Short Diffusion Length Research Articles

Enhanced collection efficiencies and performance of interband cascade structures for narrow bandgap semiconductor thermophotovoltaic devices

We report on a comparative study of narrow-bandgap (∼0.2 eV at 300 K) thermophotovoltaic (TPV) devices with InAs/GaSb type-II superlattice absorbers. By comparing the characteristics of three narrow bandgap TPV structures with a single absorber or multiple discrete absorbers, it is clearly demonstrated that the device performance of a conventional single-absorber TPV cell is limited mainly by the small collection efficiency associated with a relatively short diffusion length (1.5 μm at 300 K). Furthermore, this study revealed that multi-stage interband cascade (IC) TPV structures with thin individual absorbers can circumvent the diffusion length limitation and are capable of achieving a collection efficiency approaching 100% for photo-generated carriers. Additionally, the open-circuit voltage, the fill factor, the output power, and the power conversion efficiency can be significantly increased in IC TPV devices compared to the conventional single-absorber TPV structure. These results have further validated the potential and advantages of narrow bandgap IC structures for TPV cells.

A facile method to hunt for durable high-rate capability Na0.44MnO2

Na0.44MnO2 as a potential cathode for sodium-ion batteries (SIBs) has been widely investigated with longer one-dimension (1D) morphology. In this work, we propose a facile and effective method to hunt for comprehensive performance of tunnel Na0.44MnO2, especially the rate property. The method is based on a fact that the crystal growth direction and sodium ions intercalation de-intercalation direction are consistent (both along c-axis). Therefore, once the long rod-like cathodes break to two or more shorter 1D Na0.44MnO2, the density of more (001) active planes and short diffusion length are both acquired. In addition, the smashed samples with short nano-bars can still be able to accommodate strain during the cycle process and can be favorable for the contact with electrolyte, which could provide good cycle stability. As a consequence, the materials deliver 90.4 mAh g−1 discharge capacity at 10C (78% of 0.1C capacity) and maintains 93.91% capacity after 200 cycles at 5C. The sodium-ion chemical diffusion coefficient has been improved with an order of magnitude by galvanostatic intermittent titration technique (GITT) and electrochemical impedance spectroscopy (EIS) test, respectively.

Extraction of samarium using a serpentine Y-junction microreactor with 2-ethylhexyl phosphonic acid mono-2-ethylhexyl

In the modern industrialized rare earths production, solvent extraction facilities possess many problems such as long extraction time, large occupation area, high processing cost and so on. The present work attempts to extract samarium (III) from hydrochloric acid solution in a rectangular cross-section Y-junction microchannel, using 2-ethylhexyl phosphonic acid mono-2-ethylhexyl (EHEHPA or P507). The effects of flow rate, channel length and width on the extraction efficiency, slug length and mass behavior of a liquid-liquid extraction system are assessed. The slug length decreased with increase in the flow rate, increased in channel length and channel width. The maximum extraction efficiency of 75.1% could be achieved at the longer channel length (pH = 1.5, channel width = 300 μm, flow rate = 10 μL/min). The volumetric mass transfer coefficients (kLa) of the microfluidic extractor was compared with the conventional extractor and found to be several orders of magnitude higher, authenticating the beneficial effects such as: Higher specific interfacial area and shorter diffusion length.

Control over Self‐Doping in High Band Gap Perovskite Films

AbstractIt is reported how differences in the composition of high bandgap Pb bromide‐based perovskites affect their carrier diffusion length and junction type. Pb‐based, APbX3, halide perovskite (HaP) films and devices are studied, where A can be a mixture of formamidinium, methylammonium (MA), and Cs, and X a mixture of Br and Cl, using a combination of dark‐ and photoconductivity and steady‐state photocarrier grating. The results show the cation and anion compositions affect both majority and minority carrier diffusion lengths. In particular, using electron beam‐induced current measurements, FTO\dTiO2mp‐TiO2HaP\PTAA (poly‐triarylamine)\Au devices are studied. The results enable identifying junction and built‐in voltage formation and track position and size of the space charge region width with changes in the HaP composition. As far as it is known, it is found for the first time that a mixed‐cation HaP forms a junction that has characteristics of a p‐i‐n one, with relatively long and comparable carrier diffusion lengths, while the single cation‐based bromide HaPs form clear p‐n junctions at the interface with the TiO2 [pure CsPbBr3 and MAPbBr3(Cl)] or a buried one (MAPbBr3) and shorter diffusion lengths. These differences are attributed to lower carrier density in MAPbBr3, and especially in the mixed cation HaP, which is comparable to iodide‐based HaP films.

