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Utilizing ionic liquids (ILs) with low flammability as the precursor component for a gel polymer electrolyte is a smart strategy out of safety concerns. Solvate ionic liquids (SILs) consist of equimolar lithium bis(trifluoromethylsulfonyl)imide and tetraglyme, alleviating the main problems of high viscosity and low Li

Ti2Nb10O29 (TNO) is a suitable electrode for high-performance lithium-ion batteries and capacitors because of its large lithium storage capacity and high Li+ diffusivity. Currently, the rate or power capability of TNO-based systems is limited by the poor electronic conductivity of the material. Here we report our findings in design, synthesis, and characterization of a hierarchical N-rich carbon conductive layer wrapped TNO structure (TNO@NC) using a novel polypyrrole-chemical vapor deposition (PPy-CVD) process. It was found that carbon coating with PPy–carbon partially reduces Ti and Nb cations, forms TiN, and creates oxygen vacancies in the TNO@NC structure that further increase overall electronic and ionic conductivity. Various defect models and density functional theory (DFT) calculations are used to show how oxygen vacancies influence the electronic structure and Li-ion diffusion energy of the TNO@NC composite. The optimized TNO@NC sample shows notable rate capability in half-cells with a reversible capacity of 300 mAh g−1 at 1 C rate and maintains 211 mAh g−1 at a rate of 100 C, which is superior to that of most MxNbyOz materials. Full cell LiNi0.5Mn1.5O4 (LNMO)||TNO@NC lithium-ion batteries (LIB) and active carbon (AC)||TNO@NC hybrid lithium-ion capacitors (LIC) exhibited notable volumetric and gravimetric energy and power densities.

Fe-N-C single-atom catalysts (SACs) are emerging as a promising class of electrocatalysts for the oxygen reduction reaction (ORR) to replace Pt-based catalysts. However, due to the limited loading of Fe for SACs and the inaccessibility of internal active sites, only a small portion of the sites near the external surface are able to contribute to the ORR activity. Here, this work reports a metal-organic framework-derived Fe-N-C SAC with a hierarchically porous and concave nanoarchitecture prepared through a facile but effective strategy, which exhibits superior electrocatalytic ORR activity with a half-wave potential of 0.926 V (vs RHE) in alkaline media and 0.8 V (vs RHE) in acidic media while maintaining excellent stability. The superior ORR activity of the as-designed catalyst stems from the unique architecture, where the hierarchically porous architecture contains micropores as Fe SAC anchoring sites, meso-/macro-pores as accessible channels, and concave shell for increasing external surface area. The unique architecture has dramatically enhanced the utilization of previously blocked internal active sites, as confirmed by a high turnover frequency of 3.37 s

While numerous oxygen electrocatalysts have been reported to enhance zinc-air battery (ZAB) performance, highly efficient electrocatalysts for the oxygen electrocatalysis need to be developed for broader commercialization of ZABs. Furthermore, areal (instead of volumetric) power density has been used to benchmark the performance of ZABs, often causing ambiguities or confusions. Here, we propose a methodology for evaluating the performance of a ZAB using the volumetric (rather than the areal) power density by taking into consideration the air electrode thickness. A nitrogen and sulfur co-doped metal-free oxygen reduction electrocatalyst (N-S-PC) is used as a model catalyst for this new metric. The electrocatalyst exhibited a half-wave potential of 0.88 V, which is similar to that of the Pt/C electrocatalyst (0.89 V) due to the effects of co-doping and a highly mesoporous structure. In addition, the use of volumetric activity allows fair comparison among different types of air electrodes. The N-S-PC-loaded air electrode demonstrated a higher peak power density (5 W cm-3) than the carbon felt or paper electrode in the ZAB test under the same testing conditions.

The functional microporous layer, acting as a mass-transfer control medium with a rational structure and surface morphology as well as high electrical conductivity, significantly affects the performance of micro-direct methanol fuel cells (μDMFCs). Bioinspired by the architecture and multi-functional properties of mangrove roots, this study develops a simple and versatile strategy based on magnetron sputtering and chemical vapor deposition to fabricate a mangrove root-inspired carbon nanotube film (MR-CNTF) as the functional interface in μDMFCs. It has features such as ultralightweight, high porosity, and good electrical conductivity. During the synthesis process, an apex-growth model of CNTF is identified. The results indicate that the MR-CNTF used as a cathodic microporous layer can remarkably facilitate the oxygen transport and water management. Because of its multi-functional structure and excellent material characteristics, the passive μDMFC displays a peak power density of 14.9 mW cm

Ge is considered a promising anode candidate for Li-ion batteries (LIBs); however, its practical applicability is hindered by the relatively slow Li-ion diffusion owing to the stiffness of the diamond-like structure. Inspired by little difference in electronegativity between Ge and P, we have designed a novel layered GeP anode for LIBs, which can be readily synthesized using a mechano-chemical method and a subsequent low-temperature annealing. In particular, GeP demonstrates the best performances among all Ge-based anode materials studied, attributed to its fast Li-ion diffusion compared to Ge counterpart and a unique Li-storage mechanism that involves intercalation, conversion, and alloying, as confirmed by XRD, TEM, XPS, and Raman spectroscopy. Specially, the initial layered crystal structure of GeP can be reconstructed during charging due to its low formation energy, thus offering remarkable reversibility during cycling. Further, this study implies that the formation energy of crystal structures could be an important parameter for strategic design of large-capacity anode materials for LIBs.

