Controlled Growth of Porous α‐Fe2O3 Branches on β‐MnO2 Nanorods for Excellent Performance in Lithium‐Ion Batteries

Hierarchical nanocomposites rationally designed in component and structure, are highly desirable for the development of lithium‐ion batteries, because they can take full advantages of different components and various structures to achieve superior electrochemical properties. Here, the branched nanocomposite with β‐MnO₂ nanorods as the back‐bone and porous α‐Fe₂O₃ nanorods as the branches are synthesized by a high‐temperature annealing of FeOOH epitaxially grown on the β‐MnO₂ nanorods. Since the β‐MnO₂ nanorods grow along the four‐fold axis, the as‐produced branches of FeOOH and α‐Fe₂O₃ are aligned on their side in a nearly four‐fold symmetry. This synthetic process for the branched nanorods built by β‐MnO₂/α‐Fe₂O₃ is characterized. The branched nanorods of β‐MnO₂/α‐Fe₂O₃ present an excellent lithium‐storage performance. They exhibit a reversible specific capacity of 1028 mAh g^?1 at a current density of 1000 mA g^?1 up to 200 cycles, much higher than the building blocks alone. Even at 4000 mA g^?1, the reversible capacity of the branched nanorods could be kept at 881 mAh g^?1. The outstanding performances of the branched nanorods are attributed to the synergistic effect of different components and the hierarchical structure of the composite. The disclosure of the correlation between the electrochemical properties and the structure/component of the nanocomposites, would greatly benefit the rational design of the high‐performance nanocomposites for lithium ion batteries, in the future.     

Novel Composites of α‐Fe2O3 Tetrakaidecahedron and Graphene Oxide as an Effective Photoelectrode with Enhanced Photocurrent Performances

Novel composites composed of α‐Fe₂O₃ tetrakaidecahedrons and graphene oxide have been easily fabricated and demonstrated to be efficient photoelectrodes for photoelectrochemical water splitting reaction with superior photocurrent response. α‐Fe₂O₃ tetrakaidecahedrons are facilely synthesized in a green manner without any organic additives and then modified with graphene oxide. The morphological and structural properties of α‐Fe₂O₃/graphene composite are intensively investigated by several means, such as X‐ray diffraction, field‐emission scanning electron microscope, transmission electron microscope, X‐ray photoelectron spectroscopy, Fourier Transform infrared spectroscopy, and Raman spectroscopy. The tetrakaidecahedronal hematite particles have been indicated to be successfully coupled with graphene oxide. Systematical photoelectrochemical and impedance spectroscopy measurements have been carried out to investigate the favorable performance of α‐Fe₂O₃/graphene composites, which are found to be effective photoanodes with rapid, steady, and reproducible feature. The coupling of graphene with α‐Fe₂O₃ particles has greatly enhanced the photoelectrochemical performance, resulting in higher photocurrent and lower onset potential than that of pure α‐Fe₂O₃. This investigation has provided a feasible method to synthesize α‐Fe₂O₃ tetrakaidecahedron and fabricate an efficient α‐Fe₂O₃/graphene photoelectrode for photoelectrochemical water oxidation, suggesting a promising route to design noble metal free semiconductor/graphene photocatalysts.     

Systematic Study of the Growth of Aligned Arrays of α‐Fe2O3 and Fe3O4 Nanowires by a Vapor–Solid Process

Growth of aligned and uniform α‐Fe₂O₃ nanowire (NW) arrays has been achieved by a vapor–solid process. The experimental conditions, such as type of substrate, local growth and geometrical environment, gas‐flow rate, and growth temperature, under which the high density α‐Fe₂O₃ NW arrays can be grown by a vapor–solid route via the tip‐growth mechanism have been systematically investigated. The density of the α‐Fe₂O₃ NWs can be enhanced by increasing the concentration of Ni atoms inside the alloy substrate. The synthesized temperature can be as low as 400 °C. Fe₃O₄ NWs can be produced by converting α‐Fe₂O₃ NWs in a reducing atmosphere at 450 °C. The transformation of phase and structure have been observed by in situ transmission electron microscopy. The magnetic and field‐emission properties of the NWs indicate their potential applications in nanodevices.     

