•New material: Sn/SnOx/nanocarbon composites.•New method: one-step solvothermal method.•High performance: ultrafast-charging/long-life performance, 3 min charging time, 5000 cycles.•New mechanism: complex synergistic effect.•Potential application: promising candidates for high-performance Li battery.Pomegranate-shaped Sn/SnOx/nanocarbon composites are fabricated via a simple one-step solvothermal method. The Sn and SnOx nanoparticles are uniformly embedded in the sheet-like nanocarbon membranes. As the anode of lithium-ion battery, the pomegranate-shaped Sn/SnOx/nanocarbon composites exhibit ultrafast-charging and long-life performance. At super high current rate of 10 C, 15 C and 20 C (the charging process is shortened to merely 6, 4 and 3 min, respectively), the reversible capacity of pomegranate-shaped Sn/SnOx/nanocarbon composites is 545, 467 and 421 mAh g−1, respectively. After 2000 cycles, the capacity can still maintain at 192, 139 and 101 mAh g−1 at 10 C, 15 C and 20 C rate, respectively. Even after 5000 cycles at 15 C rate, the discharge capacity can still keep at 135 mAh g−1. Such superior performance can be attributed to the unique structure, good electronic conductivity, short paths for lithium diffusion and interfacial charging mechanism. The present results indicate a new way to produce pomegranate-shaped metal/metal-oxide/nanocarbon composites with ultrafast-charging/long-life lithium-storage performance.Download high-res image (491KB)Download full-size image

•Ag/ZnO nanotetrapods are firstly used as piezo/solar-photocatalyst.•Ag/ZnO nanotetrapods can co-use the solar and mechanical energy in the nature to degrade various organic pollutants.•High piezo/solar-photocatalytic efficiency has been realized.•A new physical-chemical mechanism has been proposed by coupling surface plasmon resonance and piezophototronic effects.Ag/ZnO nanotetrapods are synthesized in mass production via a simple thermal-evaporation/hydrothermal route, and Ag nanoparticles are randomly coated on ZnO nanotetrapods. Ag/ZnO nanotetrapods can co-use the solar and mechanical energy to degrade various organic pollutants, and the solar-photocatalytic activity is significantly enhanced by the piezo-assistance. For instance, under ultrasonic stimulation (200 W) and solar illumination (500 W), Ag/ZnO nanotetrapods can completely degrade methyl orange (MO) within 25 min. The high piezo/solar-photocatalytic efficiency of Ag/ZnO nanotetrapods can be ascribed to the coupling of surface plasmon resonance and piezophototronic effect in the solar-photocatalytic process. The localized surface plasmon resonance effect of Ag nanoparticles can increase the visible light absorption. Ag/ZnO interface can facilitate the interfacial charge transfer and induce the separation of photo-induced charge carriers. The piezoelectric field originated from the deformation of ZnO nanotetrapods can further enhance the separation of photo-induced electron/hole pairs. Our results imply that Ag/ZnO nanotetrapods have great potentials of using sustainable energy in the nature for environmental remediation.

•All-solid-state flexible self-charging power cells have been fabricated.•The solid piezo-electrolyte can act as both the electrolyte and piezo-separator.•All-solid-state SCPC has high energy conversion/storage efficiency and stability.•All-solid-state SCPC can power various wearable electronics and LEDs.A new all-solid-state self-charging power cell (SCPC) has been fabricated using mesoporous PVDF-LiPF6 film as piezo-electrolyte. The solid piezo-electrolyte can act as both the electrolyte and piezo-separator, which is prepared through immobilizing the liquid electrolyte in mesoporous PVDF film. The all-solid-state flexible SCPC can be efficiently charged up by mechanical deformation, and thus can directly harvest/store the body-motion energy. The SCPC sealed in stainless-steel cell can be charged by compressive deformation (30 N, 1 Hz) and the storage capacity is 0.118 μA h within 240 s, which is about 5 times larger than that of the traditional non-integrated system. The SCPC sealed in flexible shell can be charged by the bending deformation. The all-solid-state flexible SCPCs can power a variety of wearable electronic devices, including sports bracelets, smart watches and LEDs. This work provides an innovative approach for developing new self-sustainable battery and self-powered wearable electronics.All-solid-state flexible self-charging power cell (SCPC) is fabricated using solid piezo-electrolyte. The solid piezo-electrolyte (mesoporous PVDF-LiPF6 film) can act as both the electrolyte and piezo-separator. The SCPC can be efficiently charged up by mechanical deformation, and thus can directly harvest/store the body-motion energy. The SCPC can power a variety of wearable electronic devices.Download high-res image (192KB)Download full-size image

•PVDF/TiO2 nanofibers are synthesized by high voltage electrospinning method.•The e-skin can be self-powered through applied deformation.•The e-skin can detect various body motions.•The e-skin has distinct self-cleaning characteristic through piezo-photocatalytic coupling process.A flexible self-powering/self-cleaning electronic-skin (e-skin) for actively detecting body motion and degrading organic pollutants has been fabricated from PVDF/TiO2 nanofibers. PVDF/TiO2 nanofibers are synthesized by high voltage electrospinning method. The e-skin can be driven by external mechanical vibration, and actively output piezoelectric impulse. The outputting piezoelectric voltage can be significantly influenced by different applied deformation, acting as both the body-motion-detecting signal and the electricity power for driving the device. The e-skin can detect various body motions, such as pressing, stretching, bending finger and clenching fist. The e-skin also has distinct self-cleaning characteristic through piezo-photocatalytic coupling process. The photocatalytic activity of TiO2 and the piezoelectric effect of PVDF are coupled in a single physical/chemical process, which can efficiently degrade organic pollutants on the e-skin. For example, methylene blue (MB) can be completely degraded within 40 min under UV/ultrasonic irradiation. The present results could provoke a possible new research direction for realizing self-powering multifunctional e-skin.Download high-res image (111KB)Download full-size image

The emerging electronic-skins (e-skins) are designed to mimic the comprehensive properties of human perception via flexible device techniques, and the achievement of a vision e-skin for image recognition is a highly interesting topic for applications in bionic organs and robots. In this paper, a new self-powered flexible vision e-skin has been realized from a pixel-addressable matrix of piezophototronic ZnO nanowire arrays. Under applied deformation, the e-skin can actively output piezoelectric voltage (piezoelectric effect), and the output piezoelectric voltage can be significantly influenced by UV illumination. The piezoelectric output can be regarded as both a photodetecting signal and electrical power for driving the device (no external power source is needed). The working mechanism is based on the optoelectronic/piezoelectric coupling effect (piezophototronic effect) of ZnO. The photo-generated carriers inside the ZnO nanowires can partially screen the piezoelectric field, affecting the piezoelectric output. The e-skin device has a 6 × 6 pixel-addressable matrix structure, and can map multi-point UV-stimuli through a multichannel data acquisition method, realizing image recognition. This new device structure and working mechanism may provoke a new research direction for the development of multi-functional e-skins.

