95 V. The mechanism of triboelectric perturbation to the skin has also been discussed. The system developed in this work is a new, facile approach toward effective drug delivery that replaces the existing EP method and expands the application of TENGs.

Contrary to traditional planar flexible piezoelectric nanogenerators (PNGs), highly adaptable hemispherical shape-flexible piezoelectric composite strip (HS-FPCS) based PNGs are required to harness/measure non-linear surface motions. Therefore, a feasible, cost-effective and less-time consuming groove technique was developed to fabricate adaptable HS-FPCSs with multiple lengths. A single HS-CSPNG generates 130 V/0.8 μA and can also work as a self-powered muscle monitoring system (SP-MMS) to measure maximum human body part movements, i.e., spinal cord, throat, jaw, elbow, knee, foot stress, palm hand/finger force and inhale/exhale breath conditions at a time or at variable time intervals.

The intrinsic properties of paper, such as its light weight, flexibility, foldability, portability and degradability, have led to increasing interest in fabricating flexible energy storage devices and power supply devices on paper-based substrates. Hereby, a robust honeycomb-like thermoelectric generator (TEG) inspired by the origami and kirigami techniques was established in the present study. A thermoelectric ink with the properties of high electrical conductivity and low thermal conductivity was formulated by Bi2Te3 and bacterial cellulose (BC). The formulated ink was printed on a paper surface using a facile processing method. The manufactured paper was further folded and bonded to fabricate a honeycomb-like TEG. This honeycomb-like paper-based TEG exhibited 96 p-n junctions, achieving a maximum voltage and output power of ∼70.5 mV and ∼596 nW, respectively, at a 55 K temperature difference. Moreover, the honeycomb structure was able to withstand a large number of bending and stretching cycles while maintaining its pristine structure. This unique honeycomb structure thus provides a new strategy for future development of paper-based TEGs.

The solar-to-electric conversion efficiency of mesoscopic solar cells is highly dependent on electron extraction under solar irradiation and determines the charge recombination processes within devices. Boosting charge transfer via building energy level alignment has been proved to be a promising method to enhance the output power of solar cells. In the current work, we present the successful fabrication of functional biomass-converted carbon quantum dots with graded energy levels by doping nitrogen or sulphur atoms from lotus root powder. When employed as light absorbers for mesoscopic solar cells, light harvesting and electron extraction can be markedly increased arising from the band alignment of graded carbon quantum dots, yielding maximal power conversion efficiencies of 0.158% and 0.208% for bi- and tri-cascaded photovoltaics, respectively. The primary results demonstrate that the employment of an energy-graded architecture is a promising strategy to optimize the device output. Following this line of thought, we further fabricate a co-sensitized device by integrating graded carbon quantum dots with N719 dyes to enhance the electron extraction capability. The final device yields an efficiency as high as 9.04%, showing the potential application of carbon quantum dots in high-performance solar cells.

As the concentration of different biomarkers in human body fluids are an important parameter of chronic disease, wearable biosensors for in situ analysis of body fluids with high sensitivity, real-time detection, flexibility and biocompatibility have significant potential therapeutic applications. In this paper, a flexible self-powered implantable electronic-skin (e-skin) for in situ body fluids analysis (urea/uric-acid) as a real-time kidney-disease diagnoser has been proposed based on the piezo-enzymatic-reaction coupling process of ZnO nanowire arrays. It can convert the mechanical energy of body movements into a piezoelectric impulse, and the outputting piezoelectric signal contains the urea/uric-acid concentration information in body fluids. This piezoelectric-biosensing process does not need an external electricity supply or battery. The e-skin was implanted under the abdominal skin of a mouse and provided in situ analysis of the kidney-disease parameters. These results provide a new approach for developing a self-powered in situ body fluids-analysis technique for chronic-disease diagnosis.

