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Hierarchical architectures composed of nanomaterials in different forms are essential to improve the performance of lithium-ion battery (LIB) anodes. Here, we systematically studied the effects of hierarchical ZnO nanostructures on the electrochemical performance of LIBs. ZnO nanowire (NW) trunks were decorated with ZnO NWs or ZnO nanosheets (NSs) by successive hydrothermal synthesis to create hierarchical three-dimensional nanostructures. The branched ZnO NSs on the ZnO NW trunk exhibited a two-fold higher specific gravimetric capacity compared to ZnO NWs and branched ZnO NWs on ZnO NW trunks after 100 cycles of charging–discharging at 0.2C (197.4 mA g−1). The improvement in battery anode performance is attributable to the increased interfacial area between the electrodes and electrolyte, and the void space of the branched NSs that facilitates lithium ion transport and volume changes during cycling.

A new class of 2D nanosheets of nitrogen-integrated phosphate-rich ammonium manganese phosphate hydrate, (NH4MnPO4·H2O) (AMP), has been developed as pseudocapacitive electrode materials. The optimi...

Lattice mismatch induced epitaxial strain has been widely used to tune functional properties in complex oxide heterostructures. Apart from the epitaxial strain, a large lattice mismatch also produces other effects including modulations in microstructure and stoichiometry. However, it is challenging to distinguish the impact of these effects from the strain contribution to thin film properties. Here, we use La0.9Sr0.1MnO3 (LSMO), a lightly doped manganite close to the vertical phase boundary, as a model system to demonstrate that both epitaxial strain and cation stoichiometry induced by strain relaxation contribute to functionality tuning. The thinner LSMO films are metallic with a greatly enhanced TC which is 97 K higher than the bulk value. Such anomalies in TC and transport cannot be fully explained by the epitaxial strain alone. Detailed microstructure analysis indicates La deficiency in thinner films and twin domain formation in thicker films. Our results have revealed that both epitaxial strain and strain relaxation induced stoichiometry/microstructure modulations contribute to the modified functional properties in lightly doped manganite perovskite thin films.

Titanium dioxide in the form of one-dimensional (1D) nanostructure arrays represent widely studied morphological arrangement for light harvesting and charge transfer applications such as photocatalysis and photoelectrochemistry (PEC). Here we report a comparative structural and PEC study of variously grown 1D TiO2 nanostructures including i) nanorod arrays prepared by a hydrothermal method (TNR), ii) nanotube arrays fabricated by a two-step hydrothermal method using a ZnO nanorod array film as a template (THNT) and finally iii) nanotubes grown by self-organized electrochemical anodization of Ti films deposited on the FTO substrate (TNT). These nanostructures are assumed to be utilized as photoanodes in PEC water splitting devices. Field-emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), TEM images and UV–vis absorption spectra were used to characterize TiO2 nanostructures. The SEM and TEM morphology images revealed that the main difference among the nanostructures grown on the FTO are the shape and diameter of the individual nanotubes/nanorods and also the array’s density in the range of TNR > THNT > TNT and the degree of organization in the range of TNT > TNR > THNT. The obtained photocurrents at 0 V vs. Ag/AgCl increased in the order of THNT (110 μA cm−2)

