Ion-Sieve-Confined Synthesis of Size-Tunable Ru for Electrochemical Hydrogen Evolution.

The controllable and low-cost synthesis of nanometal particles is highly desired in scientific and industrial research. Herein, size-tunable Ru nanoparticles were synthesized by using a novel ion-sieve-confined reduction method. The H2TiO3 ion-sieve was used to adsorb Ru3+ into the hydroxyl-enriched porous [TiO3]2- layers. The confined environment of the interlayer space facilitates Ru-Ru collision and bonding during annealing, achieving a precise reduction from Ru3+ to Ru0 without additional reductants. Owing to the confinement effect, Ru0 nanoparticles are uniformly embedded in the pores on the surface of the postannealed TiO2 matrix (Ru@TiO2). Ru@TiO2 exhibited a lower overpotential than Pt/C (57 vs 87 mV at 10 mA cm-2) for the HER in 0.1 M KOH solution. The confinement-induced reduction of metal ions was also preliminarily proved in ion-exchanged zeolites, which provides facile and abundant approaches for the size-controllable synthesis of nanometal catalysts with high catalytic activity.

Soft-in-Rigid Strategy Promoting Rapid and High-Capacity Lithium Storage by Chemical Scissoring.

Large and rapid lithium storage is hugely demanded for high-energy/power lithium-ion batteries; however, it is difficult to achieve these two indicators simultaneously. Sn-based materials with a (de)alloying mechanism show low working potential and high theoretical capacity, but the huge volume expansion and particle agglomeration of Sn restrict cyclic stability and rate capability. Herein, a soft-in-rigid concept was proposed and achieved by chemical scissoring where a soft Sn-S bond was chosen as chemical tailor to break the Ti-S bond to obtain a loose stacking structure of 1D chain-like Sn1.2Ti0.8S3. The in situ and ex situ (micro)structural characterizations demonstrate that the Sn-S bonds are reduced into Sn domains and such Sn disperses in the rigid Ti-S framework, thus relieving the volume expansion and particle agglomeration by chemical and physical shielding. Benefiting from the merits of large-capacity Sn with an alloying mechanism and high-rate TiS2 with an intercalation mechanism, the Sn1.2Ti0.8S3 anode offers a high specific capacity of 963.2 mA h g-1 at 0.1 A g-1 after 100 cycles and a reversible capacity of 250 mA h g-1 at 10 A g-1 after 3900 cycles. Such a strategy realized by chemical tailoring at the structural unit level would broaden the prospects for constructing joint high-capacity and high-rate LIB anodes.

Measured Regional Division Optimization for Acoustic Tomography Velocity Field Reconstruction in a Circular Area.

The acoustic tomography (AT) velocity field reconstruction technique has become a research hotspot in recent years due to its noninvasive nature, high accuracy, and real-time measurement advantages. However, most of the existing studies are limited to the reconstruction of the velocity field in a rectangular area, and there are very few studies on a circular area, mainly because the layout of acoustic transducers, selection of acoustic paths, and division of measured regions are more difficult in a circular area than in a rectangular area. Therefore, based on AT and using the reconstruction algorithm of the Markov function and singular value decomposition (MK-SVD), this paper proposes a measured regional division optimization algorithm for velocity field reconstruction in a circular area. First, an acoustic path distribution based on the multipath effect is designed to solve the problem of the limited emission angle of the acoustic transducer. On this basis, this paper proposes an adaptive optimization algorithm for measurement area division based on multiple sub-objectives. The steps are as follows: first, two optimization objectives, the condition number of coefficient matrix and the uniformity of acoustic path distribution, were designed. Then, the weights of each sub-objective are calculated using the coefficient of variation (CV). Finally, the measured regional division is optimized based on particle swarm optimization (PSO). The reconstruction effect of the algorithm and the anti-interference ability are verified through the reconstruction experiments of the model velocity field and the simulated velocity field.