The features of a carbon substrate are crucial for the electrochemical performance of lithium-sulfur (Li-S) batteries. Nitrogen doping of carbon materials is assumed to play an important role in sulfur immobilisation. In this study, natural silk fibroin protein is used as a precursor of nitrogen-rich carbon to fabricate a novel, porous, nitrogen-doped carbon material through facile carbonisation and activation. Porous carbon, with a reversible capacity of 815 mA h g(-1) at 0.2 C after 60 cycles, serves as the cathode material in Li-S batteries. Porous carbon retains a reversible capacity of 567 mA h g(-1), which corresponds to a capacity retention of 98% at 1 C after 200 cycles. The promising electrochemical performance of porous carbon is attributed to its mesoporous structure, high specific surface area and nitrogen doping into the carbon skeleton. This study provides a general strategy to synthesise nitrogen-doped carbons with a high specific surface area, which is crucial to improve the energy density and electrochemical performance of Li-S batteries.

Novel mesoporous TiO2@DNA nanohybrid electrodes, combining covalently encoded DNA with mesoporous TiO2 microbeads using dopamine as a linker, were prepared and characterised for application in supercapacitors. Detailed information about donor density, charge transfer resistance and chemical capacitance, which have an important role in the performance of an electrochemical device, were studied by electrochemical methods. The results indicated the improvement of electrochemical performance of the TiO2 nanohybrid electrode by DNA surface functionalisation. A supercapacitor was constructed from TiO2@DNA nanohybrids with PBS as the electrolyte. From the supercapacitor experiment, it was found that the addition of DNA played an important role in improving the specific capacitance (Cs) of the TiO2 supercapacitor. The highest Cs value of 8 F g(-1) was observed for TiO2@DNA nanohybrids. The nanohybrid electrodes were shown to be stable over long-term cycling, retaining 95% of their initial specific capacitance after 1500 cycles.

NiO nanoparticles (NPs) were hybridized on the surface of reduced graphene oxide (RGO) by dry plasma reduction (DPR) at atmospheric pressure without any toxic chemicals and at a low temperature. NiO-NPs of 0.5-3 nm size, with a typical size of 1.5 nm, were uniformly hybridized on the surface of RGO. An XPS analysis and the Raman spectra also revealed the repair of some structural damage on the basal plane of the graphene. The material when applied to the counter electrode (CE) of dye-sensitized solar cells (DSCs) exhibited a power conversion efficiency of 7.42% (± 0.10%), which is comparable to a conventional Pt-sputtered CE (8.18% (± 0.08%)). This material outperformed CEs produced using NiO-NPs (1.53% (± 0.15%)), GO (4.48% (± 0.12%)) and RGO (5.18% (± 0.11)) due to its high electrochemical catalytic activity and high conductivity. The charge transfer resistance for NiO-NP-RGO was as low as 1.93 Ω cm(2), while those of a NiO-NP-immobilized electrode and a GO-coated electrode were 44.39 Ω cm(2) and 12.19 Ω cm(2), respectively, due to a synergistic effect.

We report herein that the particle size of Li2O2, which is the discharged product of a Li-O2 battery, remarkably influences the charging performance. As the particle size decreases, the average voltage of charge plateaus is lowered due to reduced electrode polarization and enhanced kinetics of the oxidation reaction of Li2O2.

Hollow core-shell structured Si/C nanocomposites were prepared to adapt for the large volume change during a charge-discharge process. The Si nanoparticles were coated with a SiO2 layer and then a carbon layer, followed by etching the interface SiO2 layer with HF to obtain hollow core-shell structured Si/C nanocomposites. The Si nanoparticles are well encapsulated in a carbon matrix with an internal void space between the Si core and the carbon shell. The hollow core-shell structured Si/C nanocomposites demonstrate a high specific capacity and excellent cycling stability, with capacity decay as small as 0.02% per cycle. The enhanced electrochemical performance can be attributed to the fact that the internal void space can accommodate the volume expansion of Si during lithiation, thus preserving the structural integrity of electrode materials, and the carbon shell can increase the electronic conductivity of the electrode.

The rapid development of numerous microscale electronic devices, such as smart dust, micro or nano bio-sensors, medical implants and so on, has induced an urgent demand for integratable micro or nano battery supplies with high energy and power densities. In this work, 3D hexagonal bottle-like Si/Ge composite nanorod (NR) array electrodes with good uniformity and mechanical stability potentially used in micro or nano rechargeable Li-ion batteries (LIBs) were fabricated on Si substrates by a cost-effective, wafer scale and Si-compatible process. The optimized Ge nano-islands coated Si NR composite arrays as anode materials exhibit superior areal capacities and cycling performances by virtue of their favourable structural and improved conductivity features. The unique Si-based composite electrode in nanostructures can be technically and fundamentally employed to configurate all-solid-state Li-ion micro-batteries as on-chip power systems integrated into micro-electronic devices such as M/NEMS devices or autonomous wireless microsystems.