Solar driven photoelectrochemical water splitting (PEC-WS) using semiconductor photoelectrodes represents a promising approach for a sustainable and environmentally friendly production of renewable energy vectors and fuel sources, such as dihydrogen (H2). In this context, titanium dioxide (TiO$_2$) and iron oxide (hematite, $\alpha$-Fe$_2$O$_3$) are among the most investigated candidates as photoanode materials, mainly owing to their resistance to photocorrosion, non-toxicity, natural abundance, and low production cost. Major drawbacks are, however, an inherently low electrical conductivity and a limited hole diffusion length that significantly affect the performance of TiO$_2$ and $\alpha$-Fe$_2$O$_3$ in PEC devices. To this regard, one-dimensional (1D) nanostructuring is typically applied as it provides several superior features such as a significant enlargement of the material surface area, extended contact between the semiconductor and the electrolyte and, most remarkably, preferential electrical transport that overall suppress charge carrier recombination and improve TiO$_2$ and $\alpha$-Fe$_2$O$_3$ photo-electrocatalytic properties. The present review describes various synthetic methods, properties and PEC applications of 1D-photoanodes (nanotubes, nanorods, nanofibers, nanowires) based on titania, hematite, and on $\alpha$-Fe$_2$O$_3$/TiO$_2$ heterostructures. Various routes towards modification and enhancement of PEC activity of 1D photoanodes are also discussed including doping, decoration with co-catalysts and heterojunction engineering. Finally, the challenges related to the optimization of charge transfer kinetics in both oxides are highlighted.

In spite of having several advantages such as low cost, high chemical stability, and environmentally safe and benign synthetic as well as operational procedures, the full potential of carbon dots (CDs) is yet to be explored as photosensitizers due to the challenges associated with the fabrication of well-arrayed CDs with many other photocatalytic heterostructures. In the present study, a unique combination of metal-organic framework (MOF)-decorated zinc oxide (ZnO) 1D nanostructures as host and CDs as guest species are explored on account of their potential application in photoelectrochemical (PEC) water splitting performance. The synthetic strategy to incorporate well-defined nitrogen-doped carbon dots (N-CDs) arrays onto a zeolitic imidazolate framework-8 (ZIF-8) anchored on ZnO 1D nanostructures allows a facile unification of different components which subsequently plays a decisive role in improving the material's PEC water splitting performance. Simple extension of such strategies is expected to offer significant advantages for the preparation of CD-based heterostructures for photo(electro)catalytics and other related applications.

A variety of Titanium dioxide (TiO 2 ) phases and nanostructures have been explored for their applications in photoelectrochemical cells (PECs) for solar-driven water splitting. In this case, anatase phase and TiO 2 nanotubes offer significant advantages especially for PEC-based applications. Though, significant efforts have already been engaged to combine the advantages from both the fields, poor activation and the high electron-hole pair recombination rate of TiO 2 electrodes, originating from intrinsic physicochemical properties, limits its practical use. As an alternative, we report directly grown TiO 2 nanotubes (synthesized on Fluorine doped Tin Oxide (FTO) via facile electrospinning technique) on carbon nanofibers, using hydrothermal method. The hierarchical branch type configuration has an intimate contact between the TiO 2 nanotube and carbon nanofiber backbone and offers higher photocatalytic activity than their respective individual components (namely TiO 2 nanotubes and carbon nanostructures).

Bilayer films of La 0.8 Sr 0.2 MnO 3 and La 0.7 Ca 0.3 MnO 3 with different layer thicknesses and stacking sequences were synthesized via pulsed laser deposition. The magnetic properties and magnetocaloric effects were systematically investigated. We found that the phase transition associated with the layers tends to merge together at an optimal thickness and a stacking sequence. The operating temperature span of the entropy change broadens at the expense of its magnitude, leading to an enhancement of the refrigerant capacity by over 40%. The optimized bilayer film possesses a refrigerant capacity of ∼ 6.0 J / kg, compared to a value of ∼ 4.2 J / kg for the single-phase films. The phase transition broadening induced by epitaxial strain is responsible for the enhanced window of operating temperature as well as refrigerant capacity. The design principle developed here may be applied to ferroelastic and ferroelectric materials to enhance elastocaloric and electrocaloric effects.

Vertically aligned nanocomposite thin films with ordered two phases, grown epitaxially on substrates, have attracted tremendous interest in the past decade. These unique nanostructured composite thin films with large vertical interfacial area, controllable vertical lattice strain, and defects provide an intriguing playground, allowing for the manipulation of a variety of functional properties of the materials via the interplay among strain, defect, and interface. This field has evolved from basic growth and characterization to functionality tuning as well as potential applications in energy conversion and information technology. Here, the remarkable progress achieved in vertically aligned nanocomposite thin films from a perspective of tuning functionalities through control of strain, defect, and interface is summarized.