“Naked” Magnetically Recyclable Mesoporous Au–γ‐Fe2O3 Nanocrystal Clusters: A Highly Integrated Catalyst System

Naked magnetically recyclable mesoporous Au–γ‐Fe₂O₃ clusters, combining the inherent magnetic properties of γ‐Fe₂O₃ and the high catalytic activity of Au nanoparticles (NPs), are successfully synthesized. Hydrophobic Au–Fe₃O₄ dimers are first self‐assembled to form sub‐micrometer‐sized Au–Fe₃O₄ clusters. The Au–Fe₃O₄ clusters are then coated with silica, calcined at 550 °C, and finally alkali treated to dissolve the silica shell, yielding naked‐Au–γ‐Fe₂O₃ clusters containing Au NPs of size 5–8 nm. The silica protection strategy serves to preserve the mesoporous structure of the clusters, inhibit the phase transformation from γ‐Fe₂O₃ to α‐Fe₂O₃, and prevent cluster aggregation during the synthesis. For the reduction of p‐nitrophenol by NaBH₄, the activity of the naked‐Au–γ‐Fe₂O₃ clusters is ≈22 times higher than that of self‐assembled Au–Fe₃O₄ clusters. Moreover, the naked‐Au–γ‐Fe₂O₃ clusters display vastly superior activity for CO oxidation compared with carbon‐supported Au–γ‐Fe₂O₃ dimers, due to the intimate interfacial contact between Au and γ‐Fe₂O₃ in the clusters. Following reaction, the naked‐Au–γ‐Fe₂O₃ clusters can easily be recovered magnetically and reused in different applications, adding to their versatility. Results suggest that naked‐Au–γ‐Fe₂O₃ clusters are a very promising catalytic platform affording high activity. The strategy developed here can easily be adapted to other metal NP–iron oxide systems.     

p‐Si/SnO2/Fe2O3 Core/Shell/Shell Nanowire Photocathodes for Neutral pH Water Splitting

Silicon is one of the promising materials for solar water splitting and hydrogen production; however, it suffers from two key factors, including the large external potential required to drive water splitting reactions at its surface and its instability in the electrolyte. In this study, a successful fabrication of novel p‐Si/n‐SnO₂/n‐Fe₂O₃ core/shell/shell nanowire (css‐NW) arrays, consisting of vertical Si NW cores coated with a thin SnO₂ layer and a dense Fe₂O₃ nanocrystals (NCs) shell, and their application for significantly enhanced solar water reduction in a neutral medium is reported. The p‐Si/n‐SnO₂/n‐Fe₂O₃ css‐NW structure is characterized in detail using scanning, transmission, and scanning transmission electron microscopes. The p‐Si/n‐SnO₂/n‐Fe₂O₃ css‐NWs show considerably improved photocathodic performances, including higher photocurrent and lower photocathodic turn‐on potential, compared to the bare p‐Si NWs or p‐Si/n‐SnO₂ core/shell NWs (cs‐NWs), due to increased optical absorption, enhanced charge separation, and improved gas evolution. As a result, photoactivity at 0 V versus reversible hydrogen electrode and a low onset potential in the neutral solution are achieved. Moreover, p‐Si/n‐SnO₂/n‐Fe₂O₃ css‐NWs exhibit long‐term photoelectrochemical stability due to the Fe₂O₃ NCs shell well protection. These results reveal promising css‐NW photoelectrodes from cost‐effective materials by facile fabrication with simultaneously improved photocathodic performance and stability.     

One‐Step Hydrothermal Synthesis of 2D Hexagonal Nanoplates of α‐Fe2O3/Graphene Composites with Enhanced Photocatalytic Activity