Nanoscale Borate Coating Network Stabilized Iron Oxide Anode for High-Energy-Density Bipolar Lithium-Ion Batteries.

High-capacity metal oxides based on non-toxic earth-abundant elements offer unique opportunities as advanced anodes for lithium-ion batteries (LIBs). But they often suffer from large volumetric expansion, particle pulverization, extensive side reactions, and fast degradations during cycling. Here, an easy synthesis method is reported to construct amorphous borate coating network, which stabilizes conversion-type iron oxide anode for the high-energy-density semi-solid-state bipolar LIBs. The nano-borate coated iron oxide anode has high tap density (1.6 g cm-3 ), high capacity (710 mAh g-1 between 0.5 - 3.0 V, vs Li/Li+ ), good rate performance (200 mAh g-1 at 50 C), and excellent cycling stability (≈100% capacity resention over 1,000 cycles at 5 A g-1 ). When paired with high-voltage cathode LiCoO2 , it enables Cu current collector-free pouch-type classic and bipolar full cells with high voltage (7.6 V with two stack layers), achieving high energy density (≈350 Wh kg-1 ), outstanding power density (≈6,700 W kg-1 ), and extended cycle life (75% capacity retention after 2,000 cycles at 2 C), superior to the state-of-the-art high-power LIBs using Li4 Ti5 O12 anode. The design and methodology of the nanoscale polyanion-like coating can be applied to other metal oxides electrode materials, as well as other electrochemical materials and devices.

Ruthenium-Doped Cobalt-Chromium Layered Double Hydroxides for Enhancing Oxygen Evolution through Regulating Charge Transfer.

Exploring the origin of transition metal (TM) lattice-doped layered double hydroxides (LDHs) toward the oxygen evolution reaction (OER) plays a crucial role in engineering efficient electrocatalysts. Without understanding the physics behind the TM-induced catalytic enhancements, it would be challenging to design the next generation of electrocatalysts. Herein, single Ru atoms are introduced into a CoCr LDHs lattice to improve activity. In 0.1 m KOH, CoCrRu LDHs require only 290 mV overpotential to drive to 10 mA cm-2 and show a Tafel slope of 56.12 mV dec-1 . Electronic structure analyses based on density functional theory confirm that promoted OER activity originates from synergetic charge transfer among Ru, Cr, and Co elements. Specifically, Ru dopants can downshift d states of Co and enhance electron donation of Cr to oxygenates, which essentially breaks the scaling relation and achieves higher activity. This work provides insights into how single atomic Ru dopant tunes the electronic structures of its neighbor's active site Co and thus increases OER activities.

ZnO-Templated Selenized and Phosphorized Cobalt-Nickel Oxide Microcubes as Rapid Alkaline Water Oxidation Electrocatalysts.

Oxygen electrocatalysis is of remarkable significance for electrochemical energy storage and conversion technologies, together with fuel cells, metal-air batteries, and water splitting devices. Substituting noble metal-based electrocatalysts by decidedly effective and low-cost metal-based oxygen electrocatalysts is imperative for the commercial application of these technologies. Herein, a novel strategy is presented to fabricate selenized and phosphorized porous cobalt-nickel oxide microcubes by using a sacrificial ZnO spherical template and the resulting microcubes are employed as an oxygen evolution reaction (OER) electrocatalyst. The selenized samples manifest desirable and robust OER performance, with comparable overpotential at 10 mA cm-2 (312 mV) as RuO2 (308 mV) and better activity when the current reaches 13.7 mA cm-2 . The phosphorized samples exhibit core-shell structure with low-crystalline oxides inside amorphous phosphides, which ensures superior activity than RuO2 with the same overpotential (at 10 mA cm-2 ) yet lower Tafel slope. Such a surface doping method possibly will provide inspiration for engineering electrocatalysts applied in water oxidation.

