pi.-Bond feedback interpreted from the binding energy of the "2p" electrons of phosphorus

Is Carbon Heteroatom Doping the Key to Active and Stable Carbon Supported Cobalt Fischer-Tropsch Catalysts?

Carbon supports are an interesting alternative to established oxidic catalyst supports for Co-based Fischer-Tropsch synthesis (FTS) catalysts as they allow high Co reducibility and do not suffer from the formation of Co/support compounds. To optimize Co-based carbon-supported FTS catalysts, significant research has focused on doping carbon supports with heteroatoms, aiming to enhance both catalytic activity and stability. While improvements in FTS performance have been reported for N-doped carbon supports, the exact effects of heteroatom doping are still poorly understood, largely due to difficulties in directly comparing Co FTS catalysts supported on doped versus nondoped carbon materials. In this study, we synthesized a series of highly comparable N-, S-, and P-doped carbon nanofiber (CNF) model supports, which were combined with size-controlled, colloidal Co nanoparticles to create well-defined model FTS catalysts. Comprehensive characterization of these catalysts using in situ X-ray absorption spectroscopy (XAS), in situ X-ray diffraction (XRD), and in situ magnetometry revealed that the presence of dopants significantly altered the structure and properties of the catalytically active Co0 phase, affecting Co coordination numbers, crystal phase composition, and magnetic behavior. Challenging optimistic literature reports, our findings demonstrate that all the studied heteroatoms negatively impact either FTS activity or catalyst stability. Co on N-doped CNFs experienced rapid deactivation due to increased sintering as well as Co phase transformations, which were not observed for Co on nondoped CNFs. Co on S-doped CNF suffered from instability of carbon-bound S species in a hydrogen atmosphere, contributing to low FTS performance by S-poisoning. Finally, Co on P-doped CNFs displayed strong metal-support interactions that improved sintering stability, but FTS activity was hampered by low Co reducibility and the loss of active Co0 due to a complex sequence of cobalt phosphide formation and its subsequent decomposition into phosphorus oxides and cobalt oxide species under FTS conditions.

Enable Rechargeable Carbon Fluoride Batteries with Unprecedented High Rate and Long Life by Oxygen Doping and Electrolyte Formulation

Here, a rechargeable carbon fluoride battery is demonstrated with unprecedented high rate and long life by oxygen doping and electrolyte formulation. The introductions of Mn2+-O catalyst and porous structure during the oxidation process of CFx cathode can promote the splitting of Li-F during charging. By further modulating the electrolyte with triphenylantimony chloride (TSbCl) as anion acceptor and CsF as product modulator, the more readily dissociable CsLiF2 product instead of LiF is preferentially formed, and the TSbCl-salt protection interface is constructed to confine Li-F based products and reduce fluoride loss at cathode side. These effects endow Li-CFx batteries with durable reversible conversion reaction (for at least 600 cycles), ultrahigh rate performance (e.g., 364 mAh g-1 at 20 A g-1) and low charging plateau voltage down to 3.2 V. The cathode exhibits the maximum power density of 38342 W kg-1 and energy density of 1012 Wh kg-1. Furthermore, this Li-CFx system demonstrates the promising prospects for applications in view of its low temperature operation (e.g., 280 mAh g-1 at -20 °C), low self-discharge ability, large-scale pouch cell fabrication and high cathode loading (5-6 mg cm-2), enabling it to move beyond previous role as primary battery and into new role as fast-charging rechargeable battery with high energy density.

Unveiling the Role of Heteroatom Gradient-Distributed Carbon Fibers for Vanadium Redox Flow Batteries with Long Service Life

The fundamental understanding of electrocatalytic reaction process is anticipated to guide electrode upgradation and acquirement of high-performance vanadium redox flow batteries (VRFBs). Herein, a carbon fiber prototype system with a heteroatom gradient distribution has been developed with enlarged interlayer spacing and a high graphitization that improve the electronic conductivity and accelerate the electrocatalytic reaction, and the mechanism by which gradient-distributed heteroatoms enhance vanadium redox reactions was elucidated with the assistance of density functional theory calculations. All these contributions endow the obtained electrode prominent redox reversibility and durability with only 1.7% decay in energy efficiency over 1000 cycles at 150 mA cm^-2 in the VRFBs. Our work sheds light on the significance of elaborated electrode design and impels the in-depth investigation of VRFBs with long service life.

Conversion of Carbon Dots from Fluorescence to Ultralong Room-Temperature Phosphorescence by Heating for Security Applications

Stimuli-responsive optical materials have received tremendous interest in the last several decades due to their numerous promising applications. Here, fluorescence emissive polymer carbon dots (F-CDs), prepared with a simple heating treatment from ethylenediamine and phosphoric acid, are found to produce unexpected ultralong room-temperature phosphorescence (URTP), which lasts for about 10 s with a lifetime of 1.39 s. This is the first example to achieve the conversion of a fluorescence material to URTP by means of an external heating stimulus. Further investigations reveal that the doping of N and P elements and self-immobilization of the excited triplet species are likely mainly responsible for the observed URTP after the heating treatment, due to the facilitation of the intersystem crossing and formation of more compact cores for effective intraparticle hydrogen bonds, respectively. Importantly, this study also demonstrates the potential for aqueous dispersion of the F-CDs as an advanced security ink for information encryption and anticounterfeiting; this is a feature that has not been reported before. This study is believed to open possibilities to extend stimuli-responsive optical materials to rarely exploited phosphorescence-relevant systems and applications, and also to provide a novel strategy to easily prepare URTP materials.