There has been significant progress in the field of semiconductor photocatalysis, but it is still a challenge to fabricate low‐cost and high‐activity photocatalysts because of safety issues and non‐secondary pollution to the environment. Here, 2D hexagonal nanoplates of α‐Fe₂O₃/graphene composites with relatively good distribution are synthesized for the first time using a simple, one‐step, template‐free, hydrothermal method that achieves the effective reduction of the graphene oxide (GO) to graphene and intimate and large contact interfaces of the α‐Fe₂O₃ nanoplates with graphene. The α‐Fe₂O₃/graphene composites showed significantly enhancement in the photocatalytic activity compared with the pure α‐Fe₂O₃ nanoplates. At an optimal ratio of 5 wt% graphene, 98% of Rhodamine (RhB) is decomposed with 20 min of irradiation, and the rate constant of the composites is almost four times higher than that of pure α‐Fe₂O₃ nanoplates. The decisive factors in improving the photocatalytic performance are the intimate and large contact interfaces between 2D hexagonal α‐Fe₂O₃ nanoplates and graphene, in addition to the high electron withdrawing/storing ability and the highconductivity of reduced graphene oxide (RGO) formed during the hydrothermal reaction. The effective charge transfer from α‐Fe₂O₃ nanoplates to graphene sheets is demonstrated by the significant weakening of photoluminescence in α‐Fe₂O₃/graphene composites.     

Highly Efficient Photoelectrochemical Water Splitting: Surface Modification of Cobalt‐Phosphate‐Loaded Co3O4/Fe2O3 p–n Heterojunction Nanorod Arrays

Hematite (α‐Fe₂O₃) as a photoanode material for photoelectrochemical (PEC) water splitting suffers from the two problems of poor charge separation and slow water oxidation kinetics. The construction of p–n junction nanostructures by coupling of highly stable Co₃O₄ in aqueous alkaline environment to Fe₂O₃ nanorod arrays with delicate energy band positions may be a challenging strategy for efficient PEC water oxidation. It is demonstrated that the designed p‐Co₃O₄/n‐Fe₂O₃ junction exhibits superior photocurrent density, fast water oxidation kinetics, and remarkable charge injection and bulk separation efficiency (η_inj and η_sep), attributing to the high catalytic behavior of Co₃O₄ for the oxygen evolution reaction as well as the induced interfacial electric field that facilitates separation and transportation of charge carriers. In addition, a cocatalyst of cobalt phosphate (Co‐Pi) is introduced, which brings the PEC performance to a high level. The resultant Co‐Pi/Co₃O₄/Ti:Fe₂O₃ photoanode shows a photocurrent density of 2.7 mA cm^?2 at 1.23 V_RHE (V vs reversible hydrogen electrode), 125% higher than that of the Ti:Fe₂O₃ photoanode. The optimized η_inj and η_sep of 91.6 and 23.0% at 1.23 V_RHE are achieved on Co‐Pi/Co₃O₄/Ti:Fe₂O₃, respectively, corresponding to the 70 and 43% improvements compared with those of Ti:Fe₂O₃. Furthermore, Co‐Pi/Co₃O₄/Ti:Fe₂O₃ shows a low onset potential of 0.64 V_RHE and long‐time PEC stability.     

α‐Fe2O3 Nanoflakes as an Anode Material for Li‐Ion Batteries

Nanoflakes of α‐Fe₂O₃ were prepared on Cu foil by using a thermal treatment method. The nanoflakes were characterized by X‐ray diffraction, scanning electron microscopy, high‐resolution transmission electron microscopy, and Raman spectroscopy. The reversible Li‐cycling properties of the α‐Fe₂O₃ nanoflakes have been evaluated by cyclic voltammery, galvanostatic discharge–charge cycling, and impedance spectral measurements on cells with Li metal as the counter and reference electrodes, at ambient temperature. Results show that Fe₂O₃ nanoflakes exhibit a stable capacity of (680 ± 20) mA h g^–1, corresponding to (4.05 ± 0.05) moles of Li per mole of Fe₂O₃ with no noticeable capacity fading up to 80 cycles when cycled in the voltage range 0.005–3.0 V at 65 mA g^–1 (0.1 C rate), and with a coulombic efficiency of > 98 % during cycling (after the 15th cycle). The average discharge and charge voltages are 1.2 and 2.1 V, respectively. The observed cyclic voltammograms and impedance spectra have been analyzed and interpreted in terms of the ‘conversion reaction' involving nanophase Fe⁰–Li₂O. The superior performance of Fe₂O₃ nanoflakes is clearly established by a comparison of the results with those for Fe₂O₃ nanoparticles and nanotubes reported in the literature.     

