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Covalent organic frameworks (COFs) are an emerging kind of photocatalysts which convert CO2 to value-added fuels. However, COFs usually exhibit lower catalytic efficiency without using metal, sacrificial reagent, or photosensitizer due to their easy electron-hole recombination. Herein, a series of imine-linked COFs with different asymmetric linkage structures have been synthesized to enhance the separation efficiency of photoexcited electron-hole pairs in the COFs by tuning the intramolecular built-in electric-field strength. The OH-COF exhibits a high CO production rate of 616 mu mol g(-1) in the 4 h reaction with similar to 100% selectivity, which surpasses most of the metal-free COF photocatalysts reported in the literature. This reveals that the higher polarity of OH-COF with an asymmetric linkage structure leads to a stronger built-in electric-field strength and a faster charge-transfer rate and thus more efficient photocatalytic performance. This work would provide some insights into the built-in electric-field design of COFs for efficient CO2 photoreduction.
This is a review of theoretical and methodological development over the past decade pertaining to computational characterization of thermoelectric materials from first principles. Primary focus is on electronic and thermal transport in solids. Particular attention is given to the relationships between the various methods in terms of the theoretical hierarchy as well as the tradeoff of physical accuracy and computational efficiency of each. Further covered are up-and-coming methods for modeling defect formation and dopability, keys to realizing a material's thermoelectric potential. We present and discuss all these methods in close connection with parallel developments in high-throughput infrastructure and code implementation that enable large-scale computing and materials screening. In all, it is demonstrated that advances in computational tools are now ripe for efficient and accurate targeting of the needles in the haystack, which are “next-generation” thermoelectric materials.
Abstract This overview shines a spotlight on the often-neglected realm of p-/π-hole halogen bonds, a topic that has garnered relatively scant attention despite being pivotal in molecular chemistry over the past two decades. Historically, research on halogen bonding has predominantly centered on the more familiar σ-hole interactions within molecules, complexes, and crystals, as well as efforts to define noncovalent interactions involving main group elements of the periodic table. The academic landscape is replete with original studies, comprehensive reviews, and detailed analyses of σ-hole halogen bonds, including both experimental and computational investigations. These studies frequently highlight instances where ordinary halogen derivatives serve as σ-hole bond donors. Yet, there remains a notable absence of rigorous exploration into the fundamental principles governing the physical chemistry and chemical physics of electrophilic p-/π-holes within halogen-containing molecules, particularly those featuring hypervalent halogens. A p-/π-hole (or p-/π-belt) halogen bond arises when a halogen atom, possessing a p-/π-hole (or p-/π-belt), engages inductively with a nucleophile from a neighboring molecule, which may be identical or distinct. This overview aims to address this gap by delving into the conceptual evolution of p-/π-hole (or p-/π-belt) across various representative molecules, with or without halogen derivatives, thereby advancing our understanding of this crucial yet underexplored facet of molecular interactions.
This study employs aerosol-assisted chemical vapor deposition (AACVD) to fabricate WO3/BiVO4 heterojunction photoanodes with an inverted architecture (WO3 atop BiVO4). The unique permeable nanofiber morphology of WO3 provides a solution to enhance water oxidation performance. By correlating precursor volume (10-40 mL) and spatial position within the deposition chamber (inlet/mid/outlet) with film properties, we demonstrate that a midreactor position yields "grass-like" WO3 nanofibers (diameter: 100-230 nm, length: 3.5-3.98 μm), enabling dual functionality: (i) > 50% light transmittance to the underlying BiVO4 absorber, and (ii) electrolyte penetration into the heterointerface between WO3 and BiVO4. In contrast, rod-like WO3 produced near the inlet causes severe light scattering, reducing the incident photon-to-current efficiency (IPCE) by six times above wavelengths of 350 nm. Optimized samples, produced with a deposition volume of 30 mL to deposit WO3 atop of BiVO4 positioned in the middle of the deposition chamber (i.e., WO3-30/BiVO4-mid), achieve a photocurrent density of 0.82 mA·cm-2 at 1.23 VRHE under 1 sun irradiance, which is 121% higher than single-layer BiVO4 (0.37 mA·cm-2) and exceeds some conventional WO3-under/BiVO4 heterojunctions in which WO3 is underneath BiVO4. Transient absorption spectroscopy confirms prolonged carrier lifetimes in our unique heterostructure through improved charge-carrier separation. This work challenges current traditional heterojunction design rules for the WO3/BiVO4 system by showcasing how permeable WO3 nanostructures atop BiVO4 photoanodes can improve light harvesting and facilitate charge-carrier separation to significantly improve activity.