In situ wrapping of the cathode material in lithium-sulfur batteries

While lithium–sulfur batteries are poised to be the next-generation high-density energy storage devices, the intrinsic polysulfide shuttle has limited their practical applications. Many recent investigations have focused on the development of methods to wrap the sulfur material with a diffusion barrier layer. However, there is a trade-off between a perfect preassembled wrapping layer and electrolyte infiltration into the wrapped sulfur cathode. Here, we demonstrate an in situ wrapping approach to construct a compact layer on carbon/sulfur composite particles with an imperfect wrapping layer. This special configuration suppresses the shuttle effect while allowing polysulfide diffusion within the interior of the wrapped composite particles. As a result, the wrapped cathode for lithium–sulfur batteries greatly improves the Coulombic efficiency and cycle life. Importantly, the capacity decay of the cell at 1000 cycles is as small as 0.03% per cycle at 1672 mA g^–1.

To suppress the polysulfide shuttling effect in Li-S batteries, here the authors report a carbon/sulfur composite cathode with a wrapping layer that overcomes the trade-off between limiting polysulfide diffusion and allowing electrolyte infiltration, and affords extraordinary cycling stability.

Evolution of Phosphorus-Containing Groups on Activated Carbons during Heat Treatment

Two types of activated carbons have been prepared by H₃PO₄ activation of lignocellulose and by H₃PO₄ modification of activated carbon, and then heat-treated at temperatures from 400 to 900 °C in an atmosphere of N₂ or H₂ to investigate the evolution of phosphorus-containing groups. Elemental analysis, X-ray photoelectron spectroscopy, ³¹P nuclear magnetic resonance, nitrogen adsorption, and scanning electron microscopy have been used to analyze the physicochemical properties of the activated carbons. The results show that C-O-P linkages of phosphorus-containing groups can progressively evolve into C-P-O, C₃-P═O, C₃-P, and eventually elemental phosphorus as a result of heat treatment. Phosphate-like groups are much more thermally stable in an N₂ than in an H₂ atmosphere. In N₂, C-O-P linkages significantly evolve into C-P-O and C₃-P═O at up to 800 °C, whereas C₃-P linkages are not formed even at 900 °C. In H₂, the corresponding evolution remarkably occurs at 500 °C, forming C₃-P linkages and eventually elemental phosphorus. Moreover, the two activated carbons exhibit different evolution trends, suggesting that the evolution happens more easily for phosphorus-containing groups located on the edges of graphite-like crystallites than those in the lattice. Finally, we propose different evolution pathways of phosphorus-containing groups upon heat treatment in N₂ and H₂ atmospheres.

One-pot and ultrafast synthesis of nitrogen and phosphorus co-doped carbon dots possessing bright dual wavelength fluorescence emission

Very brief microwave heating of aniline, ethylene diamine, and phosphoric acid in water at ambient pressure generated nitrogen and phosphorus co-doped carbon dots (N,P-CDs) that exhibit bright dual blue (centred at 450 nm; 51% quantum yield) and green (centred at 510 nm, 38% quantum yield) fluorescence emission bands. The N,P-CDs were characterized using TEM, XRD, XPS, IR, UV-vis, and fluorescence spectroscopy, demonstrating their partially crystalline carbon, partially amorphous structures, and the incorporation of O, N, and P into the carbogenic scaffold. The N,P-CDs demonstrated excitation-dependent and nearly pH-independent emission properties. The unique dual emission properties lay the foundation for the use of N,P-CDs in ratiometric sensing applications.

Activated Li2S as a High-Performance Cathode for Rechargeable Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries with a high theoretical energy density of ∼2500 Wh kg(-1) are considered as one promising rechargeable battery chemistry for next-generation energy storage. However, lithium-metal anode degradation remains a persistent problem causing safety concerns for Li-S batteries, hindering their practical utility. One possible strategy to circumvent the aforementioned problems is to use alternative, high-capacity, lithium-free anodes (e.g., Si, Sn, carbon) and a Li2S cathode. However, a large potential barrier was identified on the initial charge of insulating bulk Li2S particles, limiting the cell performance. In this work, the bulk Li2S particles were effectively activated with an electrolyte containing P2S5, resulting in a lowered initial charging voltage plateau. This permits the direct use of commercially available bulk Li2S particles as a high-capacity cathode for room-temperature, rechargeable Li-S batteries, significantly lowering the manufacturing cost of Li-S cells.