Diffusion Path Length Research Articles

Electrodeposited Magnesium Nanoparticles Linking Particle Size to Activation Energy

The kinetics of hydrogen absorption/desorption can be improved by decreasing particle size down to a few nanometres. However, the associated evolution of activation energy remains unclear. In an attempt to clarify such an evolution with respect to particle size, we electrochemically deposited Mg nanoparticles on a catalytic nickel and noncatalytic titanium substrate. At a short deposition time of 1 h, magnesium particles with a size of 68 ± 11 nm could be formed on the nickel substrate, whereas longer deposition times led to much larger particles of 421 ± 70 nm. Evaluation of the hydrogen desorption properties of the deposited magnesium nanoparticles confirmed the effectiveness of the nickel substrate in facilitating the recombination of hydrogen, but also a significant decrease in activation energy from 56.1 to 37.8 kJ·mol−1 H2 as particle size decreased from 421 ± 70 to 68 ± 11 nm. Hence, the activation energy was found to be intrinsically linked to magnesium particle size. Such a reduction in activation energy was associated with the decrease of path lengths for hydrogen diffusion at the desorbing MgH2/Mg interface. Further reduction in particle size to a few nanometres to remove any barrier for hydrogen diffusion would then leave the single nucleation and growth of the magnesium phase as the only remaining rate-limiting step, assuming that the magnesium surface can effectively catalyse the dissociation/recombination of hydrogen.

Ultra-fine SnO2 nanoparticles doubly embedded in amorphous carbon and reduced graphene oxide (rGO) for superior lithium storage

SnO2 is a well-studied anode material for lithium ion batteries (LIBs). However, it undergoes severe capacity fading because of a large volume change (∼300%) during cycling. Composites of SnO2 with electro-conductive graphene would deliver improved capacity and rate performance. Nevertheless, achieving the theoretical capacity of SnO2 is still elusive, mainly because of disintegration of the active material from graphene and severe aggregation of SnO2, or Sn nanoparticles produced upon cycling. To surmount these limitations, in this work, nanocomposites containing ultra-fine sized SnO2 nanoparticles (UFSN) with reduced graphene oxide and amorphous carbon were synthesized in a single step at low temperature and environmentally benign way, in which ascorbic acid was employed as the carbon source and reducing agent. UFSN could decrease the lithium ion diffusion path length. As a result of effective buffering effect afforded by the mesoporous structure against volume change and improved lithium ion diffusivity, the ternary nanocomposite achieves ultra-high capacity of 1245mAhg−1 after 210 cycles at 100mAg−1 and excellent cycling stability. Since the proposed approach is facile, straightforward, and highly reproducible, it is anticipated that this system would be a potential alternative to the conventional graphite anode for LIBs.

Capacitive storage performance of nanorod assembly of polyaniline

Herein, we report a good capacitive storage performance of nanorod assembly of polyaniline (PANI). PANI was synthesized by a facile method using nanostructured γ-MnO2 as a sacrificial template as well as an oxidant. As-synthesized PANI was characterized by powder X-ray diffraction, Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy and surface area analysis. X-ray diffraction and FTIR spectroscopic studies confirmed the formation of PANI. Microscopic studies revealed that the morphology of PANI is spherical brushes comprising of straight and radially grown nanorods of different lengths. Capacitive storage performance of PANI was studied in a mixed perchlorate electrolyte consisting of HClO4 and NaClO4. A specific capacitance of 394 F g−1 with good rate capability was obtained for nanorod assembly of PANI. The improved storage performance of PANI is attributed to its morphology, which provides easy access to the electrolyte and short diffusion path length for ions.

Microsized Porous SiOx@C Composites Synthesized through Aluminothermic Reduction from Rice Husks and Used as Anode for Lithium-Ion Batteries.

Microsized porous SiOx@C composites used as anode for lithium-ion batteries (LIBs) are synthesized from rice husks (RHs) through low-temperature (700 °C) aluminothermic reduction. The resulting SiOx@C composite shows mesoporous irregular particle morphology with a high specific surface area of 597.06 m2/g under the optimized reduction time. This porous SiOx@C composite is constructed by SiOx nanoparticles uniformly dispersed in the C matrix. When tested as anode material for LIBs, it displays considerable specific capacity (1230 mAh/g at a current density of 0.1 A/g) and excellent cyclic stability with capacity fading of less than 0.5% after 200 cycles at 0.8 A/g. The dramatic volume change for the Si anode during lithium-ion (Li+) insertion and extraction can be successfully buffered because of the formation of Li2O and Li4SiO4 during initial lithiation process and carbon coating layer on the surface of SiOx. The porous structure could also mitigate the volume change and mechanical strains and shorten the Li+ diffusion path length. These characteristics improve the cyclic stability of the electrode. This low-cost and environment-friendly SiOx@C composite anode material exhibits great potential as an alternative for traditional graphite anodes.