A new self-powered, stretchable, fiber-based electronic-skin (e-skin) has been fabricated for actively detecting human motion and environmental atmosphere. Several bundles of carbon fibers (coated with polydimethylsiloxane (PDMS) or polypyrrole (Ppy)) were woven together, forming a flexible fiber-based e-skin. The triboelectric current of the e-skin was dependent on the strain deformation and the environmental atmosphere. The e-skin can actively detect various human motions, such as finger touch, joint motion, skin deformation and slight stretching. Each PDMS–Ppy crossing point can be employed as an independent unit, and these units can output triboelectric current individually, realizing the tactile perception. The e-skin can also monitor volatile organic compounds in the atmosphere with high sensitivity, recovery and selectivity, (e.g. upon exposure to 1200 ppm methanol vapor, the triboelectric current of the e-skin decreased from 41.17 (in air) to 15.12 nA). The working mechanism is based on the triboelectrification/gas-sensing coupling effect. This new device architecture and material system can promote the development of a self-powered multifunctional e-skin.

•SGN paper as both the anode and current collector of LIB has been investigated.•SGN paper exhibits high capacity, good cyclability, lightweight and excellent flexibility.•SGN paper can be used to fabricate flexible cells.•The performance can be attributed to the synergistic effect between the two components.SnO2-graphene nanocomposites (SGNs) are synthesized by a facile hydrothermal method, and SGN paper as both the anode and current collector of lithium-ion battery has been investigated. The paper exhibits high capacity, good cyclability, lightweight and excellent flexibility. At 0.1 C rate (10 h per half cycle), the discharge capacity of SGN paper is 1195 mAh g−1 at 10th cycle and can maintain at 1094 mAh g−1 after 80 cycles. The paper based flexible cells also show high performance. It can be attributed to the synergistic effect. The present results indicate that SGN paper is one of good candidates for fabricating flexible lithium-ion batteries.

•A multi-functional self-powered electronic-skin (e-skin) has been realized.•The e-skin can output piezo-voltage and it can be influenced by deformation, O2 and H2O.•The organic pollution and bacteria on the e-skin can be cleaned under photo-irradiation.•Application of e-skin for detecting elbow banding has been simply demonstrated.A flexible self-powered e-skin has been presented with multi-functions of tactile-perception, atmosphere-detection and self-clean. Piezoelectric PVDF and tetrapod ZnO (T-ZnO) nanostructures are hybridizing on the flexible fabric substrate. The piezoelectric, gas sensing and photocatalytic properties of T-ZnO nanostructures are combined together. The piezoelectric effect of T-ZnO/PVDF leads to the motion-powered tactile-perception behavior, e.g. the e-skin can detect elbow bending or finger pressing. The piezoelectric/gas-sensing coupling effect of T-ZnO nanostructures delivers the motion-powered atmosphere-detection performance, and the piezoelectric output of the e-skin is different upon exposure to different atmosphere conditions, acting as the gas-sensing signal. The piezo-photocatalytic activity of T-ZnO nanostructures results in the distinct self-clean characteristics, and the organic-pollutants/bacteria can be degraded/sterilized on the surface of the e-skin. This novel material system and device architecture can promote the development of flexible self-powered multi-functional e-skin.A flexible self-powered T-ZnO/PVDF/fabric e-skin has been presented with multi-functions of tactile-perception, atmosphere-detection and self-clean. The piezoelectric, gas sensing, photocatalytic and antibacterial activities of T-ZnO nanostructures are combined together. This novel material system can promote the development of flexible motion-powered multi-functional e-skin.

Core–shell Co3O4/ZnCo2O4 coconut-like hollow spheres are synthesized by a facile two-step method. As the anode of lithium-ion batteries, their reversible capacity is up to 1278 mA h g−1 at 0.1C rate and remains at 1093 mA h g−1 after 50 cycles, much higher than that of pure Co3O4. Even after 300 cycles (cycling for more than 4 months), their reversible capacity can maintain at 934 mA h g−1 at 0.2C rate. Such superior electrochemical performance (high reversible capacity, excellent long-term cycling stability and good rate capability) can be ascribed to the unique core–shell hollow structure, complex synergistic effect, good electrical conductivity and interfacial charging mechanism. The present results demonstrate that the core–shell Co3O4/ZnCo2O4 hollow spheres are promising anode materials for high-performance lithium-ion batteries.

High piezo-photocatalytic efficiency of degrading organic pollutants has been realized from CuS/ZnO nanowires using both solar and mechanical energy. CuS/ZnO heterostructured nanowire arrays are compactly/vertically aligned on stainless steel mesh by a simple two-step wet-chemical method. The mesh-supported nanocomposites can facilitate an efficient light harvesting due to the large surface area and can also be easily removed from the treated solution. Under both solar and ultrasonic irradiation, CuS/ZnO nanowires can rapidly degrade methylene blue (MB) in aqueous solution, and the recyclability is investigated. In this process, the ultrasonic assistance can greatly enhance the photocatalytic activity. Such a performance can be attributed to the coupling of the built-in electric field of heterostructures and the piezoelectric field of ZnO nanowires. The built-in electric field of the heterostructure can effectively separate the photogenerated electrons/holes and facilitate the carrier transportation. The CuS component can improve the visible light utilization. The piezoelectric field created by ZnO nanowires can further separate the photogenerated electrons/holes through driving them to migrate along opposite directions. The present results demonstrate a new water-pollution solution in green technologies for the environmental remediation at the industrial level.Keywords: CuS/ZnO nanowire; heterostructure; photocatalytic activity; piezo-photocatalytic process; piezoelectric effect

•New material. CoMoO4/Fe2O3 core-shell nanorods are firstly synthesized.•High performance. Both the capacity and cyclability are very high.•New mechanism. The mechanism is based on the complex synergistic effect.•Potential application. The nanocomposites are promising candidates for Li battery.CoMoO4/Fe2O3 core-shell nanorods are synthesized by a two-step hydrothermal method, and Fe2O3 nanoparticles as shell are uniformly distributed on the whole surface of CoMoO4 nanorods. The core-shell nanorods as the anode of lithium-ion battery exhibit high reversible capacity of 1354 mAh g−1 at 0.2 C rate (5 h per half cycle), which is higher than that of bare CoMoO4 nanorods. The discharge capacity can still maintain at 1335 mAh g−1 (after 50 cycles) and 1236 mAh g−1 (after 100 cycles). The capacity retention between 2nd and 50th cycles is up to 98.6%. The superior lithium-storage performance can be owned to the stable crystal structure, good electrical conductivity and complex synergistic effect between CoMoO4 and Fe2O3. The present results indicate that CoMoO4/Fe2O3 core-shell nanorods are promising candidates for the anode of lithium-ion battery.