Carbon Nitride/Reduced Graphene Oxide Film with Enhanced Electron Diffusion Length: An Efficient Photo‐Electrochemical Cell for Hydrogen Generation

AbstractPolymeric carbon nitride (CN) has emerged as a promising semiconductor for energy‐related applications. However, its utilization in photo‐electrochemical cells is still very limited owing to poor electron–hole separation efficiency, short electron diffusion length, and low absorption coefficient. Here the synthesis of a highly porous carbon nitride/reduced graphene oxide (CN‐rGO) film with good photo‐electrochemical properties is reported. The CN‐rGO film exhibits long electron diffusion length and high electrochemical active surface area, good charge separation, and enhanced light‐harvesting properties. The film displays a 20‐fold enhancement of photocurrent density over pristine CN, reaching up to 75 µA cm−2 at 1.23 V versus reversible hydrogen electrode (RHE) in an alkaline solution, as well as stability over a wide pH range. Photocurrent measurements with a hole scavenger reveal a photocurrent density of 660 µA cm−2 at 1.23 V versus RHE and a quantum efficiency of 60% at 400 nm, resulting in the production of 0.8 mol h−1 g−1 of hydrogen. The substantial photo‐electrochemical activity enhancement and hydrogen production together with the low price, high electrochemical surface area, long electron diffusion length, stability under harsh condition, and tunable photophysical properties of CN materials open many possibilities for their utilization in (photo)electrochemical and electronic devices.

Enhanced photoelectrochemical water splitting of BiVO4 photonic crystal photoanode by decorating with MoS2 nanosheets

Bismuth vanadate (BiVO4) has been considered as one of the promising Photoelectrochemical (PEC) photoanode materials. However, the performances remain poorly rated due to inefficient carrier separation, short carrier diffusion length, and sluggish water oxidation kinetics. Herein, a photoanode consisting of MoS2 nanosheet coating on the three-dimensional ordered BiVO4 inverse opal is fabricated by a facile combination of nanosphere lithography and hydrothermal methods. By taking advantage of the photonic crystal and two-dimensional material, the optimized MoS2/BiVO4 inverse opal photoanode exhibits a 560% improvement of the photocurrent density and threefold enhancement of the incident photon-to-current efficiency than that of the pristine BiVO4 film photoanode. Systematic studies reveal that the excellent PEC activity should be attributed to enhanced light harvesting and charge separation efficiency.

Fully Depleted Ti-Nb-Ta-Zr-O Nanotubes: Interfacial Charge Dynamics and Solar Hydrogen Production.

Poor kinetics of hole transportation at the electrode/electrolyte interface is regarded as a primary cause for the mediocre performance of n-type TiO2 photoelectrodes. By adopting nanotubes as the electrode backbone, light absorption and carrier collection can be spatially decoupled, allowing n-type TiO2, with its short hole diffusion length, to maximize the use of the available photoexcited charge carriers during operation in photoelectrochemical (PEC) water splitting. Here, we presented a delicate electrochemical anodization process for the preparation of quaternary Ti-Nb-Ta-Zr-O mixed-oxide (denoted as TNTZO) nanotube arrays and demonstrated their utility in PEC water splitting. The charge-transfer dynamics for the electrodes was investigated using time-resolved photoluminescence, electrochemical impedance spectroscopy, and the decay of open-circuit voltage analysis. Data reveal that the superior photoactivity of TNTZO over pristine TiO2 originated from the introduction of Nd, Ta, and Zr elements, which enhanced the amount of accessible charge carriers, modified the electronic structure, and improved the hole injection kinetics for expediting water splitting. By modulating the water content of the electrolyte employed in the anodization process, the wall thickness of the grown TNTZO nanotubes can be reduced to a size smaller than that of the depletion layer thickness, realizing a fully depleted state for charge carriers to further advance the PEC performance. Hydrogen evolution tests demonstrate the practical efficacy of TNTZO for realizing solar hydrogen production. Furthermore, with the composition complexity and fully depleted band structure, the present TNTZO nanotube arrays may offer a feasible and universal platform for the loading of other semiconductors to construct a sophisticated heterostructure photoelectrode paradigm, in which the photoexcited charge carriers can be entirely utilized for efficient solar-to-fuel conversion.