Quantifying the Role of Transition Metal (Re)Plating in the Cathodic Activation of Corroding Magnesium

Magnesium (Mg) and magnesium-based alloys as biodegradable implants form a distinct pole of attraction for the scientific world due to their advantages over conventional biodegradable metallic materials. Regardless, though, of the promising properties that magnesium offers, its extensive use in vivo is restricted with the main limiting factor to be its high rate of degradation. This paper examines the effect that the transition metals, which have been intentionally or unintentionally added as traces within the metal bulk composition, have on the corrosion properties of commercially high purity magnesium. Furthermore, a series of experiments provide an indication regarding the ability of the selected transition metals to accelerate corrosion through the process of (re)plating aiming to gain an insight on the Mg corrosion activation described in recent publications. Consequently, the current research presents the kinetics involved behind the role of the transition metals in the cathodic activation of corroding magnesium. During the experimental procedure, high purity magnesium samples containing <80ppm Fe were used, while the kinetics of the effect of Fe2+, Cu2+, Zn2+ and Mn2+ transition metal ions were studied as these are the most common traces of addition alloying or impurities found within the bulk composition of magnesium and magnesium alloys. The transition metals were either added into a corrosive electrolyte of 5% aqueous NaCl at near neutral pH at concentrations ranging from 10-6M to 8·10-3M or they were injected in solid form directly on the immediate vicinity of the corroding surface at a weight range of 5mg to 50mg. Following this step was the volumetrically recording of the evolution of hydrogen gas over a constant period of time in order to follow the kinetics of magnesium corrosion. The results indicate that the presence of transition metal ions within the solution leads to transition metal (re)plating and to an increase of the magnesium corrosion rate. Furthermore, by systematically varying the transition metal ion concentration it was possible to determine the relative efficiencies of the selected metal cations. During the experiment, it was also observed that the metal (re)plating process and the efficiency of the cathodic activation were limited by the formation of insoluble transition metal (hydr)oxide precipitates and the time-dependent hydrolysis. It was possible, though, to minimize the negative effect of hydrolysis by introducing the metal cations directly on the magnesium surface as it may be assumed then that both the diffusion path length and the time period during which hydrolysis can initiate are shorter.

Novel Potassium Titanate As Potential Anodes for Sodium Ion Battery

Sodium ion batteries (SIBs) have been intensively investigated as a low cost alternative for lithium ion batteries due to the abundance of sodium ion on the earth and its similar chemical properties to lithium.[1] Taking low cost, wide abundance and high security into consideration, titanium based intercalation materials should be the most promising choice for their low redox potential (Ti3+/Ti4+) relative to the Na+/Na redox potential and abundant reserves among various sodium storage anode materials.[2] In the past few years, researchers have explored many titanium-based materials as potential anode materials for SIBs, such as various TiO2 polymorphs, including anatase, rutile, TiO2-B. Ternary sodium titanates-based materials with related crystal structures also greatly enrich the kinds of anode materials. While, the practical application of Ti-based anodes in SIBs is severely hindered by their inferior rate capabilities and relatively low capacity resulting from both extremely poor electronic conductivity and sluggish sodium ion diffusion. Here, we proposed K2Ti6O13 with an analogue tunnel structure with Na2Ti6O13 as a new anode for sodium ion batteries.[3] And by a soft chemistry method, we can successfully get ultrafine K2Ti6O13 nanowires with a diameter of only 5-10 nm, which grow perpendicularly to the tunnel direction. The ultrafine nanowires greatly shorten the diffusion path length of Na-ion and endow K2Ti6O13 a remarkably improved reactivity as shown in Fig.1. This new titanium based anode material exhibits a high charge capacity of 186 mAh g-1 at 20 mA g-1 and excellent rate performance of 61 mAh g-1 at 1000 mA g-1. The capacity is nearly 3 times that of the bulk phase. This suggests that shortening the diffusion length especially in the diffusion direction by design nanostructure is very important to promote the reactivity of Ti-based material for sodium storage. Furthermore, we introduce Ti3+ into this Ti-based material to enhance the inherent electronic conductivity. We synthesized the hollandite-type KxTiO2 nanorod by a facile carbothermal reduction method and used it as a new sodium ion anode. The as-prepared hollandite-type KxTiO2 shows uniform nanorod of 50 nm with a carbon coating. The carbon can not only partially reduce the Ti (IV) of the precursor to Ti (III), but also limit the particle-size growth to some extent during the heat treatment process. Morever, the carbon coating could also efficiently improve the conductivity of the active materials. This new material can deliver about 135 mAh g-1 at 20 mA g-1 and exhibit great rate capability with 67 mAh g-1 at 1000 mA g-1. It is obvious that these new potassium titanates with the high capacity and excellent rate performance can serve as potential sodium ion anodes.

