On the correlation between mechanical flexibility, nanoscale structure, and charge storage in periodic mesoporous CeO(2) thin films

Efficient optimization of the synthetic conditions for aerosol-assisted high-quality mesoporous CeO2 powders

The morphology of surfactant-assisted mesoporous metal oxides was tuned to obtain high surface-area particles by utilizing the synthetic conditions for fabricating transparent thin films through an evaporation-induced self-assembly (EISA) process. For investigating their potential applications, especially for designing heterogeneous catalysts, mesoporous metal oxides should be obtained in powder forms; however, a serious limitation associated with their reproducibility persists. Herein, along with a rapid optimization approach, starting from determining and improving chemical composition for the fabrication of mesoporous metal oxide films, an advanced approach to obtain highly porous metal oxide powders is presented using a temperature-controlled spray-drying process with step-by-step but smooth optimization by combining several EISA processes, involving the utilization of a precursor solution optimized for a slow-drying process in the case of ceria (CeO2) using poly(styrene)-block-poly(ethylene oxide) (PS-b-PEO).

Ordered Mesoporous Crystalline Frameworks Toward Promising Energy Applications

Ordered mesoporous crystalline frameworks (MCFs), which possess both functional frameworks and well-defined porosity, receive considerable attention because of their unique properties including high surface areas, large pore sizes, tailored porous structures, and compositions. Construction of novel crystalline mesoporous architectures that allows for rich accessible active sites and efficient mass transfer is envisaged to offer ample opportunities for potential energy-related applications. In this review, the rational synthesis, unique structures, and energy applications of MCFs are the main focus. After summarizing the synthetic approaches, an emphasis is placed on the delicate control of crystallites, mesophases, and nano-architectures by concluding basic principles and showing representative examples. Afterward, the currently fabricated components of MCFs such as metals, metal oxides, metal sulfides, and metal-organic frameworks are described in sequence. Further, typical applications of MCFs in rechargeable batteries, supercapacitors, electrocatalysis, and photocatalysis are highlighted. This review ends with the possible development and synthetic challenges of MCFs as well as a future prospect for high-efficiency energy applications, which underscores a pathway for developing advanced materials.

Preparation of a CeO2 ball-core structure and its application in quantum dot sensitized solar cells

A pomegranate-like nanosphere structure of CeO₂ was prepared by a simple one-step hydrothermal method, and the novel CeO₂ structure was printed on a TiO₂ film to form a scattering layer, which constituted the composite structure of a photoanode in a thin film optoelectronic device. Then ZnCuInSe quantum dots, a ZnS passivation layer and a CuS counter electrode were prepared, and these parts were assembled into quantum dot-sensitized solar cells. By changing the thickness of the scattering layer film in the photoanode, the quantum dots were adsorbed on TiO₂ more effectively. By using the special ball-core structure, light was scattered so that the photoanode used the light many times, which effectively increased the efficiency of photoelectron production. After electrochemical testing of the device, it was found that the photoconversion efficiencies of the TiO₂ transparent layer and the CeO₂ scattering layer composite photoanode were greater than that of a single TiO₂ photoanode without a scattering layer. The results showed that when the thickness of the scattered layer was 10 ± 1 μm, the highest photoelectric conversion efficiency (PCE) was obtained, which was 20% higher than that seen with TiO₂ alone.

Synergistic effect of intercalation and EDLC electrosorption of 2D/3D interconnected architectures to boost capacitive deionization for water desalination via MoSe2/mesoporous carbon hollow spheres

Transition-metal dichalcogenides can be used for capacitive deionization (CDI) via pseudocapacitive ion intercalation/de-intercalation due to their unique two-dimensional (2D) laminar structure. MoS₂ has been extensively studied in the hybrid capacitive deionization (HCDI), but the desalination performance of MoS₂-based electrodes remains only 20-35 mg g^-1 on average. Benefiting from the higher conductivity and larger layer spacing of MoSe₂ than MoS₂, it is expected that MoSe₂ would exhibit a superior HCDI desalination performance. Herein, for the first time, we explored the use of MoSe₂ in HCDI and synthesized a novel MoSe₂/MCHS composite material by utilizing mesoporous carbon hollow spheres (MCHS) as the growth substrate to inhibit the aggregation and improve the conductivity of MoSe₂. The as-obtained MoSe₂/MCHS presented unique 2D/3D interconnected architectures, allowing for synergistic effects of intercalation pseudocapacitance and electrical double layer capacitance (EDLC). An excellent salt adsorption capacity of 45.25 mg g^- 1 and a high salt removal rate of 7.75 mg g^- 1 min^-1 were achieved in 500 mg L^- 1 NaCl feed solution at an applied voltage of 1.2 V in batch-mode tests. Moreover, the MoSe₂/MCHS electrode exhibited outstanding cycling performance and low energy consumption, making it suitable for practical applications. This work demonstrates the promising application of selenides in CDI and provides new insights for ration design of high-performance composite electrode materials.