Oxygen Evolution Activity of Co-Ni Nanochain Alloys: Promotion by Electron Injection.

Metal alloy nanoparticles have shown promising applications in electrocatalysis. However, the nanoparticles usually suffer from limited charge-transfer efficiency, which can be solved by preparing one-dimensional materials. Herein, Co-Ni alloy nanochains are prepared by a direct-current arc-discharge method. The nanochains, comprised of mutually coupled uniform nanospheres, can range up to several micrometers in size. When the alloy is exposed to air or under the electro-oxidation process, a metal-metal-oxide heterostructure is obtained. The alloy can inject electrons into the oxide, which makes it more suitable for electrocatalysis. The composition of the samples can be changed by varying the ratio of Ni/Co (i.e., Co, Co7 Ni3 , Co5 Ni5 , Co3 Ni7 , Ni) in the synthesis process. The nanochains show good oxygen evolution performance that correlates with the Ni/Co ratio. Co7 Ni3 demonstrates optimal activity with an onset point of 1.50 V vs. reversible hydrogen electrode (RHE) and overpotential of 350 mV at 10 mA cm-2 . The alloy nanochains also show excellent durability with 95.0 % current retention after a long-term test for 12 h.

Accelerating ion/electron transport by engineering an indium-based heterostructure toward large and reversible lithium storage.

The high activity of the In2O3/In2S3 heterostructure can be activated into homogeneous In2OxS3-x nanodots, thereupon stabilizing the subsequent cycles. The In2O3/In2S3 can offer a high capacity of 1140 mA h g-1 at 0.1 A g-1 after 290 cycles, and even at 1 A g-1, it harvests a reversible capacity of 900 mA h g-1 after 600 cycles.

Tailoring Ultrafast and High-Capacity Sodium Storage via Binding-Energy-Driven Atomic Scissors.

Controllably tailoring alloying anode materials to achieve fast charging and enhanced structural stability is crucial for sodium-ion batteries with high rate and high capacity performance, yet remains a significant challenge owing to the huge volume change and sluggish sodiation kinetics. Here, a chemical tailoring tool is proposed and developed by atomically dispersing high-capacity Ge metal into the rigid and conductive sulfide framework for controllable reconstruction of GeS bonds to synergistically realize high capacity and high rate performance for sodium storage. The integrated GeTiS3 material with stable Ti-S framework and weak GeS bonding delivers high specific capacities of 678 mA h g-1 at 0.3 C over 100 cycles and 209 mA h g-1 at 32 C over 10 000 cycles, outperforming most of the reported alloying type anode materials for sodium storage. Interestingly, in situ Raman, X-ray diffraction (XRD), and ex situ transmission electron microscopy (TEM) characterizations reveal the formation of well-dispersed Nax Ge confined in the rigid Ti-S matrix with suppressed volume change after discharge. The synergistically coupled alloying-conversion and surface-dominated redox reactions with enhanced capacitive contribution and high reaction reversibility by a binding-energy-driven atomic scissors method would break new ground on designing a high-rate and high-capacity sodium-ion batteries.

Alloying Motif Confined in Intercalative Frameworks toward Rapid Li-Ion Storage.

High-capacity alloying-type anodes suffer poor rate capability due to their great volume expansion, while high-rate intercalation-type anodes are troubled with low theoretical capacity. Herein, a novel mechanism of alloying in the intercalative frameworks is proposed to confer both high-capacity and high-rate performances on anodes. Taking the indium-vanadium oxide (IVO) as a typical system, alloying-typed In is dispersed in the stable intercalative V2 O3 to form a solid solution. The alloying-typed In element provides high lithium storage capacity, while the robust, Li-conductive V-O frameworks effectively alleviate the volume expansion and aggregation of In. Benefiting from the above merits, the anode exhibits a high specific capacity of 1364 mA h g-1 at 1 A g-1 and an extraordinary cyclic performance of 814 mA h g-1 at 10 A g-1 after 600 cycles (124.9 mA h g-1 after 10 000 cycles at 50 A g-1 ). The superior electrochemical rate capability of (In,V)2 O3 solid solution anode rivals that of the reported alloying anode materials. This strategy can be extended for fabricating other alloying/intercalation hybrid anodes, such as (Sn,V)O2 and (Sn,Ti)O2 , which demonstrates the universality of confining alloying motifs in intercalative frameworks for rapid and high-capacity lithium storage.