The lithium oxygen battery is a promising energy storage system due to its high theoretical energy density and ability to use oxygen from air as a “fuel”. Although various carbonaceous materials have been widely used as a cathode material due to their high electronic conductivity and facial processability, previous studies mainly focused on the electrochemical properties associated with the materials (such as graphene and carbon nanotubes) and the electrode configuration. Recent reports demonstrated that the polarization associated with cycling could be significantly increased by lithium carbonates generated from the reaction between the carbon cathode and an electrolyte, which indicates that the physicochemical properties of the carbon cathode could play an important role on the electrochemical performances. However, there is no systematic study to understand these phenomena. Here, we systematically explore the electrochemical properties of carbon nanofibers (CNF) webs with different graphitization degree as a cathode for Li oxygen batteries. The physicochemical properties and electrochemical properties of CNF webs were carefully monitored before and after cycling. CNF webs are prepared at 1000, 1200 and 1400 °C. CNF web pyrolyzed at 1400 °C shows lowered polarization and improved cycle retention compared to those of CNF webs pyrolyzed at 1000 and 1200 °C.

Producing clean fuel (O2 and H2) using semiconductors through solar driven water splitting process has been considered as a promising technology to mitigate the existing environmental issues. Unlike the conventional single photoabsorbers, heterostructured semiconductors exhibit the merits of improved solar light photon harvesting and rapid charge separation, which are anticipated to result in high quantum yield of solar fuel generation in photoelectrochemical (PEC) cells. In this report, we demonstrate the electrospun derived WO3 backbone fibrous channel as heteropartner to the primary photoabsorber (Fe2O3 and BiVO4) for promoting the electron transport from charge injection point to charge collector as well as photoholes to the electrolyte. We examine structure, optical, photoelectrochemical and charge transfer property of Fe2O3/WO3 and BiVO4/WO3 electrodes. These results were compared with directly coated Fe2O3 and BiVO4 photoabsorber onto conducting substrate without WO3 backbone. The optical results showed that the absorbance and visible light activity of Fe2O3 and BiVO4 is significantly improved by WO3 backbone fibers due to high amount of photo absorber loading. In addition, one dimensional (1-D) WO3 fibers beneficially enhance the optical path length to the photoanode through light scattering mechanism. The electrochemical impedance analysis exhibits WO3 nanofiber backbone reduces charge transfer resistance at Fe2O3 and BiVO4 by rapid charge collection and charge separation compare to backbone-free Fe2O3 and BiVO4. As a result, Fe2O3/WO3 and BiVO4/WO3 fibrous hetero interface structures showed fourfold higher photocurrent generation from PEC cell.

As the density of graphite anode is increasing, the pore size and volume in the graphite anode is reduced, which results in a decrease in the electrolyte permeability of electrode. The electrochemical degradation of high density graphite anode due to the low permeability is a major obstacle to its use as anode for lithium ion batteries. In this study, we report on high density graphite anode with the carbon additive added that provides micron size pore structure of the high density graphite anode, which results in an increase in the rate capability. The high density graphite anode with carbon additive exhibited 32.4% higher rate capability at 1 C compared to the high density graphite anode without carbon additive. This improvement is mainly attributed to the increased micron-size pores, which enhances the kinetic associated with lithium by improved electrolyte permeation and increased interface between the electrolyte and active material.