Engineering MoS2 Nanosheets on Spindle‐Like α‐Fe2O3 as High‐Performance Core–Shell Pseudocapacitive Anodes for Fiber‐Shaped Aqueous Lithium‐Ion Capacitors

Fiber‐shaped aqueous lithium‐ion capacitors (FALICs) featured with high energy and power densities together with outstanding safety characteristics are emerging as promising electrochemical energy‐storage devices for future portable and wearable electronics. However, the lack of high‐capacitance fibrous anodes is a major bottleneck to achieve high performance FALICs. Here, hierarchical MoS₂@α‐Fe₂O₃ core–shell heterostructures consisting of spindle‐shaped α‐Fe₂O₃ cores and MoS₂ nanosheet shells on a carbon nanotube fiber (CNTF) are successfully fabricated. Originating from the unique core/shell architecture and prominent synergetic effects for multi‐components, the resulting MoS₂@α‐Fe₂O₃/CNTF anode delivers a remarkable specific capacitance of 2077.5 mF cm^?2 (554.0 F cm^?3) at 2 mA cm^?2, substantially outperforming most of the previously reported fibrous anode materials. Further density functional theory calculations reveal that the MoS₂@α‐Fe₂O₃ nano‐heterostructure possesses better electrical conductivity and stronger adsorption energy of Li⁺ than those of the individual MoS₂ and α‐Fe₂O₃. By paring with the self‐standing LiCoO₂/CNTF battery‐type cathode, a prototype quasi‐solid‐state FALIC with a maximum operating voltage of 2.0 V is constructed, achieving impressive specific capacitance (253.1 mF cm^?2) and admirable energy density (39.6 mWh cm^?3). Additionally, the newly developed FALICs can be woven into the flexible textile to power wearable electronics. This work presents a novel effective strategy to design high‐performance anode materials for next‐generation wearable ALICs.     

Highly Stable Cycling of Amorphous Li2CO3‐Coated α‐Fe2O3 Nanocrystallines Prepared via a New Mechanochemical Strategy for Li‐Ion Batteries

In this study, an amorphous Li₂CO₃‐coated nanocrystalline α‐Fe₂O₃ hierarchical structure is synthesized for the first time using a facile one‐step mechanochemical process at room temperature, taking advantage of the concurrence of repeated fracture‐cold welding of material's particles and a gas‐solid redox reaction. The conformal coating and hierarchical structure significantly increase the cycling durability and rate capability. Typically, a 1–3 nm thick amorphous Li₂CO₃ layer is conformally coated on Fe₂O₃ nanocrystallines (≈10 nm in size) that form hierarchically aggregated particles 400–800 nm in size by ball milling α‐Fe₂O₃ with LiH in CO₂. The prepared Li₂CO₃‐coated nanocrystalline α‐Fe₂O₃ exhibits highly stable long‐term cyclability as it delivers a reversible capacity of 975 mAh g^?1 with 99% of retention after 400 cycles at 100 mA g^?1. At a high rate of 3000 mA g^?1, its reversible capacity still remains at 537 mAh g^?1, superior to the uncoated counterpart (311 mAh g^?1). Moreover, amorphous Li₂O and Li₂CO₃ coatings are also similarly produced on Fe₂O₃ and NiO nanocrystallines, respectively, representing the general applicability of this mechanochemical approach.     

Morphological Evolution and Magnetic Property of Rare‐Earth‐Doped Hematite Nanoparticles: Promising Contrast Agents for T1‐Weighted Magnetic Resonance Imaging

A series of uniform rare‐earth‐doped hematite (α‐Fe₂O₃) nanoparticles are synthesized by a facile hydrothermal strategy. In a typical case of gadolinium (Gd)‐doped α‐Fe₂O₃, the morphology and chemical composition can be readily tailored by tuning the initial proportion of Gd³⁺/Fe³⁺ sources. As a result, the products are observed to be stretched into more elongated shapes with an increasing dopant ratio. As a benefit of such an elongated morphological feature and Gd³⁺ ions of larger effective magnetic moment than Fe³⁺, the doped product with the highest ratio of Gd³⁺ at 5.7% shows abnormal ferromagnetic features with a remnant magnetization of 0.605 emu g^?1 and a coercivity value of 430 Oe at 4 K. Density of states calculations also reveal the increase of total magnetic moment induced by Gd³⁺ dopant in α‐Fe₂O₃ hosts, as well as possible change of magnetic arrangement. As‐synthesized Gd‐doped α‐Fe₂O₃ nanoparticles are probed as contrast agents for T1‐weighted magnetic resonance imaging, achieving a remarkable enhancement effect for both in vitro and in vivo tests.     