Ge-based anodes for Na-ion batteries (NIB) usually suffer from sluggish reaction kinetics, low initial Coulombic efficiency, poor reversible capacity, and short cycling life due mainly to its rigid diamond-like structure. Here we report our findings in characterization and application of a GeP anode with a flexible layered structure, synthesized by a simple mechanochemical method. When tested as the anode for NIBs, the GeP undergoes a self-healing Na-storage process that involves intercalation, conversion, and alloying, as co-revealed by ex-situ X-ray diffraction, HRTEM, Raman spectroscopy, and X-ray photoelectron spectroscopy analysis. The peculiar self-healing phenomenon derives from its ultra-low formation energy (−0.19 eV) for reconstruction of the original layered structure, as confirmed by first-principle calculations. The low formation energy also enables the formation of chemical bonding between layered GeP and graphite, thus achieving unprecedented performances among all reported anode materials based on Group IVA- and Group VA elements. The structural design strategy guided by formation energy of desirable phases is also applicable to the development of other energy-storage materials.

Organic polysulfanes are new type of attractive organosulfur electrode materials for next generation lithium-sulfur (Li-S) batteries because of their high sulfur content, low cost, and desirable energy density. However, conventional organic polysulfanes usually suffer from poor reversibility due to structure variation and irreversible conversion during cycling. Here we report the synthesis and characterization of a novel two-dimensional (2D) organic polysulfane with a unique molecular structure of polycyclic sulfur directly substituting the carboxyls of poly(acrylic acid) and grafted on the carbon chain through a coupling reaction with KI as a catalyst and KCl as a template. The obtained organic polysulfane nanosheets with 72 wt% sulfur (OPNS-72) exhibit high initial capacity of 891 mAh/g (based on whole composite), excellent cycling stability (0.014% capacity fading per cycle over 620 cycles at 1 C rate), superior rate capability (562 mAh/g at 10 C) and high mass loading of 9.7 mg/cm2. The remarkable cycling stability of the Li-S battery is attributed to the structural stability and highly reversible electrochemical reaction of the OPNS-72 electrode, as confirmed by the TEM image after cycling and operando Raman spectroscopy measurements under battery operating conditions. Further, the developed synthesis approach is applicable for the preparation of other organic polysulfane nanosheets as highly reversible electrodes for Li-S batteries.

Electrification of transportation has spurred the development of fast-charge energy storage devices. High-power lithium-ion batteries require electrode materials that can store lithium quickly and reversibly. Herein, the design and construction of a Nb

Design and fabrication of supercapacitors (SCs) with high energy density, fast discharge rate, and long cycle life is of great importance; however, the performances of SCs depend critically on advances in materials development. Here we report the development of a high-performance electrode material composed of hierarchical, porous interlaced ultrathin Zn and Ni co-substituted Co carbonate hydroxides (ZnNiCo-CHs) nanosheets branched on N-doped carbon nanotube arrays (C@ZnNiCo-CHs), which were grown directly on a nickel foam current collector. The mesoporous features and large open spaces of the interlaced ultrathin ZnNiCo-CHs nanosheets provide more active sites for redox reactions and facilitate fast mass transport; the self-standing N-doped carbon nanotube arrays offer large surface area, promote fast electron transport, and enhance structure stability, resulting in outstanding rate capability and long-term stability. Density functional theory calculations suggest that the ZnNiCo-CHs nanosheets have low deprotonation energy, greatly facilitating the rate of redox reactions. Further, an asymmetric SC constructed from a C@ZnNiCo-CHs positive electrode and an N-, S-codoped rGOs negative electrode demonstrates a high energy density of 70.9 W h kg−1 at a power density of 966 W kg−1 while maintaining a capacity retention of 91% even after 20,000 cycles at 20 A g−1. The findings provide some important insight into rational design of transition metal compounds based materials for fast energy storage, which may be applicable to creating efficient and robust electrode materials for other energy-related devices.

The surface structure and material composition of current collectors have significant effects on the electrochemical performances of lithium-ion batteries (LIBs). In this work, a three-dimensional (3D) porous composite framework is applied as the anode current collector in LIBs. This unique 3D skeleton is composed of conductive carbon fiber/Cu core/shell fibrous structure. With an oxidation treatment upon the copper shell, the porous framework is assembled with CuO microspheres. Using mesocarbon microbead (MCMB) graphite powders as the active material, the cell with this 3D porous composite current collector shows an improved reversible discharge-charge capacity of 415 mAh g–1 at a current rate of 0.1 C after 50 cycles, which is much higher than that of the cell with a flat Cu foil (127 mAh g–1). It is demonstrated that this unique fibrous network of the 3D current collector coupled with the morphological effects of the CuO microspheres greatly improve the cell performance in terms of electrical conductivity, reversible capacity and cycling stability.