Enhancing electrocatalytic water splitting by surface defect engineering in two-dimensional electrocatalysts.

Overall electrocatalytic water splitting can efficiently and sustainably produce clean hydrogen energy to alleviate the global energy crisis and environmental pollution. Two-dimensional (2D) materials with a unique band structure and surface conformation have emerged as promising electrocatalysts for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). However, the intrinsic activities of primitive 2D materials in the catalytic process are still inferior to those of noble metal-based electrocatalysts. Surface defect engineering can modulate the electronic structure of 2D materials and induce new physicochemical properties, promoting their electrocatalytic performance. Herein, this minireview focuses on some recent developments in surface defect engineering, including the contribution of active sites, the derivation of the heterogeneous interface, and the anchoring of active substances, which provides an effective way to further optimize 2D electrocatalysts for water splitting. Furthermore, the typical morphological characteristics, catalytic activity, stability and catalytic mechanism of these 2D electrocatalysts are introduced. We believe that this minireview will help design more efficient and economical electrocatalysts for overall water splitting.

Proton-insertion-pseudocapacitance of tungsten bronze tunnel structure enhanced by transition metal ion anchoring.

The one-dimensional channel array of hexagonal tungsten bronze (WO3) offers an electron transfer matrix, but its overwhelming H+ adsorption hinders it from being a good supercapacitor electrode material. Inspired by the Volcano plot on the relation between transition-metal and free energy of H-adsorption, we propose a new strategy to anchor transition metal ions (Zn2+, Cu2+, Ni2+, Ag+, Au3+ and Ir3+) into the WO3 lattice to improve proton-insertion based pseudocapacitance. Among the variety of transition metals, Zn2+ exhibits the optimal O 2p band center, which matches well with the best experimental capacitive behavior. The molar ratio of Zn/WO3 ranges from 0.2 to 0.6. The specific capacitance for Zn2+-anchored WO3 (390 F g-1) reaches 202% of that of WO3 (193 F g-1) at 0.5 A g-1 with robust stability (259 F g-1 at 3 A g-1 for 3000 cycles). Density functional theory confirms that O 2p is shifted down by the d-filling cations, which corresponds to alleviated O-H interaction and facilitated H+ desorption. The band tuning by transition-metal-ion incorporation would break new ground on developing high-capacitance metal oxide supercapacitors.

Ultrasonic Thermometry Algorithm Based on Inverse Quadratic Function.

At present, there are two ways to obtain temperature information: contact type and nonintrusive type. As a nonintrusive temperature measurement method, ultrasonic thermometry can be used to acquire the temperature distribution of complex fields conveniently. By measuring the time-of-flight (TOF) between ultrasonic transmitters and receivers, and according to the relationship between temperature and ultrasonic velocity, the temperature distribution can be reconstructed. Among the existing algorithms, the least square method (LSM) will lose much information near the edges of the temperature field, and the algebra reconstruction technique (ART) is time-consuming with low reconstruction accuracy. In this article, an improved reconstruction algorithm based on an inverse quadratic function and singular value decomposition (IQ-SVD) is proposed, which can effectively increase the reconstruction accuracy. The simulations of the real temperature data are conducted in ideal and noisy environments, respectively. Moreover, the influence of region division and shape parameters on reconstruction accuracy is discussed. The simulation results indicate that, compared with conventional algorithms, the proposed algorithm can accurately reflect the temperature distribution, and the root mean square error in the central region and the edge region is reduced by 0.49% at least, and 1.28% at most.