Sn-doped LiTi2(PO4)3/C composite nanofibers are synthesized by a facile electrospinning process. The unique one dimensional nanostructure combined with a uniform electrically conductive carbon matrix allows high-rate transportation of lithium ions and electrons. Besides, Sn-doping could further decrease the electrochemical resistance. Sn-doped LiTi2(PO4)3/C composite nanofibers exhibit excellent electrochemical performance, especially ultra-fast charging/discharge capability. At a charging rate of about 600 C (64 A g−1, 6 s), 66.2% capacity (68.9 mA h g−1) could be obtained when matched with a Li metal counter electrode. They also exhibit excellent electrochemical properties as an anode material for aqueous rechargeable lithium batteries. Sn-doped LiTi2(PO4)3/C composite nanofibers are promising electrode materials for both nonaqueous and aqueous lithium ion batteries.

Porous LiMnPO4/C composite nanofibers between 150 and 250 nm have been synthesized as a cathode material for lithium ion batteries via electrospinning. The porous LiMnPO4/C composite nanofibers show excellent electrochemical performance including a high reversible capacity of 112.7 mA h g−1 at 0.2C, a stable cycle retention of 95% after 100 cycles at 1C, and excellent rate capability (73.1 mA h g−1 at 5C) in constant current mode between 2.0 and 4.5 V. These improved electrochemical properties are attributed to the one-dimensional geometry and porous structure, which significantly enhanced kinetics associated with electrons and Li ions.

We report the fabrication of 3D hierarchical hetero-nanostructures composed of thin α-Fe2O3 nanoflakes branched on TiO2 nanotubes. The novel α-Fe2O3/TiO2 hierarchical nanostructures, synthesized on FTO through a multi-step hydrothermal process, exhibit enhanced performances in photo-electrochemical water splitting and in the photocatalytic degradation of an organic dye, with respect to pure TiO2 nanotubes. An enhanced separation of photogenerated charge carriers is here proposed as the main factor for the observed photo-activities: electrons photogenerated in TiO2 are efficiently collected at FTO, while holes are transferred to the α-Fe2O3 nanobranches that serve as charge mediators to the electrolyte. The morphology of α-Fe2O3 that varies from ultrathin nanoflakes to nanorod/nanofiber structures depending on the Fe precursor concentration was shown to have a significant impact on the photo-induced activity of the α-Fe2O3/TiO2 composites. In particular, it is shown that for an optimized photo-electrochemical structure, a combination of critical factors should be achieved such as (i) TiO2 light absorption and photo-activation vs. α-Fe2O3-induced shadowing effect and (ii) the availability of free TiO2 surface vs. α-Fe2O3-coated surface. Finally, theoretical analysis, based on DFT calculations, confirmed the optical properties experimentally determined for the α-Fe2O3/TiO2 hierarchical nanostructures. We anticipate that this new multi-step hydrothermal process can be a blueprint for the design and development of other hierarchical heterogeneous metal oxide electrodes suitable for photo-electrochemical applications.

The inherently low electrical conductivity of TiO2-based electrodes as well as the high electrical resistance between an electrode and a current collector represents a major obstacle to their use as an anode for lithium ion batteries. In this study, we report on high-density TiO2 nanotubes (NTs) branched onto a carbon nanofiber (CNF) “tree” that provide a low resistance current path between the current collector and the TiO2 NTs. Compared to a TiO2 NT array grown directly on the current collector, the branched TiO2 NTs tree, coupled with the CNF electrode, exhibited ∼10 times higher areal energy density and excellent rate capability (discharge capacity of ∼150 mA·h·g−1 at a current density of 1,000 mA·g−1). Based on the detailed experimental results and associated theoretical analysis, we demonstrate that the introduction of CNFs with direct electric contact with the current collector enables a significant increase in areal capacity (mA·h·cm−2) as well as excellent rate capability.