To minimize the impact of occasional fuel disruption or starvation during operation on fuel cell performance, an auxiliary power source is required, which increases the system complexity and cost. Here we report our findings in exploration of a bi-functional device that functions not only as a fuel cell to convert a chemical fuel to electricity but also as a battery to continue providing power when there is an interruption of fuel supply. The key component of this device is the bi-functional anode composed of Pt-WO3 nanowires. When hydrogen is continuously supplied to the fuel cell, it operates just like a normal fuel cell; when there is disruption of fuel supply, however, the device could deliver electric power for a longer period of time (additional 390 s) than a fuel cell with a normal Pt/C anode. Hydrogen inserts into the lattice of WO3 in the presence of Pt catalyst, as revealed by in situ Raman analysis, which can be released when there is a starvation of fuel. This work demonstrates the feasibility of a bi-functional fuel cell with energy storage capability, which may be applicable to other energy-related applications as well.

Developing advanced architectures using a cost-effective synthesis strategy is still a challenge for wide-spread commercial application of Nb2O5 in high-power rechargeable lithium-ion batteries (LIBs). Here we report a new two-dimensional (2D) architecture composed of oxygen-vacancy-rich T-Nb2O5 on reduced graphene oxide nanosheet and carbon (2D Nb2O5-C-rGO), which is synthesized via a one-pot hydrolysis route followed by a heat-treatment. As an anode for LIBs, the 2D Nb2O5-C-rGO architecture shows excellent rate capability (achieving a capacity of 114 mAh g−1 at 100 C or 20 A g−1) and cycling stability (maintaining a capacity of 147 mAh g−1 at 5 C for 1,500 cycles and 107 mAh g−1 at 50 C for 5,000 cycles). Experimental investigations and density functional theory (DFT)-based calculations reveal that the outstanding Li+ storage performance of the 2D Nb2O5-C-rGO electrode is attributed to the enhanced electronic conductivity facilitated by the C-rGO electronic network and fast Li+ migration within small Nb2O5 grains enhanced by in-situ formed lattice oxygen vacancies, which alter the Nb d band structure and Li+ interaction. This work results in an anode with advanced architecture for fast Li+ storage and provides more insight into the energy storage mechanism in the Nb2O5-based carbonaceous composite electrodes.

Hierarchically porous electrodes made of electrochemically active materials and conductive additives may display synergistic effects originating from the interactions between the constituent phases, and this approach has been adopted for optimizing the performances of many electrode materials. Here we report our findings in design, fabrication, and characterization of a hierarchically porous hybrid electrode composed of α-NiS nanorods decorated on reduced graphene oxide (rGO) (denoted as R-NiS/rGO), derived from water-refluxed metal–organic frameworks/rGO (Ni-MOF-74/rGO) templates. Microanalyses reveal that the as-synthesized α-NiS nanorods have abundant (101) and (110) surfaces on the edges, which exhibit a strong affinity for OH− in KOH electrolyte, as confirmed by density functional theory-based calculations. The results suggest that the MOF-derived α-NiS nanorods with highly exposed active surfaces are favorable for fast redox reactions in a basic electrolyte. Besides, the presence of rGO in the hybrid electrode greatly enhances the electronic conductivity, providing efficient current collection for fast energy storage. Indeed, when tested in a supercapacitor with a three-electrode configuration in 2 M KOH electrolyte, the R-NiS/rGO hybrid electrode exhibits a capacity of 744 C g−1 at 1 A g−1 and 600 C g−1 at 50 A g−1, indicating remarkable rate performance, while maintaining more than 89% of the initial capacity after 20 000 cycles. Moreover, when coupled with a nitrogen-doped graphene aerogel (C/NG-A) negative electrode, the hybrid supercapacitor (R-NiS/rGO/electrolyte/C/NG-A) achieved an ultra-high energy density of 93 W h kg−1 at a power density of 962 W kg−1, while still retaining an energy density of 54 W h kg−1 at an elevated working power of 46 034 W kg−1.

Composition design and morphology control of electrode materials are effective strategies to enhance the specific capacity, rate capability, and cycling life of electrochemical energy storage devices. Here we report our findings in the design and synthesis of a three-phase nickel sulfide (NiS-Ni 3 S 2 -Ni 3 S 4 , denoted as TP-Ni x S y ) with 3D flower-like architecture assembled from interconnected nanoflakes, which delivers a specific capacity of 724 C g −1 at a current density of 1 A g −1 . When integrated with reduced graphene oxide (rGO), a TP-Ni x S y /rGO composite electrode, derived from a hydrothermal process, demonstrates not only higher specific capacity (807 C g −1 at 1 A g −1 ) but also better rate capability (~72% capacity retention as the current density was increased from 1 to 20 A g −1 ). Moreover, a hybrid energy storage device, constructed from a TP-Ni x S y /rGO positive electrode and a graphene-based negative electrode, shows a high energy density of 46 Wh kg −1 at a power density of 1.8 kW kg −1 . It retains an energy density of 32 Wh kg −1 at power density of 17.2 kW kg −1 , demonstrating its viability and potential for practical applications.