•Simple synthesis method: a facile two-step solvothermal route for preparing nanocomposites has been presented.•Excellent performance: ultrafast/stable cycling performance as anode of lithium battery has been achieved.•Theoretical discussion: the work mechanism is based on synergistic effect.Fe/Fe3O4/carbon nanocomposites are synthesized by a facile two-step solvothermal method. Some (Fe3O4, Fe) nanoparticles are embedded in carbon nanosheets, and some other (Fe3O4, Fe) nanoparticles form core-shell structure (Fe3O4/C, Fe/C) on the surface of carbon nanosheets. As anode of lithium-ion battery, the nanocomposites exhibit ultrafast/stable cycling performance. Their charging time can be shortened to merely ~4 min with reversible capacity of 330 mAh/g and maintains 108 mAh/g after 3500 cycles. At 0.2 C rate, the reversible capacity is up to 690 mAh/g and it increases to 755 mAh/g after 100 cycles. The present results demonstrate a right way to produce metal-oxide/carbon nanocomposites in mass production for realizing ultrafast-charging lithium-ion battery.

•Room-temperature ethanol sensing with high sensitivity has been realized.•Self-powered gas sensors have been fabricated, and no external power is needed.•The sensing performance is very high.•New piezo-surface coupling effect of heterostructures.At room temperature, high sensitivity for detecting ethanol has been achieved from α-Fe2O3/ZnO nanowire piezo-nanogenerator as self-powered gas sensor. Such ethanol sensing can be ascribed to piezo-surface coupling effect of the heterostructured nanocomposites. The results demonstrate a novel approach for room-temperature ethanol sensors and promote the development of self-powered sensing.

•A self-powered electronic-skin (e-skin) for detecting glucose level has been realized.•The e-skin can output piezo-voltage and it can be influenced by glucose concentration.•Working mechanism is coupling surface enzymatic reaction and piezoelectric effect.•Application of e-skin for detecting rabbit blood glucose has been simply demonstrated.The body electric (the integration of flexible biosensors and the human body) has attracted worldwide research attention because of its potential applications in the future health care. In this paper, a self-powered electronic-skin (e-skin) for detecting glucose level in body fluid has been realized basing on the piezo-enzymatic-reaction coupling process of GOx@ZnO (GOx: glucose-oxidase) nanowire arrays. The e-skin under applied deformation can actively output electric impulse through piezoelectric effect, and the outputting piezoelectric voltage can be significantly influenced by the glucose concentration in the solution. The piezoelectric output can be regarded as both the biosensing signal and the electricity power for driving the device. In this process, the e-skin does not need external electricity power source, and can long-lived work through harvesting the mechanical energy of human motion. The working mechanism has been proposed basing on the coupling of surface enzymatic reaction and piezoelectric effect. A practical application of the e-skin for detecting rabbit blood glucose concentration has been simply demonstrated. The present results could provoke a possible research field for the development of the body electric and widen the study scope for self-powered nano-devices/systems.A self-powered electronic-skin (e-skin) for detecting glucose level in body fluid has been realized basing on the piezo-enzymatic-reaction coupling process of GOx@ZnO (GOx: glucose-oxidase) nanowire arrays. The piezoelectric output of the e-skin can be regarded as both the biosensing signal and the electricity power for driving the device.

•NiO/ZnO nanowire arrays as a self-powered/active gas sensor have been realized.•This sensing system can work without any external electric power source.•Compared with bare ZnO, high and fast H2S response has been obtained.•New coupling effect between the piezoelectric characteristic of ZnO and the conversion of NiO/ZnO heterojunctions can influence the piezoelectric screening effect.High and fast response of H2S sensing at room temperature has been realized from NiO/ZnO hetetojunction nanowire (NW) arrays as a self-powered gas sensor. The piezoelectric output generated by NiO/ZnO NW nanogenerator (NG) can act as both the power source and sensing signal. Upon exposure to 1000 ppm H2S at room temperature, the piezo-voltage of NiO/ZnO NW arrays decreases from 0.388 V (in dry air) to 0.061 V, and the response is approximately 10 times higher than that of bare ZnO NW arrays. Such a high performance can be attributed to the piezoelectric effect of ZnO and the conversion of NiO/ZnO PN-junctions. Our study confirms that introducing heterostructures into NG is a right direction for the development of self-powered gas sensors.

Room-temperature self-powered ethanol sensing has been realized from ZnO nanowire (NW) arrays by combining their piezoelectric, photoelectric and gas sensing characteristics. Under the assistance of UV illumination, the piezoelectric output of ZnO NWs acts not only as a power source, but also as a response signal to ethanol gas at room temperature. Upon exposure to 700 ppm ethanol at room temperature under 67.5 mW cm−2 UV illumination, the piezoelectric output voltage of ZnO NWs (under 34 N compressive forces) decreases from 0.80 V (in air) to 0.12 V and the response is up to 85. The room-temperature reaction between the UV-induced chemisorbed oxygen ions and ethanol molecules increases the carrier density in ZnO NWs, resulting in a strong piezoelectric screening effect and very low piezoelectric output. Our study can stimulate a research trend on designing new gas sensors and investigating new gas sensing mechanisms.

Highly stable piezo-immunoglobulin-biosensing has been realized from a SiO2/ZnO nanowire (NW) nanogenerator (NG) as a self-powered/active biosensor. The piezoelectric output generated by the SiO2/ZnO NW NG can act not only as a power source for driving the device, but also as a sensing signal for detecting immunoglobulin G (IgG). The stability of the device is very high, and the relative standard deviation (RSD) ranges from 1.20% to 4.20%. The limit of detection (LOD) of IgG on the device can reach 5.7 ng mL−1. The response of the device is in a linear relationship with IgG concentration. The biosensing performance of SiO2/ZnO NWs is much higher than that of bare ZnO NWs. A SiO2 layer uniformly coated on the surface of the ZnO NW acts as the gate insulation layer, which increases mechanical robustness and protects it from the electrical leakages and short circuits. The IgG biomolecules modified on the surface of the SiO2/ZnO NW act as a gate potential, and the field effect can influence the surface electron density of ZnO NWs, which varies the screening effect of free-carriers on the piezoelectric output. The present results demonstrate a feasible approach for a highly stable self-powered/active biosensor.

α-MoO3–In2O3 core–shell nanorods were prepared by a facile two-step hydrothermal method. As the anode of lithium-ion batteries, their reversible capacity was up to 1304 mA h g−1 at 0.2 C rate (5 hours per half cycle) and maintains 1114 mA h g−1 after 50 cycles. At a rate of 0.3 C, 0.5 C, 1 C and 2 C, the discharge capacities after 50 cycles were maintained at 938, 791, 599 and 443 mA h g−1, respectively. The enhanced electrochemical performance can be ascribed to the synergistic effect between α-MoO3 and In2O3, one-dimensional core–shell nanostructures, short paths for lithium diffusion and interface spaces.