In this work, we report a facile synthesis of uniform SnO2@C yolk-shell nanospheres as high-performance anode materials for lithium ion batteries (LIBs). The yolk-shell structured SnO2@C nanospheres were fabricated through a two-step sol-gel coating process by using tetraethyl orthosilicate (TEOS) and resorcinol-formaldehyde (RF) as precursors, where the silica interlayer not only acts as a template to produce the void space, but also promotes the coating of the RF layer. The synthesis is easy to operate and allows tailoring the carbon shell thickness and void space size. The resultant SnO2@C yolk-shell nanospheres possess a hollow highly crystalline SnO2 core (280-380 nm), tailored carbon shell thickness (15-25 nm) and a large void space size (100-160 nm), a high surface area (∼205 m(2) g(-1)), a large pore volume (∼0.25 cm(3) g(-1)), as well as a high SnO2 content (77 wt%). When evaluated as an anode of LIBs, the materials manifest superior electrochemical performance with a high lithium storage capability (2190 mA h g(-1) in initial discharge capacity;950 mA h g(-1) in the first 10 cycles), a good cycling performance and an excellent rate capability.

Traditional metal anode materials in lithium-ion batteries are plagued by instability upon discharge-charge cycling. We report that a unique sandwiched Zn2GeO4-graphene oxide nanocomposite has been synthesized on a large scale through a simple ion-exchange reaction, whereby Zn2GeO4 nanorods with lengths of 600 nm and widths of 40 nm are homogeneously sandwiched into the graphene oxide matrix. Compared with bare Zn2GeO4 nanorods, a dramatic improvement in the electrochemical performance of the resulting nanocomposite has been achieved. In the voltage window of 0.001-3 V, the electrode of the Zn2GeO4-graphene oxide nanocomposite delivers a specific capacity as high as 1150 mA h g(-1) at 200 mA g(-1) after 100 discharge-charge cycles. Even at a high current density of 3.2 A g(-1), a capacity of 522 mA h g(-1) can be retained. The unusual electrochemical performance including highly reversible capacity and excellent rate capability arise from synergetic chemical coupling effects between Zn2GeO4 and graphene oxide.

Charge transport and bimolecular recombination dynamics were correlated with nanomorphology in polymer solar cells. The morphology of poly(diketopyrrolopyrrole-terthiophene) (PDPP3T) and phenyl-C61-butyric acid methyl ester (PC60BM) blend films was modified using different solvent additives namely 1-chloronaphthalene (CN), 1,8-diiodooctane (DIO) and 1,8-octanedithiol (ODT) and their role on steady state and transient optoelectronic properties was investigated. The energy filtered transmission electron microscopy (EFTEM) images showed that additives (e.g. CN and DIO) improved the domain purity which leads to significantly higher short circuit current densities (Jsc). However when the cells were processed with the ODT additive, the fill factor (FF) and open circuit voltage (Voc) decreased dramatically. Films processed with the ODT additive showed a smaller domain size but were more connected compared to films processed using CN and DIO additives. Transient photocurrent analysis indicates faster charge collection in the case of CN and DIO processed solar cells and the slowest charge collection in ODT processed solar cells. Interestingly devices processed with the ODT additive also showed the longest charge carrier recombination lifetime and lowest bimolecular recombination coefficient. This is attributed to the smaller donor domains that are connected with each other to provide a more interconnected and efficient charge transport matrix but longer pathways in ODT films. Such a matrix helped the charge to escape from the donor-acceptor interfaces and thus reduces the bimolecular recombination, while the longer pathway increases the charge collection time. Further insight is provided into the selection of processing conditions to achieve an ideal active layer morphology consisting of domains with higher polymer purity and optimal size that lead to higher Jsc and FF.

