Three-dimensional Bi 2 O 3 fractal nanostructures (f-Bi 2 O 3) were directly self-assembled on carbon fiber papers (CFP) using a scalable hot-aerosol synthesis strategy. This approach provides high versatility in modulating the physiochemical properties of the Bi 2 O 3 catalyst by a tailorable control of its crystalline size, loading, electron density as well as providing exposed stacking of the nanomaterials on the porous CFP substrate. As a result, when tested for electrochemical CO 2 reduction reactions (CO 2 RR), these f-Bi 2 O 3 electrodes demonstrated superior conversion of CO 2 to formate (HCOO-) with low onset overpotential and a high mass-specific formate partial current density of-52.2 mA mg-1 , which is ~ 3 times higher than that of the drop-casted control Bi 2 O 3 catalyst (-15.5 mA mg-1), and a high Faradaic This article is protected by copyright. All rights reserved. efficiency (FE HCOO-) of 87% at an applied potential of-1.2 V vs reversible hydrogen electrode (RHE). Our findings reveal that the high exposure of roughened -phase Bi 2 O 3 /Bi edges and the improved electron density of these fractal structures are key contributors in attainment of high CO 2 RR activity.
Advances in the understanding and fabrication of plasmonic nanostructures have led to a plethora of unprecedented optoelectronic and optochemical applications. Plasmon resonance has found widespread use in efficient optical transducers of refractive index changes in liquids. However, it has proven challenging to translate these achievements to the selective detection of gases, which typically adsorb non-specifically and induce refractive index changes below the detection limit. Here, it's shown that integration of tailored fractals of dielectric TiO nanoparticles on a plasmonic metasurface strongly enhances the interaction between the plasmonic field and volatile organic molecules and provides a means for their selective detection. Notably, this superior optical response is due to the enhancement of the interaction between the dielectric fractals and the plasmonic metasurface for thickness of up to 1.8 μm, much higher than the evanescent plasmonic near-field (≈30 nm) . Optimal dielectric-plasmonic structures allow measurements of changes in the refractive index of the gas mixture down to <8 × 10 at room temperature and selective identification of three exemplary volatile organic compounds. These findings provide a basis for the development of a novel family of dielectric-plasmonic materials with application extending from light harvesting and photocatalysts to contactless sensors for noninvasive medical diagnostics.
The understanding of recombination of photogenerated electron/hole pairs at defect sites is a key enabler to develop bismuth vanadate (BiVO 4 ) photoanodes at scale and low cost for photoelectrochemical water splitting. Here, we report a systematic investigation of the impact of vanadium vacancies on the efficiency of BiVO 4 photoanodes for water photooxidation. X-ray photoelectron and photoluminescence spectroscopies reveal that the surfaces of nanostructured BiVO 4 photoanodes obtained by high-temperature synthesis, here used as the model system, suffer from vanadium deficiency and display an increased recombination rate of photoexcited electron/hole pairs. Our simulation indicates that these vanadium vacancies (V V ) create a new sub-band gap level in the proximity of the Fermi level of BiVO 4 . These levels act as recombination centers, explaining the subpar onset potentials and photocurrent densities for water photooxidation observed with these vanadium-deficient BiVO 4 photoanodes. We show that once the V V are eliminated, by a facile post-treatment of the BiVO 4 photoanodes, the photoluminescence lifetimes of the photogenerated carriers are significantly prolonged and the number of catalytically accessible sites is increased. As a result, the photocurrent during water oxidation is increased twofold, achieving 2 mA cm −2 against the standard hydrogen electrode in a 1 M potassium borate buffer electrolyte. These findings provide insights into the critical role played by the vanadium vacancies on the optoelectronic properties of BiVO 4 and a scalable approach for its effective fabrication on large-scale surfaces.
Lithium–sulfur batteries are one of the most promising next-generation high-density energy storage systems. Despite progress, the poor electrical conductivity and cycling stability of sulfur cathodes still hinder their practical implementation. Here, we developed a facile approach for the engineering of Janus double-sided conductive/insulating microporous ion-sieving membranes that significantly enhance recharge efficiency and long-term stability of Li–S batteries. Our membrane consists of an insulating Li-anode side and an electrically conductive S-cathode side. The insulating side consists of a standard polypropylene separator, while the conductive side is made of closely packed multilayers of high-aspect-ratio MOF/graphene nanosheets having a thickness of few nanometers and a specific surface area of 996 m2 g–1 (MOF, metal–organic framework). Our models and experiments reveal that this electrically conductive microporous nanosheet architecture enables the reuse of polysulfide trapped in the membrane and decreases the polysulfide flux and concentration on the anode side by a factor of 250× over recent microporous membranes made of granular MOFs and standard battery separators. Notably, Li–S batteries using our Janus microporous membranes achieve an outstanding rate capability and long-term stability with 75.3% capacity retention over 1700 cycles. We demonstrate the broad applicability of our high-aspect-ratio MOF/graphene nanosheet preparation strategy by the synthesis of a diverse range of MOFs, including ZIF-67, ZIF-8, HKUST-1, NiFe-BTC, and Ni-NDC, providing a flexible approach for the design of Janus microporous membranes and electrically conductive microporous building blocks for energy storage and various other electrochemical applications.
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