In-Bi Electrocatalyst for the Reduction of CO2 to Formate in a Wide Potential Window.

The CO2 atmospheric concentration level hit the record at more than 400 ppm and is predicted to keep increasing as the dependence on fossil fuels is inevitable. The CO2 electrocatalytic conversion becomes an alternative due to its environmental and energy-friendly properties and benign operation condition. Lately, bimetallic materials have drawn significant interest as electrocatalysts due to their distinct properties, which the parents' metal cannot mimic. Herein, the indium-bismuth nanosphere (In16Bi84 NS) was fabricated via the facile liquid-polyol technique. The In16Bi84 NS exhibits exceptional performance for CO2 reduction to formate, with the faradaic efficiency (FE) approaching ∼100% and a corresponding partial current density of 14.1 mA cm-2 at -0.94 V [vs the reversible hydrogen electrode (RHE)]. Furthermore, the FE could be maintained above 90% in a wide potential window (-0.84 to -1.54 V vs the RHE). This superior performance is attributed to the tuned electronic properties induced by the synergistic interaction between In and Bi, enabling the intermediates to be stably adsorbed on the catalyst surface to generate more formate ions.

Porous carbon microspheres with highly graphitized structure for potassium-ion storage.

Porous carbon materials are promising candidates for anode materials in rechargeable potassium-ion batteries. However, their high surface area and low crystallinity usually cause side reactions with electrolytes and slanted charge/discharge profiles. Herein, we report the synthesis of porous carbon microspheres with highly graphitized structure and enhanced potassium-ion storage properties. The prepared carbon microspheres exhibit a low working potential of ~0.2 V, high Coulombic efficiency, and a stable reversible capacity of 292.0 mAh/g after 100 cycles, which is significantly higher than that of commercial graphite (137.5 mAh/g after 100 cycles). These desirable performances are attributed to the high crystallinity of carbon and its porous structure, which provide active sites for potassium-ion storage and alleviate the stress caused by the large volume change during the insertion and extraction of potassium ions.

One-Pot Formation of Sb-Carbon Microspheres with Graphene Sheets: Potassium-Ion Storage Properties and Discharge Mechanisms.

Low-cost rechargeable batteries are ardently required for large-scale energy storage applications. In this regard, nonaqueous potassium-ion batteries (KIBs) are ascendant candidates due to the abundance of potassium resources, yet their energy density and cycle stability are insufficient for practical use. In this study, we report the Sb-based multicomposite comprising Sb nanoparticles, amorphous carbon (C), and reduced graphene oxide (rGO) as an anode material for KIBs. By adopting the tartaric acid as a carbon source and a chelating agent simultaneously, a multicomposite electrode with uniform and fine-sized Sb particles is realized. The Sb-C-rGO multicomposite exhibits a reversible capacity of 310 mAh g-1 at 0.5 A g-1 and 79% of it is retained after 100 cycles. Electrochemical tests show that the capacity fading in the Sb-C-rGO cell is attributed to the side reactions in the K metal and electrolyte, rather than the degradation of Sb nanoparticles. Furthermore, the formation of the metastable product is elucidated by Ostwald's step rule and density functional theory calculations. The present synthesis approach and the understanding of the failure and working mechanisms provide general insight into developing the alloying-type electrode materials for rechargeable batteries.

Hollow Cobalt Selenide Microspheres: Synthesis and Application as Anode Materials for Na-Ion Batteries.

The electrochemical properties of hollow cobalt oxide and cobalt selenide microspheres are studied for the first time as anode materials for Na-ion batteries. Hollow cobalt oxide microspheres prepared by one-pot spray pyrolysis are transformed into hollow cobalt selenide microspheres by a simple selenization process using hydrogen selenide gas. Ultrafine nanocrystals of Co3O4 microspheres are preserved in the cobalt selenide microspheres selenized at 300 °C. The initial discharge capacities for the Co3O4 and cobalt selenide microspheres selenized at 300 and 400 °C are 727, 595, and 586 mA h g(-1), respectively, at a current density of 500 mA g(-1). The discharge capacities after 40 cycles for the same samples are 348, 467, and 251 mA h g(-1), respectively, and their capacity retentions measured from the second cycle onward are 66, 91, and 50%, respectively. The hollow cobalt selenide microspheres have better rate performances than the hollow cobalt oxide microspheres.

Electrochemical properties of ultrafine Sb nanocrystals embedded in carbon microspheres for use as Na-ion battery anode materials.

Ultrafine Sb nanocrystals, uniformly distributed in a carbon matrix with a microspherical morphology, were synthesized by one-pot spray pyrolysis. The Sb-carbon composite microspheres exhibited good Na-storage properties with stable cyclability, a capacity retention of 90% over 100 cycles, and good rate performance.