While Li-ion battery cathode–electrolyte interfaces (CEIs) have been extensively investigated in recent decades, accurately identifying the chemical nature and tracking the dynamics of the CEIs during electrochemical cycling still remain a grand challenge. Here we report our findings in the investigation into the dynamic evolution of the interface between a LiNi0.33Co0.33Mn0.33O2 (LNMC) cathode and an ethylene carbonate/dimethyl carbonate (EC/DMC)-based electrolyte using surface-enhanced Raman spectroscopy (SERS) performed on a model cell under typical battery operating conditions. In particular, the strong SERS activity provided by a monolayer of Au nanocubes deposited on a model LNMC electrode (additive-free) enables quasi-quantitative assessment of the CEI evolution during cycling, proving information vital to revealing the dynamics of the species adsorbed on the LNMC surface as a function of cell potential. Furthermore, our theoretical calculation, which is based on the interaction between a model int...

Mixed transition metal oxides with hierarchical, porous structures, constructed from interconnected nano-building blocks, are considered promising positive electrodes for high-performance hybrid supercapacitors. Here we report our findings in design, fabrication, and characterization of 3D hierarchical, porous quaternary zinc-nickel-aluminum-cobalt oxide (ZNACO) architectures assembled from well-aligned nanosheets grown directly on nickel foam using a facile and scalable chemical bath deposition process followed by calcination. When tested as a binder-free electrode in a 3-electrode configuration, the ZNACO display high specific capacity (839.2 C g−1 at 1 A g−1) and outstanding rate capability (~82% capacity retention from 1 A g−1 to 20 A g−1), superior to those of binary-component NiCo2O4 and ZnCo2O4 as well as single-component Co3O4 electrode. More remarkably, a hybrid supercapacitor consisting of an as-fabricated ZNACO positive electrode and an activated carbon negative electrode exhibits a high energy density of 72.4 Wh kg−1 at a power density of 533 W kg−1 while maintaining excellent cycling stability (~90% capacitance retention after 10,000 cycles at 10 A g−1), demonstrating a promising potential for development of high-performance hybrid supercapacitors. Further, the unique electrode architecture is also applicable to other electrochemical systems such as batteries, fuel cells, and membrane reactors.

Hollow nanofibers of PrBa0.5Sr0.5Co2O5+δ (PBSC), created by an electrospinning process, are assembled into a three dimensional (3D) fibrous porous electrode, providing facile pathways for gas transport and excellent electrical conductivity for efficient charge transfer and, thus, greatly enhancing the rate of oxygen reduction reactions (ORR), as confirmed by the small electrode polarization resistance and low activation energy. A simple geometric modeling suggests that an electrode with longer fibers tends to be more efficient in facilitating mass and charge transfer under the conditions studied. A solid oxide fuel cell based on this 3D fibrous cathode demonstrates a peak power density of 1.11 W cm−2 at 550 °C when humidified H2 was used as fuel and ambient air as oxidant. The fibrous architecture also shows excellent stability under the operating conditions. Further and in particular, the high-performance hollow-fiber electrodes are also applicable to other energy storage and conversion systems.

The durability and electro-catalytic activity for oxygen reduction reaction (ORR) of solid oxide fuel cells (SOFCs) cathode often suffer from severe degradation due to poisoning effects such as Cr from interconnectors. Here we report our findings in the development of a Cr-tolerant catalyst, BaCoO3-x (BCO) nano-particles, which can dramatically enhance the ORR activity and durability of a state-of-the-art La0.6Sr0.4Co0.2Fe0.8O3-x (LSCF) cathode exposed to Crofer 22APU. For example, the polarization resistance (Rp) of a bare LSCF cathode increases from ~0.4 to ~1.5 Ωcm2 after 100 hs exposure to Cr in air with 3% H2O at 750 °C. In contrast, Rp of a BCO-coated LSCF cathode remains to be ~0.05 Ωcm2 under the same condition, suggesting that BCO is catalytically active to ORR but inert to Cr-poisoning. At 700 °C, the single cells with the BCO-coated LSCF cathode show an excellent peak power density of ~0.514 Wcm−2 and significantly enhanced durability (degradation rate of 0.086 %h−1 at 0.8 V), much better than those of cells with a bare LSCF cathode (~0.448 Wcm−2 and degradation rate of 0.31 %h−1 at 0.8 V). Raman analysis indicated that the presence of the BCO catalyst coating greatly reduced the amount of Cr accumulated on the cathode surface, thus alleviating the formation of SrCrO4.

Inspired by the structures and functions of sand barriers in the desert region, in article number https://doi.org/10.1002/advs.201800031 Wei Yuan, Meilin Liu, and co‐workers report a 3D composite current collector with checkerboard‐like surface structure for lithium‐ion batteries. Like the windbreak and sand fixation effects of the sand barrier, the checkerboard‐like surface structure helps to effectively alleviate the pulverization of electrode materials and enhance the electrochemical performance of lithium‐ion batteries.

