N-regulated three-dimensional turf-like carbon nanosheet loaded with FeCoNi nanoalloys as bifunctional electrocatalysts for durable zinc-air batteries.

N-regulated three-dimensional (3D) turf-like carbon material loaded with FeCoNi nanoalloys (F-CNS-CNT), composed of carbon nanotubes (CNT) grown in situ on carbon nanosheets(CNS), was synthesized using a low-temperature solution combustion method and organic compounds rich in pyridinic-N. This distinct structure significantly expands the effective electrochemical surface area, revealing an abundance of active sites and enhancing the mass transfer capability for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Both experimental observations and theoretical calculations corroborate that the synergy between the FeCoNi nanoalloy and the highly pyridinic N-doped carbon substrate optimizes the adsorption and desorption-free energy of oxygen intermediates, resulting in a remarkable improvement of intrinsic ORR/OER activity. Therefore, the derived F-CNS-CNT electrocatalyst can present a favorable half-wave potential of 0.85 V (ORR) and a lower overpotential of 260 mV (corresponding to a current density of 10 mA cm-2, OER) in alkaline media. Moreover, when employed in the air cathode of a flowable zinc-air battery, the electrocatalyst exhibits exceptional discharge and charge performance, including a high power density of 144.6 mW cm-2, a high specific capacity of 801 mAh g-1, and an impressive cycling stability of 600 cycles at a current density of 10 mA cm-2. Notably, these results markedly surpass those of the commercial catalyst Pt/C + IrO2.

Self-Powered Photodetector Based on Ag/CH3NH3PbI3/C Asymmetric Dual-Terminal Device.

CH3NH3PbI3 is capable of exhibiting a superior photoresponse to visible light, but its self-powered devices are typically formed through p-n junctions. In this study, we fabricated a Ag/CH3NH3PbI3/C dual-terminal asymmetric electrode device using a single CH3NH3PbI3 perovskite micro/nanowire, enabling both the photoresponse and self-powered characteristics of CH3NH3PbI3 to visible light. Compared with traditional p-n junction devices, this simple device demonstrates enhanced interface photovoltaic effects by optimizing the combination of the Ag electrode with CH3NH3PbI3, resulting in superior self-powered characteristics. Under low bias voltage, the device achieves a significant on/off ratio of 103, with superior sensitivity and responsivity as well as a maximum rectification ratio of about 12. The photogenerated voltage and current reach approximately 0.8 V and 2 nA, respectively. This simple, compact, and self-powered asymmetric device exhibits great potential for applications in self-powered optoelectronics and wearable devices. This research provides a promising approach for recognizing and utilizing surface state effects in single nanoscale structures.

Controllably modulated asymmetrical photoresponse with a nonvolatile memory effect in a single CH3NH3PbI3 micro/nanowire for photorectifiers and photomemory.

Nanostructured hybrid organic-inorganic perovskites exhibit remarkable photodetection performance due to their abundant surface states and high responsivity to visible light. However, in traditional photodetectors with a symmetrical configuration of two-terminal electrodes, the photoresponse is independent of bias polarity. Moreover, for self-powered photodetectors, an asymmetric structure of the chemical composition, such as p-n and Schottky junctions, and two different electrodes are necessary. Herein, we demonstrate a modulable asymmetrical photoresponse by packing only one electrode end in a single CH3NH3PbI3 micro/nanowire with two symmetrical Ag electrodes. This not only enables the high performance of light- and bias-modulated multifunctional photorectifiers and self-powered photodetectors, but also allows controllable implementation of nonvolatile photomemory with a tunable spectral responsivity and range. At an unpacked electrode interface, trace moisture in the environment promotes a good bonding of Ag+ and I-, substantially decreasing the interface barrier. Conversely, at a packed electrode interface, abundant surface states can be well preserved, leading to a high interface barrier. Notably, under a large voltage and strong light, the redox of Ag/AgI at the unpacked electrode interface and the injection and ejection of holes at the packed electrode interface can be reversibly conducted by inverting the voltage polarity, enabling a controllable nonvolatile modulation. Therefore, by clarifying the actual origin of the photoelectrical response of CH3NH3PbI3 micro/nanowires at electrode interfaces, high-performance multifunctional photorectifiers and self-powered photodetectors based on asymmetrical interface photovoltaic effects with two symmetrical electrodes can be controllably realized. Furthermore, by precise cooperative modulation of two electrode interface states with a large voltage and strong illumination, nonvolatile photomemory with a tunable spectral responsivity and range can be implemented.