Preparation of yolk-shell and filled Co9S8 microspheres and comparison of their electrochemical properties.

In this study, we report the first preparation of phase-pure Co9S8 yolk­shell microspheres in a facile two-step process and their improved electrochemical properties. Yolk­shell Co3O4 precursor microspheres are initially obtained by spray pyrolysis and are subsequently transformed into Co9S8 yolk­shell microspheres by simple sulfidation in the presence of thiourea as a sulfur source at 350 °C under a reducing atmosphere. For comparison, filled Co9S8 microspheres were also prepared using the same procedure but in the absence of sucrose during the spray pyrolysis. The prepared yolk­shell Co9S8 microspheres exhibited a Brunauer­Emmett­Teller (BET) specific surface area of 18 m(2) g(−1) with a mean pore size of 16 nm. The yolk­shell Co9S8 microspheres have initial discharge and charge capacities of 1008 and 767 mA h g(−1) at a current density of 1000 mA g(−1), respectively, while the filled Co9S8 microspheres have initial discharge and charge capacities of 838 and 638 mA h g(−1), respectively. After 100 cycles, the discharge capacities of the yolk­shell and filled microspheres are 634 and 434 mA h g(−1), respectively, and the corresponding capacity retentions after the first cycle are 82% and 66%.

Electrochemical properties of cobalt hydroxychloride microspheres as a new anode material for Li-ion batteries.

The use of cobalt hydroxychloride [Co2(OH)3Cl] as an anode material for lithium ion batteries (LIBs) is investigated using spherical shape and ultrafine nanocrystals directly formed by spray pyrolysis from spray solution of cobalt chloride salt. Dot-mapping images of the resulting powders reveal a uniform distribution of Co, O, and Cl throughout the powder. The Co2(OH)3Cl powder prepared directly by spray pyrolysis exhibits a high thermal stability at temperatures below 220 °C, as well as having superior electrochemical properties compared with those of the CoCl2(H2O)2 and CoO powders prepared by the same process. The initial discharge capacities of the Co2(OH)3Cl and CoO powders at a constant current density of 1000 mA g(-1) are found to be 1570 and 1142 mA h g(-1), respectively, and their initial Coulombic efficiencies are 72 and 70%. The discharge capacities of the Co2(OH)3Cl and CoO powders after 100 cycles are 955 and 632 mA h g(-1), respectively. The Co2(OH)3Cl powders have a high discharge capacity of 609 mA h g(-1) even after 1000 cycles at a high current density of 5000 mA g(-1).

Rapid continuous synthesis of spherical reduced graphene ball-nickel oxide composite for lithium ion batteries.

In this study, we synthesized a powder consisting of core-shell-structured Ni/NiO nanocluster-decorated graphene (Ni/NiO-graphene) by a simple process for use as an anodic material for lithium-ion batteries. First, a crumpled graphene powder consisting of uniformly distributed Ni nanoclusters was prepared by one-pot spray pyrolysis. This powder was subsequently transformed into the Ni/NiO-graphene composite by annealing at 300 °C in air. The Ni/NiO-graphene composite powder exhibited better electrochemical properties than those of the hollow-structured NiO-Ni composite and pure NiO powders. The initial discharge and charge capacities of the Ni/NiO-graphene composite powder were 1156 and 845 mA h g(-1), respectively, and the corresponding initial coulombic efficiency was 73%. The discharge capacities of the Ni/NiO-graphene, NiO-Ni, and pure NiO powders after 300 cycles were 863, 647, and 439 mA h g(-1), respectively. The high stability of the Ni/NiO-graphene composite powder, attributable to the unique structure of its particles, resulted in it exhibiting long-term cycling stability even at a current density of 1500 mA g(-1), as well as good rate performance. The structural stability of the Ni/NiO-graphene composite powder particles during cycling lowered the charge transfer resistance and improved the Li-ion diffusion rate.

Electrochemical properties of yolk-shell structured ZnFe2O4 powders prepared by a simple spray drying process as anode material for lithium-ion battery.

ZnFe2O4 yolk-shell powders were prepared by applying a simple spray-drying process. Dextrin was used as a drying additive and carbon source material, and thus played a key role in the preparation of the powders. The combustion of precursor powders consisting of zinc and iron salts and dextrin obtained by a spray-drying process produced the yolk-shell-structured ZnFe2O4 powders even at a low post-treatment temperature of 350 °C. The ZnFe2O4 powders prepared from the spray solution without dextrin had a filled and pockmarked structure. The initial discharge capacities of the ZnFe2O4 yolk-shell and filled powders post-treated at 450 °C at a current density of 500 mA g(-1) were 1226 and 993 mA h g(-1), respectively, and the corresponding initial Coulombic efficiencies were 74 and 58%. The discharge capacities of the ZnFe2O4 powders with yolk-shell and filled structures post-treated at 450 °C after 200 cycles were 862 and 332 mA h g(-1), respectively. The ZnFe2O4 yolk-shell powders with high structural stability during cycling had superior electrochemical properties to those of the powders with filled structure.