We demonstrate one-step gold nanoparticle (AuNP) coating and the surface nitridation of TiO2 nanowires (TiO2-NWs) to amplify visible-light photon reflection. The surface nitridation of TiO2-NW arrays maximizes the anchoring of AuNPs, and the subsequent reduction of the band gap energy from 3.26 eV to 2.69 eV affords visible-light activity. The finite-difference time-domain (FDTD) simulation method clearly exhibits the enhancement in the strengths of localized electric fields between AuNPs and the nanowires, which significantly improves the photocatalytic (PC) performance. Both nitridation and AuNP decoration of TiO2-NWs result in beneficial effects of high (e−/h+) pair separation through healing of the oxygen vacancies. The combined effect of harvesting visible-light photons and reducing recombination in Au/N-doped TiO2-NWs promotes the photocatalytic activity towards degradation of methyl orange to an unprecedented level, ∼4 fold (1.1 × 10−2 min) more than does TiO2-NWs (2.9 × 10−3 min−1). The proposed AuNP decoration of nitridated TiO2-NW surfaces can be applied to a wide range of n-type metal oxides for photoanodes in photocatalytic applications.

Spinel lithium titanate (Li4Ti5O12) has attracted great interest as an anode material for lithium ion batteries due to its safe operation, low cost, and zero-strain effect during Li insertion/extraction. However, the poor rate capability caused by low electronic conductivity limits its practical use. We synthesized surface functionalized one-dimensional (1D) Li4Ti5O12 nanofibers using simple electro-spinning and subsequent nitridation process. Uniformly coated conducting TiN/TiOxNy layer on the surface of Li4Ti5O12 nanofiber enables fast electron transport along its one dimensional geometry, which leads to significant improvement in rate capability. Nitridated Li4Ti5O12 nanofibers electrode delivers about 1.35 times larger discharge capacity than that of pristine nanofibers electrode at a current density of 10 C.

Hybrid nanofibers of polyaniline/polyoxometalate are synthesized via a facile interfacial polymerization method for the first time, and evaluated as a cathode material for lithium ion batteries. The hybrid nanofibers with 100 nm diameter consisted of phosphomolybdic acid polyanion, [PMo12O40]3–, and polyaniline matrix. Their 1D geometry improves the utilization of electrode materials and accommodates the volume change during cycling, which enables the significant improvement in lithium storage capacity and capacity retentions. The phosphomolybdic acid polyanions not only exhibit a large theoretical capacity of about 270 mAh g–1, but also reduce the charge transfer resistance of electrode leading to the enhanced reversible capacity and rate capability. The polyaniline/polyoxometalate nanofibers delivered a remarkably improved electrochemical performance in terms of lithium storage capacity (183.4 mAh g–1 at 0.1C rate), cycling stability (80.7% capacity retention after 50 cycles), and rate capability (94.2 ...

Tin oxide (SnO2) is a promising candidate as an anode for lithium ion batteries because of its high theoretical capacity. However, poor capacity retention caused by large volume changes during cycling, large initial irreversible capacity, and low rate capability frustrate its practical application. We have developed a ternary nanocomposite based on tin indium oxide (SnO2–In2O3) and graphene nanosheet (GNS) synthesized via a facile solvothermal method. The incorporation of In2O3 into SnO2 can improve the electrochemical property of SnO2 and reduce the charge transfer resistance of electrode leading to the enhanced reversible capacity and rate capability. The graphene nanosheet in the composite electrode can accommodate high volume expansion/contraction during cycling resulting in excellent capacity retention. As an anode for lithium ion batteries, the SnO2–In2O3/GNS nanocomposite exhibits a remarkably improved electrochemical performance in terms of lithium storage capacity (962 mAh g−1 at 60 mA g−1 rate), initial coulombic efficiency (57.2%), cycling stability (60.8% capacity retention after 50 cycles), and rate capability (393.25 mAh g−1 at 600 mA g−1 rate after 25 cycles) compared to SnO2/GNS and pure SnO2–In2O3 electrode.

Problems related to tremendous volume changes associated with cycling and the low electron conductivity and ion diffusivity of Si represent major obstacles to its use in high-capacity anodes for lithium ion batteries. We have developed a group IVA based nanotube heterostructure array, consisting of a high-capacity Si inner layer and a highly conductive Ge outer layer, to yield both favorable mechanics and kinetics in battery applications. This type of Si/Ge double-layered nanotube array electrode exhibits improved electrochemical performances over the analogous homogeneous Si system, including stable capacity retention (85% after 50 cycles) and doubled capacity at a 3C rate. These results stem from reduced maximum hoop strain in the nanotubes, supported by theoretical mechanics modeling, and lowered activation energy barrier for Li diffusion. This electrode technology creates opportunities in the development of group IVA nanotube heterostructures for next generation lithium ion batteries.

