Tuning the Mn Dopant To Boost the Hydrogen Evolution Performance of CoP Nanowire Arrays.

Because of its advantages such as abundant resources, low cost, simple synthesis, and high electrochemical stability, cobalt phosphide (CoP) is considered as a promising candidate for electrocatalytic hydrogen evolution reaction. Through element doping, the morphology and electronic structure of the catalyst can be tuned, resulting in both the increase of the active site number and the improvement of the intrinsic activity of each site. Herein, we designed and fabricated Mn-doped CoP nanowires with a length of 3 µm, a diameter of 50 nm, and the pores between the grains of 10 nm. As a highly efficient electrocatalyst for alkaline hydrogen evolution, the Mn10-doped CoP/NF (doping amount is about 10 atom %) electrode presented overpotentials of 60 mV @ 10 mA cm-2 and 112 mV @ 100 mA cm-2, improved by 35 and 23%, respectively, compared with CoP/NF. Characterizations indicate that Mn doping increases the electrochemical active area, reduces the impedance, and tunes the electronic structure of the material. Density functional theory calculations also revealed that an appropriate amount of Mn dopant at a suitable location can both react as an active site itself and boost the activity of the surrounding Co sites, delivering favorable H* adsorption and rapid reaction kinetics. This result may not only promote the development of hydrogen evolution reaction catalysts but also encourage explorations of the relationship between the property and fine doping structure.

Hollow Multishelled Structured SrTiO3 with La/Rh Co-Doping for Enhanced Photocatalytic Water Splitting under Visible Light.

La- and Rh-co-doped SrTiO3 (STO:La/Rh) hollow multishelled structures (HoMSs) are fabricated by adding La3+ and Rh3+ ions during the hydrothermal process of converting TiO2 HoMSs to STO HoMSs. STO:La/Rh HoMSs have successfully expanded the light absorption edge to 520 nm. Accompanied with the benefits of the unique hierarchical structure and relatively thin shells, STO:La/Rh HoMSs exhibit elevated light-harvesting capacity and charge separation efficiency. Compared with STO:La/Rh nanoparticles (NPs), STO:La/Rh HoMSs demonstrate enhanced photocurrent response, photocatalytic hydrogen evolution activity, and the quantum efficiency. Moreover, overall water splitting is realized by a Z-scheme system combining STO:La/Rh HoMSs with BiVO4 (BVO) nanosheets with 1 wt% Pt as the co-catalyst. Steady evolution of hydrogen and oxygen is performed under both visible light and simulated sunlight irradiation. The solar-to-hydrogen efficiency of double-shelled STO:La/Rh HoMS-BVO photocatalysts reaches 0.08%, which is twofold higher than STO:La/Rh NP-BVO photocatalysts.

A Hollow Multi-Shelled Structure for Charge Transport and Active Sites in Lithium-Ion Capacitors.

The lithium-ion capacitor (LIC) has attracted tremendous research interest because it meets both the requirement on high energy and power densities. The balance between effective surface areas and mass transport is highly desired to fabricate the optimized electrode material for LIC. Now, triple-shelled (3S) Nb2 O5 hollow multi-shelled structures (HoMSs) were synthesized for the first time through the sequential templating approach and then applied for the anode of LIC. The unique structure of HoMSs, such as large efficient surface area, hierarchical pores, and multiple shells, provides abundant reaction sites, decreases the electron transport resistance, and increases the diffusion rate for ion transport. In this case, the best combination performance has been achieved among all the reported Nb2 O5 -based materials, which delivered an excellent energy and power densities simultaneously, and superb cycling stability.

Dual-Defects Adjusted Crystal-Field Splitting of LaCo1-x Nix O3-δ Hollow Multishelled Structures for Efficient Oxygen Evolution.

To boost the performance for various applications, a rational bottom-up design on materials is necessary. The defect engineering on nanoparticle at the atomic level can efficiently tune the electronic behavior, which offers great opportunities in enhancing the catalytic performance. In this paper, we optimized the surface oxygen vacancy concentration and created the lattice distortion in rare-earth-based perovskite oxide through gradient replacement of the B site with valence alternated element. The dual defects make the electron spin state transit from low spin state to high spin state, thus decreasing the charge transport resistance. Furthermore, assembly the modified nanoparticle subunits into the micro-sized hollow multishelled structures can provide porous shells, abundant interior space and effective contact, which enables an enhanced mass transfer and a shorter charge transport path. As a result, the systemic design in the electronic and nano-micro structures for catalyst has brought an excellent oxygen evolution performance.