High sensitivity, selectivity, and reliability have been achieved from ZnSnO3/ZnO nanowire (NW) piezo-nanogenerator (NG) as self-powered gas sensor (SPGS) for detecting liquefied petroleum gas (LPG) at room temperature (RT). After being exposed to 8000 ppm LPG, the output piezo-voltage of ZnSnO3/ZnO NW SPGS under compressive deformation is 0.089 V, much smaller than that in air ambience (0.533 V). The sensitivity of the SPGS against 8000 ppm LPG is up to 83.23, and the low limit of detection is 600 ppm. The SPGS has lower sensitivity against H2S, H2, ethanol, methanol and saturated water vapor than LPG, indicating good selectivity for detecting LPG. After two months, the decline of the sensing performance is less than 6%. Such piezo-LPG sensing at RT can be ascribed to the new piezo-surface coupling effect of ZnSnO3/ZnO nanocomposites. The practical application of the device driven by human motion has also been simply demonstrated. This work provides a novel approach to fabricate RT-LPG sensors and promotes the development of self-powered sensing system.Keywords: gas sensing; liquefied petroleum gas; nanogenerator; self-powered; ZnSnO3/ZnO nanowire;

Room-temperature self-powered H2S sensing with high response and selectivity has been realized from a Cu–ZnO nanowire nanogenerator. Upon exposure to 1000 ppm H2S at room temperature, the piezoelectric output voltage of the device (5 at% Cu–ZnO) under compressive force decreases from 0.552 (in dry air) to 0.049 V, and the response is up to 1045, over 8 times larger than that of undoped ZnO nanowires. The selectivity against H2S is also very high at room temperature. The enhanced room-temperature H2S sensing performance can be attributed to the coupling of the piezoelectric screening effect of ZnO nanowires and the synergistic effect of the Cu dopant. This study should stimulate research into designing a new gas sensor for detecting toxic gases at room temperature.

Highly sensitive humidity sensing has been realized from a Cd-doped ZnO nanowire (NW) nanogenerator (NG) as a self-powered/active gas sensor. The piezoelectric output of the device acts not only as a power source, but also as a response signal to the relative humidity (RH) in the environment. The response of Cd–ZnO (1:10) NWs reached up to 85.7 upon exposure to 70% relative humidity, much higher than that of undoped ZnO NWs. Cd dopant can increase the number of oxygen vacancies in the NWs, resulting in more adsorption sites on the surface of the NWs. Upon exposure to a humid environment, a large amount of water molecules can displace the adsorbed oxygen ions on the surface of Cd–ZnO NWs. This procedure can influence the carrier density in Cd–ZnO NWs and vary the screening effect on the piezoelectric output. Our study can stimulate a research trend on exploring composite materials for piezo-gas sensing.

A high sensitive and repeatable self-powered humidity sensor has been realized from Co-doped ZnO nanowires (NWs). The piezoelectric output of the device acts not only as a power source, but also as a response signal to the relative humidity (RH) in the environment. When the relative humidity is 70% RH at room temperature, the piezoelectric output voltage of the humidity sensor under compressive force decreases from 1.004 (at 20% RH) to 0.181 V. The sensitivity of self-powered humidity sensing based on Co-doped ZnO nanoarrays is much higher than that of undoped ZnO nanoarrays. The device exhibits good repeatability for humidity detection, and the response maintains ∼90% after one month. Such a high performance can be attributed to the piezo-surface coupling effect of the nanocomposites and more active sites introduced by the Co dopants. Our study can stimulate a research trend on exploring composite materials for piezo-gas sensing.

•New portable room-temperature humidity sensor is realized, and no external electric power is needed.•Sb-doped ZnO nanowire arrays are synthesized via a very facile way.•The device has high sensitivity against humidity.•New piezo-sensing mechanism with element doping for humidity detecting is established.Room-temperature self-powered/active humidity sensing has been realized from Sb-doped ZnO nanowire (NW) arrays by coupling their piezoelectric and gas sensing characteristics. The piezoelectric output of the device acts as both the power source and the response signal against relative humidity (RH). Upon exposure to 70% RH, the piezoelectric output of Sb-doped ZnO NWs decreases from 1.35 V (10% RH) to 0.22 V, and the response is 83.70 (much higher than that of undoped ZnO).

A flexible room-temperature self-powered active ethanol sensor has been realized from a Pd/ZnO nanoarray nanogenerator. Pd nanoparticles are uniformly loaded on the whole surface of the ZnO nanowire arrays by a simple hydrothermal method. The piezoelectric output of the Pd/ZnO nanowire arrays can act as both the power source of the device and the room-temperature ethanol sensing signal. Upon exposure to 800 ppm ethanol gas at room temperature, the piezoelectric output voltage decreased from 0.52 V (in air) to 0.25 V. Such a room-temperature self-powered ethanol sensing behavior can be attributed to the catalytic effect of Pd, the Schottky barrier at the Pd/ZnO interface, and the piezotronics effect of the ZnO nanowires. Moreover, this flexible device can be driven by tiny mechanic energy in the environment, such as human finger movement. The present results can stimulate a research trend on designing new material systems and device structures in self-powered ethanol sensing at room temperature.

•α-MoO3@MnO2 core-shell nanorods were synthesized via a facile two-step method.•α-MoO3@MnO2 exhibits a high capacity up to 1475 mAh/g at 0.1 C rate as LIB anodes.•The performances are attributed to synergistic effect between MnO2 and MoO3.α-MoO3@MnO2 core-shell nanorods are synthesized via a facile two-step method. The electrochemical measurement of lithium-ion batteries (LIBs) shows that prepared α-MoO3@MnO2 core-shell nanorods as the anode exhibit high discharge capacity, high rate capability, and excellent cycling stability. The reversible capacity of α-MoO3@MnO2 core-shell nanorods is 1475 mAh/g at 0.1 C rate (10 hours per charging cycle) and retains at 1127 mAh/g after 50 cycles, much higher than that of pure α-MoO3 and MnO2. Even at high current rate of 6 C, the reversible capacity of α-MoO3@MnO2 core-shell nanorods is 394 mAh/g and retains at 286 mAh/g after 50 cycles. Our results indicate that α-MoO3@MnO2 core-shell nanocomposites have enormous potential for application in lithium-ion batteries.

FeWO4-SnO2 core-shell nanorods are assembled via a two-step method. SnO2 nanoparticles are uniformly coated on the surface of FeWO4 nanorods. And high lithium storage performance has been achieved from them. At C/10 rate (10 hours per charging cycle), the reversible capacity (the 2nd cycle) of FeWO4-SnO2 core-shell nanorods is up to 1286.9 mAh g−1, much higher than that of FeWO4 nanorods, SnO2 and traditional theoretical results. Such behaviour is attributed to the synergistic effect between nanostructured SnO2 and FeWO4. Our results imply that core-shell nanocomposites are good candidates for high-capacity anodes of lithium ion battery.

Al-doped ZnO nanowire arrays are used to fabricate a piezoelectric nanogenerator, and its output is significantly dependent on the humidity in the environment, showing its applications as a self-powered active humidity sensor. The piezoelectric output of the device acts as both the power source and response signal to the humidity.

