The E‐W trending Central Qiangtang metamorphic belt (CQMB) is correlated to the Triassic orogeny of the Paleo‐Tethys Ocean prior to Cenozoic growth of the Tibetan Plateau. The well‐exposed Lanling high‐pressure, low‐temperature (HP‐LT) metamorphic complex was chosen to decipher the process by which it was exhumed, which thereby provides insights into the origin of the CQMB and Qiangtang terrane. After a detailed petrological and structural mapping, three distinct N‐S‐trending metamorphic domains were distinguished. Microscopic observations show that core domain garnet (Grt)‐bearing blueschist was exhumed in a heating plus depressurization trajectory after peak eclogitic conditions, which is more evident in syntectonic vein form porphyroblastic garnets with zoning typical of a prograde path. Grt‐free blueschist of the mantle domain probably underwent an exhumation path of temperature increasing and dehydration, as evidenced by pervasive epidote veins. The compilation of radiometric results of high‐pressure mineral separates in Lanling and Central Qiantang, and reassessments on the published phengite data sets of Lanling using Arrhenius plots allow a two‐step exhumation model to be formulated. It is suggested that core domain eclogitic rocks were brought onto mantle domain blueschist facies level starting at 244–230 Ma, with exhumation continuing to 227–223.4 Ma, and subsequently were exhumed together starting at 223–220 Ma, reaching lower greenschist facies conditions generally after 222–217 Ma. These new observations indicate that the CQMB formed as a Triassic autochthonous accretionary complex resulting from the northward subdcution of the Paleo‐Tethys Ocean and that HP‐LT rocks therein were very probably exhumed in an extensional regime.
Covalent organic polymers (COPs) are a class of rising electrocatalysts for the oxygen reduction reaction (ORR) due to the atomically metrical control of the organic molecular components along with highly architectural robustness and thermodynamic stability even in acid or alkaline media. However, the direct application of pristine COPs as acidic ORR electrocatalysts, especially in device manner, e.g., in proton‐exchange‐membrane fuel cells (PEMFCs), remains a big challenge. Currently, the decoration toward electronic structures of active sites is considered a vital pathway to enhancing the acidic ORR activity of carbon‐based electrocatalysts. Here, an initial F‐decorated fully closed π‐conjugated quasi‐phthalocyanine COP (denoted as COPBTC‐F) is reported. The introduction of the closed‐F edges stepwise drags more electrons from FeN4 sites in COPBTC‐F into the catalyst margin, which weakens the occupied numbers of bonding orbitals between COPBTC‐F and OH* intermediates at the rate‐determining step, exhibiting over five times intrinsic performance beyond the counterpart without F functionalities (termed as COPBTC). Significantly, the maximum power density utilizing COPBTC‐F as a cathode catalyst in PEMFCs is remarkably increased by an order of magnitude compared with COPBTC, which is a stride forward among catalysts based on a pyrolysis‐free conjugated‐polymer network in device manner to date.
Nitrogen‐coordinated single‐cobalt‐atom electrocatalysts, particularly ones derived from high‐temperature pyrolysis of cobalt‐based zeolitic imidazolate frameworks (ZIFs), have emerged as a new frontier in the design of oxygen reduction cathodes in polymer electrolyte fuel cells (PEFCs) due to their enhanced durability and smaller Fenton effects related to the degradation of membranes and ionomers compared with emphasized iron‐based electrocatalysts. However, pyrolysis techniques lead to obscure active‐site configurations, undesirably defined porosity and morphology, and fewer exposed active sites. Herein, a highly stable cross‐linked nanofiber electrode is directly prepared by electrospinning using a liquid processability cobalt‐based covalent organic polymer (Co‐COP) obtained via pyrolysis‐free strategy. The resultant fibers can be facilely organized into a free‐standing large‐area film with a uniform hierarchical porous texture and a full dispersion of atomic Co active sites on the catalyst surface. Focused ion beam‐field emission scanning electron microscopy and computational fluid dynamics experiments confirm that the relative diffusion coefficient is enhanced by 3.5 times, which can provide an efficient route both for reactants to enter the active sites, and drain away the produced water efficiently. Resultingly, the peak power density of the integrated Co‐COP nanofiber electrode is remarkably enhanced by 1.72 times along with significantly higher durability compared with conventional spraying methods. Notably, this nanofabrication technique also maintains excellent scalability and uniformity.
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