Stable α‐CsPbI3 Perovskite Nanowire Arrays with Preferential Crystallographic Orientation for Highly Sensitive Photodetectors

All‐inorganic metal‐halide perovskites CsPbX₃ (X = Cl, Br, I) exhibit higher stability than their organic–inorganic hybrid counterparts, but the thermodynamically instable perovskite α phase at room temperature of CsPbI₃ restricts the practical optoelectronic applications. Although the stabilization of α‐CsPbI₃ polycrystalline thin films is extensively studied, the creation of highly crystalline micro/nanostructures of α‐CsPbI₃ with large grain size and suppressed grain boundary remains challenging, which impedes the implementations of α‐CsPbI₃ for lateral devices, such as photoconductor‐type photodetectors. In this work, stable α‐CsPbI₃ perovskite nanowire arrays are demonstrated with large grain size, high crystallinity, regulated alignment, and position by controlling the dewetting dynamics of precursor solution on an asymmetric‐wettability topographical template. The correlation between the higher photoluminescence (PL) intensity and longer PL lifetime indicates the nanowires exhibit stable α phase and suppressed trap density. The preferential (100) orientation is characterized by discrete diffraction spots in grazing incidence wide‐angle scattering patterns, suggesting the long‐range crystallographic order of these nanowires. Based on these high‐quality nanowire arrays, highly sensitive photodetectors are realized with a responsivity of 1294 A W^?1 and long‐term stability with 90% performance retention after 30‐day ambient storage.     

Nanowire Structural Evolution from Fe3O4 to ϵ‐Fe2O3

The ?‐Fe₂O₃ phase is commonly considered an intermediate phase during thermal treatment of maghemite (γ‐Fe₂O₃) to hematite (α‐Fe₂O₃). The routine method of synthesis for ?‐Fe₂O₃ crystals uses γ‐Fe₂O₃ as the source material and requires dispersion of γ‐Fe₂O₃ into silica, and the obtained ?‐Fe₂O₃ particle size is rather limited, typically under 200 nm. In this paper, by using a pulsed laser deposition method and Fe₃O₄ powder as a source material, the synthesis of not only one‐dimensional Fe₃O₄ nanowires but also high‐yield ?‐Fe₂O₃ nanowires is reported for the first time. A detailed transmission electron microscopy (TEM) study shows that the nanowires of pure magnetite grow along [111] and <211> directions, although some stacking faults and twins exist. However, magnetite nanowires growing along the <110> direction are found in every instance to accompany a new phase, ?‐Fe₂O₃, with some micrometer‐sized wires even fully transferring to ?‐Fe₂O₃ along the fixed structural orientation relationship, (001) ∥ (111), [010] ∥ <110>. Contrary to generally accepted ideas regarding epsilon phase formation, there is no indication of γ‐Fe₂O₃ formation during the synthesis process; the phase transition may be described as being from Fe₃O₄ to ?‐Fe₂O₃, then to α‐Fe₂O₃. The detailed structural evolution process has been revealed by using TEM. 120° rotation domain boundaries and antiphase boundaries are also frequently observed in the ?‐Fe₂O₃ nanowires. The observed ?‐Fe₂O₃ is fundamentally important for understanding the magnetic properties of the nanowires.     

Single‐Crystalline Dodecahedral and Octodecahedralα‐Fe2O3 Particles Synthesized by a Fluoride Anion–Assisted Hydrothermal Method