•Core–shell SnO2@TiO2–B nanowires are synthesized via a two-step hydrothermal route.•SnO2@TiO2–B nanowires exhibit high Li storage capacity and well rate capability.•The performance is attributed to synergistic effect between SnO2 and TiO2–B.Core–shell SnO2@TiO2–B nanowires are synthesized via a two-step hydrothermal route. SnO2 nanoparticles are uniformly coated on the whole surface of TiO2–B nanowires. As the anode of lithium ion batteries, core–shell SnO2@TiO2–B nanowires exhibit high lithium storage capacity and superior rate capability. The reversible capacity is ~1160 mAh g−1 at C/5 rate (5 h per charging cycle) and the retention is 790 mAh g−1 after 30 cycles. At the rate of 2C, the capacity can be maintained at 556 mAh g−1. Such a good lithium storage performance can be attributed to the synergistic effect between SnO2 and TiO2–B nanostructures.

•Co3O4 nanorods and nanobelts are fabricated by a template-free hydrothermal method.•The morphologies of Co3O4 can be easily controlled by hydrothermal reaction time.•Lithium-ion battery performance of nanobelts is much higher than that of nanorods.Co3O4 nanorods and nanobelts can be synthesized controllably by a template-free hydrothermal method. Enhanced lithium-ion battery performances are obtained from Co3O4 nanorods and nanobelts. After 50 cycles, the reversible capacity is up to 1124 and 1260 mAh g−1 at C/20 rate (20 h per half cycle), respectively, and the cyclability are excellent. Lithium-ion battery performance of nanobelts is much higher than that of nanorods. Such a behavior is attributed to more efficient Li insertion, less volume change and no agglomeration of nanobelts. The present results open a way for fabrication of porous 1D nanostructures and imply that porous 1D nanostructures are good candidates for high performance lithium-ion battery anodes.

•NiO/GNSs are synthesized by a hydrothermal method.•NiO/GNSs exhibit extremely high cyclability and capacity as LIB anodes.•High performance is attributed to the use of GNSs support and NiO nanowall structure.NiO nanowalls/graphene nanosheets (NiO/GNSs) nanocomposites are synthesized by a hydrothermal method, and their application as anodes of lithium-ion batteries has been investigated. NiO nanowalls were uniformly coated over the surface of graphene. NiO/GNSs nanocomposites exhibit extremely high cyclability and capacity. The reversible capacity is 844.9 mA h g−1 at 0.1C rate (10 h per half cycle) and fades merely 7.1% after 50 cycles. The present results indicate that NiO/GNS nanocomposites have potential applications in lithium-ion battery anodes.

•SnS2–graphene nanocomposites are synthesized by a hydrothermal method.•SnS2–graphene nanocomposites exhibit high cyclability and capacity as LIB anodes.•High performance is attributed to the use of graphene support and SnS2 nanostructure.SnS2–graphene nanocomposites are synthesized by a hydrothermal method, and their application as anodes of lithium-ion batteries has been investigated. SnS2 nanosheets are uniformly coating on the surface of graphene. SnS2–graphene nanocomposites exhibit high cyclability and capacity. The reversible capacity is 766 mAh/g at 0.2C rate and maintains at 570 mAh/g after 30 cycles. Such a high performance can be attributed to high electron and Li-ion conductivity, large surface area, good mechanical flexibility of graphene nanosheets and the synergetic effect between graphene and SnS2 nanostructures. The present results indicate that SnS2–graphene nanocomposites have potential applications in lithium-ion battery anodes.

•New portable room-temperature H2 sensor is realized, and no external electric power is needed.•New piezo-sensing mechanism for H2 detecting is established.•The device has extremely high sensitivity and selectivity against H2.•Self-powered/active H2 sensor driven by human motion is a next generation of H2 sensors.Room-temperature high H2 sensing has been realized from SnO2/ZnO nanoarray nanogenerator. Without any external electricity power source, the portable device can be self-powered under the driving of human motion, in which the piezoelectric output can actively act as both the power source and H2 sensing signal. Upon exposure to 800 ppm H2 at room temperature, the piezoelectric output voltage of the device under the same applied deformation decreases from 0.80 V (in dry air) to 0.14 V, and the sensitivity is up to 471.4. The detection limit is ~10 ppm H2, and the selectivity against H2 at room temperature is very high. The excellent room-temperature H2 sensing performance can be attributed to the coupling of the piezoelectric screening effect of ZnO nanowires and the conversion of SnO2/ZnO heterojunctions. This study can stimulate a research trend for the development of the next generation of portable room-temperature H2 sensors.Room-temperature high H2 sensing has been realized from SnO2/ZnO nanoarray nanogenerator. Without any external electricity power source, the portable device can be self-powered under the driving of human motion. Such a behavior can be attributed to the coupling of the piezoelectric screening effect of ZnO nanowires and the conversion of SnO2/ZnO heterojunctions.

•New self-powered active biosensor has been realized without external electric power.•The piezoelectric output of ZnO NWs acts as both energy source and biosensing signal.•The sensitivity is much higher than the traditional biosensor (I–V behavior).•It opens a new direction for the development self-powered active biosensors.Self-powered active biosensor has been realized from ZnO nanowire (NW) nanogenerator (NG). The piezoelectric output generated by ZnO NW NG can act not only as a power source for driving the device, but also as a biosensing signal. After immersing in 10−3 g ml−1 human immunoglobulin G (IgG), the piezoelectric output voltage of the device under compressive deformation decreases from 0.203±0.0176 V (without IgG) to 0.038±0.0035 V. Such a self-powered biosensor has higher response than transistor-type biosensor (I–V behavior). The response of self-powered biosensor is in a linear relationship with IgG concentration (logarithm, 10−7–10−3 g ml−1) and the limit of detection (LOD) on IgG of the device is about 6.9 ng ml−1. The adsorption of biomolecules on the surface of ZnO NWs can modify the free-carrier density, which vary the screening effect of free-carriers on the piezoelectric output. The present results demonstrate a feasible approach for actively detecting biomolecules by coupling the piezotronic and biosensing characteristics of ZnO NWs.

Self-powered active gas sensing has been realized from core–shell In2O3/ZnO nanoarray nanogenerator, and extremely high H2S sensitivity and selectivity at room temperature have been obtained. In2O3/ZnO nanoarrays have two functions: one is an energy source because In2O3/ZnO nanoarrays can produce piezoelectric output power; the other is a H2S sensor because the piezoelectric output of In2O3/ZnO nanoarrays varies with the concentration of H2S. Upon exposure to 700 ppm of H2S at room temperature, the piezoelectric output of In2O3/ZnO nanoarrays decreases from 0.902 V (in air) to 0.088 V, and the sensitivity is up to 925, much higher than that of bare ZnO nanoarrays. The heterostructure conversion of In2O3/ZnO to In2S3/ZnO, in which the electron depletion layer on the surface of ZnO changes to the accumulation layer, has stronger adjustment on the free-carrier piezo-screening effect of ZnO than the gas adsorption. Our results demonstrate that a heterostructured nanoarray nanogenerator has potential applications in actively detecting toxic gas without using any external electricity power.