Trench-Wall Carbon Nanotube Sponges As Effective Dual Hosts for High-Areal-Capacity Sulfur Cathodes and Lithium Anodes

High-energy-density batteries are seeing increasingly demand for many applications. Traditional Li-ion batteries based on metal oxide cathode and graphite anode, though under continuous improvement, cannot meet the requirement in the long term due to the theoretical limitation on reaction chemistry. The lithium-sulfur battery is a promising candidate for future energy storage because of its high energy density in theory. However, to achieve high energy density in practical applications, a high areal loading (~10 mg cm-2) of active material – sulfur is required, which is hindered by deteriorating polysulfides shuttle and lithium dendrite formation. Previous research tackled the problems from either cathode side or anode side, and showed performance improvement based on a low areal loading (<3 mg cm-2) of sulfur. Here we report a novel trench-wall carbon nanotube sponge acting as a dual host for high-areal-capacity sulfur cathodes and lithium anodes. Created by a controllable mechano-chemical method, the unique trench-wall structure provides nano-reactors for active materials with shortened diffusion length, polysulfides-philic and lithiophilic surface for hosting active materials, and increased surface area for promoting electrochemical reactions. The cell showed excellent areal capacity (10.3 mAh cm-2) after 100 cycles under a high current density of 4.8 mA cm-2, demonstrating both high “cell-level” energy density and power. The trench-wall CNT sponge is, to our best knowledge, the first single material used to simultaneously and effectively tackle the problems from both cathode and anode sides of lithium-sulfur batteries. The strategy of creating nano-trenches on the wall of carbon nanotubes paves a new way for designing new materials for high-energy-density batteries.

(Invited) Nanoporous Materials for Fast and Reversible Electrochemical Energy Storage

In this talk, we examine ways that solution processed nanostructured materials can be used to address both fundamental and practical issues relevant to next generation electrochemical energy storage. Materials with appropriate porous architectures can be synthesized using a range of solution phase methods, including polymer templating, nanoparticle assembly, and selective solution phase dealloying of mixed metal solid-state precursors. We begin with nanoporous materials for application in fast charging pseudocapacitors, with a goal of both defining the limits of pseudocapacitance in nanostructured materials and of establishing design rules for synthesizing highly capacitive materials. We find that in optimized nanoporous materials, the nanoscale structure and porosity can produce a very desirable combination of electrical connectivity, electrolyte access to the interior of the material, ample surface redox sites, and very short solid-state diffusion lengths for lithium ions, all of which facilitate fast charge and discharge. Perhaps more importantly, many nanoscale materials appear to show suppression of the intercalation induced phase transition that can cause kinetic limitations in bulk materials. Similar porous architectures can also be used to increase stability and cycle life in high capacity alloy-type anode materials that normal show significant strain related degradation. Using X-ray microscopy, we are able to directly image changes in pore structure upon cycling, so that materials and architectures can be optimized for stable cycling. Taken together, these results emphasize the key role played by nanoscale porosity in electrochemical energy storage materials.

Three-Dimensional Tin Oxide Nanohelix Structures with Thin Iron Oxide Layer for Efficient Visible Light Driven Water Splitting