Cost-effective akermanite derived from industrial waste for working electrodes in supercapacitor applications

The aim of this study is the synthesis of an akermanite (Ca2MgSi2O7) material by sol–gel method using industrial waste (fly ash (FA) and ground-granulated blast furnace slag (GGBS)) as an initial precursor for the first time.

Rare Earth-Based Nanomaterials for Supercapacitors: Preparation, Structure Engineering and Application

Supercapacitors (SCs) can effectively alleviate problems such as energy shortage and serious greenhouse effect. The properties of electrode materials directly affect the performance of SCs. Rare earth (RE) is known as "modern industrial vitamins", and their functional materials have been listed as key strategic materials. In the past few years, the number of scientific reports on RE-based nanomaterials for SCs has increased rapidly, confirming that adding RE elements or compounds to the host electrode materials with various nanostructured morphologies can greatly enhance their electrochemical performance. Although RE-based nanomaterials have made rapid progress in SCs, there are very few works providing a comprehensive survey of this field. In view of this, a comprehensive overview of RE-based nanomaterials for SCs is provided here, including the preparation methods, nanostructure engineering, compounds, and composites, along with their capacitance performances. The structure-activity relationships are discussed and highlighted. Meanwhile, the future challenges and perspectives are also pointed out. This Review can not only provide guidance for the further development of SCs but also arouse great interest in RE-based nanomaterials in other research fields such as electrocatalysis, photovoltaic cells, and lithium batteries.

In Situ Orthorhombic to Amorphous Phase Transition of Nb2O5 and Its Temperature Effect on Pseudocapacitive Behavior

Niobium pentoxide (Nb₂O₅) represents an exquisite class of negative electrode materials with unique pseudocapacitive kinetics that engender superior power and energy densities for advanced electrical energy storage devices. Practical energy devices are expected to maintain stable performance under real-world conditions such as temperature fluctuations. However, the intercalation pseudocapacitive behavior of Nb₂O₅ at elevated temperatures remains unexplored because of the scarcity of suitable electrolytes. Thus, in this study, we investigate the effect of temperature on the pseudocapacitive behavior of submicron-sized Nb₂O₅ in a wide potential window of 0.01-2.3 V. Furthermore, ex situ X-ray diffraction and X-ray photoelectron spectroscopy reveal the amorphization of Nb₂O₅ accompanied by the formation of NbO via a conversion reaction during the initial cycle. Subsequent cycles yield enhanced performance attributed to a series of reversible Nb^V, IV/Nb^III redox reactions in the amorphous Li_xNb₂O₅ phase. Through cyclic voltammetry and symmetric cell electrochemical impedance spectroscopy, temperature elevation is noted to increase the pseudocapacitive contribution of the Nb₂O₅ electrode, resulting in a high rate capability of 131 mAh g^-1 at 20,000 mA g^-1 at 90 °C. The electrode further exhibits long-term cycling over 2000 cycles and high Coulombic efficiency ascribed to the formation of a robust, [FSA]^--originated solid-electrolyte interphase during cycling.

Solution Processing of Topochemically Converted Layered WO3 for Multifunctional Applications

Solution processing of nanomaterials is a promising technique for use in various applications owing to its simplicity and scalability. However, the studies on liquid-phase exfoliation (LPE) of tungsten oxide (WO₃ ) are limited, unlike others, by a lack of commercial availability of bulk WO₃ with layered structures. Herein, a one-step topochemical synthesis approach to obtain bulk layered WO₃ from commercially available layered tungsten disulfide (WS₂ ) by optimizing various parameters like reaction time and temperature is reported. Detailed microscopic and spectroscopic techniques confirmed the conversion process. Further, LPE was carried out on topochemically converted bulk layered WO₃ in 22 different solvents; among the solvents studied, the propan-2-ol/water (1 : 1) co-solvent system appeared to be the best. This indicates that the possible values of surface tension and Hansen solubility parameters for bulk WO₃ could be close to that of the co-solvent system. The obtained WO₃ dispersions in a low-boiling-point solvent enable thin films of various thickness to be fabricated by using spray coating. The obtained thin films were used as active materials in supercapacitors without any conductive additives/binders and exhibited an areal capacitance of 31.7 mF cm^-2 at 5 mV s^-1 . Photo-electrochemical measurements revealed that these thin films can also be used as photoanodes for photo-electrochemical water oxidation.