α-Fe2O3–SnO2 core–shell nanorod arrays on titanium foil have been assembled by a facile template-free method. At a rate of C/5 (5 h per charging cycle), their reversible capacity is ∼1059.9 mA h g−1, higher than that of pure α-Fe2O3 nanorod array electrodes (∼858.3 mA h g−1). After 30 cycles, the capacity is maintained at 807.1 mA h g−1. Such high performances can be attributed to the synergistic effect between nanostructured SnO2 and α-Fe2O3 and the nanoarray structures. α-Fe2O3 nanostructures with high electrochemical activity can activate the irreversible capacity of SnO2, and the nanoarray structures can provide good contact, short electron transporting paths, a high surface-to-volume ratio and open space in the system. These results indicate that one-dimensional nanocomposite arrays on metal foils are good candidates for high performance lithium ion batteries.

Uniformly loaded Pd–SnO2 nanorods are synthesized via a simple one-step hydrothermal route. The gas sensors fabricated from Pd–SnO2 nanorods exhibit high sensitivity and fast response. The sensor response at 300 °C is up to 9.9, 36.8, 55.6, 89.1 and 168.2 upon exposure to 100, 200, 300, 500 and 1000 ppm ethanol, respectively. And the work temperature can be lowered down to 200 °C. Such behaviors can be attributed to Schottky barrier at Pd/SnO2 interface and catalytic effect of Pd nanoparticles. Our results open a way for uniform modification of SnO2 nanorods with Pd nanoparticles and enhancing their gas sensing performance.

•Co3O4/graphene nanocomposites are firstly synthesized by a hydrothermal method.•Co3O4/graphene nanocomposites exhibit extremely high cyclability and capacity as LIB anodes, much higher than Co3O4 nanostructures/composites reported previously.•Such excellent performances can be attributed to the synergistic effect between Co3O4 nanowires and graphene nanosheets.Co3O4/graphene nanocomposites are synthesized by a hydrothermal method, and their extremely high capacity and stability as the anode of lithium-ion battery is obtained. Co3O4 nanowires with the length of ~500 nm and the diameter of ~50 nm are uniformly coated on the surface of graphene nanosheets. The reversible capacity is 906.6 mA h g−1 at 0.1 C rate (10 h per charging cycle) and fades merely 6.9% after 50 cycles. Such behaviors can be attributed to high electron and Li-ion conductivity, large surface area, good mechanical flexibility of graphene nanosheets and the synergetic effect between graphene and Co3O4 nanostructures. The present results indicate that Co3O4/graphene nanocomposites have potential applications in the anode of LIB.

SnO2/NiO core-shell nanobelts have been synthesized simply by coating NiO nanobelts with a thin layer of SnO2 nanoparticles. As the anode material of lithium-ion battery, SnO2/NiO core-shell nanobelts exhibit higher reversible capacity (∼900 mAh/g at C/20 rate) and better cycling performance than individual NiO or SnO2 materials. The excellent performance can be attributed to the synergistic effect between SnO2 and NiO. Our results demonstrate the potential applications of SnO2/NiO core-shell nanobelts in high-performance lithium-ion batteries.Highlights► SnO2/NiO core-shell nanobelts are firstly synthesized, and firstly used as anodes of lithium-ion battery. ► SnO2/NiO core-shell nanobelts shows very high reversible lithium storage capacity, higher than individual SnO2, NiO materials or traditional theoretical results. ► A new lithium insertion/extraction mechanism based on synergistic effect has been investigated. And the experimental data and theoretical discussion can provoke a new direction for fabricating high-performance lithium-ion battery.

•Novel SnO2–MnO2–SnO2 SNTs are synthesized via a simple wet-chemical route.•SNTs exhibit high reversible capacity, cyclability and rate capability as LIBs anodes.•Excellent performances are attributed to synergistic effect and the tubular nanostructures.SnO2–MnO2–SnO2 sandwich-structured nanotubes are synthesized by uniformly coating SnO2 nanoparticles on both the inner and outer walls of α-MnO2 nanotubes via a simple wet-chemical route. As the anodes of lithium ion batteries, SnO2–MnO2–SnO2 sandwich-structured nanotubes exhibit high reversible capacity, cyclability and rate capability. The reversible capacity of the nanocomposites is 847.5 mAh/g and retains 716.0 mAh/g after 50 cycles, which is higher than that of α-MnO2 or SnO2. At 20C rate, SnO2–MnO2–SnO2 sandwich-structured nanotubes can deliver a capacity of 224.2 mAh/g. Such excellent performances can be attributed to the synergistic effect and the tubular nanostructures. Our results imply that one-dimensional sandwich-structured nanocomposites have potential applications in lithium ion batteries.

In the paper, we find that graphene has a strong dielectric loss, but exhibits very weak attenuation properties to electromagnetic waves due to its high conductivity. As polyaniline nanorods are perpendicularly grown on the surface of graphene by an in situ polymerization process, the electromagnetic absorption properties of the nanocomposite are significantly enhanced. The maximum reflection loss reaches −45.1 dB with a thickness of the absorber of only 2.5 mm. Theoretical simulation in terms of the Cole–Cole dispersion law shows that the Debye relaxation processes in graphene/polyaniline nanorod arrays are improved compared to polyaniline nanorods. The enhanced electromagnetic absorption properties are attributed to the unique structural characteristics and the charge transfer between graphene and polyaniline nanorods. Our results demonstrate that the deposition of other dielectric nanostructures on the surface of graphene sheets is an efficient way to fabricate lightweight materials for strong electromagnetic wave absorbents.

The paper describes for the first time the successful synthesis of Fe2O3/TiO2 tube-like nanostructures, in which TiO2 shell is of quasi-single crystalline characteristic and its thickness can be controlled through adjusting the added amount of aqueous Ti(SO4)2 solution. The characterization of samples obtained at different stages using transmission electron microscope indicates that the outer TiO2 shell is changed gradually from amorphous and polycrystalline phase into quasi-single crystal under thermal actions through the Ostwald ripening process, accompanying the corrosion of the central parts of Fe2O3 nanorods, and the formation of small particles separating each other, leading to the special core/shell nanorods. Furthermore, Fe2O3/TiO2 tube-like nanostructures can be transformed into Fe2TiO5 nanostructures after they are thermally treated at higher temperatures. Those nanostructures exhibit enhanced ethanol sensing properties with respect to the monocomponent. Our results imply that not only hollow nanostructures, but also a novel type of nanostructures can be fabricated by the present method for nanodevices.Keywords: gas sensing; heterostructures; hollow nanostructures; iron oxide; iron titanium oxide; titanium dioxide;

Hybrid SnO2/nanocarbon families (graphene nanosheets (GNSs), single-wall carbon nanotubes (SWCNTs), multi-wall carbon nanotubes (MWCNTs) and carbon nanospheres (CNSs)) have been synthesized by a similar wet chemical method. SnO2 nanoparticles are uniformly loaded on the surface of the nanocarbon families. As lithium battery anodes, their electrochemical properties of the reaction of lithium are investigated under the same conditions. To compare between them, SnO2/GNSs have the largest capacity; SnO2/GNSs and SnO2/SWCNTs have high cyclability; and SnO2/MWCNTs can maintain the capacity at high current density. Such behaviors are ascribed to their surface-to-volume ratio, structure flexibility, ion mobility and electron conductivity. The present results are the bases for their practical applications in lithium-ion battery anodes.