Solar-powered photoelectrochemical (PEC) water splitting has been a promising candidate for producing hydrogen in a clean and renewable way. Photoelectrodes are key components in PEC cells for efficient and stable hydrogen generation because they play crucial roles in absorption of photons, the separation and transportation of photo-generated charge carriers, as well as the chemical reactions with water. A variety of metal oxides for efficient photoelectrode have been intensively explored, but it is still challenging to find desirable materials to satisfy lots of requirements for PEC water splitting. Iron oxide (hematite, Fe2O3) has recently attracted much attention due to its earth abundance, low cost as well as desirable material properties for PEC water oxidation including narrow band gap energy of 2.0~2.2eV for visible light absorption and proper energy band alignment, etc. However, Fe2O3 has very short hole diffusion length and low carrier mobility, which causes considerable recombination of photo-generated electrons and holes. A lot of approaches such as nanostructures, heterojunction with other materials, surface modification, etc. have been reported to improve electrical properties of Fe2O3 which unfortunately cause poor light absorption. In this study, three-dimensional tin oxide (SnO2) nanohelix (NH) structures were fabricated as scaffolds for a thin Fe2O3 layer on fluorine-doped SnO2 glass substrate by oblique angle deposition method using electron beam evaporator. SnO2 NH structures based photoelectrode can simultaneously enhance light absorption and charge separation and transport for efficient PEC water splitting by trapping the incident light through strong light scattering effect as well as by providing pathways for charge separation and transport and large surface area. In addition, SnO2 NH structures are easy to be hybridized with Fe2O3 through only simple solution-based spin-coating method due to its high porosity, aspect ratio and large surface area. Thin Fe2O3 layer was coated along the surface of SnO2 NH structures forming a type-II band hetero-junction and these Fe2O3 coated SnO2 NH are significantly desirable for efficient visible light driven water splitting by simultaneously improving light absorption, charge separation and transport. Highly efficient PEC performance of our hybridized photoelectrode (including more than 5.0mAcm-2 photocurrent density at 1.23VRHE under AM1.5G solar spectrum and 1 sun illumination which is a significantly excellent performance for Fe2O3 based photoelectode) will be investigated and the advantages of three-dimensional SnO2 NH structures as scaffolds for very thin Fe2O3 layer as well as its potential for practical application will be discussed in detail based on electrochemical analysis, FEM simulation, angular-dependent reflectance, PEC analysis at different intensity of incident light, etc.

Ultra-High Sensitivity Surface Photovoltage Measurement of Heavy Metal Contamination in Silicon Wafers with Fast Metal Identification

The Surface Photovoltage (SPV) minority carrier diffusion length method is the most sensitive and widely used technique for monitoring heavy metal contamination in silicon wafers starting from crystal growth through various IC processing steps. Relentless IC fabline purity refinement, exhibited by a Fe contamination decrease of about 10 times per decade has been matched by corresponding progress in SPV detection capabilities. An iron contamination limit of mid 107 atoms/cm3 is projected for new IC fablines by the year 2020. For SPV this represents a detection goal for a new generation of metrology. In this paper we discuss this newest version of the SPV technique. The key element is the improvement of accuracy and repeatability of the minority carrier diffusion length determination, demonstrated by the coefficient of variance of 0.01% that is an order of magnitude better than the capability of the previous digital SPV version. This translates directly to an order of magnitude better sensitivity in SPV metal concentration measurements quantified by the change in diffusion length (L) caused by activation of the metal recombination activity. Results are presented for some of the purest state-of-the-art 300mm wafers. They illustrate an ultra-high sensitivity procedure for whole wafer mapping of Fe that includes for the first time a quick Fe identification test. This test is done with very short transient diffusion length measurements made possible by the enhanced precision of the L measurements. The test takes minutes compared to hours or days used in previous SPV measurements. Previous digital SPV metrology incorporated concentration measurements of Fe and Cu. SPV versions for photovoltaics include measurement of light-induced degradation related to boron-oxygen defects. The next generation digital SPV extends this measurement to include other interstitial metals Co, Mn and Cr that at room temperature form stable pairs with substitutional boron acceptors. Identification of the metals and separation of their individual contribution is based on metal-specific features of dissociation and association kinetics of the pairing reaction, Mi+Bs ↔ (Mi Bs), involving interstitial metal donors Mi and substitutional boron acceptors, Bs. Cu is differentiated from the other metals due to different irreversible reactions that change the minority carrier diffusion length. A distinctive feature of the SPV metrology is the use of photo-dissociation of pairs, effective for Fe and Co, but not for Mn and Cr. For the latter two metals, thermal dissociation is used. Thermal dissociation is effective for all pairs, therefore in multi-metal measurement cycles it is used as a post photo-dissociation step. Accordingly, the diffusion length measurement in the initial state, Linit, then after photo-dissociation, LPD, and then after thermal-dissociation, LTD, is used in the example illustrating the case of the simultaneous presence of Fe and Mn. After dissociation, a transient diffusion length measurement is performed which determines the association (pairing) time constant, τp. The value of τp is inversely proportional to metal diffusivity and it increases in the order Co→Fe→Mn→Cr. The digital SPV tool incorporates variable temperature wafer stages facilitating optimization of thermal treatment used in monitoring of dissociation or association kinetics. It is believed that these refinements ensure the latest generation of digital SPV tools will meet the demands of Fe contamination monitoring in IC fablines well beyond the 2020 projection while also enabling for the first time fast heavy metal identification testing.