Adsorption of phenol in flow systems by a monolithic carbon cryogel with a microhoneycomb structure

Adsorption of phenol from an aqueous solution in batch and continuous flow systems using carbon gels with a microhoneycomb structure (carbon gel microhoneycombs, CMHs) was studied. The obtained monolithic CMHs had fairly straight channels, 25–45 μm in diameter, and the thickness of the walls which form the channels was around 5 μm. The CMHs showed 370 times lower hydraulic resistance when compared with a column packed with particles having the same diffusion path length as it. The obtained CMHs have a hierarchical micro-meso porous structure giving BET surface area in the range of 513–1070 m2·g−1.When used for phenol adsorption from an aqueous solution, the CMHs quickly adsorbed phenol at first, and then, the uptake gradually increased, which indicates that the adsorption mechanism is based on not only simple physisorption. The phenol adsorption capacity increased with the increase in carbonization temperature of the CMH and the decrease in its hydrophilicity. CMHs carbonized at temperatures higher than 1073 K showed the highest phenol adsorption capacity which was around 160 mg·g−1. The CMHs could continuously adsorb phenol from aqueous solutions, and their length of unused bed (LUB) values depended on operation conditions but were in the range of 0.3–0.7 cm. The experimental results indicated that carbon cryogels with a microhoneycomb structure have a high potential to be used for effective separation of phenol.

Three-Dimensional Oxygen-Deficient Li4Ti5O12 Nanospheres as High-Performance Anode for Lithium Ion Batteries

The poor electrical conductivity of lithium titanate (Li4Ti5O12) has limited its practical application as high rate performance anode for lithium ion batteries. Having this in mind, we utilize the oxygen vacancy strategy to improve the electrical conductivity of Li4Ti5O12 nanospheres by synthesizing three-dimensional (3D) oxygen-deficient Li4Ti5O12 on a titanium mesh from Ti3+-doped anatase TiO2. When the oxygen-deficient Li4Ti5O12 nanospheres are used as anode material for high-rate lithium ion batteries, the electrode exhibits excellent lithium storage performance delivering a capacity of 143mAhg−1 at a current density of 100C. The outstanding performance is due to the 3D architecture from the 3D substrates with large space and increased surface area that facilitate rapid transfer of lithium ion and small diameter of nanospheres, which provides shorter diffusion path-length.

Enhanced High Rate Performance of a NaTi2(PO4)3/Reduced Graphene Oxide Composite Electrode Via Pyro Synthesis for Sodium Ion Batteries

The present study reports on a highly rate capable NASICON-structured NaTi2(PO4)3/ reduced graphene oxide (NTP/rGO) composite electrode synthesized by polyol-assisted pyro synthesis for Na-ion batteries (NIBs). X-ray diffraction (XRD) studies confirmed the presence of a rombohedral NaTi2(PO4)3 phase in the composite while Raman spectroscopy studies helped to identify the existence of rGO in the composite. Electron microscopy studies established that NaTi2(PO4)3 nanoparticles of average sizes ranging between 20 and 30 nm were uniformly distributed and embedded on the GO sheets. When tested for sodium storage properties, the obtained NTP/rGO composite electrode registered high rate capacities (95 mAh g-1 at 9.2 C and 78 mAh g-1 at 36.8 C) when compared to that of the NTP/C electrode (~1 mAh g-1 at 9.2 and 36.8 C). The enhanced performance of the composite electrode can be attributed to the nano-sized NaTi2(PO4)3 particles with shorter diffusion path lengths embedded on the rGO sheets with enhanced electrolyte/electrode contact areas that ultimately leads to an improvement in the electrical conductivity at high current densities. Ex-situ XANES studies confirmed reversible Na-ion intercalation/de-intercalation into/from NTP/rGO. The study thus demonstrates that the NaTi2(PO4)3/rGO nanocomposite electrode is a promising candidate for the development of high power/energy density anodes for NIBs.