Lanthanide-Doped Photoluminescence Hollow Structures: Recent Advances and Applications.

Lanthanide-doped nanomaterials have attracted significant attention for their preeminent properties and widespread applications. Due to the unique characteristic, the lanthanide-doped photoluminescence materials with hollow structures may provide advantages including enhanced light harvesting, intensified electric field density, improved luminescent property, and larger drug loading capacity. Herein, the synthesis, properties, and applications of lanthanide-doped photoluminescence hollow structures (LPHSs) are comprehensively reviewed. First, different strategies for the engineered synthesis of LPHSs are described in detail, which contain hard, soft, self-templating methods and other techniques. Thereafter, the relationship between their structure features and photoluminescence properties is discussed. Then, niche applications including biomedicines, bioimaging, therapy, and energy storage/conversion are focused on and superiorities of LPHSs for these applications are particularly highlighted. Finally, keen insights into the challenges and personal prospects for the future development of the LPHSs are provided.

Constructing SrTiO3 -TiO2 Heterogeneous Hollow Multi-shelled Structures for Enhanced Solar Water Splitting.

Constructing hollow multi-shelled structures (HoMSs) has a significant effect on promoting light absorption property of catalysts and enhancing their performance in solar energy conversion applications. A facile hydrothermal method is used to design the SrTiO3 -TiO2 heterogeneous HoMSs by hydrothermal crystallization of SrTiO3 on the surface of the TiO2 HoMSs, which will realize a full coverage of SrTiO3 on the TiO2 surface and construct the SrTiO3 /TiO2 junctions. The broccoli-like SrTiO3 -TiO2 heterogeneous HoMSs exhibited a fourfold higher overall water splitting performance of 10.6 µmol h-1 for H2 production and 5.1 µmol h-1 for O2 evolution than that of SrTiO3 nanoparticles and the apparent quantum efficiency (AQE) of 8.6 % at 365 nm, which can be mainly attributed to 1) HoMS increased the light absorption ability of the constructed photocatalysts and 2) the SrTiO3 -TiO2 junctions boosted the separation efficiency of the photogenerated charge carriers.

Triple-Shelled Manganese-Cobalt Oxide Hollow Dodecahedra with Highly Enhanced Performance for Rechargeable Alkaline Batteries.

Precisely carving of multi-shelled manganese-cobalt oxide hollow dodecahedra (Co/Mn-HD) with shell number up to three is achieved by a controlled calcination of the Mn-doped zeolitic imidazolate framework ZIF-67 precursor (Co/Mn-ZIF). The unique multi-shelled and polycrystalline structure not only provides a very large electrochemically active surface area (EASA), but also enhances the structural stability of the material. The residual C and N in the final structures might aid stability and increase their conductivity. When used in alkaline rechargeable battery, the triple-shelled Co/Mn-HD exhibits high electrochemical performance, reversible capacity (331.94 mAh g-1 at 1 Ag-1 ), rate performance (88 % of the capacity can be retained with a 20-fold increase in current density), and cycling stability (96 % retention over 2000 cycles).

High Phase-Purity 1T-MoS2 Ultrathin Nanosheets by a Spatially Confined Template.

The crystal phase plays an important role in controlling the properties of a nanomaterial; however, it is a great challenge to obtain a nanomaterial with high purity of the metastable phase. For instance, the large-scale synthesis of the metallic phase MoS2 (1T-MoS2 ) is important for enhancing electrocatalytic reaction, but it can only be obtained under harsh conditions. Herein, a spatially confined template method is proposed to synthesize high phase-purity MoS2 with a 1T content of 83 %. Moreover, both the confined space and the structure of template will affect the purity of 1T-MoS2 ; in this case, this approach was extended to other similar spatially confined templates to obtain the high-purity material. The obtained ultrathin nanosheets exhibit good electrocatalytic activity and excellent stability in the hydrogen evolution reaction.

Hollow Multi-Shelled Structure with Metal-Organic-Framework-Derived Coatings for Enhanced Lithium Storage.