Defect-Pairs of Titanium and Carbon in Iron Oxide Film for Efficient Visible Light Driven Water Splitting

Solar-powered photoelectrochemical (PEC) water splitting has been a promising candidate for producing hydrogen in a clean and renewable way. Photoelectrodes are key components in PEC cells for efficient and stable hydrogen generation because they play crucial roles in absorption of photons, the separation and transportation of photo-generated charge carriers, as well as the chemical reactions with water. A variety of metal oxides for efficient photoelectrode have been intensively explored, but it is still challenging to find desirable materials to satisfy lots of requirements for PEC water splitting. Iron oxide (hematite, Fe2O3) has recently attracted much attention due to its earth abundance, low cost as well as desirable material properties for PEC water oxidation including narrow band gap energy of 2.0~2.2eV for visible light absorption and proper energy band alignment, etc. However, Fe2O3 has very short hole diffusion length and low carrier mobility, which causes considerable recombination of photo-generated electrons and holes. A lot of approaches such as nanostructures, heterojunction with other materials, surface modification, etc. have been reported to prevent the recombination of charge carriers and improve electrical properties of Fe2O3; however, these require complex manufacturing processes. In the present work, we found a much simpler way to improve the electrical properties of Fe2O3 film, namely defect-pairs due to co-doping. Titanium (Ti) and carbon (C) co-doped thin Fe2O3 film (i.e. (Ti,C)-Fe2O3) has been realized via a combination of simple solution-based spin-coating and tube furnace annealing process. This film turns out to lead significantly enhanced PEC performance when used as a photoanode: an impressively high photocurrent density of more than 4.5mAcm-2 was achieved at 1.23VRHE under AM1.5G solar spectrum and 1 sun illumination. This is compared to the value of Ti-doped Fe2O3 film, which is only about 2.6mAcm-2 photocurrent density at 1.23VRHE even though the optical properties of each film are similar. The origin for such substantial enhancement was revealed using a series of experimental and computational spectroscopies. X-ray absorption spectroscopy, electrochemical impedance measurements and density-functional-theory calculations both indicate that C atoms can be more deeply and heavily doped under the existence of Ti dopants in Fe2O3 film and then the defect-pairs of Ti and C increase not only charge carrier density but also electron’s mobility. An emphasis should be placed on the fact that this achievement was not assisted by co-catalysts and complex nanostructuring methods; hence even higher performance is expected when the film is further treated with extra-cares.

Morphological Control Effect of Hierarchical Heterostructure α-Fe2O3/TiO2 Nanotube for Photoelectrochemical Water Splitting

Large-band gap metal oxide TiO2 have suitable band positions for photoelectrochemical cells (PECs) for solar-driven water splitting, but uses only UV light region in the solar spectrum which represent only about 5 % of the energy. On the other hand, α-Fe2O3 with suitable bandgaps for efficient absorption in the solar spectrum require an external bias to drive hydrogen generation at the cathode due to the conduction band of α-Fe2O3 below the H2 evolution potential and have short carrier diffusion lengths. Synthesizing the metal oxide nanomaterials which have both suitable band position to drive reaction and visible light absorbed band gap is one of the major challenge in PECs for water splitting field. Hetero structure of α-Fe2O3 and TiO2 offer a potential solution to improve this problem. However, the inherent low electrical conductivity resulting in the high electron-hole pair recombination rate and short carrier diffusion length of α-Fe2O3 limit its practical use. Here we report a novel hierarchical heterostructure of α-Fe2O3 ultrathin nanoflakes branched on TiO2 nanotube strategy for PECs for water splitting. On the basis of the detailed experimental results and associated theoretical analysis, we demonstrate that suitable morphological control of α-Fe2O3 and TiO2 plays an important role in enhancing the photoelectrochemical water splitting performance.