Synthesis of Wool-Ball-Like ZSM-5 with Enlarged External Surfaces and Improved Diffusion: A Potential Highly-Efficient FCC Catalyst Component for Elevating Pre-cracking of Large Molecules and Catalytic Longevity

A hierarchical ZSM-5 zeolite composed of nano-sized MFI zeolite crystals was synthesized without using secondary template by a traditional hydrothermal procedure. The as-synthesized hierarchical ZSM-5 and a reference catalyst were both characterized by XRD, SEM, FT-IR, in situ infrared (IR) spectrometry of pyridine, NH3-TPD, N2 adsorption–desorption, intelligent gravimetric analyzer, and by thermogravimetry analyses. After examining and comparing the results, it is discovered that the hierarchical ZSM-5 catalyst displays excellent catalytic performance with an improved conversion of isopropylbenzene and a longer catalytic life because of its dramatically enlarged external surfaces. The results also display that the shortened diffusion path length contributes to enhancing the stability of the hierarchical catalyst by depressing the coking deposit during the catalytic cracking of n-octane. A wool-ball-like zeolite composed of nano-sized MFI crystals was synthesized without a secondary template by the traditional hydrothermal procedure. Nanocrystallization of crystal particles in the hierarchical ZSM-5 zeolite gives the catalyst an improved diffusion and a dramatically enhanced external surface which contributes to elevating pre-cracking of large molecules and catalytic longevity, and to offering a potential and high-efficiency FCC catalyst component.

Disordered spinel LiNi0.5Mn1.5O4 cathode with improved rate performance for lithium-ion batteries

The high voltage LiNi0.5Mn1.5O4 cathode with a disordered spinel structure is synthesized by a glycine-assisted low-temperature reaction follows by a thermal treatment at 750°C, 850°C, and 950°C for 12h. Glycine is used as a chelating agent for the first time to build required environment for shaping the precursor of LiNi0.5Mn1.5O4 materials. The microstructure and morphology of the LiNi0.5Mn1.5O4 product are characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, Brunauer-Emmett-Teller, and transmission electron microscopy. The sample prepares at 750°C reveals small particles with well-defined crystals as confirmed by electron microscopy. Electrochemical results demonstrate that LiNi0.5Mn1.5O4 electrode anneal at 750°C (compare to other two samples) delivers the highest reversible capacity of 110mAhg−1 at 0.2C after 100 cycles with good rate capability. The enhanced electrochemical performance could be attributed to the smaller particle sizes as well as well-defined crystals which provide a directional and shorter diffusion path length for Li+ transportation within the crystals.

Electrochemical Deposition of Cu2O Thin Film As Efficient Photocatalyst for Water Splitting Reaction

Solar water splitting can form the basis of a sustainable hydrogen based energy economy, however the system requires optimisation in terms of cost and performance on a scale commensurate with the global energy demand. Photocatalysts consist of solar spectrum absorber semiconductor materials and co-catalysts as the redox mediator for hydrogen and oxygen evolution reactions. The key factors for efficient solar water splitting process to occur with such photocatalysts are a semiconductor with a sufficiently narrow band gap to absorb visible lights, a suitable thermodynamic potential for the redox reactions, and stability against photocorrosion. However, current photocatalysts also suffer from undesirable photoelectron-hole (charge carrier) recombination within the semiconductor due to their short diffusion path lengths and lifetimes, which results in fewer than 10% of the incident photons being used for water splitting. Cuprous Oxide (Cu2O), one of the few naturally occurring p-type metal oxides, is the most promising candidate for an efficient photocathode because of its earth abundance, a band gap of 2.0 eV, which enables efficient visible light absorption, a scalable CMOS compatible deposition technique (e.g., electrodeposition), and favourable energy band position i.e. conduction band lies 0.7 eV negative of the hydrogen evolution potential that drives off half of the water reduction reaction without of any external bias. However, the application of Cu2O as photocathode is limited by two drawbacks; fast photoelectron–hole recombination owing to short carrier diffusion length and self-photo corrosion in aqueous solution under illumination since the potentials of Cu2O reduction and oxidation to metallic Cu and CuO, respectively, lie within the bandgap. Hence, the solar-to-fuel conversion efficiency on Cu2O depends on how fast the photoelectron can be extracted to the reduction reaction sites and inhibition of electrolyte access to Cu2O surface. A thin protective coating and a heterostructure in the seed layer of the electrochemically deposited Cu2O film enhance the overall photocatalytic performance versus the Cu2O film alone. The thickness of the Cu2O film was optimised to avoid the charge carrier recombination towards the efficient and stable photocatalytic performance. The photocatalytic performance of Cu2O thin film is shown in Fig 1, in which the film performance is unexpectedly high and only dropped to 22% after the first cycle at 0.0 VRHE, after which it stabilises. This presentation will discuss our current research to develop cheap and efficient photocatalysts and their enhancement mechanism towards photocatalytic water splitting reactions. Figure 1