We report the growth of linked silicon/carbon (Si/C) nanospheres on Cu substrate as an integrated anode for Li-ion batteries. The Si/C nanospheres were synthesized by a catalytic chemical vapor deposition (CCVD) on Cu substrate as current collector using methyltrichlorosilane as precursor, a cheap by-product of the organosilane industry. The samples were characterized by X-ray diffraction, transmission electron microscopy, scanning electron microscopy, thermal gravimetry, Raman spectroscopy, nitrogen adsorption, inductively coupled plasma optical emission spectrometry, and X-ray photoelectron spectroscopy. It was found that the linked Si/C nanospheres with a diameter of 400-500 nm contain Si, Cu(x)Si, and Cu nanocrystals, which are highly dispersed in the amorphous carbon nanospheres. A CCVD mechanism was tentatively proposed, in which the evaporated Cu atoms play a critical role to catalytically grown Si nanocrystals embedded within linked Si/C nanospheres. The electrochemical measurement shows that these Si/C nanospheres delivered a capacity of 998.9, 713.1, 320.6, and 817.8 mA h g(-1) at 50, 200, 800, and 50 mA g(-1) respectively after 50 cycles, much higher than that of commercial graphite anode. This is because the amorphous carbon, Cu(x)Si, and Cu in the Si/C nanospheres could buffer the volume change of Si nanocrystals during the Li insertion and extraction reactions, thus hindering the cracking or crumbling of the electrode. Furthermore, the incorporation of conductive Cu(x)Si and Cu nanocrystals and the integration of active electrode materials with Cu substrate may improve the electrical conductivity from the current collector to individual Si active particles, resulting in a remarkably enhanced reversible capacity and cycling stability. The work will be helpful in the fabrication of low cost binder-free Si/C anode materials for Li-ion batteries.

High-quality fluorographene (FG) was prepared by solvothermal exfoliation of fluorinated graphite (F-graphite) through intercalation of acetonitrile and chloroform with low boiling points. High-yield production of FG was demonstrated by wrinkled few-layered structures with disordered edges and poor regularity along the stacking direction. X-ray photo electron spectroscopy (XPS) spectra indicated that the intercalation of chloroform led to the partial transformation from covalent C-F bonds to semi-ionic C-F bonds. A lithium primary battery (Li-battery) using a FG cathode exhibited a remarkable discharge rate performance because of good Li(+) diffusion and charge mobility through nanosheets. FG nanosheets exfoliated using chloroform showed a high specific capacity of 520 mA h g(-1) and a voltage platform of 2.18 V at a current density of 1 C, accompanied by a maximum power density of 4038 W kg(-1) at 3 C, which is almost four times higher than that of F-graphite. The results indicate that the solvothermal exfoliation using a low-boiling-point solvent is a facile, efficient and high-yield approach to prepare high-purity FG nanosheets for high-performance Li-batteries.

Supercapacitors with both high energy and high power densities are critical for many practical applications. In this paper, we discuss the design and demonstrate the fabrication of flexible asymmetric supercapacitors based on nanocomposite electrodes of MnO(2), activated carbon, carbon nanotubes and graphene. The combined unique properties of each of these components enable highly flexible and mechanically strong films that can serve as electrodes directly without using any current collectors or binders. Using these flexible electrodes and a roll-up approach, asymmetric supercapacitors with 2 V working voltage were successfully fabricated. The fabricated device showed excellent rate capability, with 78% of the original capacitance retained when the scan rate was increased from 2 mV s(-1) to 500 mV s(-1). Owing to the unique composite structure, these supercapacitors were able to deliver high energy density (24 W h kg(-1)) under high power density (7.8 kW kg(-1)) conditions. These features could enable supercapacitor based energy storage systems to be very attractive for a variety of critical applications, such as the power sources in hybrid electric vehicles and the back-up powers for wind and solar energy, where both high energy density and high power density are required.

Efficient reduction of graphene oxide (GO) by chemical, thermal, electrochemical, and photo-irradiation techniques has been reviewed. Particular emphasis has been directed towards the proposed reduction mechanisms of GO by different reducing agents and techniques. The advantages of using different kinds of reducing agents on the basis of their availability, cost-effectiveness, toxicity, and easy product isolation processes have also been studied extensively. We provide a detailed description of the improvement in physiochemical properties of reduced GO (RGO) compared to pure GO. For example, the electrical conductivity and electrochemical performance of electrochemically obtained RGO are much better than those of chemically or thermally RGO materials. We provide examples of how RGO has been used as supercapacitor electrode materials. Specific capacitance of GO increases after reduction and the value has been reported to be 100-300 F g(-1). We conclude by proposing new environmentally friendly types of reducing agents that can efficiently remove oxygen functionalities from the surface of GO.