Lithium-Sulfur Batteries: The Effect of High Sulfur Loading on the Electrochemical Performance

It is no secret that sulfur as a cathode material is a promising candidate for next generation Li metal-based batteries. However, the intrinsic limitations associated with low conductivity of sulfur and instability of sulfur based composite prevents the commercialization of lithium sulfur batteries. For the past years of Li-S batteries research, many research has been carried out on the cathode design to improve the electrochemical performance. However, it has been mathematically determined that even with high sulfur loading amount and effective sulfur utilization, the true value of energy density cannot outperform the currently available LIBs. That is, other inactive materials must be utilized to address the inherent sulfur issues which would only add more weight. Thus, we propose a novel and facile synthesis of binder-free three-dimensional carbon nanotubes (3D CNTs)/sulfur (S) hybrid composite as an electrode material, where 3D CNTs provide a high conduction path and short diffusion length for Li-ions, while providing ample amount of space for higher sulfur loading. In addition to sulfur loading, the amount of electrolyte also determines the electrochemical performance of Li-S cell in terms of sulfur utilization and cycling stability. However, the statistical analysis shows that more than 90% of reported publications have neglected this E/S ratio. This is important parameter for determining sulfur utilization and energy density of the cell. Here, we report the performance of three-dimensional carbon nanotubes/sulfur hybrid composite with different sulfur loading amounts from 1 to 9 mg/cm2 while tuning the electrolyte/sulfur (E/S) ratio from 12 to 1. The results have demonstrated the E/S ratio of 7 (60 µL electrolyte to 8.5 mg cm-2 sulfur) with reversible specific capacity of ~1068 mAh g-1 at 0.1C rate (~1.4mA cm-2) for up to 150 cycles.

A comparative study of single-needle and coaxial electrospun amyloid-like protein nanofibers to investigate hydrophilic drug release behavior

In this study, nanofibers containing an amyloid-like bovine serum albumin (AL-BSA) carrier and a model drug (ampicillin) were produced by electrospinning. The release behavior of ampicillin was compared from electrospun nanofibers prepared as either coaxial or single-needle types. SEM images showed that the membranes had a uniform and smooth structure and the core/shell fibers were found to be thicker than the core fibers. Core/shell production was proved by transmission electron microscopy images. Fourier transform infrared spectroscopy indicated the existence of compatibility between ampicillin and the AL-BSA matrix. The in vitro antimicrobial properties of ampicillin were studied through the comparison of bacterial inhibition zones and ampicillin was found to be more effective against Gram-positive Staphylococcus aureus than Gram-negative Escherichia coli. Moreover, in vitro drug release tests were conducted to explore the relationship between the shell thickness and the drug release rate. A burst release was observed for all membranes owing to the small fiber diameters and thus short diffusion lengths. For core membranes, the drug release mechanism followed Fickian transport, which was close to zero-order kinetic. A typical biphasic release mechanism was observed for the core/shell nanofibers. Overall, we present the first evidence of AL-BSA as a potential core/shell drug mediator.

Facile Synthesis of Pt-Functionalized Meso/Macroporous SnO2 Hollow Spheres through in Situ Templating with SiO2 for H2S Sensors.

Although single-nozzle electrospraying seems a versatile technique in the synthesis of spherical semiconducting metal oxide structures, the synthesized structures find limited use in gas-sensing applications because of their thick and dense morphology, which minimizes the accessibility of their inner surfaces. Herein, unprecedented spherical SiO2@SnO2 core-shell structures are synthesized upon calcination of single-nozzle as-electrosprayed spheres (SPs) containing tin (Sn) and silicon (Si) precursors. Subsequent etching of SiO2 in NaOH (pH 12) affords meso/macroporous SnO2 hollow spheres (HSPs) with short diffusion length (31.4 ± 3.1 nm), small crystallites (15.5 nm), and large Brunauer-Emmett-Teller surface area (124.8 m2 g-1). Apart from surface meso/macropores, diffusion of gases into porous SnO2 sensing layers is realized through inner interconnection of voids of the SnO2 HSPs into a three-dimensional network. Functionalization of the postetched SnO2 HSPs with platinum (Pt) nanoparticles at 0.08 wt % yields gas-sensing materials with outstanding response ( Ra/ Rg = 1.6, 10.8, and 105.1-0.1, 1, and 5 ppm of H2S, respectively) and selectivity toward H2S against interfering gas molecules at 250 °C. The SiO2 phase in the postcalcined SiO2@SnO2 SPs acts as a sacrificial template for pore creation and crystal growth inhibition, whereas the small amount of SiO2 residues in HSPs enhances the selectivity.

Pseudocapacitance of TiO2-x /CNT Anodes for High-Performance Quasi-Solid-State Li-Ion and Na-Ion Capacitors.

