Abstract 3D batteries continue to be of widespread interest for flexible energy storage where the 3D nanostructured cathode is the key component to achieve both high energy and power densities. While current work on flexible cathodes tends to emphasize the use of flexible scaffolds such as graphene and/or carbon nanotubes, this approach is often limited by poor electrical contact and structural stability. This communication presents a novel synthetic approach to form 3D array cathode for the first time, the single‐crystalline Na 3 (VO) 2 (PO 4 ) 2 F (NVOPF) by using VO 2 array as a seed layer. The NVOPF cathode exhibits both high‐rate capability (charge/discharge in 60 s) and long‐term durability (10,000 cycles at 50 C) for Na ion storage. Utilizing in situ X‐ray diffraction and first principles calculations, the high‐rate properties are correlated with the small volume change, 2D fast ion transport, and the array morphology. A novel all‐array flexible Na + hybrid energy storage device based on pairing the intercalation‐type NVOPF array cathode with a cogenetic pseudocapacitive VO 2 nanosheet array anode is demonstrated.
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The development of freestanding bifunctional air cathodes for the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) is highly desirable for the next generation of flexible rechargeable metal–air batteries. It remains challenging to achieve efficient OER and ORR bifunctionality on a single lightweight and inexpensive electrode. In this article, a metal-free, and freestanding air cathode based on vertically aligned carbon nanotubes (VACNTs) functionalized with N, P heteroatoms doped carbon is first reported. In addition to the high catalytic activity caused by N, P heteroatoms doping, the importance of efficient gas diffusion and electron transfer provided by the VACNT-GF hierarchical structure is highlighted. The carbonization temperature has been identified to have pronounced effect on catalytic activity, and the samples with P–N bonds have smaller ORR and OER overpotentials, while the quantitative atomic ratio of either P or N has little effect on catalytic activity. The resulting air electrode achieved a high peak power density of 56 mW cm–2 at a current density of 120 mA cm–2, outperforming Pt/C- and IrO2-based rechargeable Zn–air batteries. The zinc–air battery assembled with the air electrode also showed good cyclability, which exceeded that of cells with the Pt/C//IrO2 catalyst. The increase of voltage difference between the charge and discharge platform was 0.2 V for the cell assembled with N,P-doped VACNT-based freestanding air cathode after 75 h of operation at 10 mA cm–2, which was less than half of that of cells with Pt/C//IrO2 catalyst. Impedance analysis further reveals the good performance results from the favorable mass transfer of the electrode.
We present two different ways to fabricate nitrogen-doped graphene (N-graphene) and demonstrate its use as a metal-free catalyst to study the catalytic active center for the oxygen reduction reaction (ORR). N-graphene was produced by annealing of graphene oxide (G-O) under ammonia or by annealing of a N-containing polymer/reduced graphene oxide (RG-O) composite (polyaniline/RG-O or polypyrrole/RG-O). The effects of the N precursors and annealing temperature on the performance of the catalyst were investigated. The bonding state of the N atom was found to have a significant effect on the selectivity and catalytic activity for ORR. Annealing of G-O with ammonia preferentially formed graphitic N and pyridinic N centers, while annealing of polyaniline/RG-O and polypyrrole/RG-O tended to generate pyridinic and pyrrolic N moieties, respectively. Most importantly, the electrocatalytic activity of the catalyst was found to be dependent on the graphitic N content which determined the limiting current density, while the pyridinic N content improved the onset potential for ORR. However, the total N content in the graphene-based non-precious metal catalyst does not play an important role in the ORR process.
Numerous Paleozoic deposits have been found in the Tianshan Mountains. Postmineralization burial plays an important role in the preservation of Paleozoic epizonal deposits. However, the preservation mechanisms for mesozonal deposits in the Tianshan Mountains need further investigation. The late Paleozoic Katebasu gold–copper deposit (with a reported mineralization age varying from ∼ 270 Ma to ∼ 330 Ma) in the Chinese Western Tianshan is a mesothermal magmatic hydrothermal deposit that formed at mesozonal depths. The exhumation process and preservation mechanisms of this deposit remain ambiguous. In this study, (U–Th)/He and fission-track dating were applied to samples from a vertical profile to constrain the exhumation history of the Katebasu deposit. Apatite (U–Th)/He and fission-track ages vary systematically with elevation, ranging from 32.4 ± 9.0 Ma to 176.4 ± 18.0 Ma and 106.4 ± 3.1 Ma to 181.7 ± 5.1 Ma, respectively. Zircon (U–Th)/He ages range from 220.4 ± 11.0 Ma to 260.1 ± 17.4 Ma. The age–elevation relationship and inverse thermal modeling reveal that the Katebasu deposit underwent two phases of exhumation. The first phase of exhumation, which caused at least 4 km of erosion, occurred during the late Paleozoic to Early Jurassic. The second exhumation started during the Early Oligocene, resulting in ∼ 0.9 km of erosion. A protracted period of tectonic stability during the middle–late Mesozoic to early Cenozoic and limited exhumation during the late Cenozoic uplift played important roles in the preservation of the Katebasu deposit.
Abstract Van der Waals semiconductors exemplified by two-dimensional transition-metal dichalcogenides have promised next-generation atomically thin optoelectronics. Boosting their interaction with light is vital for practical applications, especially in the quantum regime where ultrastrong coupling is highly demanded but not yet realized. Here we report ultrastrong exciton-plasmon coupling at room temperature in tungsten disulfide (WS 2 ) layers loaded with a random multi-singular plasmonic metasurface deposited on a flexible polymer substrate. Different from seeking perfect metals or high-quality resonators, we create a unique type of metasurface with a dense array of singularities that can support nanometre-sized plasmonic hotspots to which several WS 2 excitons coherently interact. The associated normalized coupling strength is 0.12 for monolayer WS 2 and can be up to 0.164 for quadrilayers, showcasing the ultrastrong exciton-plasmon coupling that is important for practical optoelectronic devices based on low-dimensional semiconductors.
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