Assembling Iron Oxide Nanoparticles into Aggregates by Li3PO4: A Universal Strategy Inspired by Frogspawn for Robust Li-Storage.

The poor ionic conductivity of transition metal oxides (TMOs) is a huge obstacle to their practical application as anodes for lithium-ion batteries (LIBs). Although good performance can be harvested by constructing nanostructures, some other foundmental issues including low tap density and serious electrolyte consumption come along. Herein, inspired by frogspawn, we propose a universal strategy of using lithium salts to assemble TMO nanoparticles into large aggregates to improve their Li+ conductivity. In such a frogspawn-like structure, lithium salt networks can not only realize the rapid transmission of Li+ but also alleviate the volume change during the charging/discharging process. When Li3PO4 is applied to assemble iron oxides nanoparticles, aggregates with size over 1 µm and tap density up to 1.33 g cm-3 can be obtained, which even hasve an ionic conductivity up to 9.61 × 10-5 S cm-1. Fe3O4 was also introduced through reduction to boost electron transfer. Consequently, this carbon-free composite delivered a capacity up to 896 mA h g-1 even after 1000 cycles at 5 A g-1, which can also be maintained under high mass loading. When using lithium salts such as Li2SO4, Li2CO3, LiBO2, and LiCl, the corresponding composites also showed similar performance. This strategy is also effective for TMOs such as NiO, Co3O4, and ZnO, demonstrating the universality of this frogspawn-inspired design.

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.

Renewable P-type zeolite for superior absorption of heavy metals: Isotherms, kinetics, and mechanism.

Zeolite is a characteristic material for removing heavy metals exhibiting by low tolerance quantities. It is particularly desirable although challenging to cultivate an unmodified and reusable zeolite for eradicating heavy metals with great capacity. Herein, we sought out and firstly synthesized the uniform octahedral zeolite Na6Al6Si10O32·12H2O for heavy metal ions trap, proven extraordinarily effective decontamination of M2+ (Pb2+, Cd2+, Cu2+, and Zn2+). The maximum capacities of Pb2+, Cd2+, Cu2+, and Zn2+ were 649, 210, 90 and 88 mg/g, and the distribution coefficients (Kd) was ~108 mL/g for Pb2+ which emphasized the superior effectiveness of Na6Al6Si10O32·12H2O contrasted with other zeolites. Rapid adsorption was observed that Pb2+ concentration (7.5 ppm) was reduced to 0.6 ppb in 2 min. The removal mechanism was ascribed to the ion exchange and hydroxyl groups thereby affording high adsorption capacity. We also investigated the heavy metal removal of zeolite 13X and 4A for comparison and concluded the determining factor affecting absorption capacity. The removal rate of Pb remained at 97% even after five regeneration recycles. The zeolite was therefore promising for practical water purification and industrialization.

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.

Enhancing the n-Type Conductivity and Thermoelectric Performance of Donor-Acceptor Copolymers through Donor Engineering.

Conjugated polymers with high thermoelectric performance enable the fabrication of low-cost, large-area, low-toxicity, and highly flexible thermoelectric devices. However, compared to their p-type counterparts, n-type polymer thermoelectric materials show much lower performance, which is largely due to inefficient doping and a much lower conductivity. Herein, it is reported that the development of a donor-acceptor (D-A) polymer with enhanced n-doping efficiency through donor engineering of the polymer backbone. Both a high n-type electrical conductivity of 1.30 S cm-1 and an excellent power factor (PF) of 4.65 µW mK-2 are obtained, which are the highest reported values among D-A polymers. The results of multiple characterization techniques indicate that electron-withdrawing modification of the donor units enhances the electron affinity of the polymer and changes the polymer packing orientation, leading to substantially improved miscibility and n-doping efficiency. Unlike previous studies in which improving the polymer-dopant miscibility typically resulted in lower mobilities, the strategy maintains the mobility of the polymer. All these factors lead to prominent enhancement of three orders magnitude in both the electrical conductivity and the PF compared to those of the non-engineered polymer. The results demonstrate that proper donor engineering can enhance the n-doping efficiency, electrical conductivity, and thermoelectric performance of D-A copolymers.

Well-Dispersed Ruthenium in Mesoporous Crystal TiO2 as an Advanced Electrocatalyst for Hydrogen Evolution Reaction.

TiO2 mesoporous crystal has been prepared by one-step corroding process via an oriented attachment (OA) mechanism with SrTiO3 as precursor. High resolution transmission electron microscopy (HRTEM) and nitrogen adsorption-desorption isotherms confirm its mesoporous crystal structure. Well-dispersed ruthenium (Ru) in the mesoporous nanocrystal TiO2 can be attained by the same process using Ru-doped precursor SrTi1- xRu xO3. Ru is doped into lattice of TiO2, which is identified by HRTEM and super energy dispersive spectrometer (super-EDS) elemental mapping. X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance spectroscopy (EPR) suggest the pentavalent Ru but not tetravalent, while partial Ti in TiO2 accept an electron from Ru and become Ti3+, which is observed for the first time. This Ru-doped TiO2 performs high activity for electrocatalytic hydrogen evolution reaction (HER) in alkaline solution. First-principles calculations simulate the HER process and prove TiO2:Ru with Ru5+ and Ti3+ holds high HER activity with appropriate hydrogen-adsorption Gibbs free energies (Δ GH).