A rational synthesis route towards

Advanced electrical energy storage technology is a game changer for a clean, sustainable, and secure energy future because efficient utilization of newable energy hinges on cost-effect and efficient energy storage. Further, the viability of many emerging technologies depends on breakthroughs in energy storage technologies, including electric vehicles (EVs) or hybrid electric vehicles (HEVs) and smart grids. Lithium-ion batteries (LIBs), a great success in the portable electronics sector, are believed also the most promising power sources for emerging technologies such as EVs and smart grids. To date, however, the existing LIBs (with LiCoOx cathode and graphite anode) are still unable to meet the strict requirements for safety, cycling stability, and rate capability. The development of advanced anode materials, which can overcome the shortcomings of graphite anode (such as formation of dendritic lithium during charge and undesirable solid electrolyte interface), is of critical importance to enhancing the cycling stability and operational safety of LIBs. Lithium titanate (Li4Ti5O12) has recently attracted considerable attentions as a potential anode material of LIBs for high power applications due to several outstanding features, including a flat charge/discharge plateaus (around 1.55 V vs. Li/Li+) because of the two-phase lithium insertion/extraction mechanism and minimum chance for the formation of SEI and dendritic lithium, dramatically enhance the potential for high rate capability and safety. In addition, there is almost no volume change during the lithium insertion and extraction processes, ensuring a high cycling stability and long operational life. However, the electronic conductivity of Li4Ti5O12 is relatively low, resulting in large polarization lose, more so at higher cycling rates, and poor rate performance. Currently, considerable research efforts have been devoted to improving the performance of Li4Ti5O12 at fast charge/discharge rates, and some important progresses have been made. In this review, we first present a general overview of the structural features, thermodynamic properties, transport properties, and the electrochemical behavior of Li4Ti5O12 under typical battery operating conditions. We then provide a comprehensive review of the recent advancements made in characterization, modification, and applications of Li4Ti5O12 electrodes to LIBs, including nanostructuring, surface coating, morphological optimization, doping, and rational design of composite electrodes. Finally, we highlight the critical challenges facing us today and future perspectives for further development of Li4Ti5O12-based electrodes. It is hoped that this review may provide some useful guidelines for rational design of better electrodes for advanced LIBs.

Porous carbon materials have received considerable attention recently, particularly in the energy field. To meet the increasing demands for electrochemical energy conversion and storage-related applications, the development of novel porous carbon materials that show high electrochemical performances is highly desired. Here, a facile method for the preparation of nitrogen-doped hierarchically porous carbon materials is proposed. Cost-effective chitosan is selected as the nitrogen-containing carbon source, and the carbonation is realized in a ZnCl2 molten salt at a temperature range of 400–700 °C. Hierarchically porous carbon with a specific surface area of 1582 m2 g−1 and a high nitrogen content of 9.0 wt.% is obtained at a carbonation temperature of 600 °C with a high carbon yield of 42 wt.% based on the weight of chitosan. Importantly, using this as-synthesized carbon material as the electrode in supercapacitors, high specific capacitances of 252 and 145 F g−1 at current densities of 0.5 and 50 A g−1, respectively, and stable cycling performance without decay after 10,000 cycles at 8 A g−1 are realized. The facile synthesis, easy recovery of ZnCl2 and high carbon yield make this new method highly promising for the preparation of porous carbon materials for use in supercapacitors and other fields.

A facile hydrothermal method is utilized to produce nanostructured NiCo2S4 arrays on carbon fiber paper with controlled morphologies to study the effect of morphology on their electrochemical performance in supercapacitors. Specifically, NiCo2S4 solid nanofiber, nanotube, and hollow nanoneedle of the same crystalline structure are synthesized by controlling the conditions of the hydrothermal synthesis. Among the three different morphologies studied, the hollow nanoneedle of NiCo2S4 shows the highest capacity and the longest cycling life, demonstrating a specific capacitance of ~1154 F g−1 at a charge–discharge current density of 1 A g−1 and negligible capacity loss after 8000 cycles (at a rate of 10 A g−1). This high performance is attributed to the unique nanostructure of the hollow nanoneedle, suggesting that the morphology of NiCo2S4 plays a vital role in determining the electrochemical performance. Further, an asymmetric capacitor consisting of NiCo2S4 hollow nanoneedle electrode and a tape-cast activated carbon film electrode achieves an energy density of ~17.3 Wh kg−1 at 1 A g−1 and a power density of ~0.2 kW kg−1 at 20 A g−1 in a voltage range of 0–1.5 V, implying that it has a great potential for a wide variety of practical applications.

While the architecture, surface morphology, and electrical conductivity of current collectors may significantly affect the performance of electrochemical cells, many challenges still remain in design and cost‐effective fabrication of highly efficient current collectors for a new generation of energy storage and conversion devices. Here the findings in design and fabrication of a 3D checkerboard‐like Cu@CNF composite current collector for lithium‐ion batteries are reported. The surface of the current collector is modified with patterned grooves and amorphous carbon nanofibers, imitating the checkerboard‐like sand barriers in desert regions. Due to a combined effect of the grooves and the carbon nanofibers, a battery based on this current collector retains a reversible capacity of 410.1 mAh g−1 (beyond the theoretical capacity of carbonaceous materials of 372 mAh g−1) with good capacity retention (greater than 84.9% of the initial capacity after 50 cycles), resulting in 66.2% and 42.6% improvement in reversible capacity and capacity retention, respectively, compared to the batteries using traditional Cu current collectors. Based on the excellent electrochemical performance, this composite current collector is believed to be an attractive alternative to the traditional commercially used current collectors for the anode of high‐power energy storage systems.