Controlling over ordered porosity by self-assembly is challenging in the area of materials science. Materials with highly ordered aperture are favorable candidates in catalysis and energy conversion device. Here we describe a facile process to synthesize highly ordered mesoporous carbon (OMC) by direct tri-constituent co-assembly method, which uses resols as the carbon precursor, tri-block copolymer F127 as the soft template and tetraethoxysilane (TEOS) as the inorganic precursor. The obtained products are characterized by small-angle X-ray diffraction (SAXD), Brunauer-Emmett-Teller (BET) nitrogen sorption-desorption measurement and transmission electron microscope (TEM). The results indicate that the OMC possesses high surface areas of 1209 m(2) g(-1), homogeneous pore size of 4.6 nm and a large pore volume of 1.65 cm(3) g(-1). The advantages of high electrochemical active surface area and favorable accessible porosity of OMC benefit the catalysis of I(3)(-) to I(-). As a result, the OMC counter electrode displays a remarkable property when it was applied in dye-sensitized solar cells (DSSCs). For comparison, carbon black (CB) counter electrode and Pt counter electrode have also been prepared. When these different counter electrodes were applied for dye-sensitized solar cells (DSSCs), the power-conversion efficiency (η) of the DSSCs with CB counter electrode are measured to be 5.10%, whereas the corresponding values is 6.39% for the DSSC with OMC counter electrode, which is comparable to 6.84% of the cell with Pt counter electrode under the same experimental conditions.

Diatoms are one of the most successful photosynthetic organisms and given the important role that their shells (frustules) play in light trapping we explored their use in multilayered materials for application as photoanodes in dye sensitised solar cells (DSSCs). We find a substantial improvement in energy conversion efficiency of 30%, increasing from 3.5% to 4.6% with diatom incorporation.

Thermal decomposition of Co(acac)(3) and Cu(acac)(2) in benzylamine leads to the formation of [100] directed Cu-doped h-CoO nanorods, which are very stable in an aqueous solution. The formation mechanism of the [100] directed Cu-doped h-CoO nanorods is fully elucidated by using first-principles calculations, demonstrating that Cu-doping not only changes the growth direction but also enhances the stability of the nanorods significantly. Evaluation of the electrochemical performance of Cu-doped h-CoO nanorods shows high initial Coulombic efficiency and ultrahigh capacity with excellent cycling performance, indicating their suitability as an anode material for next generation lithium-ion batteries.

This paper reports the synthesis of carbon-coated SnO2 (SnO2-C) nanotubes through a simple glucose hydrothermal and subsequent carbonization approach by using Sn nanorods as sacrificial templates. The as-synthesized SnO2-C nanotubes have been applied as anode materials for lithium-ion batteries, which exhibit improved cyclic performance compared to pure SnO2 nanotubes. The hollow nanostructure, together with the carbon matrix which has good buffering effect and high electronic conductivity, can be responsible for the improved cyclic performance.

