Latest ArticlesThe high specific capacity and low negative electrochemical potential of lithium metal anodes (LMAs), may allow the energy density threshold of Li metal batteries (LMBs) to be pushed higher. However, the existing detrimental issues, such as dendritic growth and volume expansion, have hindered the practical implementation of LMBs. Introducing three-dimensional frameworks (e.g., copper and nickel foam), have been regarded as one of the fundamental strategies to reduce the local current density, aiming to extend the Sand' time. Nevertheless, the local environment far from the skeleton is almost the same as the typical plane Li, due to macroporous space of metal foam. Herein, we built a double-layered 3D current collector of Li alloy anchored on the metal foam, with micropores interconnected macropores, via a viable thermal infiltration and cooling strategy. Due to the excellent electronic and ionic conductivity coupled with favorable lithiophilicity, the Li alloy can effectively reduce the nucleation barrier and enhance the Li+ transportation rate, while the metal foam can role as the primary promotor to enlarge the surface area and buffer the dimensional variation. Synergistically, the Li composite anode with hierarchical structure of primary and secondary scaffolds realized the even deposition behavior and minimum volume expansion, outputting preeminent prolonged cycling performances under high rate.
Lithium-rich layered cathode material (LLM) can meet the requirement of power lithium-ion energy storage devices due to the great energy density. However, the de/intercalation of Li+ will cause the irreversible loss of lattice oxygen and trigger transition metal (TM) ions migrate to Li+ vacancies, resulting in capacity decay. Here we brought Ti4+ in substitution of TM ions in Li1.2Mn0.54Ni0.13Co0.13O2, which could stabilize structure and expand the layer spacing of LLM. Moreover, optimized Ti-substitution can regulate the anions and cations of LLM, enhance the interaction with lattice oxygen, increase Ni3+ and Co3+, and improve Mn4+ coordination, improving reversibility of oxygen redox activation, maintaining the stable framework and facilitating the Li+ diffusion. Furthermore, we found 5% Ti-substitution sample delivered a high discharge capacity of 244.2 mAh/g at 50 mA/g, an improved cycling stability to 87.3% after 100 cycles and enhanced rate performance. Thereby Ti-substitution gives a new pathway to achieve high reversible cycle retention for LLMs.
Understanding the relationship between structure and properties is critical to the development of solid-state luminescence materials with desired characteristics and performance optimization. In this work, we elaborately designed and synthesized a pair of mononuclear iridium(Ⅲ) complexes with similar structures but different degrees of cationization. [Ir2-f][2PF6] with two counterions is obtained by simple N-methylation of the ancillary ligand of [Ir1-f][PF6] which is a classic cationic iridium(Ⅲ) complex. Such a tiny modification results in tremendously different optical properties in dilute solutions and powders. [Ir1-f][PF6] exhibits weak light in solution but enhanced emission in solid-state as well as poly(methyl methacrylate) matrix, indicative of its aggregation-induced emission (AIE) activity. On the sharp contrary, [Ir2-f][2PF6] is an aggregation-caused quenching (ACQ) emitter showing strong emission in the isolated state but nearly nonemissive in aggregation states. Benefiting from the appealing characteristics of mechanochromic luminescence and AIE behavior, [Ir1-f][PF6] has been successfully applied in reversible re-writable data recording and cell imaging. These results might provide deep insights into AIE and ACQ phenomenon of iridium(Ⅲ) complexes and facilitate the development of phosphorescent materials with promising properties.
Partial substitution of polyoxometalate (POM) is an efficient route to modulate the catalytic property of maternal POM. In this work, a new Keggin type POM involving {Ni6} cluster, {[Ni(H2O)2(Dach)2][Ni(Dach)2]2}{[Ni6Cl(μ-OH)3(H2O)(Dach)3(WO4)(PW9O34)][Ni6(μ-OH)3(H2O)2(Dach)3(WO4)(PW9O34)]}Cl·27H2O, (1, Dach = 1,2-diaminocyclohexane) was synthesized. Compounds 1 shows excellent catalytic performance in the selective oxidation of aniline to azoxybenzene (AOB) in water. The apparently different results from that with the matrix {PW9O34} ({PW9}) suggest the successful regulation of the catalytic property of {PW9} by the introduction of the {Ni6} cluster into the skeleton. The experimental results indicate that the highlighted performance of 1 is contributed by the synergy of W and Ni sites, which are respectively responsible for the oxidation and condensation steps in the production of AOB. The good selectivity to AOB is essentially attributed to the effective modulation of the reaction rates of oxidation and condensation steps by W and Ni sites, respectively.