Ordered mesoporous metal oxides for electrochemical applications: correlation between structure, electrical properties and device performance

Ordered mesoporous metal oxides with a high specific surface area, tailored porosity and engineered interfaces are promising materials for electrochemical applications. In particular, the method of evaporation-induced self-assembly allows the formation of nanocrystalline films of controlled thickness on polar substrates. In general, mesoporous materials have the advantage of benefiting from a unique combination of structural, chemical and physical properties. This Perspective article addresses the structural characteristics and the electrical (charge-transport) properties of mesoporous metal oxides and how these affect their application in energy storage, catalysis and gas sensing.

The electrochemical kinetics of cerium selenide nano-pebbles: the design of a device-grade symmetric configured wide-potential flexible solid-state supercapacitor

Next-generation portable flexible electronic appliances require liquid-free energy storage supercapacitor devices to eliminate leakage and to support mechanical bending that is compatible with roll-to-roll technologies. Hence, a state-of-the-art process is presented to design a solid-state, wide-potential and flexible supercapacitor through the use of nano-pebbles of cerium selenide via a simple successive ionic layer adsorption and reaction (SILAR) method that could allow an industry scalable route. We strongly believe that this is the first approach amongst physical and chemical routes not only for synthesizing cerium selenide in thin-film form but also using it for device-grade supercapacitor applications. The designed solid-state symmetric supercapacitor assembled from cerium selenide electrodes sandwiched by PVA-LiClO₄ gel electrolyte attains a wide potential window of 1.8 V with capacitance of 48.8 F g^-1 at 2 mV s^-1 and reveals excellent power density of 4.89 kW kg^-1 at an energy density of 11.63 W h kg^-1. The formed device is capable of 87% capacitive retention even at a mechanical bending angle of 175°. Lighting up a strip of 21 parallel connected red LEDs clearly demonstrates the practical use of the designed symmetric solid-state supercapacitor, aiming towards the commercialization of the product in the future.

Understanding Stabilization in Nanoporous Intermetallic Alloy Anodes for Li-Ion Batteries Using Operando Transmission X-ray Microscopy

Tin-based alloying anodes are exciting due to their high energy density. Unfortunately, these materials pulverize after repetitive cycling due to the large volume expansion during lithiation and delithiation; both nanostructuring and intermetallic formation can help alleviate this structural damage. Here, these ideas are combined in nanoporous antimony-tin (NP-SbSn) powders, synthesized by a simple and scalable selective-etching method. The NP-SbSn exhibits bimodal porosity that facilitates electrolyte diffusion; those void spaces, combined with the presence of two metals that alloy with lithium at different potentials, further provide a buffer against volume change. This stabilizes the structure to give NP-SbSn good cycle life (595 mAh/g after 100 cycles with 93% capacity retention). Operando transmission X-ray microscopy (TXM) showed that during cycling NP-SbSn expands by only 60% in area and then contracts back nearly to its original size with no physical disintegration. The pores shrink during lithiation as the pore walls expand into the pore space and then relax back to their initial size during delithiation with almost no degradation. Importantly, the pores remained open even in the fully lithiated state, and structures are in good physical condition after the 36th cycle. The results of this work should thus be useful for designing nanoscale structures in alloying anodes.

Functional-Group Modification of Kraft Lignin for Enhanced Supercapacitors

Recent efforts to improve the capacitances of Kraft lignin (KL) in supercapacitors have mainly focused on screening KL substrates, which could either compensate the poor conductivity of KL or directly contribute to the capacitance. However, increasing the pseudocapacitance contributed by KL itself, through hydroquinone/quinone redox cycles, remains a challenge, owing to the roughly fixed content of hydroquinone species in natural KL. In this study, the capacitance of KL is greatly improved by using a functional-group modification strategy in which methoxy groups in KL are selectively converted into phenolic hydroxy groups, which facilitate the formation of additional hydroquinone moieties and thus lead to higher pseudocapacitances. The oxidized KL materials show up to 25.6 % enhancement of the phenolic hydroxy content in comparison to raw KL, which results in 21.9 % capacitance improvement from 322 to 390 F g^-1 at 0.5 A g^-1 in an acidic system.

Engineered defects in cerium oxides: tuning chemical reactivity for biomedical, environmental, & energy applications

Nanocrystalline cerium oxide (nanoceria) is a rare earth oxide with a complex surface chemistry. This material has seen substantial investigation in recent years in both fundamental and applied studies due largely to more precise characterization of the unique surface structures, which mediate its pronounced redox activity. In particular, oxygen storage/buffering capacities have been thoroughly correlated with synthesis and processing condition effects on other material features such as surface (micro-) faceting, reconstruction, and (extent of) hydration. Key material features such as these modulate nanoceria redox performance by changing the crystal microenvironment. In this review, we present nanoengineering methods, which have produced increased nanoceria performance in biomedical, energy, and catalysis applications. The impact of combined/cooperative theoretical and experimental studies are highlighted throughout.