Here, a Sb-doped SnO2 (ATO) nanorod underneath an α-Fe2 O3 nanorod sheathed with TiO2 for photoelectrochemical (PEC) water splitting is reported. The experimental results, corroborated with theoretical analysis, demonstrate that the ATO nanorod underlayer effect on the α-Fe2 O3 nanorod sheathed with TiO2 enhances the PEC water splitting performance. The growth of the well-defined ATO nanorods is reported as a conductive underlayer to improve α-Fe2 O3 PEC water oxidation performance. The α-Fe2 O3 nanorods grown on the ATO nanorods exhibit improved performance for PEC water oxidation compared to α-Fe2 O3 grown on flat fluorine-doped tin oxide glass. Furthermore, a simple and facile TiCl4 chemical treatment further introduces TiO2 passivation layer formation on the α-Fe2 O3 to reduce surface recombination. As a result, these unique nanostructures show dramatically improved photocurrent density (139% higher than that of the pure hematite nanorods).

Facile synthesis of TiO2 nanotube branched (length [similar]0.5 μm) thin hollow-nanofibers is reported. The hierarchical three dimensional photoanodes (H-TiO2-NFs) (only [similar]1 μm thick) demonstrate their excellent candidature as photoanodes in QD-sensitized solar cells, exhibiting [similar]3-fold higher energy conversion efficiency (η = 2.8%, Jsc = 8.8 mA cm−2) than that of the directly grown nanotube arrays on a transparent conducting oxide (TCO) substrate (η = 0.9%, Jsc = 2.5 mA cm−2).

TiO2 hollow nanowires (HNWs) and nanoparticles (NPs) constitute promising architectures for QDs sensitized photoanodes for H2 generation. We sensitize these structures with CdS/CdSe quantum dots by two different methods (chemical bath deposition, CBD and succesive ionic layer adsorption and reaction, SILAR) and evaluate the performance of these photoelectrodes. Remarkable photocurrents of 4 mA·cm and 8 mA·cm−2 and hydrogen generation rates of 40 ml·cm−2·day−1 and 80 ml·cm−2·day−1 have been obtained in a three electrode configuration with sacrificial hole scavengers (Na2S and Na2SO3), for HNWs and NPs respectively, which is confirmed through gas analysis. More importantly, autonomous generation of H2 (20 ml·cm−2·day−1 corresponding to 2 mA·cm−2 photocurrent) is obtained in a two electrode configuration at short circuit under 100 mW·cm−2 illumination, clearly showing that these photoanodes can produce hydrogen without the assistance of any external bias. To the best of the authors' knowledge, this is the highest unbiased solar H2 generation rate reported for these of QDs based heterostructures. Impedance spectroscopy measurements show similar electron density of trap states below the TiO2 conduction band while the recombination resistance was higher for HNWs, consistently with the much lower surface area compared to NPs. However, the conductivity of both structures is similar, in spite of the one dimensional character of HNWs, which leaves some room for improvement of these nanowired structures. The effect of the QDs deposition method is also evaluated. Both structures show remarkable stability without any appreciable photocurrent loss after 0.5 hour of operation. The findings of this study constitute a relevant step towards the feasibility of hydrogen generation with wide bandgap semiconductors/quantum dots based heterostructures.

