Development of self-standing electrodes is highly desirable for flexible electrochemical energy storage and conversion devices. Herein, we report the facile synthesis of atomized copper-decorated nitrogen-doped porous carbon nanofibers by pyrolyzing g-C3N4-modified electrospun polyacrylonitrile (PAN) fibers directly from copper paper. The concurrent PAN fiber pyrolysis and copper paper atomization allow for diffusion of Cu atoms into the nitrogen-doped carbon framework. The as-prepared atomized copper-decorated nitrogen-doped porous carbon nanofibers possess a high surface area of 604.5 m2 g–1 and a pore volume of 1.70 cm3 g–1, with Cu atomically dispersed inside the N-doped carbon framework in the form of Cu–N4 active sites. The Cu incorporation leads to a positive shift of the half-wave potential in oxygen reduction reactions by 84 mV in an alkaline electrolyte. The open-circuit voltage (OCV) of the self-assembled flexible zinc–air battery reaches 1.37 V using the synthesized nanofiber membrane as self-standing cathode and decreases slightly with the increase in bending angles. The as-prepared material is also applied in a liquid zinc–air battery, delivering a power density of 100 mW cm–2 at a current density of 150 mA cm–2 with a remaining voltage above 1.0 V after discharging at 10 mA cm–2 for 292 h.
A new method was developed to synthesize high active TiO 2 nanocrystals by the hydrolysis of titanium (IV) chloride in water at 40-80°C, employing nanocrystal cellulose (NCC) as morphology controlling agent. The obtained samples were characterized with transmission electron microscopy (TEM), X-ray diffraction (XRD), and ultraviolet-visible spectrophotometer. TEM investigations revealed that the crystals synthesized at 40-60°C were flower-like which was composed of nanoneedles, and when the temperature rose up to 70-80°C, cubic nanocrystals with an edge length of 100-200 nm were observed. XRD results showed that the crystalline phase of the nanocrystals had a strong dependence on the temperature and aging time, and the content of rutile phase increased with increasing either the temperature or the aging time. The photocatalytic activities of the samples were tested by the degradation of methyl orange in aqueous solution under high pressure mercury lamp. The experimental results revealed that cubic nanocrystals showed much higher photoactivity than flower-like ones.
With the booming of marine industry, occurrence of maritime oil spills will not only loss of life and property, but also has brought about a long-term and bad influence to ocean environment and ecosystem system. This paper introduces a platform architecture for marine oil spill response capacity visualization, and elaborates the visualization of oil spill emergency elements, emergency resources dynamic interconnection and regional oil spill response capability with marine oil spill accidents. The platform is based on the B/S (browser/server) framework along with the tools of Baidu map API and MapV visualization system to realize the oil spill emergency resources visualization, oil spill emergency capability visualization and oil spill emergency response. The successful running of the platform provides scientific support for the decision-making in handling the oil spill emergency.
Abstract The structure and valence transitions in multi‐valent transition metal oxides are closely associated with the intrinsic functionalities that exhibit wide applications in various fields, such as rechargeable batteries, supercapacitors, and catalysis. The internal strain due to intercalated and then released alkali‐ions and defects plays a critical role in tuning the energetically close correlated structures. However, such an effect is still elusive due to its fast dynamics at the atomic scale that requires both high temporal and spatial resolution. Herein, a chip‐based in situ scanning transmission electron microscope investigation is conducted, in which an abnormal tunnel to layered transition within a single MnO 2 nanowire is observed. The internal strain initiates a Jahn–Teller active Mn 3+ transition to facilitate the Mn migration, which significantly reduces the Mn migration barrier and kinetically favors this abnormal transition. This work provides an atomistic insight into a strain effect in tuning the multi‐phase and valence transitions in the functional metal oxides, e.g., the phase transition in MnO 2 during K + ‐ion extraction for K + ‐ion batteries.