Comparison of In-Plane Stress Development in Sol-Gel- and Nanoparticle-Derived Mesoporous Metal Oxide Thin Films

By using an evaporation-induced self-assembly (EISA) process, mesoporous metal oxide thin films are prepared via molecular precursors undergoing a sol-gel transition or by using nanoparticle dispersions as the starting materials. Both methods are employed together with PIB₅₀-b-PEO₄₅ as the structure-directing agent to produce porous TiO₂ and ZrO₂ thin films with spherical mesopores of around 14 nm in diameter. These nanoparticle- and sol-gel-derived films were investigated in terms of the intrinsic in-plane stress development during the heat treatment up to 500 °C to evaluate the impact of solvent evaporation, template decomposition and crystallization on the mechanical state of the film. The investigation revealed the lowest intrinsic stress for the nanoparticle-derived mesoporous film, which is assigned to the combination of the relaxing effects of the utilized diblock copolymer and the interparticular gaps between the precrystalline nanoparticles. Furthermore, the residual in-plane stress was studied after annealing steps ranging from 300 to 1000 °C and cooling down to room temperature. Here, TiO₂ nanoparticle-derived mesoporous films possess a lower residual stress than the sol-gel-derived mesoporous films, while in the case of ZrO₂ films, sol-gel-derived coatings reveal the smallest residual stress. The latter is based on the lower thermal expansion coefficient of the dominant monoclinic crystal phase compared to that of the silicon substrate. Hence, the present crystal structure has a strong influence on the mechanical state. The observation in this study helps to further understand the stress-related mechanical properties and the formation of mesoporous metal oxides.

Asymmetric supercapacitors with excellent rate performance by integrating Co(OH)F nanorods and layered Ti3C2Tx paper

Here we describe an aqueous asymmetric supercapacitor assembled using Co(OH)F nanorods on Ni foam (Co(OH)F@NF) as the positive electrode and layered Ti₃C₂T_x paper on Ni foam (Ti₃C₂T_x@NF) as the negative electrode. The Co(OH)F@NF was fabricated by a facile hydrothermal process. The nanorods were constructed as three-dimensional networks with stable structures and good durability in electrochemical reactions. As expected, the Co(OH)F@NF exhibited excellent capacitance (1265 mF cm⁻² at 1 mA cm⁻²) and wonderful rate performance (90% from 1 to 10 mA cm⁻²). The Co(OH)F@NF//Ti₃C₂T_x@NF asymmetric supercapacitor devices showed high capacitance of 376 mF cm⁻² and excellent rate capacity of 91% retention. When the two Co(OH)F@NF//Ti₃C₂T_x@NF devices were combined in series, a red led bulb could be lit for 12 minutes, further corroborating the possibility of the devices being used for practical applications.

Here we describe an aqueous asymmetric supercapacitor assembled using Co(OH)F nanorods on Ni foam (Co(OH)F@NF) as the positive electrode and layered Ti₃C₂T_x paper on Ni foam (Ti₃C₂T_x@NF) as the negative electrode.

Realizing an Asymmetric Supercapacitor Employing Carbon Nanotubes Anchored to Mn3O4 Cathode and Fe3O4 Anode

A facile route to anchor pseudocapacitive materials on multiwalled carbon nanotubes (CNTs) to realize high-performance electrode materials for asymmetric supercapacitors (ASCs) is reported. The anchoring process is developed after direct decomposition of metal-hexacyanoferrate complex on the CNT surface. Transmission electron microscopy (TEM) analysis reveals that the nanoparticles (NPs) are discretely attached over the CNT surface without forming a uniform layer, thus making most of the entire NP surface available for electrochemical reactions. Accordingly, CNT-Mn₃O₄ nanocomposite cathode shows significantly improved capacitive performance as compared to pristine CNT electrode, validating the efficacy of designing the composite electrode. With CNT-Fe₃O₄ nanocomposite as the paired anode, the hybrid ASC delivers a specific capacitance of 135.2 F/g at a scan rate of 10 mV/s within a potential window of 0-1.8 V in the aqueous electrolyte and retains almost 100% of its initial capacitance after 15,000 cycles. The serially connected ASCs can power commercial light-emitting diodes (LEDs) and mobile phones, reflecting their potential in next-generation storage applications.