Numerical simulation of nonlinear chromatography with core–shell particles applying the general rate model

Core–shell particles allow highly efficient and fast separation of complex samples. They provide advantages over fully porous particles, such as highly efficient separation with fast flow rate due to shorter diffusional path length in particle macropores. On the other hand, capacities are reduced due to the inert core. This work is focused on the numerical approximation of a nonlinear general rate model for fixed-beds packed with core–shell particles. The model equations consider axial dispersion, interfacial mass transfer, intraparticle diffusion, and multi-component Langmuir isotherm. A semi-discrete high resolution flux-limiting finite volume scheme is proposed to accurately and efficiently solve the model equations. The scheme is second order accurate in axial and radial coordinates. The resulting system of ordinary differential equations (ODEs) are solved by using a second-order TVD Runge–Kutta method. For illustration, a few selected scenarios of single solute and multi-component elution bands are generated to study theoretically the effects of the core radius fractions on the course of elution curves. Typically applied performance criteria are evaluated for identifying ranges of optimum values of the core radius fraction.

Comparative Electrochemical Charge Storage Properties of Bulk and Nanoscale Vanadium Oxide Electrodes

Vanadium oxide nanostructures have been widely researched as a cathode material for Li-ion batteries due to their layered structure and shorter Li+ diffusion path lengths, compared to the bulk material. Some oxides exhibit charge storage due to capacitive charge compensation, and many materials with cation insertion regions and rich surface chemistry have complex responses to lithiation. Herein, detailed analysis by cyclic voltammetry was used to distinguish the charge stored due to lithium intercalation processes from extrinsic capacitive effects for micron-scale bulk V2O5 and synthesized nano-scale vanadium oxide polycrystalline nanorods (poly-NRs), designed to exhibit multivalent surface oxidation states. The results demonstrate that at fast scan rates (up to 500 mV/s), the contributions due to diffusion-controlled intercalation processes for micron-scale V2O5 and nanoscale V2O3 are found to dominate irrespective of size and multivalent surface chemistry. At slow potential scan rates, a greater portion of the redox events are capacitive in nature for the polycrystalline nanorods. Low dimensional vanadium oxide structures of V2O5 or V2O3, with greater surface area do not automatically increase their (redox) pseudocapacitive behaviour significantly at any scan rate, even with multivalent surface oxidation states.

Synthesis and electrochemical performance of hole-rich Li4Ti5O12 anode material for lithium-ion secondary batteries

Hole-rich Li4Ti5O12 composites are synthesized by spray drying using carbon nanotubes as additives in precursor solution, subsequently followed calcinated at high temperature in air. The structure, morphology, and texture of the as-prepared composites are characterized with XRD, Raman, BET and SEM techniques. The electrochemical properties of the as-prepared composites are investigated systematically by charge/discharge testing, cyclic voltammograms and AC impedance spectroscopy, respectively. In comparison with the pristine Li4Ti5O12, the hole-rich Li4Ti5O12 induced by carbon nanotubes exhibits superior electrochemical performance, especially at high rates. The obtained excellent electrochemical performances of should be attributed to the hole-rich structure of the materials, which offers more connection-area with the electrolyte, shorter diffusion-path length as well faster migration rate for both Li ions and electrons during the charge/discharge process.

Structured carbons as supports for hydrogenation hybrid catalysts prepared by the immobilization of a Rh diamine complex

A CNF-monolith sample (carbon nanofibres grown on a ceramic monolith), and a granular carbon xerogel have been used as supports for hybrid catalysts where the active species is an Rh diamine complex. The advantages of these supports are their open porous structure and their morphology, which make catalyst handling easier and avoid difficult separation processes. The obtained catalysts are noticeably more active than the homogeneous Rh complex and are stable against leaching. At first use, partial reduction of the Rh complex takes place and nanometer-sized Rh particles develop, which increases the catalyst activity. Despite the open porous structure, mass transport limitations are present, especially in the case of the carbon xerogel based catalyst. Differences in internal mass transfer limitations are essentially due to the different diffusional path lengths.