Graphitic carbon nitride (g-C(3)N(4)), as an intriguing earth-abundant visible light photocatalyst, possesses a unique two-dimensional structure, excellent chemical stability and tunable electronic structure. Pure g-C(3)N(4) suffers from rapid recombination of photo-generated electron-hole pairs resulting in low photocatalytic activity. Because of the unique electronic structure, the g-C(3)N(4) could act as an eminent candidate for coupling with various functional materials to enhance the performance. According to the discrepancies in the photocatalytic mechanism and process, six primary systems of g-C(3)N(4)-based nanocomposites can be classified and summarized: namely, the g-C(3)N(4) based metal-free heterojunction, the g-C(3)N(4)/single metal oxide (metal sulfide) heterojunction, g-C(3)N(4)/composite oxide, the g-C(3)N(4)/halide heterojunction, g-C(3)N(4)/noble metal heterostructures, and the g-C(3)N(4) based complex system. Apart from the depiction of the fabrication methods, heterojunction structure and multifunctional application of the g-C(3)N(4)-based nanocomposites, we emphasize and elaborate on the underlying mechanisms in the photocatalytic activity enhancement of g-C(3)N(4)-based nanocomposites. The unique functions of the p-n junction (semiconductor/semiconductor heterostructures), the Schottky junction (metal/semiconductor heterostructures), the surface plasmon resonance (SPR) effect, photosensitization, superconductivity, etc. are utilized in the photocatalytic processes. Furthermore, the enhanced performance of g-C(3)N(4)-based nanocomposites has been widely employed in environmental and energetic applications such as photocatalytic degradation of pollutants, photocatalytic hydrogen generation, carbon dioxide reduction, disinfection, and supercapacitors. This critical review ends with a summary and some perspectives on the challenges and new directions in exploring g-C(3)N(4)-based advanced nanomaterials.

We have fabricated the flexible photoelectrode by loading graphene sheets modified with CdSe QDs. A power conversion efficiency of ∼0.6% and an incident photon to current conversion efficiency of 17% have been achieved for this flexible photovoltaic cell based on a graphene-CdSe nanocomposite.

Transitional metal oxides hold great potential for high capacity anodes. However, the low electron conductivity of such materials leads to poor cycling stability and inferior rate capability. We reported herein the use of a novel hydrogen plasma technology to improve the conductance of metal oxides, which leads great success in improving the rate performance of CuO nanotube based anodes. This method has the potential to be widely adopted in the field of lithium ion batteries and supercapacitors.

Three-dimensional (3D) nanoporous architectures, possessing high surface area, massive pores, and excellent structural stability, are highly desirable for many applications including catalysts and electrode materials in lithium ion batteries. However, the preparation of such materials remains a major challenge. Here, we introduce a novel method, instant gelation, for the synthesis of such materials. The as-prepared porous 3D MoS2@C nanocomposites, with layered MoS2 clusters or strips ingrained in porous and conductive 3D carbon matrix, indeed showed excellent electrochemical performance when applied as anode materials for lithium ion batteries. Its interconnected carbon network ensures good conductivity and fast electron transport; the micro-, and mesoporous nature effectively shortens the lithium ion diffusion path and provides room necessary for volume expansion. The large specific surface area is beneficial for a better contact between electrode materials and electrolyte.

Peanut-like MnO@C core–shell composites with an internal carbon network (P-MnO@C) were prepared via an in situ synchronous graphitization and reduction process. These P-MnO@C composites exhibit high specific capacity and rate capability, good stability and excellent long-term cycling life for application in lithium ion batteries.

Recently, hybrid carbon materials and inorganic nanocrystals have received an intensive amount of attention and have opened up an exciting new field in the design and fabrication of high-performance catalysts. Here we present a novel kind of hybrid counter electrode (CE) consisting of a carbon fiber (CF) and Co9S8 nanotube arrays (NTs) for fiber-shaped flexible quantum dot-sensitized solar cells (QDSSCs). The growth mechanisms of Co(CO3)0.35Cl0.20(OH)1.10 nanowire arrays (NWs) on the CFs were discussed, and the catalytic activity of the CF, Pt and Co9S8/CF hybrid structure (Co9S8@CF) were elucidated systematically as well. An absolute energy conversion efficiency of 3.79% has been demonstrated under 100 mW cm(-2) AM 1.5 illumination by using Co9S8@CF as a CE. This work not only demonstrates an innovative approach for growing cobalt sulfide NTs on flexible substrates that can be applied in flexible devices for energy harvesting and storage, but also provides a kind of hybrid structure and high-efficiency CE for QDSSCs.

Toward the increasing demands of portable energy storage and electric vehicle applications, silicon has been emerging as a promising anode material for lithium-ion batteries (LIBs) owing to its high specific capacity. However, serious pulverization of bulk silicon during cycling limits its cycle life. Herein, we report a novel hierarchical Si nanowire (Si NW)-reduced graphene oxide (rGO) composite fabricated using a solvothermal method followed by a chemical vapor deposition process. In the composite, the uniform-sized [111]-oriented Si NWs are well dispersed on the rGO surface and in between rGO sheets. The flexible rGO enables us to maintain the structural integrity and to provide a continuous conductive network of the electrode, which results in over 100 cycles serving as an anode in half cells at a high lithium storage capacity of 2300 mA h g(-1). Due to its [111] growth direction and the large contact area with rGO, the Si NWs in the composite show substantially enhanced reaction kinetics compared with other Si NWs or Si particles.