In-plane stress development in mesoporous thin films

Ordered mesoporous thin films of TiO2 and CexZr1-xO2 (x = 0, 0.5, 1) were prepared via an evaporation-induced self-assembly (EISA) process and subsequently investigated in terms of the developing intrinsic and residual in-plane stress. These mechanical properties were determined by the curvature method, which is based on the determination of the deflection of light due to concave or convex bending of the films on a substrate. The films were investigated with regard to the intrinsic stress during heat treatment up to 500 °C and to the residual stress at room temperature for several annealing temperatures. Following this strategy, the influence of the decomposition of a block copolymer template on the intrinsic stress as well as the pore collapsing on the residual stress was analyzed. Nanoporous TiO2 thin films were prepared using two different block copolymers (PIB50-b-PEO45 and Pluronic® F127). A comparison between the templated and non-templated TiO2 films showed the lowest intrinsic and residual stress for the ordered mesoporous material prepared with PIB50-b-PEO45 indicating that the distributed polymer and the corresponding mesopores act as relaxing agents for the system. This was verified by mesoporous CexZr1-xO2 (x = 0, 0.5, 1) thin films showing a comparable behavior in terms of the experienced intrinsic stress. This work reveals an increase in the residual in-plane stress during pore collapse, which lays the foundation for further understanding of the stress-related mechanical properties of mesoporous thin films.

Advanced Energy Storage Devices: Basic Principles, Analytical Methods, and Rational Materials Design

Tremendous efforts have been dedicated into the development of high-performance energy storage devices with nanoscale design and hybrid approaches. The boundary between the electrochemical capacitors and batteries becomes less distinctive. The same material may display capacitive or battery-like behavior depending on the electrode design and the charge storage guest ions. Therefore, the underlying mechanisms and the electrochemical processes occurring upon charge storage may be confusing for researchers who are new to the field as well as some of the chemists and material scientists already in the field. This review provides fundamentals of the similarities and differences between electrochemical capacitors and batteries from kinetic and material point of view. Basic techniques and analysis methods to distinguish the capacitive and battery-like behavior are discussed. Furthermore, guidelines for material selection, the state-of-the-art materials, and the electrode design rules to advanced electrode are proposed.

Hierarchical porous NiCo2O4/CeO2 hybrid materials for high performance supercapacitors

Hierarchical porous NiCo₂O₄/CeO₂ hybrid materials are successfully synthesized via a simple solvothermal method and subsequent heat treatment and exhibit remarkable electrochemical performances in supercapacitors.

Three-Dimensional NiCo2O4@MnMoO4 Core-Shell Nanoarrays for High-Performance Asymmetric Supercapacitors

Design of new materials with sophisticated nanostructure has been proven to be an efficient strategy to improve their properties in many applications. Herein, we demonstrate the successful combination of high electron conductive materials of NiCo₂O₄ with high capacitance materials of MnMoO₄ by forming a core-shell nanostructure. The NiCo₂O₄@MnMoO₄ core-shell nanoarrays (CSNAs) electrode possesses high capacitance of 1169 F g^-1 (4.24 F cm^-2) at a current density of 2.5 mA cm^-2, obviously larger than the pristine NiCo₂O₄ electrode. The asymmetric supercapacitors (ASCs), assembled with NiCo₂O₄@MnMoO₄ CSNAs as binder-free cathode and active carbon (AC) as anode, exhibit high energy density of 15 Wh kg^-1 and high power density of 6734 W kg^-1. Cycle performance of NiCo₂O₄@MnMoO₄ CSNAs//AC ASCs, conducted at current density of 20 mA cm^-2, remain 96.45% of the initial capacitance after 10,000 cycles, demonstrating its excellent long-term cycle stability. Kinetically decoupled analysis reveals that the capacitive capacitance is dominant in the total capacitance of NiCo₂O₄@MnMoO₄ CSNAs electrode, which may be the reason for ultra long cycle stability of ASCs. Our assembled button ASC can easily light up a red LED for 30 min and a green LED for 10 min after being charged for 30 s. The remarkable electrochemical performance of NiCo₂O₄@MnMoO₄ CSNAs//AC ASCs is attributed to its enhanced surface area, abundant electroactive sites, facile electrolyte infiltration into the 3D NiCo₂O₄@MnMnO₄ nanoarrays and fast electron and ion transport path.

Investigation into Pseudo-Capacitance Behavior of Glycoside-Containing Hydrogels

Electrochemical pseudocapacitors are an attractive choice for energy storage applications because they offer higher energy densities than electrostatic or electric double layer capacitors. They also offer higher power densities in shorter durations of time, as compared to batteries. Recent efforts on pseudocapacitors include biocompatible hydrogel electrolytes and transition metal electrodes for implantable energy storage applications. Pseudocapacitive behavior in these devices has been attributed to the redox reactions that occur within the electric double layer, which is formed at the electrode-electrolyte interface. In the present study, we describe a detailed investigation on redox reactions responsible for pseudocapacitive behavior in glycoside-containing hydrogel formulations. Pseudocapacitive behavior was compared among various combinations of biocompatible hydrogel electrolytes, using carbon tape electrodes and transition metal electrodes based on fluorine-doped tin oxide. The hydrogels demonstrated a pseudocapacitive response only in the presence of transition metal electrodes but not in the presence of carbon electrodes. Hydrogels containing amine moieties showed greater energy storage than gels based purely on hydroxyl functional groups. Furthermore, energy storage increased with greater amine content in these hydrogels. We claim that the redox reactions in hydrogels are largely based on Lewis acid-base interactions, facilitated by amine and hydroxyl side groups along the electrolyte chain backbones, as well as hydroxylation of electrode surfaces. Water plays an important role in these reactions, not only in terms of providing ionic radicals but also in assisting ion transport. This understanding of redox reactions will help determine the choice of transition metal electrodes, Lewis acid-base pairs in electrolytes, and medium for ionic transport in future biocompatible pseudocapacitors.