Solid oxide fuel cells (SOFCs), which directly convert chemical energy into electricity, have several advantages, such as fuel flexibility and low emissions. Unfortunately, the performance and stability of SOFCs with state-of-the-art Ni-based anodes are sensitive to impurities, such as sulfur, which is a common component of practical fuels, including natural gas and renewable biogas. The development of sulfur-tolerant anode materials is important for successfully operating SOFCs with sulfur-containing practical fuels. In this study, a core–shell architecture was fabricated from solution infiltration and was evaluated as a sulfur-tolerant anode for SOFCs. For the first time, we used a lithium conductive material, Li0.33La0.56TiO3 (LLTO, perovskite oxide), as the shell for anodic reactions. The resulting cell delivered higher electrochemical activities than similar cells, with widely used sulfur-tolerant perovskite anodes. In addition, the cell with the core–shell structured anode demonstrated favorable stability over 70 hours' operation when using 1000 ppm H2S–H2 fuel at 800 °C. In contrast, the cell with an anode composed of nanoparticles failed after only 5.5 hours under the same operation conditions. This study offers a new strategy for developing highly sulfur tolerant and efficient anodes for SOFCs.

Metal oxides and carbon-based materials are the most promising electrode materials for a wide range of low-cost and highly efficient energy storage and conversion devices. Creating unique nanostructures of metal oxides and carbon materials is imperative to the development of a new generation of electrodes with high energy and power density. Here we report our findings in the development of a novel graphene aerogel assisted method for preparation of metal oxide nanoparticles (NPs) derived from bulk MOFs (Co-based MOF, Co(mIM)2 (mIM = 2-methylimidazole). The presence of cobalt oxide (CoOx) hollow NPs with a uniform size of 35 nm monodispersed in N-doped graphene aerogels (NG-A) was confirmed by microscopic analyses. The evolved structure (denoted as CoOx/NG-A) served as a robust Pt-free electrocatalyst with excellent activity for the oxygen reduction reaction (ORR) in an alkaline electrolyte solution. In addition, when Co was removed, the resulting nitrogen-rich porous carbon–graphene composite electrode (d...

With an aim to develop a proton-exchange-membrane fuel cell (PEMFC) with improved water management, catalyst-coated membranes based upon Nafion 212 membrane with electrodes of dual-layer structure which consist of one hydrophilic layer of Pt/C + Nafion and one hydrophobic layer of Pt/C + PTFE arranged in a proper order, is specifically designed and successfully fabricated by a facile high-temperature spray deposition technique. Dual-layer structured anode and cathode are separately evaluated by electrochemical performance in single cells. Effect of relative thickness of the dual layers in the electrode on the cell performance is investigated. No improvement in cell performance is observed by adopting the dual-layer structure for the anode as compared to conventional anode with single hydrophilic catalyst layer. However, better cell performance is observed for the cell with dual-layer structured cathode, and the optimal cell reaches a peak power density of about 800 mW cm− 2 at 50 °C with humidified hydrogen and oxygen as fuel and oxidant respectively.

The potential to use ethanol as a fuel places solid oxide fuel cells (SOFCs) as a sustainable technology for clean energy delivery because of the renewable features of ethanol versus hydrogen. In this work, we developed a new class of anode catalyst exemplified by Ni+BaZr0.4Ce0.4Y0.2O3 (Ni+BZCY) with a water storage capability to overcome the persistent problem of carbon deposition. Ni+BZCY performed very well in catalytic efficiency, water storage capability and coking resistance tests. A stable and high power output was well maintained with a peak power density of 750 mW cm(-2) at 750 °C. The SOFC with the new robust anode performed for seven days without any sign of performance decay, whereas SOFCs with conventional anodes failed in less than 2 h because of significant carbon deposition. Our findings indicate the potential applications of these water storage cermets as catalysts in hydrocarbon reforming and as anodes for SOFCs that operate directly on hydrocarbons.

Cobalt-free perovskite-type oxides with the nominal composition of BaNbyFe1−yO3−δ (y=0.025–0.20) are synthesized and evaluated as materials used in ceramic membranes for oxygen separation. The effects of Nb-doping on the crystal structure, surface morphology, electrical conductivity, chemical bulk diffusion and surface exchange, and oxygen permeability of the oxides are systematically investigated using XRD, SEM, four-probe DC conductivity, electrical conductivity relaxation technique, and oxygen permeation studies. A small amount of Nb-doping induces a sharp increase in electrical conductivity. A further increase in the Nb-doping amount, however, lowers the electrical conductivity as a result of the blocking effect of Nb5+ on electronic conduction. A small amount of Nb-doping has less impact on the sintering capability. From the oxygen permeation test, it was found that Nb-doping could significantly enhance the oxygen permeability, especially below 750 °C. Among all of the compositions, BaNb0.05Fe0.95O3−δ shows the highest oxygen permeation fluxes, reaching 1.35 and 0.61 mL cm−2 min−1 for a membrane with a thickness of 1.0 mm at 900 and 700 °C, respectively. Furthermore, the membrane is rate-controlled mainly by bulk diffusion, indicating the potential to further improve the oxygen permeation flux via a thinner membrane.