Self-absorption correction method for one-point calibration laser-induced breakdown spectroscopy.

As an important variant of calibration-free laser-induced breakdown spectroscopy (CF-LIBS), one-point calibration LIBS (OPC-LIBS) corrects the Boltzmann plot of the unknown sample by using one known sample and obtains higher quantitative accuracy than CF-LIBS. However, the self-absorption effect restricts its accuracy. In this work, a new self-absorption correction (SAC) method for OPC-LIBS is proposed to solve this problem. This method uses an algorithm to correct the self-absorption and does not require the calculation of the self-absorption coefficient. To verify the effectiveness of this SAC method, Ti, V, and Al elements in two titanium alloys were determined by classical OPC-LIBS and OPC-LIBS with SAC. The average relative errors (AREs) of all elements in the two samples were decreased from 8.78% and 9.28% to 8.07% and 7.56%, respectively. The results demonstrated the effectiveness of this SAC method for OPC-LIBS.

FeCoNi Ternary Nano-Alloys Embedded in a Nitrogen-Doped Porous Carbon Matrix with Enhanced Electrocatalysis for Stable Lithium-Sulfur Batteries.

The application of composite materials that combine the advantages of carbonaceous material and metal alloy proves to be a valid method for improving the performance of lithium-sulfur batteries (LSBs). Herein iron-cobalt-nickel (FeCoNi) ternary alloy nanoparticles (FNC) that spread on nitrogen-doped carbon (NC) are obtained by a strategy of low-temperature sol-gel followed by annealing at 800 °C under an argon/hydrogen atmosphere. Benefiting from the synergistic effect of different components of FNC and the conductive network provided by the NC, not only can the "shuttle effect" of lithium polysulfides (LiPS) be suppressed, but also the conversion of LiPS, the diffusion of Li+, and the deposition of Li2S can be accelerated. Taking advantage of those merits, the batteries assembled with an FNC@NC-modified polypropylene (PP) separator (FNC@NC//PP) can deliver a high reversible specific capacity of 1325 mAh g-1 at 0.2 C and maintain 950 mAh g-1 after 200 cycles, and they can also achieve a low capacity fading rate of 0.06% per cycle over 500 cycles at 1 C. More impressively, even under harsh test conditions (the ratio of electrolyte to sulfur (E/S) = 6 µL mg-1 and sulfur loading = 4.7 mg cm-2 and E/S = 10 µL mg-1 and sulfur loading = 5.9 mg cm-2), the area capacity of batteries is still much higher than 4 mAh cm-2.

Actual origin and precise control of asymmetrical hysteresis in an individual CH3NH3PbI3 micro/nanowire for optical memory and logic operation.

Although CH3NH3PbI3 can present an excellent photoresponse to visible light, its application in solar cells and photodetectors is seriously hindered due to hysteresis behaviour. Moreover, for its origin, there exist different opinions. Herein, we demonstrate a route to realize precise control for the electrical transport of a single CH3NH3PbI3 micro/nanowire by constructing a two-terminal device with asymmetric Ag and C electrodes, and its hysteresis can be clearly identified as a synergistic effect of the redox reaction at the interface of the Ag electrode and the injection and ejection of holes in the interfacial traps of the C electrode rather than its bulk effect. The device can show superior bias amplitude and illumination intensity dependence of hysteresis loops with typical bipolar resistive switching features. Thus, an excellent multilevel nonvolatile optical memory can be effectively realized by the modulation of the illumination and bias, and moreover a logic OR gate operation can be successfully implemented with voltage and illumination as input signals as well. This work clearly reveals and provides a new insight of hysteresis origin that can be attributed to a synergistic effect of two asymmetrical electrode interfaces, and therefore precisely controlling its electrical transport to realize an outstanding application potential in multifunctional devices integrated with optical nonvolatile memory and logic OR gate operation.

Revealing the synergistic mechanism of multiply nanostructured V2O3 hollow nanospheres integrated with doped N, Ni heteroatoms, in-situ grown carbon nanotubes and coated carbon nanolayers for the enhancement of lithium-sulfur batteries.