Extraordinarily high reversible capacity of lithium-ion battery anodes is realized from SnO2/α-MoO3 core-shell nanobelts. The reversible capacity is much higher than traditional theoretical results. Such behavior is attributed to α-MoO3 that makes extra Li2O reversibly convert to Li+.

Ultrafast charging/discharging of lithium-ion battery anodes is realized from porous Co3O4 nanoneedle arrays growing on copper foils. Their charge time can be shortened to ∼6 s, their reversible capacity at 0.5C rate is 1167 mAh/g. This implies that nano-arrays growing directly on copper foils are good candidates for anodes.

Uniformly loaded α-Fe2O3/graphene nanocomposites are synthesized via hydrothermal routs. Enhanced lithium storage performance of lithium-ion battery anodes is realized from α-Fe2O3/graphene nanocomposites. Compared with pure α-Fe2O3 nanostructures, α-Fe2O3/graphene nanocomposites exhibit higher reversible capacity and better cycling performance. Their reversible capacity is up to 771 mA h g−1 at C/10 rate, and maintains 73% after 30 cycles. Such behaviors can be attributed to high electron and Li-ion conductivity, large surface area, good mechanical flexibility of graphene nanosheets and the synergetic effect of graphene and α-Fe2O3 nanostructures. Our results indicate that α-Fe2O3/graphene nanocomposites are good candidates for high performance lithium-ion battery anodes.Highlights► α-Fe2O3/graphene nanocomposites are obtained by hydrothermal method. ► Enhanced lithium storage performance is realized from the nanocomposites. ► Both reversible capacity and cycling performance are higher than pure materials. ► Such behaviors can be attributed to the characteristics of graphene nanosheets.

α-MnO2/graphene nanocomposites are synthesized via a facile wet-chemical route, and α-MnO2 nanosheets are uniformly distributed on the surface of graphene. Their high performance as lithium ion battery anodes is obtained. Their reversible capacity at C/10 rate is up to 726.5 mA h/g, and maintains up to 635.5 mA h/g after 30 cycles. Such a performance can be partly attributed to high electron conductivity, excellent flexibility and high specific surface area of graphene. Also, α-MnO2 nanostructures can play a role in preventing the pile of graphene nanosheets with the loss of their active surface area. The present results indicate that α-MnO2/graphene nanocomposites have potential applications in lithium-ion battery anodes.

Highly sensitive gas sensors are realized from uniformly loaded Pt@SnO2 nanorods, which are synthesized via one-step hydrothermal routes. At 300 °C, the sensitivity of the sensors upon exposure to 200 ppm ethanol is up to 39.5. Such a high gas sensing can be attributed to both the chemical and the electrical contribution of Pt. Interestingly, at 200 °C, the response of the sensors is characterized by opposite variations of resistances, which probably arise from temperature-dependent forms of surface oxygen ions. The present results demonstrate an available direction for realizing high-performance gas sensors.

Pt−ZnO nanoflowers are prepared via a novel one-step hydrothermal route, and Pt nanoparticles are uniformly loaded on the whole surface of the nanoflowers. The growth mechanism of Pt−ZnO nanoflowers is proposed to be a four-stage process. With the help of Raman scattering, photoluminescence, and gas sensing measurements, it has been demonstrated that the optical and sensing properties of Pt−ZnO nanoflowers are greatly enhanced. The surface defects decrease, the concentration of bound excitons under UV illumination increases, and the surface adsorption is enhanced and accelerated. These probably arise from the chemical and electrical effect of Pt. Our results could provoke a promising direction to achieve higher optical and sensing properties of ZnO one-dimensional nanostructures.

Electrical transport experiments are performed on individual α-MnO2 and β-MnO2 nanorods. Both of α-MnO2 and β-MnO2 nanorods are synthesized via hydrothermal routes. A three-region method is used to analyze their nonlinear current–voltage characteristics. Under low biases, the effective contact barrier height is roughly estimated to be 0.05 eV for α-MnO2 and 0.15 eV for β-MnO2, respectively. As the applied bias is high enough, the contact barriers are significantly tilted and the current is largely tunneling. The conductance of α-MnO2 and β-MnO2 nanorods at room temperature is roughly estimated to be 5.98 and 1.74 × 10−3 cm−1 Ω−1, respectively. And the thermal-activation energy is roughly estimated to be 0.047 and 0.226 eV, respectively. Our results are probably the bases for their applications in nanosized electrical devices.

One-dimensional nanosized core/shell PN-junctions are formed from N-type SnO2 nanorods (synthesized via a hydrothermal method; diameter ∼10 nm, length ∼100 nm) uniformly coated with P-type CuO nanoparticles (diameter ∼4 nm). Gas sensors are realized from these PN-junction nanorods, and their resistances greatly decrease upon exposed to H2S at room temperature. The sensitivity against 10 ppm H2S at 60 °C is up to 9.4 × 106. At the same time, the sensors have very good selectivity against H2S. Such good performances are probably attributed to the destruction of PN-junctions and the small size effect of nanostructures. Our results imply that one-dimensional heterostructured nanomaterials are promising candidates for high-performance gas sensors.

•Novel Co3O4/graphene nanocomposites.•New plasma-assisted treatment method.•High electrochemical performance as the anode of lithium battery.•New synergistic effect.Co3O4/graphene nanocomposites are synthesized by a plasma-assisted treatment, and Co3O4 nanoparticles are uniformly embedded into graphene nanosheets. The nanocomposites exhibit high electrochemical performance as the anode of lithium-ion battery. The reversible capacity is up to 1368 mAh g−1 at the current density of 125 mA g−1 (about 10 h per half cycle), and maintains at 1269 mAh g−1 after 50 cycles. At high current density of 1700 mA g−1, the charging time can be shortened to merely ∼8 min. Under this high current surge, the capacity maintains at ∼210 mAh g−1 even after 1000 cycles. The high capacity, cyclability and rate capability of the nanocomposites can be attributed to the unique structure, good electronic conductivity, short paths for lithium diffusion and interfacial charging mechanism. The present work indicates that plasma-treated metal-oxide/graphene nanocomposites are good candidates for realizing high-performance lithium-ion battery.