A three-dimensionally ordered macroporous (3DOM) Li3V2(PO4)3/C cathode material with small-sized macropores (50-140 nm) is successfully synthesized using a colloidal crystal array. The 3DOM architecture is built up from fully densely sintered Li3V2(PO4)3/C nanocomposite ceramics particles. Such a 3DOM Li3V2(PO4)3/C micrometer sized particle combines the advantages of both Li3V2(PO4)3 nanocrystal and micrometer sized particle. The resultant 3DOM Li3V2(PO4)3/C nanocomposite exhibits a stable and highly reversible discharge capacity up to 151 mA g(-1) at 0.1 C, and an excellent high-rate capability of 132 mA g(-1) at 5 C in the voltage range of 3.0-4.4 V. Compared to the corresponding bulk nanocomposite, the 3DOM Li3V2(PO4)3/C cathode exhibits a significantly improved high-rate performance, which promises new opportunities in the development of high energy and high power lithium-ion batteries.

Hierarchically porous materials are an ideal material platform for constructing high performance Li-ion batteries (LIBs), offering great advantages such as large contact area between the electrode and the electrolyte, fast and flexible transport pathways for the electrolyte ions and the space for buffering the strain caused by repeated Li insertion/extraction. In this work, NiO microspheres with hierarchically porous structures have been synthesized via a facile thermal decomposition method by only using a simple precursor. The superstructures are composed of nanocrystals with high specific surface area, large pore volume, and broad pore size distribution. The electrochemical properties of 3D hierarchical mesoporous NiO microspheres were examined by cyclic voltammetry and galvanostatic charge-discharge studies. The results demonstrate that the as-prepared NiO nanospheres are excellent electrode materials in LIBs with high specific capacity, good retention and rate performance. The 3D hierarchical mesoporous NiO microspheres can retain a reversible capacity of 800.2 mA h g(-1) after 100 cycles at a high current density of 500 mA g(-1).

Iron pyrite is an earth-abundant and inexpensive material that has long been interesting for electrochemical energy storage and solar energy conversion. A large-scale conversion synthesis of phase-pure pyrite nanowires has been developed for the first time. Nano-pyrite cathodes exhibited high Li-storage capacity and excellent capacity retention in Li/pyrite batteries using a liquid electrolyte, which retained a discharge capacity of 350 mAh g(-1) and a discharge energy density of 534 Wh kg(-1) after 50 cycles at 0.1 C rate.

We demonstrated an efficient method for the fabrication of novel, flexible electrodes based on ZnO nanoflakes and nickel-cobalt layered double hydroxides (denoted as ZnONF/NiCoLDH) as a core-shell nanostructure on textile substrates for wearable energy storage devices. NiCoLDH coated ZnO nanowire (denoted as ZnONW/NiCoLDH) flexible electrodes are also prepared for comparison. As an electrode for supercapacitors, ZnONF/NiCoLDH exhibits a high specific capacitance of 1624 F g(-1), which is nearly 1.6 times greater than ZnONW/NiCoLDH counterparts. It also shows a maximum energy density of 48.32 W h kg(-1) at a power density of 27.53 kW kg(-1), and an excellent cycling stability with capacitance retention of 94% and a Coulombic efficiency of 93% over 2000 cycles. We believe that the superior performance of the ZnONF/NiCoLDH hybrids is due primarily to the large surface area of the nanoflake structure and the open spaces between nanoflakes, both of which provide a large space for the deposition of NiCoLDH, resulting in reduced internal resistance and improved capacitance performance. Our results are significant for the development of electrode materials for high-performance wearable energy storage devices.