Lithium sulfur (Li-S) batteries are regarded as one of the most promising future energy storage candidates on account of high theoretical specific capacity of 1675 mAh g-1 and energy density of 2600 Wh kg-1. However, their practical application is seriously hindered due to the poor conductivity and volume expansion of sulfur, the weak redox kinetics of lithium polysulfide (LPS), and the severe shuttle effect of LPS. Herein, V2O3@N,Ni-C nanostructures, multiply integrated with zero-dimensional (0D) V2O3 nanoparticles, 1D carbon nanotubes, 2D carbon coating layers and graphene, 3D hollow spheres, and doped N and Ni heteroatoms, were synthesized via a solvothermal method followed by chemical vapor deposition. After being used as a modifier for traditional commercial separator of Li-S batteries, the shuttle effect of LPS can be effectively suppressed owing to the abundant active physical and chemical adsorption sites derived from large specific surface area, rich porosity, and tremendous polarity of the V2O3 nanoparticles with multiple secondary nanostructure integration. Meanwhile, the transfer of Li+ ions and electrons can be effectively enhanced by the highly conductive 2D carbon network, and the kinetics of redox reaction (Li2Sn â†” Li2S) can be accelerated by the doped N and Ni heteroatoms, leading to a synergistic promotion on the reutilization of the adsorbed LPS. Additionally, the unique 3D hollow structure can not only enhance the penetration of electrolyte, but also buffer the volume expansion of sulfur to some extent. Therefore, the rate capacity and cycling performance can be significantly enhanced by the multifunction synergism of adsorption, conductivity, catalysis, and volume buffering. An initial discharge capacity of 1590.4 mAh g-1can be achieved at 0.1C, and the discharge capacity of 803.5 mAh g-1can be still exhibited when increasing to 2C. After a long period of 500 cycles, additionally, the discharge specific capacity of 1142.2 mAh g-1 and capacity attenuation of 0.0617% per cycle can be obtained at 1C.

An individual sandwich hybrid nanostructure of cobalt disulfide in-situ grown on N doped carbon layer wrapped on multi-walled carbon nanotubes for high-efficiency lithium sulfur batteries.

Binding and trapping of lithium polysulfide (LPS) are being conceived as the most effective strategies to improve lithium-sulfur (Li-S) battery performance. Therefore, exploiting a simple but cost-effective approach for the absorption and conversion of LPS and the transfer of electrons and Li+ ions is of paramount importance. Herein, sandwich structure MWCNTs@N-doped-C@CoS2 integrated with multiple nanostructures of zero-dimensional (0D) CoS2 nanoparticles, 1D carbon nanotubes (CNTs), and 2D N-doped amorphous carbon layer was obtained, where MWCNTs was firstly uniformly attached with a polydopamine (PDA) of excellent adhesion, followed by hydrothermal method, the Co2+ nanoparticles were in-situ grown on the PDA by the formation of complex compound of Co2+ and N atoms in PDA, and then the CoS2 nanoparticles were in-situ grown on CNTs in a point-surface contact way by a bridging of N-doped amorphous carbon layer derived from the carbonization of attached PDA after the vulcanization at 500 °C under Ar atmosphere. The multifunction synergism of absorption, conductivity, and the kinetics of LPS redox is significantly improved, consequently effectively suppressing the shuttle effect and tremendously increasing the utilization rate of active substance. For the Li-S battery assembled with MWCNTs@N-doped-C@CoS2-modified separator, its rate capacity and cycling performance can be greatly enhanced. It can exhibit a high initial discharge capacity of 1590 mAh g-1 at 0.1 C, a stable long-term cycling performance with a relatively low capacity decay of 0.07% per cycle during 500 cycles at 1 C, and a reversible capacity of 772 mAh g-1 and a capacity decay of 0.04% per cycle during 250 cycles at 2 C. Even at a large current density of 4 C, an initial specific discharge capacity of 634 mAh g-1 can still be delivered. With a high sulfur loading of 5.0 mg cm-2, additionally, an outstanding cycling stability can also be well maintained at 685 mAh g-1 at 0.1 C after 50 cycles. This work provides a novel and simple but effective strategy to develop such sandwich hybrid materials comprised of polar metal sulfides and conductive networks via an effective bridging to help realize durable and stable Li-S battery.

Giant Piezoresistive Effect of CdS@C Hybrid Nanobelts for Volatile Real-Time Sensor and Erasable Nonvolatile Memory to Stress.