Herein, we present heterogeneous hollow multi-shelled structures (HoMSs) prepared by exploiting the properties of the metal-organic framework (MOFs) casing. Through accurately controlling the transformation of MOF layer into different heterogeneous casings, we can precisely design HoMSs of SnO2 @Fe2 O3 (MOF) and SnO2 @FeOx -C(MOF), which not only retain properties of the original SnO2 -HoMSs, but also structural information from the MOFs. Tested as anode materials in LIBs, SnO2 @Fe2 O3 (MOF)-HoMSs demonstrate superior lithium-storage capacity and cycling stability to the original SnO2 -HoMSs, which can be attributed to the topological features from the MOF casing. Making a sharp contrast to the electrodes of SnO2 @Fe2 O3 (particle)-HoMSs fabricated by hydrothermal method, the capacity retention after 100 cycles for the SnO2 @Fe2 O3 (MOF)-HoMSs is about eight times higher than that of the SnO2 @Fe2 O3 (particle)-HoMS.

Construction of Multishelled Binary Metal Oxides via Coabsorption of Positive and Negative Ions as a Superior Cathode for Sodium-Ion Batteries.

Multishelled binary metal oxide, which can exert a synergetic effect of different oxides, is a promising electrochemical electrode material. However, it is challenging to synthesize this kind of binary metal oxide due to the severe hydrolysis and/or precipitation reactions of the precursors between cations and anions of different metals. Herein, by using citric acid as a chelating agent to inhibit hydrolysis and precipitation, a series of multishelled binary metal oxide hollow spheres (Fe2(MoO4)3, NiMoO4, MnMoO4, CoWO4, MnWO4, etc.) were obtained via coabsorption of negative and positive metal ions. In addition, the chelation between a metal ion and citric acid is systematically validated by NMR, MS, Raman, and UV-vis. In particular, multishelled Fe2(MoO4)3 hollow spheres show excellent electrochemical performance as cathode material for sodium-ion batteries benefited from their structural superiorities. Especially, the quintuple-shelled Fe2(MoO4)3 hollow sphere shows the highest specific capacity (99.03 mAh g-1) among all Fe2(MoO4)3 hollow spheres, excellent stability (85.6 mAh g-1 was retained after 100 cycles at a current density of 2.2 C), and outstanding rate capability (67.4 mAh g-1 can be obtained at a current density of 10 C). This general approach can be extended to the synthesis of other multishelled multielement metal oxides and greatly enrich the diversity of hollow multishelled structures.

Metallic Cobalt-Carbon Composite as Recyclable and Robust Magnetic Photocatalyst for Efficient CO2 Reduction.

CO2 conversion into value-added chemical fuels driven by solar energy is an intriguing approach to address the current and future demand of energy supply. Currently, most reported surface-sensitized heterogeneous photocatalysts present poor activity and selectivity under visible light irradiation. Here, photosensitized porous metallic and magnetic 1200 CoC composites (PMMCoCC-1200) are coupled with a [Ru(bpy)3 ]Cl2 photosensitizer to efficiently reduce CO2 under visible-light irradiation in a selective and sustainable way. As a result, the CO production reaches a high yield of 1258.30 µL with selectivity of 64.21% in 6 h, superior to most reported heterogeneous photocatalysts. Systematic investigation demonstrates that the central metal cobalt is the active site for activating the adsorbed CO2 molecules and the surficial graphite carbon coating on cobalt metal is crucial for transferring the electrons from the triplet metal-to-ligand charge transfer of the photosensitizer Ru(bpy)32+ , which gives rise to significant enhancement for CO2 reduction efficiency. The fast electron injection from the excited Ru(bpy)32+ to PMMCoCC-1200 and the slow backward charge recombination result in a long-lived, charge-separated state for CO2 reduction. More impressively, the long-time stability and easy magnetic recycling ability of this metallic photocatalyst offer more benefits to the photocatalytic field.

Isotropic Zero Thermal Expansion and Local Vibrational Dynamics in (Sc,Fe)F3.

Scandium fluoride (ScF3) exhibits a pronounced negative thermal expansion (NTE), which can be suppressed and ultimately transformed into an isotropic zero thermal expansion (ZTE) by partially substituting Sc with Fe in (Sc0.8Fe0.2)F3 (Fe20). The latter displays a rather small coefficient of thermal expansion of -0.17 × 10-6/K from 300 to 700 K. Synchrotron X-ray and neutron pair distribution functions confirm that the Sc/Fe-F bond has positive thermal expansion (PTE). Local vibrational dynamics based on extended X-ray absorption fine structure indicates a decreased anisotropy of relative vibration in the Sc/Fe-F bond. Combined analysis proposes a delicate balance between the counteracting effects of the chemical bond PTE and NTE from transverse vibration. The present study extends the scope of isotropic ZTE compounds and, more significantly, provides a complete local vibrational dynamics to shed light on the ZTE mechanism in chemically tailored NTE compounds.