Rapid preparation of block copolymer templated mesoporous Zr1−xCexO2 thin films

A rapid deposition method for the preparation of ordered mesoporous Zr_1−xCe_xO₂ thin films using commercial templates is developed, with a comprehensive study on the relationship between synthesis conditions and the properties of the resulting films.

Tracking Pseudocapacitive Contribution to Superior Energy Storage of MnS Nanoparticles Grown on Carbon Textile

Transition metal chalcogenides have emerged as a new class of electrode materials for energy storage devices with superior electrochemical performance. We have directly synthesized manganese sulfide nanoparticles on carbon textile substrate and used them as electrodes to fabricate flexible all-solid-state supercapacitors. By voltammetry analysis, we have studied the electrochemical properties of MnS-CT composites, which reveal that the Faradaic diffusion-controlled process dominates at low scan rates (82.85% at 5 mV s(-1)) and even at high scan rates (39% at 20 mV s(-1)). The MnS-CT electrode shows high capacitance of 710.6 F g(-1) in LiCl aqueous electrolyte, and the surface redox reactions on MnS nanoparticles are found to be responsible for the high pseudocapacity, which is further analyzed by XRD and HRTEM. Furthermore, MnS-CT supercapacitor exhibits excellent pseudocapacitive performance (465 Fg(-1) at 5 mV s(-1)), excellent stability, light weight (0.83 g as a whole device), and high flexibility. The device has also achieved high energy density and high power density (52 Wh kg(-1) at 308 W kg(-1) and 1233 W kg(-1) with 28 Wh kg(-1), respectively). In practice, three charged supercapacitors in series can power four red light-emitting diodes (LEDs) (2.0 V, 15 mA) for 2 min. All of the evidence shows that MnS nanoparticles combined with carbon textile is a promising electrode material for pseudocapacitors.

Bubble-raft collapse and the nonequilibrium dynamics of two-state elastica

We report on the collapse of bubble rafts under compression in a closed rectangular geometry. A bubble raft is a single layer of bubbles at the air-water interface. A collapse event occurs when bubbles submerge beneath the neighboring bubbles under compression, causing the structure of the bubble raft to go from single-layer to multilayer. We studied the collapse dynamics as a function of compression velocity. At higher compression velocity we observe a more uniform distribution of collapse events, whereas at lower compression velocities the collapse events accumulate at the system boundaries. We propose that this system can be understood in terms of a linear elastic sheet coupled to a local internal (Ising) degree of freedom. The two internal states, which represent one bubble layer versus two, couple to the elasticity of the sheet by locally changing the reference state of the material. By exploring the collapse dynamics of the bubble raft, one may address the basic nonlinear mechanics of a number of complex systems in which elastic stress is coupled to local internal variables.

Facile preparation of free-standing rGO paper-based Ni–Mn LDH/graphene superlattice composites as a pseudocapacitive electrode

A novel film electrode was assembled via a simple filtration process, with an rGO paper as the substrate and Ni–Mn LDH/graphene superlattice composites as the functional layer.

Aqueous sol–gel synthesized anatase TiO2nanoplates with high-rate capabilities for lithium-ion and sodium-ion batteries

The graph shows the structure of anatase nanoplates that is assembled using terephthalic acid. After the acid is burned out and transforms into CO₂, the nanoplates exhibit uniform nanopores, which is suitable for Li-ion/Na-ion insertion.

Nanoparticles-in-concavities as efficient nanocatalysts for carbon dioxide reforming of methane to hydrogen and syngas

The ceria concavity-loaded Ni nanoparticle catalysts can lead to more active sites and promote CO₂ dissociative activation and CO desorption, thus enhancing significantly the catalytic performances for methane dry reforming with CO₂.