Constructing porous TiO2 crystals by an etching process for long-life lithium ion batteries.

"Zero strain" materials, which have no volume change when charging and discharging, show ultra-long cycling stabilities when used as lithium-ion battery anodes, making them an area of extreme interest in this decade. For a typical anatase TiO2 crystal, the volume change is 3-4% during Li insertion/extraction, which is not "zero strain". As the Ti/O packing in the TiO2 lattice is too tight, there is insufficient void space for Li insertion, leading to volume expansion and structural collapse. Herein, pseudo-"zero-strain" TiO2 is achieved via designing TiO2 crystals with abundant inner mesopores, making Ti/O loose-packed via the acid-etching of K2Ti8O17, providing sufficient space for Li intercalation. Instead of the traditional cut-off potential of 1 V used for Ti-/Nb-based anodes, we choose 0.01 V as the cut-off to make the best of the extra capacity contributed by the mesopores. As expected, plenty of mesopores could serve as "Li+-reservoirs" for fast lithium storage, demonstrating exceptional high-rate performance with an average capacity of 109.6 mA h g-1 after 30 000 cycles at 60 C and 100 mA h g-1 at 120 C. Such a strategy of combining a mesoporous structure and cut-off potential regulation may pave a solid pathway for constructing novel high-power anodes.

Co5.47N loaded N-doped carbon as an efficient bifunctional oxygen electrocatalyst for a Zn-air battery.

Highly active bifunctional electrocatalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) play a pivotal role in Zn-air batteries. The high cost, scarcity and instability of precious-metal-based electrocatalysts for the ORR and OER dramatically hamper their practical application in such clean-energy set-ups. Here, we report highly active Co5.47N-loaded N-doped carbon (CoNMC), prepared via the direct NH3 annealing of a millet-CoCl2 mixture, which is a cheap and mass-producible form of biomass. The optimized product shows superior ORR activity (a half-wave potential of 0.81 V vs. RHE) and electrochemical stability (a 16.5 mV negative shift of the half-wave potential after 2000 cycles) in alkaline media. Also, it shows appealing OER activity (an operating potential at 10 mA cm-2 of 1.62 V vs. RHE). This excellent electrochemical performance can be attributed to the formation of active Co5.47N nanoparticles, the large specific surface area, the abundance of nitrogen active sites, and the high graphitization degree. When assembled into a Zn-air battery, the CoNMC-based cell shows comparable performance to a Pt/C-RuO2 one.

Niobium dioxide prepared by a novel La-reduced route as a promising catalyst support for Pd towards the oxygen reduction reaction.

Strong electron coupling between an active center and support ensures a significant improvement in catalytic performance. Herein, niobium dioxide nanoparticles (NbO2 NPs), prepared by a facile and controllable La-reduced route for the first time, serve as a catalyst support for Pd and demonstrate superior activity toward the oxygen reduction reaction (ORR). In contrast to commercial Pd/C, Pd/NbO2 shows a positive shift of 32 mV in half-wave potential, better robustness and stronger tolerance against methanol, which are attributed to the electron transfer from NbO2 to Pd.

Orthorhombic Nb2O5-x for Durable High-Rate Anode of Li-Ion Batteries.

Li4Ti5O12 anode can operate at extraordinarily high rates and for a very long time, but it suffers from a relatively low capacity. This has motivated much research on Nb2O5 as an alternative. In this work, we present a scalable chemical processing strategy that maintains the size and morphology of nano-crystal precursor but systematically reconstitutes the unit cell composition, to build defect-rich porous orthorhombic Nb2O5-x with a high-rate capacity many times those of commercial anodes. The procedure includes etching, proton ion exchange, calcination, and reduction, and the resulting Nb2O5-x has a capacity of 253 mA h g-1 at 0.5C, 187 mA h g-1 at 25C, and 130 mA h g-1 at 100C, with 93.3% of the 25C capacity remaining after cycling for 4,000 times. These values are much higher than those reported for Nb2O5 and Li4Ti5O12, thanks to more available surface/sub-surface reaction sites and significantly improved fast ion and electron conductivity.