Despite significant advances in iron oxide nanoparticles, it is still a challenge to synthesize regular polyhedral single‐crystalline α‐Fe₂O₃ particles because the surface energies of several low‐index planes are fairly similar. In the work presented here, well‐dispersed and single‐crystalline dodecahedral and octodecahedral α‐Fe₂O₃ particles are synthesized by a facile hydrothermal method with the aid of F^? anions. The crystalline structure of the polyhedral particles is disclosed by various characterization techniques. The dodecahedral particles are of hexagonal bipyramidal shape and enclosed by twelve equivalent (101) planes. The octodecahedral particles are formed by adding six equivalent (111) planes on the two tips of a dodecahedral particle, that is, they are enclosed by twelve (101) planes and six (111) planes. The existence of F^? anions plays a crucial role in the control of polyhedral particle shape. The function of F^? anions in the shape formation of the polyhedral particles is proposed as follows: 1) A high concentration of exposed Fe³⁺ cations induces preferential adsorption of F^? anions on the (100) plane and leads to the slowest growth along the [100] direction. When the concentration of F^? anions is higher than 24 mM , a stable speed ratio of growth along the [001] and [100] directions results in the exposure of (101) planes. 2) With a lower concentration of F^? anions, six symmetrical (111) planes with low concentration of exposed Fe³⁺ cations are present at the tops of a dodecahedral particle to form an octodecahedron. Furthermore, the dodecahedral and octodecahedral α‐Fe₂O₃ particles show much stronger magnetism than the previously reported α‐Fe₂O₃ nanostructures, having coercivities of 4986 Oe and 6512 Oe, respectively. Such high coercivities are attributed to a large local magnetic anisotropy, which might be induced by the polyhedron with equivalent crystallographic planes and/or the presence of F^? anions.     

The β‐to‐γ Transition in BiFeO3: A Powder Neutron Diffraction Study

High‐temperature powder neutron diffraction experiments are conducted around the reported β–γ phase transition (～930 °C) in BiFeO₃. The results demonstrate that while a small volume contraction is observed at the transition temperature, consistent with an insulator–metal transition, both the β‐ and γ‐phase of BiFeO₃ exhibit orthorhombic symmetry; i.e., no further increase of symmetry occurs during this transition. The γ‐orthorhombic phase is observed to persist up to a temperature of approximately 950 °C before complete decomposition into Bi₂Fe₄O₉ (and liquid Bi₂O₃), which subsequently begins to decompose at approximately 960 °C.     

Low‐Temperature Growth of SnO2 Nanorod Arrays and Tunable n–p–n Sensing Response of a ZnO/SnO2 Heterojunction for Exclusive Hydrogen Sensors

Uniform SnO₂ nanorod arrays have been deposited at low temperature by plasma‐enhanced chemical vapor deposition (PECVD). ZnO surface modification is used to improve the selectivity of the SnO₂ nanorod sensor to H₂ gas. The ZnO‐modified SnO₂ nanorod sensor shows a normal n‐type response to 100 ppm CO, NH₃, and CH₄ reducing gas whereas it exhibits concentration‐dependent n–p–n transitions for its sensing response to H₂ gas. This abnormal sensing behavior can be explained by the formation of n‐ZnO/p‐Zn‐O‐Sn/n‐SnO₂ heterojunction structures. The gas sensors can be used in highly selective H₂ sensing and this study also opens up a general approach for tailoring the selectivity of gas sensors by surface modification.     

Ultrathin Cobalt–Manganese Nanosheets: An Efficient Platform for Enhanced Photoelectrochemical Water Oxidation with Electron‐Donating Effect

An ultrathin cobalt–manganese (Co‐Mn) nanosheet, consisting of amorphous Co(OH)_x layers and ultrasmall Mn₃O₄ nanocrystals, is designed as an efficient co‐catalyst on an α‐Fe₂O₃ film for photoelectrochemical (PEC) water oxidation. The uniformly distributed Co‐Mn nanosheets lead to a remarkable 2.6‐fold enhancement on the photocurrent density at 1.23 V versus reversible hydrogen electrode (RHE) and an impressive cathodic shift (≈200 mV) of onset potential compared with bare α‐Fe₂O₃ film. Furthermore, the decorated photoanode exhibits a prominent resistance against photocorrosion with excellent stability for over 10 h. Detailed mechanism investigation manifests that incorporation of Mn sites in the nanosheets could create electron donation to Co sites and facilitate the activation of the OH group, which drastically increases the catalytic activities for water oxidation. These findings provide valuable guidance for designing high‐performance co‐catalysts for PEC applications and open new avenues toward controlled fabrication of mixed metallic composites.     