High Energy Density Aqueous Electrochemical Capacitors with a KI-KOH Electrolyte

We report a new electrochemical capacitor with an aqueous KI-KOH electrolyte that exhibits a higher specific energy and power than the state-of-the-art nonaqueous electrochemical capacitors. In addition to electrical double layer capacitance, redox reactions in this device contribute to charge storage at both positive and negative electrodes via a catholyte of IOx-/I- couple and a redox couple of H2O/Had, respectively. Here, we, for the first time, report utilizing IOx-/I- redox couple for the positive electrode, which pins the positive electrode potential to be 0.4-0.5 V vs Ag/AgCl. With the positive electrode potential pinned, we can polarize the cell to 1.6 V without breaking down the aqueous electrolyte so that the negative electrode potential could reach -1.1 V vs Ag/AgCl in the basic electrolyte, greatly enhancing energy storage. Both mass spectroscopy and Raman spectrometry confirm the formation of IO3- ions (+5) from I- (-1) after charging. Based on the total mass of electrodes and electrolyte in a practically relevant cell configuration, the device exhibits a maximum specific energy of 7.1 Wh/kg, operates between -20 and 50 °C, provides a maximum specific power of 6222 W/kg, and has a stable cycling life with 93% retention of the peak specific energy after 14,000 cycles.

Ultrasonic-spray-assisted synthesis of metal oxide hollow/mesoporous microspheres for catalytic CO oxidation

Various transition metal oxide hollow or mesoporous microspheres with improved catalytic activities towards CO oxidation were prepared via a general ultrasonic-spray-assisted method.

Facile synthesis of CeO2decorated Ni(OH)2hierarchical composites for enhanced electrocatalytic sensing of H2O2

CeO₂–Ni(OH)₂composites with hierarchical structures were synthesizedviaa facile one-pot hydrothermal method, which were constructed with Ni(OH)₂nanosheets decorated within situformed CeO₂nanoparticles on their surface.

Mesoporous carbon-vanadium oxide films by resol-assisted, triblock copolymer-templated cooperative self-assembly

Unlike other crystalline metal oxides amenable to templating by the combined assemblies of soft and hard chemistries (CASH) method, vanadium oxide nanostructures templated by poly(ethylene oxide-b-1,4-butadiene-b-ethylene oxide) (OBO) triblock copolymers are not preserved upon high temperature calcination in argon. Triconstituent cooperative assembly of a phenolic resin oligomer (resol) and an OBO triblock in a VOCl3 precursor solution enhances the carbon yield and can prevent breakout crystallization of the vanadia during calcination. However, the calcination environment significantly influences the observed mesoporous morphology in these composite thin films. Use of an argon atmosphere in this processing protocol leads to nearly complete loss of carbon-vanadium oxide thin film mesostructure, due to carbothermal reduction of vanadium oxide. This reduction mechanism also explains why the CASH method is not more generally successful for the fabrication of ordered mesoporous vanadia. Carbonization under a nitrogen atmosphere at temperatures up to 800 °C instead enables formation of a block copolymer-templated mesoporous structure, which apparently stems from the formation of a minor fraction of a stabilizing vanadium oxynitride. Thus, judicious selection of the inert gas for template removal is critical for the synthesis of well-defined, mesoporous vanadia-carbon composite films. This resol-assisted assembly method may generally apply to the fabrication of other mesoporous materials, wherein inorganic framework crystallization is problematic due to kinetically competitive carbothermal reduction processes.

Mesoscopically structured nanocrystalline metal oxide thin films

This review describes the main successful strategies that are used to grow mesostructured nanocrystalline metal oxide and SiO₂ films via deposition of sol-gel derived solutions. In addition to the typical physicochemical forces to be considered during crystallization, mesoporous thin films are also affected by the substrate-film relationship and the mesostructure. The substrate can influence the crystallization temperature and the obtained crystallographic orientation due to the interfacial energies and the lattice mismatch. The mesostructure can influence the crystallite orientation, and affects nucleation and growth behavior due to the wall thickness and pore curvature. Three main methods are presented and discussed: templated mesoporosity followed by thermally induced crystallization, mesostructuration of already crystallized metal oxide nanobuilding units and substrate-directed crystallization with an emphasis on very recent results concerning epitaxially grown piezoelectric structured α-quartz films via crystallization of amorphous structured SiO₂ thin films.

Synthetic versatility of nanoparticles: A new, rapid, one-pot, single-step synthetic approach to spherical mesoporous (metal) oxide nanoparticles using supercritical alcohols

A simple, rapid (10 min), one-pot, single-step method for the preparation of solid and hollow spherical porous TiO2 nanoparticles with large surface areas (100–211 m2/g) was developed in supercritical alcohols using carboxylic acids as organic additives. The shell thickness of the hollow TiO2 nanoparticles (20–280 nm) was controlled by adjusting the heating rate (2.0–10.0 °C/min). The preparation of different spherical porous metal oxide nanoparticles, including CeO2, SiO2, TiO2, ZrO2, and ZnO, demonstrated the versatility of the synthetic approach. In addition, several rare earth-doped spherical mesoporous metal oxide nanoparticles, including CeO2:Er, CeO2:Er,Yb, ZrO2:Er, and TiO2:Er, which exhibit energy upconversion emission, were successfully prepared using this one-pot, single-step, supercritical methanol method. The obtained spherical mesoporous CeO2:Er and CeO2:Er,Yb nanoparticles emit green light upon excitation, even when irradiated with a low-power IR laser (980 nm, 10 mW) without calcination. Several other (metal) elements were also easily doped into spherical, mesoporous TiO2 nanoparticles, such as Eu, Ce, Yb, Fe, and N, using a similar procedure. Furthermore, the spherical mesoporous TiO2 nanoparticles were successfully applied as a new material for the transport of DNA via biolistic bombardment.