Aqueous zinc metal batteries are considered as promising candidates for next-generation electrochemical energy storage devices, especially for large-scale energy storage, due to the advantages of high-safety, high energy density and low cost. As the bridge connecting cathode and anode, electrolyte provides a realistic operating environment. In alkaline and neutral aqueous zinc metal batteries, issues associated with electrolyte and anode are still intractable. In this review, we reveal the development and evolution of electrolytes for aqueous zinc metal batteries from alkaline to neutral via the description of fundamentals and challenges in terms of comparison and connection. We also elaborate the strategies in electrolytes regulation and highlight the basic roles and progresses in additives engineering.
Electrochemical nitrate reduction reaction (NITRR) is regarded as a “two birds-one stone” method for the treatment of nitrate contaminant in polluted water and the synthesis of valuable ammonia, which is retarded by the lack of highly reactive and selective electrocatalysts. Herein, for the first time, nickel foam supported Co4N was designed as a high-performance NITRR catalyst by an in-situ nonmetal leaching-induced strategy. At the optimal potential, the Co4N/NF catalyst achieves ultra-high Faraday efficiency and NH3 selectivity of 95.4% and 99.4%, respectively. Ex situ X-ray absorption spectroscopy (XAS), together with other experiments powerfully reveal that the nitrogen vacancies produced by nitrogen leaching are stable and play a key role in boosting nitrate reduction to ammonia. Theoretical calculations confirm that Co4N with abundant nitrogen vacancies can optimize the adsorption energies of NO3- and intermediates, lower the free energy (ΔG) of the potential-determining step (*NH3 to NH3) and inhibit the formation of N-containing byproducts. In addition, we also conclude that the nitrogen vacancies can stabilize the adsorbed hydrogen, making H2 quite difficult to produce, and lowering ΔG from *NO to *NOH, which facilitates the selective reduction of nitrate. This study reveals significant insights about the in-situ nonmetal leaching to enhance the NITRR activity.
The design and development of energy storage device with high energy/power density has become a research hotspot. Zinc-ion hybrid capacitors (ZHCs) are considered as one of the most promising candidates. However, the application of ZHCs is hindered by their low energy density at high power density due to the unsatisfactory cathode material. In this study, a novel 3D phosphorus-doped carbon nanotube/reduced graphene oxide (P-CNT/rGO) aerogel cathode is synthesized through a synergistic modification strategy of CNT insertion and P doping modification combined with 3D porous design. The as-obtained P-CNT/rGO aerogel cathode manifests significantly increased surface aera, expanded interlayer spacing, and enhanced pseudocapacitance behavior, thus leading to significantly enhanced specific capacitance and superb ions transport performance. The as-assembled ZHC based on P-CNT/rGO cathode delivers a superior energy density of 42.2 Wh/kg at an extreme-high power density of 80 kW/kg and excellent cycle life. In-depth kinetic analyses are undertaken to prove the enhanced pseudocapacitance behavior and exceptional power output capability of ZHCs. Furthermore, the reaction mechanism of physical and chemical adsorption/desorption of electrolyte ions on the P-CNT/rGO cathode is revealed by systematic ex-situ characterizations. This work can provide a valuable reference for developing advanced graphene-based cathode for high energy/power density ZHCs.
Owing to the large exciton binding energy (>100 meV) of most organic materials, the process of exciton dissociation into free electrons and holes is seriously hindered, which plays a key role in the photocatalytic system. In this study, a series of chalcogen (S, Se)-substituted mesoporous covalent organic frameworks (COFs) have been synthesized for enhanced photocatalytic organic transformations. Photoelectrochemical measurements indicate that the introduction of semi-metallic Se atom and the enlargement of conjugation degree can not only reduce the exciton binding energy accelerating the charge separation, but also reduce the band gap of COFs. As a result, the COF-NUST-36 with the lowest exciton binding energy (39.5 meV) shows the highest photocatalytic performance for selective oxidation of amines (up to 98% Conv. and 97.5% Sel.). This work provides a feasible method for designing COFs with high photocatalytic activity by adjusting exciton binding energy.
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