Free-standing and binder-free porous carbon nanofibers (P-CNFs) electrodes were prepared by pyrolysis of PAN-F127/DMF nanofibers via an electrospinning process as potential anodes for Na-ion batteries (NIB). The P-CNFs delivers a reversible capacity of 266 mA h g(-1) after 100 cycles at 0.2 C, corresponding to ~80% of the initial charge capacity. When cycled at a current density as high as 500 mA g(-1) (2 C), it still delivers a reversible capacity of ~140 mA h g(-1) after 1000 cycles. The improvement of electrochemical performance is attributed to the special design and microstructure of P-CNFs, which conferred a variety of advantages: hierarchical porous channels enabling short transport length for ions and electrons, 3D interconnected structure resulting in low contact resistances, good mechanical properties leading to the excellent morphology stability.

In this work, mesoporous carbon-coated LiFePO4 nanocrystals further co-modified with graphene and Mg(2+) doping (G/LFMP) were synthesized by a modified rheological phase method to improve the speed of lithium storage as well as cycling stability. The mesoporous structure of LiFePO4 nanocrystals was designed and realized by introducing the bead milling technique, which assisted in forming sucrose-pyrolytic carbon nanoparticles as the template for generating mesopores. For comparison purposes, samples modified only with graphene (G/LFP) or Mg(2+) doping (LFMP) as well as pure LiFePO4 (LFP) were also prepared and investigated. Microscopic observation and nitrogen sorption analysis have revealed the mesoporous morphologies of the as-prepared composites. X-ray diffraction (XRD) and Rietveld refinement data demonstrated that the Mg-doped LiFePO4 is a single olivine-type phase and well crystallized with shortened Fe-O and P-O bonds and a lengthened Li-O bond, resulting in an enhanced Li(+) diffusion velocity. Electrochemical properties have also been investigated after assembling coin cells with the as-prepared composites as the cathode active materials. Remarkably, the G/LFMP composite has exhibited the best electrochemical properties, including fast lithium storage performance and excellent cycle stability. That is because the modification of graphene provided active sites for nuclei, restricted the in situ crystallite growth, increased the electronic conductivity and reduced the interface reaction current density, while, Mg(2+) doping improved the intrinsically electronic and ionic transfer properties of LFP crystals. Moreover, in the G/LFMP composite, the graphene component plays the role of "cushion" as it could quickly realize capacity response, buffering the impact to LFMP under the conditions of high-rate charging or discharging, which results in a pre-eminent rate capability and cycling stability.

Metal oxide-containing nanomaterials (MOCNMs) of controllable structures at the nano-scale have attracted considerable interest because of their great potential applications in electrochemical energy storage devices, such as lithium-ion batteries (LIBs) and supercapacitors. Among many structure-directing agents, polymers and macromolecules, including block copolymers (BCPs) and graphene, exhibit distinct advantages in the template-assisted synthesis of MOCNMs. In this feature article, we introduce the controlled preparation of MOCNMs employing BCPs and graphene as structure-directing agents. Typical synthetic strategies are presented for the control of structures and sizes as well as the improvement of physical properties and electrochemical performance of MOCNMs in LIBs and supercapacitors.

This study aims to realize controllable synthesis of Si-based nanostructures from common and easily accessible silica nanoparticles and to study their component/structure-dependent electrochemical performance as an anode of lithium-ion batteries (LIBs). To this end, a controllable route based on deliberate design has been developed to prepare hollow Si-based nanospheres with tunable composition and crystal structure at the nanoscale. The synthesis process started with coating silica nanoparticles with a carbonaceous polymer with a controllable thickness followed by magnesiothermic reduction. An Si–SiC–C composite was finally produced with a unique hollow sphere structure featuring Si–SiC nanoparticles encapsulated by a cross-linked carbon film network. In addition to the scalability of the synthetic route, the resulting composite exhibits a number of advantageous properties, including excellent electrical conductivity, highly accessible surfaces, structural coherence, and a favorable structure for the formation of a stable solid-electrolyte interphase, which makes it attractive and promising for advanced anode materials of LIBs.

Fe2O3 yolk-shell particles with two, three, and four shells are prepared by one-pot spray pyrolysis. The discharge capacity of the Fe2O3 yolk-shell particles with two shells showing the best electrochemical properties is as high as 848 mA h g(-1) after 80 cycles at a current density of 300 mA g(-1).