Silicon is one of the most promising anode materials for lithium‐ion batteries because of the highest known theoretical capacity and abundance in the earth' crust. Unfortunately, significant ...“breathing effect” during insertion/deinsertion of lithium in the continuous charge‐discharge processes causes the seriously structural degradation, thus losing specific capacity and increasing battery impedance. To overcome the resultant rapid capacity decay, significant achievements has been made in developing various nanostructures and surface coating approaches in terms of the improvement of structural stability and realizing the long cycle times. Here, the recent progress in surface and interface engineering of silicon‐based anode materials such as core‐shell, yolk‐shell, sandwiched structures and their applications in lithium‐ion batteries are reviewed. Some feasible strategies for the structural design and boosting the electrochemical performance are highlighted. Future research directions in the field of silicon‐based anode materials for next‐generation lithium‐ion batteries are summarized.
Silicon‐based materials are recognized as the most promising anode materials because of the highest theoretical capacity. However, many critical challenges such as losing specific capacity and increasing battery impedance during continuous charge‐discharge processes strongly hindered the further application. In this review, the recent progress to utilize surface and interface engineering strategies to overcome these problems is summarized.
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•Janus materials show fascinating nanoarchitecture and versatile platform for the development of numerous research areas.•The components-based synthesis methods and tailored ...structures of Janus nanoarchitectures are highlighted.•The micro/nano motors, interfacial catalysis, and photocatalytic reactions relating to Janus structures are mainly discussed.
Janus nanoarchitectures, an emerging class of nanostructures named after the Roman god having two faces, have been considered as a fascinating class of nanomaterials for promising applications in various areas, such as optical imaging, emulsion stabilizers, catalysis, drug delivery, etc. The asymmetric structures or counterparts of Janus nanostructures provide access to construct a single unit with multifunctional properties, and thus allow the design of nanocomposites with a possible synergistic effect, especially for catalytic reactions. In the last decade, Janus nanomaterials have been successfully applied in the field of catalysis, by providing solutions to some complex situations, such as biphasic reactions, catalysts recovery, self-propelled movements, and biocompatible catalysis. In this review, we intend to highlight the recent progress of Janus nanoarchitectures for the growing field of catalytic applications. Herein, the fabrication and catalytic applications of Janus nanoarchitectures are critically reviewed in terms of three categories of compositions, i.e., polymeric, inorganic, and polymeric/inorganic Janus nanostructures. Specifically, typical applications of Janus nanoarchitectures in micro/nano motors, interfacial catalysis, and photocatalytic reactions are summarized and discussed. An outlook of the future applications and possible further study of Janus nanomaterials is also provided.
Oxygen electrocatalysis, including both oxygen evolution reaction (OER) and oxygen reduction reaction (ORR), dominates the performance of various electrochemical energy conversion and storage ...systems. However, the practical applications of these devices are limited as a result of the sluggish kinetics of OER and ORR as well as the high cost and instability of the state‐of‐the‐art noble metal catalyst used in these systems. In this study, cation deficiency is introduced to the A‐site of perovskite LaCoO3 synthesized via polymer‐assisted approach to enhance the electrocatalytic activity of both OER and ORR, leading to the boosted bifunctionality of the resultant electrocatalysts, which might be attributed to oxygen vacancy introduction in perovskites. The bifunctionality of the A‐site deficiency perovskite (ΔE=0.948 V) is comparable or even better than the pristine LaCoO3 (ΔE=1.063 V) as well as the reported state‐of‐the‐art electrocatalysts, including both perovskites and noble metal electrocatalysts. The stability test also indicates their good stability under alkaline solutions, suggesting that the as‐prepared materials can be good candidates as bifunctional electrocatalysts in oxygen‐based electrochemical devices, such as fuel cells and metal‐air batteries. This work introduces the A‐site cation deficiency strategy to improve the bifunctional electrocatalytic performance of perovskites, and highlights the facile polymer‐assisted approach for perovskites synthesis.
Perovskite electrocatalysis: Cation deficiency is introduced to the A‐site of perovskite LaCoO3 synthesized by polymer‐assisted solution approach to enhance the electrocatalytic activity of both oxygen evolution reaction and oxygen reduction reaction, leading to the boosted bifunctionality of the electrocatalysts, which may be attributed to the oxygen vacancy in perovskites. The bifunctionality of the A‐site deficiency perovskite is comparable or even better than the pristine LaCoO3 as well as the reported state‐of‐the‐art perovskite electrocatalysts.