In situ Raman spectroscopy is a powerful technique for probing the structure and phase composition of the electrode materials that are undergoing charge-discharge process. Herein, the charge storage mechanism of as-prepared Ni(HCO3)2 nanomaterial is successfully studied by using the in situ Raman spectroscopy. The charge storage can be attributed to the deep oxidation of Ni2+ into Ni3+, and the irreversible phase transformation of γ-NiOOH into disordered β-Ni(OH)2 damages the crystal structure of Ni(HCO3)2, arousing the capacity loss of the electrode during the long-term cycling process. Under the guidance of the experimental investigations, a porous Ni(HCO3)2/reduced graphene oxide (rGO) nanocomposite is designed and synthesized, exhibiting ultrahigh specific capacity (846 C g−1) and excellent rate capability (618 C g−1 at 20 A g−1). When coupled with an negative electrode based on rGO, the resulting hybrid supercapacitor shows an ultrahigh energy density of 66 Wh kg−1 at power density of 1.9 kW kg−1 and good cycling stability. These findings provide important insight into the mechanism of charge storage, and scientific basis for design of high-performance energy storage materials.

Currently, metal-organic frameworks (MOFs) are intensively studied as active materials for electrochemical energy storage applications due to their tunable structure and exceptional porosities. Among them, water stable pillared MOFs with dual ligands have been reported to exhibit high supercapacitor (SC) performance. Herein, the "One-for-All" strategy is applied to synthesize both positive and negative electrodes of a hybrid SC (HSC) from a single pillared MOF. Specifically, Ni-DMOF-TM ([Ni(TMBDC)(DABCO)0.5 ], TMBDC: 2,3,5,6-tetramethyl-1,4-benzenedicarboxylic acid, DABCO: 1,4-diazabicyclo[2.2.2]-octane) nanorods are directly grown on carbon fiber paper (CFP) (denoted as CFP@TM-nanorods) with the help of triethylamine and function as the positive electrode of HSC under alkaline electrolyte. Meanwhile, calcinated N-doped hierarchical porous carbon nanorods (CFP@TM-NPCs) are produced and utilized as the negative counter-electrode from a one-step heat treatment of CFP@TM-nanorods. After assembling these two electrodes together to make a hybrid device, the TM-nanorods//TM-NPCs exhibit a wide voltage window of 1.5 V with a high sloping discharge plateau between 1-1.2 V, indicating its great potential for practical applications. This as-described "One-for-All" strategy is widely applicable and highly reproducible in producing MOF-based electrode materials for HSC applications, which shortens the gap between experimental synthesis and practical application of MOFs in fast energy storage.

Pyrolyzing Fe- and N-contained precursor together or separately with graphene results in codoped graphene dominated by bonded or separated Fe and N configuration, respectively. While the FeN bonded case greatly enhances activity toward oxygen reduction, the separated one does not. This rationally designed Fe and N codoped 3D graphene exhibits superior electrocatalytic activity than the state-of-the-art Pt/C catalyst.

Composites consisting of nanoparticles of iron oxides and graphene have attracted considerable attention in numerous applications; however, the synthesis methods used to achieve superior functionalities are often complex and unamenable to low-cost large-scale industrial production. Here, we report our findings in exploring a simple strategy for low-cost fabrication of multifunctional composites with enhanced properties. In particular, we have successfully prepared FeO(OH) nanoflake/graphene and nano-Fe3O4/graphene composites from commercially available Fe powders and graphite oxides using a simple and low-cost solid-state process, where the metallic Fe is converted to FeO(OH) nanoflake and graphite oxide is reduced/exfoliated to graphene. The resultant nano-Fe3O4/graphene composite is multifunctional, demonstrates specific capacities of 802 and 629 mA h g(-1), respectively, at 1000 and 2000 mA g(-1) as an electrode material for lithium-ion batteries (LIBs), and also displays efficient catalytic activity for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER); the nominal overpotentials are lower than those for previously reported metal-based catalysts (e.g., IrO2, RuO2, and Pt/C). The dramatically enhanced properties are attributed to the synergistic mechanochemical coupling effects between iron oxide and graphene introduced by the facile process, which is well suited for large-scale cost-effective fabrication.

Flexible V-O-C composite nanofibers were fabricated from solution precursors via electrospinning and were investigated as free-standing and additive-free film electrodes for supercapacitors. Specifically, composite nanofibers (V0, V5, V10 and V20) with different vanadyl acetylacetonate (VO(acac)2) contents of 0, 5, 10 and 20 wt% with respect to polyacrylonitrile (PAN) were prepared. The composite nanofibers were comparatively studied using XRD, Raman spectroscopy, XPS, N2 adsorption-desorption, FE-SEM, TEM and S-TEM. The vanadium element was found to be well-dispersed in the carbon nanofibers, free from the formation of an aggregated crystalline phase, even in the case of V20. A specific surface area of 587.9 m(2) g(-1) was reached for V10 after calcination, which is approximately twice that of the vanadium-free carbon nanofibers (V0, 300.9 m(2) g(-1)). To perform as an electrode for supercapacitors in an aqueous electrolyte, the V10 film delivered a specific capacitance of 463 F g(-1) at 1 A g(-1). V10 was also able to retain a specific capacitance of 380 F g(-1), even at a current density of 10 A g(-1). Additionally, very stable cycling stability was achieved, maintaining an outstanding specific capacitance of 400 F g(-1) at 5 A g(-1) after charge-discharge cycling 5000 times. Thus, V-O-C composite nanofibers are highly attractive electrode materials for flexible, high-power, thin film energy storage devices and applications.