The emerging electronic-skins (e-skins) are designed to mimic the comprehensive properties of human perception via flexible device techniques, and the achievement of a vision e-skin for image recognition is a highly interesting topic for applications in bionic organs and robots. In this paper, a new self-powered flexible vision e-skin has been realized from a pixel-addressable matrix of piezophototronic ZnO nanowire arrays. Under applied deformation, the e-skin can actively output piezoelectric voltage (piezoelectric effect), and the output piezoelectric voltage can be significantly influenced by UV illumination. The piezoelectric output can be regarded as both a photodetecting signal and electrical power for driving the device (no external power source is needed). The working mechanism is based on the optoelectronic/piezoelectric coupling effect (piezophototronic effect) of ZnO. The photo-generated carriers inside the ZnO nanowires can partially screen the piezoelectric field, affecting the piezoelectric output. The e-skin device has a 6 × 6 pixel-addressable matrix structure, and can map multi-point UV-stimuli through a multichannel data acquisition method, realizing image recognition. This new device structure and working mechanism may provoke a new research direction for the development of multi-functional e-skins.

A new self-powered, stretchable, fiber-based electronic-skin (e-skin) has been fabricated for actively detecting human motion and environmental atmosphere. Several bundles of carbon fibers (coated with polydimethylsiloxane (PDMS) or polypyrrole (Ppy)) were woven together, forming a flexible fiber-based e-skin. The triboelectric current of the e-skin was dependent on the strain deformation and the environmental atmosphere. The e-skin can actively detect various human motions, such as finger touch, joint motion, skin deformation and slight stretching. Each PDMS–Ppy crossing point can be employed as an independent unit, and these units can output triboelectric current individually, realizing the tactile perception. The e-skin can also monitor volatile organic compounds in the atmosphere with high sensitivity, recovery and selectivity, (e.g. upon exposure to 1200 ppm methanol vapor, the triboelectric current of the e-skin decreased from 41.17 (in air) to 15.12 nA). The working mechanism is based on the triboelectrification/gas-sensing coupling effect. This new device architecture and material system can promote the development of a self-powered multifunctional e-skin.

Core–shell Co3O4/ZnCo2O4 coconut-like hollow spheres are synthesized by a facile two-step method. As the anode of lithium-ion batteries, their reversible capacity is up to 1278 mA h g−1 at 0.1C rate and remains at 1093 mA h g−1 after 50 cycles, much higher than that of pure Co3O4. Even after 300 cycles (cycling for more than 4 months), their reversible capacity can maintain at 934 mA h g−1 at 0.2C rate. Such superior electrochemical performance (high reversible capacity, excellent long-term cycling stability and good rate capability) can be ascribed to the unique core–shell hollow structure, complex synergistic effect, good electrical conductivity and interfacial charging mechanism. The present results demonstrate that the core–shell Co3O4/ZnCo2O4 hollow spheres are promising anode materials for high-performance lithium-ion batteries.

In the paper, we find that graphene has a strong dielectric loss, but exhibits very weak attenuation properties to electromagnetic waves due to its high conductivity. As polyaniline nanorods are perpendicularly grown on the surface of graphene by an in situ polymerization process, the electromagnetic absorption properties of the nanocomposite are significantly enhanced. The maximum reflection loss reaches −45.1 dB with a thickness of the absorber of only 2.5 mm. Theoretical simulation in terms of the Cole–Cole dispersion law shows that the Debye relaxation processes in graphene/polyaniline nanorod arrays are improved compared to polyaniline nanorods. The enhanced electromagnetic absorption properties are attributed to the unique structural characteristics and the charge transfer between graphene and polyaniline nanorods. Our results demonstrate that the deposition of other dielectric nanostructures on the surface of graphene sheets is an efficient way to fabricate lightweight materials for strong electromagnetic wave absorbents.

Room-temperature self-powered H2S sensing with high response and selectivity has been realized from a Cu–ZnO nanowire nanogenerator. Upon exposure to 1000 ppm H2S at room temperature, the piezoelectric output voltage of the device (5 at% Cu–ZnO) under compressive force decreases from 0.552 (in dry air) to 0.049 V, and the response is up to 1045, over 8 times larger than that of undoped ZnO nanowires. The selectivity against H2S is also very high at room temperature. The enhanced room-temperature H2S sensing performance can be attributed to the coupling of the piezoelectric screening effect of ZnO nanowires and the synergistic effect of the Cu dopant. This study should stimulate research into designing a new gas sensor for detecting toxic gases at room temperature.

Highly sensitive humidity sensing has been realized from a Cd-doped ZnO nanowire (NW) nanogenerator (NG) as a self-powered/active gas sensor. The piezoelectric output of the device acts not only as a power source, but also as a response signal to the relative humidity (RH) in the environment. The response of Cd–ZnO (1:10) NWs reached up to 85.7 upon exposure to 70% relative humidity, much higher than that of undoped ZnO NWs. Cd dopant can increase the number of oxygen vacancies in the NWs, resulting in more adsorption sites on the surface of the NWs. Upon exposure to a humid environment, a large amount of water molecules can displace the adsorbed oxygen ions on the surface of Cd–ZnO NWs. This procedure can influence the carrier density in Cd–ZnO NWs and vary the screening effect on the piezoelectric output. Our study can stimulate a research trend on exploring composite materials for piezo-gas sensing.

α-MoO3–In2O3 core–shell nanorods were prepared by a facile two-step hydrothermal method. As the anode of lithium-ion batteries, their reversible capacity was up to 1304 mA h g−1 at 0.2 C rate (5 hours per half cycle) and maintains 1114 mA h g−1 after 50 cycles. At a rate of 0.3 C, 0.5 C, 1 C and 2 C, the discharge capacities after 50 cycles were maintained at 938, 791, 599 and 443 mA h g−1, respectively. The enhanced electrochemical performance can be ascribed to the synergistic effect between α-MoO3 and In2O3, one-dimensional core–shell nanostructures, short paths for lithium diffusion and interface spaces.

Room-temperature self-powered ethanol sensing has been realized from ZnO nanowire (NW) arrays by combining their piezoelectric, photoelectric and gas sensing characteristics. Under the assistance of UV illumination, the piezoelectric output of ZnO NWs acts not only as a power source, but also as a response signal to ethanol gas at room temperature. Upon exposure to 700 ppm ethanol at room temperature under 67.5 mW cm−2 UV illumination, the piezoelectric output voltage of ZnO NWs (under 34 N compressive forces) decreases from 0.80 V (in air) to 0.12 V and the response is up to 85. The room-temperature reaction between the UV-induced chemisorbed oxygen ions and ethanol molecules increases the carrier density in ZnO NWs, resulting in a strong piezoelectric screening effect and very low piezoelectric output. Our study can stimulate a research trend on designing new gas sensors and investigating new gas sensing mechanisms.

Extraordinarily high reversible capacity of lithium-ion battery anodes is realized from SnO2/α-MoO3 core-shell nanobelts. The reversible capacity is much higher than traditional theoretical results. Such behavior is attributed to α-MoO3 that makes extra Li2O reversibly convert to Li+.

Ultrafast charging/discharging of lithium-ion battery anodes is realized from porous Co3O4 nanoneedle arrays growing on copper foils. Their charge time can be shortened to ∼6 s, their reversible capacity at 0.5C rate is 1167 mAh/g. This implies that nano-arrays growing directly on copper foils are good candidates for anodes.