Multi-shelled hollow micro-/nanostructures.

Great progress has been made in the preparation and application of multi-shelled hollow micro-/nanostructures during the past decade. However, the synthetic methodologies and potential applications of these novel and interesting materials have not been reviewed comprehensively in the literature. In the current review we first describe different synthetic methodologies for multi-shelled hollow micro-/nanostructures as well as their compositional and geometric manipulation and then review their applications in energy conversion and storage, sensors, photocatalysis, and drug delivery. The correlation between the geometric properties of multi-shelled hollow micro-/nanostructures and their specific performance in relevant applications are highlighted. These results demonstrate that the geometry has a direct impact on the properties and potential applications of such materials. Finally, the emerging challenges and future development of multi-shelled hollow micro-/nanostructures are further discussed.

Y2O3:Yb³âº/Er³âº Hollow Spheres with Controlled Inner Structures and Enhanced Upconverted Photoluminescence.

Multishell Y2 O3 :Yb(3+) /Er(3+) hollow spheres with uniform morphologies and controllable inner structures are prepared successfully by using a glucose-template hydrothermal process followed by temperature-programmed calcination. Much enhanced upconverted photoluminescence of these Y2 O3 :Yb(3+) /Er(3+) are observed, which are due to the multiple reflections and the enhanced light-harvesting efficiency of the NIR light resulting from the special features of the multishell structures.

Two-dimensional carbon leading to new photoconversion processes.

Two-dimensional (2D) carbon allotropes, which are atomic thick layers made of network carbon atoms with hexagonal structured lattices, have been neglected until the direct investigation of mechanically exfoliated graphene by Novoselov et al. in 2004. Graphene is a 2D carbon allotrope with a unique structure of hexagonally arranged atoms that give it unparalleled electrical conductivity and carrier mobility, in addition to excellent mechanical flexibility and extremely high specific surface area. Graphene and its derivatives have been extensively studied for photovoltaic and photocatalytic applications due to their inherent nature to extract and transport charges from photon-absorbing semiconductors and conjugated polymers. Graphyne and graphdiyne, 2D carbon allotropes like graphene but containing not only doubly but also triply bonded carbon atoms, are predicted to possess intrinsic semiconductor bandgap and even more superior electrical properties than graphene. The current theoretical understanding and experimental status of graphyne and graphdiyne will be discussed in contrast of graphene, demonstrating those promising competitors to graphene in further lightening a new photoconversion. This review addresses the recent successes and current challenges of graphene, graphyne and graphdiyne, and provides insightful perspectives for the future applications of 2D carbon materials in photoelectric conversion and photocatalysis.

Multishelled TiO2 hollow microspheres as anodes with superior reversible capacity for lithium ion batteries.

Herein, uniform multishelled TiO2 hollow microspheres were synthesized, especially 3- and 4-shelled TiO2 hollow microspheres were synthesized for the first time by a simple sacrificial method capable of controlling the shell thickness, intershell spacing, and number of internal multishells, which are achieved by controlling the size, charge, and diffusion rate of the titanium coordination ions as well as the calcination process. Used as anodes for lithium ion batteries, the multishelled TiO2 hollow microspheres show excellent rate capacity, good cycling performance, and high specific capacity. A superior capacity, up to 237 mAh/g with minimal irreversible capacity after 100 cycles is achieved at a current rate of 1 C (167.5 mA/g), and a capacity of 119 mAh/g is achieved at a current rate of 10 C even after 1200 cycles.

Zero thermal expansion and ferromagnetism in cubic Sc(1-x)M(x)F3 (M = Ga, Fe) over a wide temperature range.