One-pot synthesis of manganese oxide-carbon composite microspheres with three dimensional channels for Li-ion batteries.

The fabrication of manganese oxide-carbon composite microspheres with open nanochannels and their electrochemical performance as anode materials for lithium ion batteries are investigated. Amorphous-like Mn3O4 nanoparticles embedded in a carbon matrix with three-dimensional channels are fabricated by one-pot spray pyrolysis. The electrochemical properties of the Mn3O4 nanopowders are also compared with those of the Mn3O4-C composite microspheres possessing macropores resembling ant-cave networks. The discharge capacity of the Mn3O4-C composite microspheres at a current density of 500 mA g(-1) is 622 mA h g(-1) after 700 cycles. However, the discharge capacity of the Mn3O4 nanopowders is as low as 219 mA h g(-1) after 100 cycles. The Mn3O4-C composite microspheres with structural advantages and high electrical conductivity have higher initial discharge and charge capacities and better cycling and rate performances compared to those of the Mn3O4 nanopowders.

Macroporous Fe3O4/carbon composite microspheres with a short Li+ diffusion pathway for the fast charge/discharge of lithium ion batteries.

Macroporous Fe3O4/carbon composite and core-shell Fe3O4@carbon composite microspheres have been prepared by means of one-pot spray pyrolysis. The addition of polystyrene (PS) nanobeads to a spray solution containing an iron salt and poly(vinylpyrrolidone) (PVP) led to macroporous Fe3O4/carbon composite microspheres, the carbon and iron components of which are uniformly distributed over the entire composite microsphere. The pore-size distribution curve for the macroporous Fe3O4/carbon composite shows distinct peaks at around 10 and 80 nm. An electrode prepared from the macroporous Fe3O4/carbon composite microspheres showed better cycling and rate performances than an electrode formed from core-shell Fe3O4@carbon composite microspheres. The initial discharge and charge capacities of the macroporous Fe3O4/carbon composite microsphere electrode were determined to be 1258 and 908 mA h g(-1) at 2 A g(-1), respectively, and the corresponding initial coulombic efficiency was 72 %. The composite microsphere electrode cycled 500 times at 5 A g(-1) showed a high discharge capacity of 733 mA h g(-1).

Design and fabrication of new nanostructured SnO2-carbon composite microspheres for fast and stable lithium storage performance.

One-pot method for metal oxide-carbon composite microsphere with three-dimensional ordered macroporous (3DOM) structure is first introduced. The 3DOM structured SnO2 -carbon microspheres prepared as the first target material show superior electrochemical properties as anode material for lithium ion batteries. The newly developed process can be applied to the preparation of 3DOM-structured metal oxide-carbon composite microspheres for wide applications.

Excellent electrochemical properties of yolk-shell MoO3 microspheres formed by combustion of molybdenum oxide-carbon composite microspheres.

Yolk-shell MoO3 microspheres are prepared by a two-step process in which molybdenum oxide-carbon (MoO(x)-C) composite microspheres are first obtained by spray pyrolysis, followed by combustion at 400 °C in air. The yolk-shell microspheres exhibit excellent electrochemical properties and structural stability.

Preparation of Li4Ti5O12 yolk-shell powders by spray pyrolysis and their electrochemical properties.

We have reported for the first time the preparation of yolk-shell-structured Li4Ti5O12 powders for use as anode materials in lithium-ion batteries. One Li4Ti5O12 yolk-shell-particle powder is directly formed from each droplet containing lithium, titanium, and carbon components inside the hot wall reactor maintained at 900 °C. The precursor Li4Ti5O12 yolk-shell-particle powders, which are directly prepared by spray pyrolysis, have initial discharge and charge capacities of 155 and 122 mA h g(-1) , respectively, at a current density of 175 mA g(-1) . Post-treatment of the yolk-shell-particle powders at temperatures of 700 and 800 °C improves the initial discharge and charge capacities. The initial discharge capacities of the Li4Ti5O12 powders with a yolk-shell structure and a dense structure post-treated at 800 °C are 189 and 168 mA h g(-1) , respectively. After 100 cycles, the corresponding capacities are 172 and 152 mA h g(-1) , respectively (retentions of 91 and 90%).

One-pot facile synthesis of ant-cave-structured metal oxide-carbon microballs by continuous process for use as anode materials in Li-ion batteries.