Although a wide variety of three-dimensional porous electrode architectures have been created for supercapacitors to markedly enhance the charge and mass transfer associated with cycling, their low volumetric energy densities limit applications in many energy storage systems. In this work, we report a unique electrode architecture consisting of Ni3S2 nanosheet-onto-Ni3S2-nanorods grown on nickel foam and prepared using a simple one-step hydrothermal method. When tested as an electrode for a supercapacitor (using a three-electrode configuration), this material exhibited excellent rate capability and cycling stability at high cycling rates. The obtainable capacitance decreased by

In operando resonance Raman spectroscopy suggests quantitative correlation between phonon band properties and the amount of charge storage of high-energy density NiO2H x battery/pseudocapacitive material. Comparing the spectroscopic evolution using different electrolytes reveals the contributions of breaking/formation of O-H bonds and insertion/extraction of cations to electrochemical charge storage of NiO2H x .

To develop high-power and fast energy storage devices, electrode materials with superior ionic and electronic transport properties should be developed. Herein, a novel composite electrode with TiO2 nanotubes connected onto a conductive carbon nanofiber network is designed and realized through a general route. The carbon matrix is first synthesized using an electrospinning technique and heat-treatment, and the embedded rutile TiO2 nanoparticles are formed in situ as the starting materials for the hydrothermal reaction. After hydrothermal treatment, a three-dimensional (3D) porous architecture is developed. The mechanistic analysis demonstrates that the raw embedded rutile TiO2 nanoparticles react with NaOH solution and go out around the carbon nanofiber matrix to form a well-connected 3D porous nanotube/nanofiber architecture. By using the as-prepared films as electrodes for lithium-ion batteries (LIBs) without the application of any additional conductive agent or binder, high initial capacity and excellent rate performance (214 mA h g−1 at 5 C rate, 180 mA h g−1 at 10 C rate, 138 mA h g−1 at 20 C rate and 112 mA h g−1 at 30 C rate) are achieved. Moreover, the electrode shows stable cycling performance, especially at a high rate of 30 C, without undergoing decay after 1000 cycles.

As a lithium-intercalation material, high crystallinity is important for Li4Ti5O12 to achieve good capacity and cycling stability, while a large surface area and a short lithium diffusion distance are critical to increase rate capacity. In this study, well-crystallized Li4Ti5O12 nanoplates with outstanding electrochemical performance were facially prepared through a two-step hydrothermal preparation with benzyl alcohol–NH3·H2O (BN) as the solvent and a subsequent intermediate-temperature calcination at 500 °C for 2 h in air. To support the superiority of benzyl alcohol–NH3·H2O (BN) for hydrothermal synthesis, ethanol–NH3·H2O (EN) was also comparatively studied as solvent. In addition, different hydrothermal reaction times were tried to locate the optimal reaction time. The nature of as-prepared Li4Ti5O12–BN (LTO–BN) and Li4Ti5O12–EN (LTO–EN) was characterized by XRD, N2 adsorption/desorption tests, SEM, TEM and TGA-DSC. Compared with EN, the BN hydrothermal solvent facilitated the formation of nanosheet-Li4Ti5O12 with wall thicknesses of 8–15 nm and better crystallization. After a 6 h hydrothermal reaction at 180 °C and subsequent calcination, well-crystallized Li4Ti5O12–BN nanoplates were produced, which demonstrate a superior discharge capacity of 160 mA h g−1, even at 40 C, maintaining a capacity of 88.8% compared with that at 1 C. The nanoplates also exhibited excellent cycling stability, retaining a discharge capacity of 153 mA h g−1 after 1000 charge–discharge cycles at 10 C.

We demonstrate a facile and effective way for the fabrication of a flexible, homogeneous and neat α-MoO3 thin-film electrode for lithium-ion batteries with high performance without using any binder and conductive additives. Single-crystalline α-MoO3 nanobelts with uniform width of around 200 nm and length at the micrometer level are first synthesized by a simple water-based hydrothermal route. The as-obtained α-MoO3 slurry is then directly deposited onto a copper foil current collector by the doctor blade method. The formation of the α-MoO3 film and its good adhesion to the current collector is realized via van der Waals attraction forces through a drying process. The structure and morphology of the α-MoO3 nanobelt particles and thin-film electrode are systematically characterized by XRD, Raman spectra, TEM, SEM and XPS techniques, and the electrochemical properties are investigated by CV and constant current discharge–charge test techniques. The α-MoO3 film electrode exhibits a reversible specific capacity of ∼1000 mA h g−1 at 50 mA g−1 and a stable capacity retention of 387–443 mA h g−1 at 2000 mA g−1, indicating its high Li storage capacity, superior rate performance and good cycling stability. The electrode material, as well as the fabrication technique, is highly promising for practical use in high energy and power density lithium-ion batteries.