High Hall Mobility P‐type Cu2SnS3‐Ga2O3 with a High Work Function

A new transparent p‐type oxide semiconductor (POS) is reported, Cu₂SnS₃‐Ga₂O₃, having high Hall mobility of 36.22 cm² V⁻¹s⁻¹, and high work function of 5.17 eV. The existence of Cu₂SnS₃ and Ga₂O₃ phases in the film is confirmed by X‐ray photoelectron spectroscopy results and the Cu₂SnS₃ shows polycrystalline structure according to Raman spectrum and X‐ray diffraction analysis. The transparent Cu₂SnS₃‐Ga₂O₃ exhibits the carrier concentration of 5.86 × 10¹⁶ cm⁻³, and electrical resistivity of 1.94 Ω·cm. The transparent POS is applied to green quantum light‐emitting diodes (QLEDs) as a hole injection layer (HIL) because of its high work function. The QLED exhibits the maximum current efficiency of 51.72 cd A⁻¹, power efficiency of 31.97 lm W⁻¹, and external quantum efficiency (EQE) of 14.93%, which are much higher than the QLED using polyethylene dioxythophene:poly(styrenesulfonate) HIL exhibiting current efficiency of 42.66 cd A⁻¹, power efficiency of 20.33 lm W⁻¹, and EQE of 12.36%. The Cu₂SnS₃‐Ga₂O₃ developed in this work can be widely used as a transparent and conductive p‐type oxide for thin‐film devices.     

Layered α‐Co(OH)2 Nanocones as Electrode Materials for Pseudocapacitors: Understanding the Effect of Interlayer Space on Electrochemical Activity

The effect of space accessible to electrolyte ions on the electrochemical activity is studied for a system of transition‐metal hydroxide‐based pseudocapacitors. Layered α‐Co(OH)₂ with various intercalated anions is used as a model material. Three types of layered α‐Co(OH)₂ with intercalated anions of dodecyl sulfate, benzoate, or nitrate, are prepared by a simple reflux and an anion‐exchange process. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations and X‐ray diffraction (XRD) data show the formation of layered α‐Co(OH)₂ nanocones with interlayer spacing between adjacent Co(OH)₂ single sheets of 1.6, 0.7, and 0.09 nm, corresponding to the anions as listed above. Electrochemical characterization reveals that interlayer space has a great effect on the electrochemical activity of α‐Co(OH)₂ nanocones as an electrode material. For the interlayer spacing of 1.6 nm, in the case of dodecyl sulfate‐intercalated α‐Co(OH)₂, the Faradaic reaction takes place more adequately than for benzoate‐ and nitrate‐intercalated α‐Co(OH)₂. As a result, a higher specific capacitance and better cycling stability is obtained for the dodecyl sulfate‐intercalated α‐Co(OH)₂. The electrochemical activity obviously reduces when the interlayer space decreases to 0.7 nm. Our results suggest the importance of rational designing the interlayer space of layered transition metal hydroxides for high‐performance pseudocapacitors.     

Fe2O3 Nanoneedles on Ultrafine Nickel Nanotube Arrays as Efficient Anode for High‐Performance Asymmetric Supercapacitors

High performance of electrochemical energy storage devices depends on the smart structure engineering of electrodes, including the tailored nanoarchitectures of current collectors and subtle hybridization of active materials. To improve the anode supercapacitive performance of Fe₂O₃ for high‐voltage asymmetric supercapacitors, here, a hybrid core‐branch nanoarchitecture is proposed by integrating Fe₂O₃ nanoneedles on ultrafine Ni nanotube arrays (NiNTAs@Fe₂O₃ nanoneedles). The fabrication process employs a bottom‐up strategy via a modified template‐assisted method starting from ultrafine ZnO nanorod arrays, ensuring the formation of ultrafine Ni nanotube arrays with ultrathin tube walls. The novel developed NiNTAs@Fe₂O₃ nanoneedle electrode is demonstrated to be a highly capacitive anode (418.7 F g^?1 at 10 mV s^?1), matching well with the similarly built NiNTAs@MnO₂ nanosheet cathode. Contributed by the efficient electron collection paths and short ion diffusion paths in the uniquely designed anode and cathode, the asymmetric supercapacitors exhibit an excellent maximum energy density of 34.1 Wh kg^?1 at the power density of 3197.7 W kg^?1 in aqueous electrolyte and 32.2 Wh kg^?1 at the power density of 3199.5 W kg^?1 in quasi‐solid‐state gel electrolyte.