Boron Embedded in Metal Iron Matrix as a Novel Anode Material of Excellent Performance.

Boron, the most ideal lithium-ion battery anode material, demonstrates highest theoretical capacity up to 12 395 mA h g-1 when forming Li5 B. Furthermore, it also exhibits promising features such as light weight, considerable reserves, low cost, and nontoxicity. However, boron-based materials are not in the hotspot list because Li5 B may only exist when B is in atomically isolated/dispersed form, while the aggregate material can barely be activated to store/release Li. At this time, an ingenious design is demonstrated to activate the inert B to a high specific capacity anode material by dispersing it in a Fe matrix. The above material can be obtained after an electrochemical activation of the precursors Fe2 B/Fe and B2 O3 /Fe. The latter harvests the admirable capacity, ultrahigh tap density of 2.12 g cm-3 , excellent cycling stability of 3180 mA h cm-3 at 0.1 A g-1 (1500 mA h g-1 ) after 250 cycles, and superlative rate capability of 2650 mA h cm-3 at 0.5 A g-1 , 2544 mA h cm-3 at 1.0 A g-1 , and 1696 mA h cm-3 at 2.0 A g-1 . Highly conductive matrix promoted reversible Li storage of boron-based materials might open a new gate for advanced anode materials.

Charge-Transfer-Promoted High Oxygen Evolution Activity of Co@Co9S8 Core-Shell Nanochains.

Co@Co9S8 nanochains with core-shell structures are prepared by a direct-current arc-discharge technique and followed sulfurization at 200 °C. The nanochains, which consist of uniform nanospheres connecting each other, can range up to several micrometers. The thickness of Co9S8 shell can be changed by regulating the sulfurization time. In this heterostructure of Co@Co9S8, Co nanochains function as a conductive network and can inject electrons into Co9S8, which manipulates the work function of Co9S8 and makes it more apposite for catalysis. The density functional theory calculation also reveals that coupling with Co can significantly reduce the overpotential needed to drive the oxygen evolution process. On the basis of the exclusive structure, Co@Co9S8 nanochains have shown high catalytic activity in the oxygen evolution reaction. Co@Co9S8 reaches an overpotential of 285 mv at 10 mA cm-2, which is much lower than that of Co nanochains (408 mV) and Co9S8 (418 mV). Co@Co9S8 also shows higher catalytic activity and robustness compared to state-of-the-art noble-metal catalyst RuO2.

Ti3+-Promoted High Oxygen-Reduction Activity of Pd Nanodots Supported by Black Titania Nanobelts.

One-dimensional nanocrystals favoring efficient charge transfer have attracted enormous attentions, and conductive nanobelts of black titania with a unique band structure and high electrical conductivity would be interestingly used in electrocatalysis. Here, Pd nanodots supported by two kinds of black titania, the oxygen-deficient titania (TiO2-x) and nitrogen-doped titania (TiO2-x:N), were synthesized as efficient composite catalysts for oxygen-reduction reaction (ORR). These composite catalysts show improved catalytic activity with lower overpotential and higher limited current, compared to the Pd nanodots supported on the white titania (Pd/TiO2). The improved activity is attributed to the relatively high conductivity of black titania nanobelts for efficient charge transfer (CT) between Ti3+ species and Pd nanodots. The CT process enhances the strong metal-support interaction (SMSI) between Pd and TiO2, which lowers the absorption energy of O2 on Pd and makes it more suitable for oxygen reduction. Because of the stronger interaction between Pd and support, the Pd/TiO2-x:N also shows excellent durability and immunity to methanol poisoning.