Soft-templating method to synthesize crystalline mesoporous α-Fe2O3 films

A new synthesis method for the preparation of crystalline mesoporous hematite films with controlled thickness is reported.

Enhancing pseudocapacitive charge storage in polymer templated mesoporous materials

Growing global energy demands coupled with environmental concerns have increased the need for renewable energy sources. For intermittent renewable sources like solar and wind to become available on demand will require the use of energy storage devices. Batteries and supercapacitors, also known as electrochemical capacitors (ECs), represent the most widely used energy storage devices. Supercapacitors are frequently overlooked as an energy storage technology, however, despite the fact that these devices provide greater power, much faster response times, and longer cycle life than batteries. Their limitation is that the energy density of ECs is significantly lower than that of batteries, and this has limited their potential applications. This Account reviews our recent work on improving pseudocapacitive energy storage performance by tailoring the electrode architecture. We report our studies of mesoporous transition metal oxide architectures that store charge through surface or near-surface redox reactions, a phenomenon termed pseudocapacitance. The faradaic nature of pseudocapacitance leads to significant increases in energy density and thus represents an exciting future direction for ECs. We show that both the choice of material and electrode architecture is important for producing the ideal pseudocapacitor device. Here we first briefly review the current state of electrode architectures for pseudocapacitors, from slurry electrodes to carbon/metal oxide composites. We then describe the synthesis of mesoporous films made with amphiphilic diblock copolymer templating agents, specifically those optimized for pseudocapacitive charge storage. These include films synthesized from nanoparticle building blocks and films made from traditional battery materials. In the case of more traditional battery materials, we focus on using flexible architectures to minimize the strain associated with lithium intercalation, that is, the accumulation of lithium ions or atoms between the layers of cathode or anode materials that occurs as batteries charge and discharge. Electrochemical analysis of these mesoporous films allows for a detailed understanding of the origin of charge storage by separating capacitive contributions from traditional diffusion-controlled intercalation processes. We also discuss methods to separate the two contributions to capacitance: double-layer capacitance and pseudocapacitance. Understanding these contributions should allow the selection of materials with an optimized architecture that maximize the contribution from pseudocapacitance. From our studies, we show that nanocrystal-based nanoporous materials offer an architecture optimized for high levels of redox or surface pseudocapacitance. Interestingly, in some cases, materials engineered to minimize the strain associated with lithium insertion can also show intercalation pseudocapacitance, which is a process where insertion processes become so kinetically facile that they appear capacitive. Finally, we conclude with a summary of simple design rules that should result in high-power, high-energy-density electrode architectures. These design rules include assembling small, nanosized building blocks to maximize electrode surface area; maintaining an interconnected, open mesoporosity to facilitate solvent diffusion; seeking flexibility in electrode structure to facilitate volume expansion during lithium insertion; optimizing crystalline domain size and orientation; and creating effective electron transport pathways.

Defect chemistry of oxide nanomaterials with high surface area: ordered mesoporous thin films of the oxygen storage catalyst CeO2-ZrO2

Herein we report the electrical transport properties of a series of ordered mesoporous ceria-zirconia (CexZr1-xO2, referred to as mp-CZO) thin films with both a cubic structure of (17±2) nm diameter pores and nanocrystalline walls. Samples over the whole range of composition, including bare CeO2 and ZrO2, were fabricated by templating strategies using the large diblock copolymer KLE as the structure-directing agent. Both the nanoscale structure and the chemical composition of the mesoporous materials were analyzed by a combination of scanning and transmission electron microscopy, grazing incidence small-angle X-ray scattering, X-ray photoelectron spectroscopy, and time-of-flight secondary ion mass spectrometry. The total conductivity as a function of the film composition, temperature, and oxygen partial pressure was measured using impedance spectroscopy. The mesoporous solid solutions of CeO2-ZrO2 prepared in this work showed a higher stability against thermal ripening than both binary oxides, making them ideal model systems to study both the charge transport properties and the oxygen storage at elevated temperatures. We find that the redox properties of nanocrystalline mp-CZO thin films differ significantly from those of bulk CZO materials reported in the literature and, therefore, propose a defect chemical model of surface regions.