Manganese oxides are attracting great interest owing to their rich polymorphism and multiple valent states, which give rise to a wide range of applications in catalysis, capacitors, ion batteries, and so forth. Most of their functionalities are connected to transitions among the various polymorphisms and Mn valences. However, their atomic-scale dynamics is still a great challenge. Herein, we discovered a strong heterogeneity in the crystalline structure and defects, as well as in the Mn valence state. The transitions are studied by in situ transmission electron microscopy (TEM), and they involve a complex ordering of [MnO6] octahedra as the basic building tunnels. MnO2 nanowires synthesized using solution-based hydrothermal methods usually exhibit a large number of multiple polymorphism impurities with different tunnel sizes. Upon heating, MnO2 nanowires undergo a series of stoichiometric polymorphism changes, followed by oxygen release toward an oxygen-deficient spinel and rock-salt phase. The impurity polymorphism exhibits an abnormally high stability with interesting small-large-small tunnel size transition, which is attributed to a preferential stabilizer (K+) concentration, as well as a strong competition of kinetics and thermodynamics. Our results unveil the complicated intergrowth of polymorphism impurities in MnO2, which provide insights into the heterogeneous kinetics, thermodynamics, and transport properties of the tunnel-based building blocks.
In battery cycling, mechanical effects introduced by electrochemical reactions are commonly observed. In return, the mechanical deformations also have a large impact on the electrochemical process. However, such a coupling effect of electrochemical reaction and mechanical deformation has a complicated interplay on the atomic scale and an explicit elucidation is still challenging. Herein, we used in situ transmission electron microscopy to directly visualize the coupling process during the lithiation of two-dimension Van der Waals MoS 2 layered electrodes. A self-sustained cracking mechanism was identified; the first crack was created by the accumulation of the linear defects originated from the strain in lithiation. The formed defects including dislocations and antiphase boundaries, in turn accelerated the Li-ion diffusion, promoting the electrochemical reaction and cooperatively gave rise to the formation of a second and following cracks that resembled the “avalanche effect”. Meanwhile, it is observed that a threshold crystal size exists, under which the lithiation stress is not sufficient to initiate the first crack, and thus the serial cracking process could be avoided. The present work provides an atomistic insight into a cooperation from the mechanical and electrochemical effects toward the formation of the arrayed cracks. It also sheds light on the enhancement of mechanical properties of layered electrode materials for rechargeable batteries.
In order to optimize the energy management strategy and solve the problem of the power quality degradation of fuel cell hybrid electric ships, a particle swarm optimization algorithm based energy management strategy is proposed in this paper. Taking a fuel cell ship as the target ship, a system simulation model is built in Matlab/Simulink to verify the proposed energy management strategy. Through simulations and comparisons, the bus voltage curve of the optimized hybrid power system fluctuates more gently, and the voltage sag is smaller. The amplitude of the voltage fluctuation under maneuvering conditions is reduced by 55% compared with that of the original ship. The charging and discharging process of the composite energy storage system is optimized under maneuvering conditions, the power quality of the marine power grid is improved, and the use of the energy management strategy can extend the service life of the battery.
In battery cycling, mechanical effects introduced by electrochemical reactions are commonly observed. In return, the mechanical deformations also have a large impact on the electrochemical process. However, such a coupling effect of electrochemical reaction and mechanical deformation has a complicated interplay on the atomic scale. Herein, we use in situ transmission electron microscopy to directly visualize the coupling process of two-dimensional Van der Waals MoS2 electrodes. A self-sustained cracking mechanism is identified, and the first crack is initiated by the defects originated from the strain accumulation at the edge of intercalation front. The formed defects, including dislocations and antiphase boundaries, can accelerate the Li-ion diffusion and promote the electrochemical reaction, giving rise to the formation of a second and following cracks that resemble the “avalanche effect.” The present work provides an atomistic insight into a cooperation from the mechanical and electrochemical effects toward the formation of the arrayed cracks.
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