Carbon dots have been recognized as one of the most promising candidates for the oxygen reduction reaction (ORR) in alkaline media. However, the desired ORR performance in metal–air batteries is ...often limited by the moderate electrocatalytic activity and the lack of a method to realize good dispersion. To address these issues, herein a biomass‐deriving method is reported to achieve the in situ phosphorus doping (P‐doping) of carbon dots and their simultaneous decoration onto graphene matrix. The resultant product, namely P‐doped carbon dot/graphene (P‐CD/G) nanocomposites, can reach an ultrahigh P‐doping level for carbon nanomaterials. The P‐CD/G nanocomposites are found to exhibit excellent ORR activity, which is highly comparable to the commercial Pt/C catalysts. When used as the cathode materials for a primary liquid Al–air battery, the device shows an impressive power density of 157.3 mW cm−2 (comparing to 151.5 mW cm−2 of a similar Pt/C battery). Finally, an all‐solid‐state flexible Al–air battery is designed and fabricated based on our new nanocomposites. The device exhibits a stable discharge voltage of ≈1.2 V upon different bending states. This study introduces a unique biomass‐derived material system to replace the noble metal catalysts for future portable and wearable electronic devices.
Phosphorus‐doped carbon dot/graphene nanocomposites are prepared via a biomass‐deriving method. This unique approach enables the uniform distribution of carbon dots on the graphene matrix. The products reach an ultrahigh phosphorus doping level and show excellent activity for the oxygen reduction reaction. The all‐solid‐state flexible metal/air batteries made from the nanocomposites exhibit comparable performance with the same device made from precious Pt/C catalysts.
Nanolayers of Al2O3 and TiO2 coatings were applied to lithium‐ and manganese‐rich cathode powder Li1.2Ni0.13Mn0.54Co0.13O2 using an atomic layer deposition (ALD) method. The ALD coatings exhibited ...different surface morphologies; the Al2O3 surface film appeared to be uniform and conformal, while the TiO2 layers appeared as particulates across the material surface. In a Li‐cell, the Al2O3 surface film was stable during repeated charge and discharge, and this improved the cell cycling stability, despite a high surface impedance. The TiO2 layer was found to be more reactive with Li and formed a LixTiO2 interface, which led to a slight increase in cell capacity. However, the repetitive insertion/extraction process for the Li+ ions caused erosion of the surface protective TiO2 film, which led to degradation in cell performance, particularly at high temperature. For cells comprised of the coated Li1.2Ni0.13Mn0.54Co0.13O2 and an anode of meso‐carbon‐micro‐beads (MCMB), the cycling stability introduced by ALD was not enough to overcome the electrochemical instability of MCMB graphite. Therefore, protection of the cathode materials by ALD Al2O3 or TiO2 can address some of the capacity fading issues related to the Li‐rich cathode at room temperature.
An atomic layer deposition (ALD) process is applied to the porous Li‐rich cathode Li1.2Ni0.13Mn0.54Co0.13O2 particle for Li‐ion batteries. The ALD coated Al2O3 using TMA precursor produces a conformal coating on the particles, which is contrary to the particulate morphology of the ALD‐coated TiO2. The paper discusses the impacts of ALD surface‐protection film on the battery performance in half‐ and full‐cell configurations at different temperatures.
BiFeO3/La0.7Sr0.3MnO3 (BFO/LSMO) epitaxial heterostructures were successfully synthesized by pulsed laser deposition on (001)-oriented SrTiO3 single-crystal substrates with Au top electrodes. Stable ...bipolar resistive switching characteristics regulated by ferroelectric polarization reversal was observed in the Au/BFO/LSMO heterostructures. The conduction mechanism was revealed to follow the Schottky emission model, and the Schottky barriers in high-resistance and low-resistance states were estimated based on temperature-dependent current–voltage curves. Further, the observed memristive behavior was interpreted via the modulation effect on the depletion region width and the Schottky barrier height caused by ferroelectric polarization reversal, combining with the oxygen vacancies migration near the BFO/LSMO interface.