It is challenging for flexible solid-state hybrid capacitors to achieve high-energy-high-power densities in both Li-ion and Na-ion systems, and the kinetics discrepancy between the sluggish faradaic anode and the rapid capacitive cathode is the most critical issue needs to be addressed. To improve Li-ion/Na-ion diffusion kinetics, flexible oxygen-deficient TiO2-x /CNT composite film with ultrafast electron/ion transport network is constructed as self-supported and light-weight anode for a quasi-solid-state hybrid capacitor. It is found that the designed porous yolk-shell structure endows large surface area and provides short diffusion length, the oxygen-deficient composite film can improve electrical conductivity, and enhance ion diffusion kinetic by introducing intercalation pseudocapacitance, therefore resulting in advance electrochemical properties. It exhibits high capacity, excellent rate performance, and long cycle life when utilized as self-supported anodes for Li-ion and Na-ion batteries. When assembled with activated carbon/carbon nanotube (AC/CNT) flexible cathode, using ion conducting gel polymer as the electrolyte, high energy densities of 104 and 109Wh kg-1 are achieved at 250 W kg-1 in quasi-solid-state Li-ion and Na-ion capacitors (LICs and SICs), respectively. Still, energy densities of 32 and 36Wh kg-1 can be maintained at high power densities of 5000 W kg-1 in LICs and SICs.

New BiVO4 Dual Photoanodes with Enriched Oxygen Vacancies for Efficient Solar-Driven Water Splitting.

Bismuth vanadate (BiVO4 ) is a promising photoanode material for photoelectrochemical (PEC) water splitting. However, owing to the short carrier diffusion length, the trade-off between sufficient light absorption and efficient charge separation often leads to poor PEC performance. Herein, a new electrodeposition process is developed to prepare bismuth oxide precursor films, which can be converted to transparent BiVO4 films with well-controlled oxygen vacancies via a mild thermal treatment process. The optimized BiVO4 film exhibits an excellent back illumination charge separation efficiency mainly due to the presence of enriched oxygen vacancies which act as shallow donors. By loading FeOOH/NiOOH as the cocatalysts, the BiVO4 dual photoanodes exhibit a remarkable and highly stable photocurrent density of 5.87 mA cm-2 at 1.23 V versus the reversible hydrogen electrode under AM 1.5 G illumination. An artificial leaf composed of the BiVO4 /FeOOH/NiOOH dual photoanodes and a single sealed perovskite solar cell delivers a solar-to-hydrogen conversion efficiency as high as 6.5% for unbiased water splitting.

Fe2O3/SnSSe Hexagonal Nanoplates as Lithium-Ion Batteries Anode.

Novel two-dimensional (2D) Fe2O3/SnSSe hexagonal nanoplates were prepared from hot-inject process in oil phase. The resulted hybrid manifests a typical 2D hexagonal nanoplate morphology covered with thin carbon layer. Serving as anode material of lithium-ion battery (LIB), the Fe2O3/SnSSe hybrid delivers an outstanding capacity of 919 mAh g-1 at 100 mA g-1 and a discharge capacity of 293 mAh g-1 after 300 cycles at the current density of 5 A g-1. Compared with pristine SnSSe nanoplates, the Fe2O3/SnSSe hybrid exhibits both higher capacity and better stability. The enhanced performance is mainly attributed to the 2D substrate together with the synergistic effects offered by the integration of SnSSe with Fe2O3. The 2D Fe2O3/SnSSe hybrid can afford highly accessible sites and short ion diffusion length, which facilitate the ion accessibility and improves the charge transport. The novel structure and high performance demonstrated here afford a new way for structural design and the synthesis of chalcogenides as LIB anodes.

Scalable synthesis of sub-100 nm hollow carbon nanospheres for energy storage applications

Sub-100 nm hollow carbon nanospheres with thin shells are highly desirable anode materials for energy storage applications. However, their synthesis remains a great challenge with conventional strategies. In this work, we demonstrate that hollow carbon nanospheres of unprecedentedly small sizes (down to ∼32.5 nm and with thickness of ∼3.9 nm) can be produced on a large scale by a templating process in a unique reverse micelle system. Reverse micelles enable a spatially confined Stober process that produces uniform silica nanospheres with significantly reduced sizes compared with those from a conventional Stober process, and a subsequent well-controlled sol–gel coating process with a resorcinol–formaldehyde resin on these silica nanospheres as a precursor of the hollow carbon nanospheres. Owing to the short diffusion length resulting from their hollow structure, as well as their small size and microporosity, these hollow carbon nanospheres show excellent capacity and cycling stability when used as anode materials for lithium/sodium-ion batteries.