Titanium dioxide (TiO(2)) is one of the most promising anode materials for lithium ion batteries due to low cost and structural stability during Li insertion/extraction. However, its poor rate capability limits its practical use. Although various approaches have been explored to overcome this problem, previous reports have mainly focused on the enhancement of both the electronic conductivity and the kinetic associated with lithium in the composite film of active material/conducting agent/binder. Here, we systematically explore the effect of the contact resistance between a current collector and a composite film of active material/conducting agent/binder on the rate capability of a TiO(2)-based electrode. The vertically aligned TiO(2) nanotubes arrays, directly grown on the current collector, with sealed cap and unsealed cap, and conventional randomly oriented TiO(2) nanotubes electrodes were prepared for this study. The vertically aligned TiO(2) nanotubes array electrode with unsealed cap showed superior performance with six times higher capacity at 10 C rate compared to conventional randomly oriented TiO(2) nanotubes electrode with 10 wt % conducting agent. On the basis of the detailed experimental results and associated theoretical analysis, we demonstrate that the reduction of the contact resistance between electrode and current collector plays an important role in improving the electronic conductivity of the overall electrode system.

Nanoparticulate SnO2 was encapsulated into TiO2 hollow nanofibers to achieve high energy density and robust electrochemical performance as an anode material for lithium ion batteries. The SnO2 encapsulated TiO2 hollow nanofibers exhibit improved electrochemical performances over the TiO2 hollow nanofibers, including a high discharge capacity of ~517 mAh g−1 and doubled capacity at a 10 C rate. These improvements on electrochemical performances are attributed to favorable mechanics and kinetics associated with lithium. Keywords: Lithium ion batteries, Anode, SnO2, TiO2

Robust composite nanofibers (NFs) are prerequisite for highly efficient electrochemical sensors. We report the electrochemical application of gold nanoparticle (Au NP)-composite Nafion NFs using a facile electrospinning technique. Owing to the uniform distribution and large surface area of the Au NPs in the NFs, the Au NP-composite electrodes gave rise to greatly improved electrochemical properties, compared to AuNP-free composite electrodes. When they were employed as reservoirs for immobilizing horseradish peroxidase (HRP), reliable and sensitive electrochemical detection by the enzyme reaction was achieved. The detection sensitivity for H2O2 was determined to be as low as 38 nM, which was one order higher than that of previous electrochemical sensors. In addition, there was no change in the enzyme stability over three weeks. In this regard, the developed NP/NF-based electrochemical sensors are anticipated to be very suitable for monitoring other enzyme reactions with high sensitivity and stability.

Germanium holds great potential as an anode material for lithium ion batteries due to its large theoretical energy density and excellent intrinsic properties related to its kinetics associated with lithium and electrons. However, the problem related to the tremendous volume change of Ge during cycling is the dominant obstacle for its practical use. The previous research has focused on the improvement in mechanics associated with lithium without consideration of the kinetics. In this study, we demonstrate that the configuration engineering of the Ge electrode enables the improvement in kinetics as well as favorable mechanics. Two types of Ge inverse opal structures with porous walls and dense walls were prepared using a confined convective assembly method and by adjusting Ge deposition parameters in a chemical vapor deposition system. The Ge inverse opal electrode with porous walls shows much improved electrochemical performances, especially cycle performance and rate capability, than the electrode with dense walls. These improvements are attributed to a large free surface, which offers a facile strain relaxation pathway and a large lithium flux from the electrolyte to the active material.

TiO2 nanofibers, TiO2 hollow nanofibers, and nitridated TiO2 hollow nanofibers were synthesized using a simple electrospinning method and subsequent nitridation treatment. The nitridated TiO2 hollow nanofibers showed twice higher rate capability compared to that of pristine TiO2 nanofibers at 5 C. This improvement is mainly attributed to shorter lithium ion diffusion length and high electronic conductivity along the surface of nitridated hollow nanofibers.

Si nanowires (SiNWs)–carbon nanofibers (CNFs) branched structures with variation in carbon densities were synthesized. SiNWs with critical density of CNFs show the best electrochemical performance, which is attributed to increase in free volume around the SiNWs as well as a buffering role of the branched CNFs against large volumetric change during cycling.