A new rhodamine B‐based fluorescent probe for the hypochlorite anion (OCl−) has been designed, synthesized, and characterized. The probe comprises a spectroscopic unit of rhodamine B and an ...OCl−‐specific reactive moiety of dibenzoylhydrazine. The probe itself is nearly nonfluorescent because of its spirolactam structure. Upon reaction with OCl−, however, a largely enhanced fluorescence is produced due to the opening of the spirolactam ring by the oxidation of the exocyclic hydrazide and subsequently the formation of the hydrolytic product rhodamine B. Most notably, the fluorescence‐on reaction shows high sensitivity and extremely high selectivity for OCl− over other common ions and oxidants, which makes it possible for OCl− to be detected directly in their presence. In addition, the reaction mechanism has been investigated and proposed. The OCl− anion selectively oxidizes the hydrazo group in the probe, and forms the analogue of dibenzoyl diimide, which in turn hydrolyzes and releases the fluorophore. The reaction mechanism that is described here might be useful in developing excellent spectroscopic probes with cleavable active bonds for other species.
A new fluorescent probe, N‐benzoyl rhodamine B–hydrazide, for the hypochlorite anion has been designed and synthesized. The probe displays a highly selective fluorescence‐on response to OCl− only, and not to any of the other ions and oxidants that were examined (see scheme). This remarkable property gives the probe great potential for the detection of OCl− directly in the presence of other species.
Copper sulfide has been regarded as a promising thermoelectric material with relatively high thermoelectric performance and abundant resource. Large-scale synthesis and low-cost production of ...high-performance thermoelectric materials are keys to widespread application of thermoelectric technology. Here, Cu2–x S particles encapsulated in a thin carbon shell are fabricated by a scalable wet chemical method (19.7 g/batch). The synthesized particles go through the crystal-phase transition from orthorhombic to tetragonal during high-temperature annealing and sintering. After the phase transition, electrical conductivity of this composite (Cu2–x S@C) increases by approximately 50% compared to that of the pure Cu2–x S sample, and can be attibuted to an increase in carrier concentration. Phonon scattering interface formation and superionic phase of Cu2–x S@C results in very low lattice thermal conductivity of 0.22 W m–1 K–1, and maximum thermoelectric figure of merit (ZT) of 1.04 at 773 K, which is excellent for thermoelectric performance in pure-phase copper sulfide produced via chemical synthesis. This discovery sets the stage for the use of facile wet chemical synthesis methods for large-scale transition-metal chalcogenide thermoelectric material production.
Monolayers of transition metal dichalcogenides (TMDs) are attractive for various modern semiconductor devices. However, the limited control over the location, yield, and size distribution of the ...products using current synthesis methods has severely limited their large-scale applicability. Herein, we identify the ability to use metal (e.g., Au) nanoparticles to seed the growth of MoS2 monolayers and thereby provide a means to achieve programmable and controllable synthesis. In this study, prepatterned Au seeds are used as heterogeneous nucleation sites to induce the formation of desired geometries of MoS2 monolayers via chemical vapor deposition. Our experimental and theoretical results shed light on the growth mechanism driving the formation of MoS2 monolayers at these sites, revealing that the seeding effect originates from the favorable formation energy of MoS2 on the Au surface. A field-effect transistor with a predesigned channel geometry exhibits electronic performance that compares nicely with previously reported MoS2 monolayer devices. We believe this study contributes fundamental insights into controlled synthesis of TMD monolayers, making integration of these materials into emerging electronic devices more attainable.
Carbon nanowalls (CNWs), two-dimensional "graphitic" platelets that are typically oriented vertically on a substrate, can exhibit similar properties as graphene. Growth of CNWs reported to date was ...exclusively carried out at a low pressure. Here, we report on the synthesis of CNWs at atmosphere pressure using "direct current plasma-enhanced chemical vapor deposition" by taking advantage of the high electric field generated in a pin-plate dc glow discharge. CNWs were grown on silicon, stainless steel, and copper substrates without deliberate introduction of catalysts. The as-grown CNW material was mainly mono- and few-layer graphene having patches of O-containing functional groups. However, Raman and X-ray photoelectron spectroscopies confirmed that most of the oxygen groups could be removed by thermal annealing. A gas-sensing device based on such CNWs was fabricated on metal electrodes through direct growth. The sensor responded to relatively low concentrations of NO
2
(g) and NH
3
(g), thus suggesting high-quality CNWs that are useful for room temperature gas sensors.
PACS: Graphene (81.05.ue), Chemical vapor deposition (81.15.Gh), Gas sensors (07.07.Df), Atmospheric pressure (92.60.hv)
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