Self-Assembled Graphene/Polyaniline/Co3O4 Ternary Hybrid Aerogels for Supercapacitors

A novel three-dimensional (3D) porous graphene/polyaniline/Co3O4 (GPC) ternary hybrid aerogels is firstly fabricated via self-assembly of graphene oxide/polyaniline (GO/PANI) by in situ polymerization and GO/cobalt salts hybrid sols through hydrothermal treatment. The prepared ternary hybrid aerogels features an interconnected 3D macroporous structure in which PANI/Co3O4 nanoparticles (PANI/Co3O4 NPs) with a diameter ∼ 20nm uniformly distributed on the surface of graphene nanosheets (GNs), and possesses an excellent performance with high specific capacitance of 1247Fg−1at a current density of 1Ag−1 and the capability can reach to 755Fg−1 even at 20Ag−1. Furthermore, no obvious capacitance loss is observed during 3500 cycles, indicating an outstanding cycling stability. The extraordinary electrochemical performance of the 3D GPC hybrid can be attributed to not only the high capacitance of PANI and Co3O4 with pseudocapacitive, but also the strong synergistic effect between the uniformly dispersed PANI/Co3O4 NPs and graphene aerogel, in which a powerful 3D porous structure with short diffusion path length for fast electron transportation.

The reaction current distribution in battery electrode materials revealed by XPS-based state-of-charge mapping.

Morphologically complex electrochemical systems such as composite or nanostructured lithium ion battery electrodes exhibit spatially inhomogeneous internal current distributions, particularly when driven at high total currents, due to resistances in the electrodes and electrolyte, distributions of diffusion path lengths, and nonlinear current-voltage characteristics. Measuring and controlling these distributions is interesting from both an engineering standpoint, as nonhomogenous currents lead to lower utilization of electrode material, as well as from a fundamental standpoint, as comparisons between theory and experiment are relatively scarce. Here we describe a new approach using a deliberately simple model battery electrode to examine the current distribution in a electrode material limited by poor electronic conductivity. We utilize quantitative spatially resolved X-ray photoelectron spectroscopy to measure the spatial distribution of the state-of-charge of a V2O5 model electrode as a proxy measure for the current distribution on electrodes discharged at varying current densities. We show that the current at the electrode-electrolyte interface falls off with distance from the current collector, and that the current distribution is a strong function of total current. We compare the observed distributions with a simple analytical model which reproduces the dependence of the distribution on total current, but fails to predict the correct length scale. A more complete numerical simulation suggests that dynamic changes in the electronic conductivity of the V2O5 concurrent with lithium insertion may contribute to the differences between theory and experiment. Our observations should help inform design criteria for future electrode architectures.

Hollow Silica Spheres Embedded in a Porous Carbon Matrix and Its Superior Performance as the Anode for Lithium‐Ion Batteries

Silica (SiO2) is regarded as one of the most promising anode materials for lithium‐ion batteries due to the high theoretical specific capacity and extremely low cost. However, the low intrinsic electrical conductivity and the big volume change during charge/discharge cycles result in a poor electrochemical performance. Here, hollow silica spheres embedded in porous carbon (HSS–C) composites are synthesized and investigated as an anode material for lithium‐ion batteries. The HSS–C composites demonstrate a high specific capacity of about 910 mA h g−1 at a rate of 200 mA g−1 after 150 cycles and exhibit good rate capability. The porous carbon with a large surface area and void space filled both inside and outside of the hollow silica spheres acts as an excellent conductive layer to enhance the overall conductivity of the electrode, shortens the diffusion path length for the transport of lithium ions, and also buffers the volume change accompanied with lithium‐ion insertion/extraction processes.

Cerium-doped porous K-birnessite manganese oxides microspheres as pseudocapacitor electrode material with improved electrochemical capacitance

Cerium-doped nanosheet-based porous δ-MnO2 microspheres have been successfully prepared via a simple hydrothermal process. Electrochemical measurements showed that appropriate amount of cerium doping can significantly increase the speicific capacitance of δ-MnO2. It is found that 1.5% cerium-doped manganese oxides exhibit the best specific capacitance of 382.38Fg−1 at a current density of 1Ag−1. In terms of ion transport kinetics, cerium doping can shorten the diffusion path length and increase the ion transfer rate by changing the partical size, porosity density and conductivity of manganese oxides materials.