Here, CdS@C nanohybrid composites, where CdS quantum dots (QDs) are uniformly embedded in carbon micro-/nanobelt matrixes, are synthesized via a combustion synthesis followed by a postvulcanization. In the nanohybrids, trap centers are effectively created by the introduction of QDs and moreover their barrier height and filling level can be effectively modulated through a coupling of externally loaded strain and bias. Thus, a single CdS@C micro-/nanobelt-based two-terminal device can exhibit an ultrahigh real-time response to compressive and tensile strains with a tremendous gauge factor of above 104, high sensitivity, and fast response and recovery. More importantly, the trapped charges can be mechanically excited by stress, and furthermore, the stress-triggered high-resistance state can be well-maintained at room temperature and a relatively low operation bias. However, it can be back to its initial low resistance state by loading a relatively large bias, showing a superior erasable stress memory function with a window of about 103. By an effective construction of trap centers in hybrid composites, not only can an ultrahigh performance of volatile real-time stress sensor be obtained under the synergism of external stress and electric field but also can an outstanding erasable nonvolatile stress memory be successfully realized.

Effects of interface states on photoexcited carriers in ZnO/Zn(2)SnO(4) type-II radial heterostructure nanowires.

Type-II band alignment of heterostructure contributes to spatially separate electrons and holes leading to an increase in minority carrier lifetime, which has much more advantages in photocatalytic activities and photovoltaic device applications. Here, Zn2SnO4-sheathed ZnO radial heterostructure nanowires were constructed to investigate systematically interfacial charge separation. The lattice mismatch between ZnO and Zn2SnO4 induces interface states to exist at their heterointerface. At low pump fluence, photoexcited charges are localized within the ZnO core rather than separated due to the large interface barrier. Correspondingly, only ZnO-related bandedge ultraviolet (UV) and green emissions are dominated in photoluminescence spectra. At high pump fluence, however, impurities are ionized and electrons trapped in interface states are excited, resulting in a decrease in interface barrier, which makes photogenerated charges efficiently separated at their heterointerface by direct tunneling, and, consequently, an additional blue-violet emission, attributed to the heterointerface recombination of electrons in Zn2SnO4 conduction band (CB) and holes in ZnO valence band. Additionally, the heterointerface can separate effectively photoexcited carriers and form a photovoltaic effect. Our results provide the localization/separation condition of photogenerated charges for the type-II band alignment of core/shell heterostructure, which should be very useful for the realization of underpinned mechanism of the developed optoelectronic devices.

Individual Zn2SnO4-sheathed ZnO heterostructure nanowires for efficient resistive switching memory controlled by interface states.

Resistive switching (RS) devices are widely believed as a promising candidate for next generation nonvolatile resistance random access memory. Here, Zn2SnO4-sheathed ZnO core/shell heterostructure nanowires were constructed through a polymeric sol-gel approach followed by post-annealing. The back-to-back bipolar RS properties were observed in the Ohmic contact two-terminal devices based on individual core/shell nanowires. With increasing bias to about 1.5 V, it changes from high-resistance states (HRS) to low-resistance states, and however, it can be restored to HRS by reverse bias. We propose a new mechanism, which is attributed to the injection of electrons into/from interfacial states, arising from the lattice mismatch at ZnO/Zn2SnO4 heterointerface. Upon applying negative/positive voltage at one end of devices, where interfacial states are filled/emptied, barrier will be eliminated/created, resulting into symmetric RS characteristics. The behavior of storage and removal charges demonstrates that the heterostructures have excellent properties for the application in resistance random access memory.

Individual ZnO nanowires for photodetectors with wide response range from solar-blind ultraviolet to near-infrared modulated by bias voltage and illumination intensity.

ZnO nanowires have relatively high sensitivity as ultraviolet (UV) photodetectors, while the bandgap of 3.37 eV is an important limitation for their applications in solar-blind UV (SBUV), visible (VIS) and near infrared (NIR) range. Besides UV response, in this study, we demonstrate the promising applications of individual undoped ZnO NWs as high performance SBUV-VIS-NIR broad-spectral-response photodetectors, strongly depended on applied bias voltage and illumination intensity. The dominant mechanism is attributed to the existence of surface states in nanostructured ZnO. At a negative bias voltage electrons can be injected into surface states from electrode, and moreover, under light illumination photogenerated electron-hole pairs can be separated efficiently by surface built-in electric field, resulting into a decrease of potential barrier height and depletion region width, and simultaneously accompanying a filling of oxygen vacancy and a rise of ZnO Fermi level.