This paper introduces a facile one-pot method for synthesizing a new structured material, named "ant-cave microball", by continuous ultrasonic spray pyrolysis. The ant-cave-structured microballs are prepared from a colloidal spray solution with polystyrene nanobeads and sucrose. Networking between the nanovoids formed by decomposition of the polystyrene nanobeads results in the formation of nanochannels. The electrochemical properties of these ant-cave-structured MoO3-C microballs, prepared as the first target material for lithium ion batteries, are investigated. The nanochannels are uniformly distributed inside the microballs with MoO3 and carbon components uniformly distributed within the microballs. Further, the microballs have initial discharge and charge capacities of 1212 and 841 mA h g(-1), respectively, at a current density of 2 A g(-1), and the initial discharge and charge capacities based on the weight of MoO3 (disregarding carbon component) are as high as 1814 and 1259 mA h g(-1). The microballs deliver a high discharge capacity of 733 mA h g(-1) even after 300 cycles. This is although microsized MoO3 powders with a filled structure have discharge capacities of 1256 and 345 mA h g(-1) for the first and 300th cycles, respectively.

A new strategy for synthesizing yolk-shell V2O5 powders with low melting temperature for high performance Li-ion batteries.

This paper presents the fabrication of yolk-shell V2O5 powders with a low melting temperature of 690 °C by using a simplified two-step process. The spherical V2O3-C composite obtained by spray pyrolysis transforms into yolk-shell V2O5 powder by a simple combustion process at 400 °C. The yolk-shell V2O5 powders are composed of nanoplate crystals several tens of nanometers in size, and have a BET surface area of 15 m(2) g(-1). The powders exhibit initial discharge and charge capacities of 271 and 264 mA h g(-1) at a current density of 1000 mA g(-1), respectively, and a corresponding Coulombic efficiency of 97.4%. After 100 cycles, the discharge capacity of the yolk-shell V2O5 powders is 201 mA h g(-1). In contrast, spherical V2O5 powders with a dense structure exhibit low initial discharge and charge capacities of 160 and 145 mA h g(-1), respectively. The structural stability of the yolk-shell during Li-ion insertion and extraction improves the electrochemical properties of the V2O5 powders, even at high current densities.

Continuous one-pot synthesis of sandwich structured core-shell particles and transformation to yolk-shell particles.

Scalable continuous ultrasonic spray pyrolysis is used to develop a facile one-pot method of synthesizing sandwich structured core-shell particles consisting of a Pd core, a V2O5 inner layer, and a porous SiO2 outer layer. Pd@SiO2 yolk-shell particles are easily formed by removing the V2O5 inner layer.

Electrochemical properties of ZrO2-doped V2O5 amorphous powders with spherical shape and fine size.

Amorphous V2O5 powders with zirconia (ZrO2) dopant are prepared by one-pot spray pyrolysis at temperatures above the melting temperature of V2O5. The powders with 7 wt % ZrO2 are completely spherical and dense with a clean surface, on which crystals of pure V2O5 powders are scarcely observed. The V2O5 powders with 7 wt % ZrO2 have uniformly distributed V and Zr components. The uniformly distributed Zr component disturbs the crystallization of V2O5 during the quenching of the melted powders. These powders also give smooth initial discharge curves with a single slope, which is typical to amorphous materials. The discharge capacities of the V2O5 powders with 7 wt % ZrO2 are 309, 269, and 222 mA h g(-1) after the first, second, and 50th cycles, respectively, even at a high current density of 294 mA g(-1). The capacity retention measured after the first cycle is 83% after 50 cycles.

Synthesis of nano-sized biphasic calcium phosphate ceramics with spherical shape by flame spray pyrolysis.

Nanometer size biphasic calcium phosphate (BCP) powders with various Ca/P molar ratios satisfied with appropriate phase ratios of HA/beta-TCP were prepared by high temperature flame spray pyrolysis process. The BCP powders had spherical shapes and narrow size distributions irrespective of the ratios of Ca/P. The mean size of the BCP powders measured from the TEM image was 38 nm. The composition ratio of Ca/P was controlled from 1.500 to 1.723 in the spray solution, and required phase ratios of HA/TCP are controlled systematically. The calcium dissolution of the pellets obtained from the BCP powders directly prepared by flame spray pyrolysis in buffer solution increased with the decrease of Ca/P ratios except with the Ca/P ratio of 1.713. The pellet surface with Ca/P ratio of 1.500, which consisted of beta-TCP, was eroded dramatically for 7 days. On the other hand, the pellet surface with Ca/P ratio of 1.667 was stable and did not disintegrate after immersion in Tris-HCl buffer solution based on the SEM observation.