The rare physical property of zero thermal expansion (ZTE) is intriguing because neither expansion nor contraction occurs with temperature fluctuations. Most ZTE, however, occurs below room temperature. It is a great challenge to achieve isotropic ZTE at high temperatures. Here we report the unconventional isotropic ZTE in the cubic (Sc1-xMx)F3 (M = Ga, Fe) over a wide temperature range (linear coefficient of thermal expansion (CTE), αl = 2.34 × 10(-7) K(-1), 300-900 K). Such a broad temperature range with a considerably negligible CTE has rarely been documented. The present ZTE property has been designed using the introduction of local distortions in the macroscopic cubic lattice by heterogeneous cation substitution for the Sc site. Even though the macroscopic crystallographic structure of (Sc0.85Ga0.05Fe0.1)F3 adheres to the cubic system (Pm3̅m) according to the results of X-ray diffraction, the local structure exhibits a slight rhombohedral distortion. This is confirmed by pair distribution function analysis of synchrotron radiation X-ray total scattering. This local distortion may weaken the contribution from the transverse thermal vibration of fluorine atoms to negative thermal expansion, and thus may presumably be responsible for the ZTE. In addition, the present ZTE compounds of (Sc1-xMx)F3 can be functionalized to exhibit high-Tc ferromagnetism and a narrow-gap semiconductor feature. The present study shows the possibility of obtaining ZTE materials with multifunctionality in future work.

Strategies for Advanced Supercapacitors Based on 2D Transition Metal Dichalcogenides: From Material Design to Device Setup.

Recently, the development of new materials and devices has become the main research focus in the field of energy. Supercapacitors (SCs) have attracted significant attention due to their high power density, fast charge/discharge rate, and excellent cycling stability. With a lamellar structure, 2D transition metal dichalcogenides (2D TMDs) emerge as electrode materials for SCs. Although many 2D TMDs with excellent energy storage capability have been reported, further optimization of electrode materials and devices is still needed for competitive electrochemical performance. Previous reviews have focused on the performance of 2D TMDs as electrode materials in SCs, especially on their modification. Herein, the effects of element doping, morphology, structure and phase, composite, hybrid configuration, and electrolyte are emphatically discussed on the overall performance of 2D TMDs-based SCs from the perspective of device optimization. Finally, the opportunities and challenges of 2D TMDs-based SCs in the field are highlighted, and personal perspectives on methods and ideas for high-performance energy storage devices are provided.

Interfaces Engineering of Ultrafine Ni@Ni2P/C Core-Shell Heterostructure for High Yield Hydrogen Peroxide Electrosynthesis.

Developing cost-effective and sustainable catalysts with exceptional activity and selectivity is essential for the practical implementation of on-site H2O2 electrosynthesis, yet it remains a formidable challenge. Metal phosphide core-shell heterostructures anchored in carbon nanosheets (denoted as Ni@Ni2P/C NSs) are designed and synthesized via carbonization and phosphidation of the 2D Ni-BDC precursor. This core-shell nanostructure provides more accessible active sites and enhanced durability, while the 2D carbon nanosheet substrate prevents heterostructure aggregation and facilitates mass transfer. Theoretical calculations further reveal that the Ni/Ni2P heterostructure-induced optimization of geometric and electronic structures enables the favored adsorption of OOH* intermediate. All these features endow the Ni@Ni2P/C NSs with remarkable performance in 2e ORR for H2O2 synthesis, achieving a top yield rate of 95.6 mg L-1 h-1 with both selectivity and Faradaic efficiency exceeding 90% under a wide range of applied potentials. Furthermore, when utilized as the anode of an assembled gas diffusion electrode (GDE) device, the Ni@Ni2P/C NSs achieve in situ H2O2 production with excellent long-term durability (>32 h). Evidently, this work provides a unique insight into the origin of 2e ORR and proposes optimization of H2O2 production through nano-interface manipulation.

Unusual transformation from strong negative to positive thermal expansion in PbTiO3-BiFeO3 perovskite.

Tetragonal PbTiO(3)-BiFeO(3) exhibits a strong negative thermal expansion in the PbTiO(3)-based ferroelectrics that consist of one branch in the family of negative thermal expansion materials. Its strong negative thermal expansion is much weakened, and then unusually transforms into positive thermal expansion as the particle size is slightly reduced. This transformation is a new phenomenon in the negative termal expansion materials. The detailed structure, temperature dependence of unit cell volume, and lattice dynamics of PbTiO(3)-BiFeO(3) samples were studied by means of high-energy synchrotron powder diffraction and Raman spectroscopy. Such unusual transformation from strong negative to positive thermal expansion is highly associated with ferroelectricity weakening. An interesting zero thermal expansion is achieved in a wide temperature range (30-500 °C) by adjusting particle size due to the negative-to-positive transformation character. The present study provides a useful method to control the negative thermal expansion not only for ferroelectrics but also for those functional materials such as magnetics and superconductors.