Hollow porous carbon nanospheres containing polar cobalt sulfide (Co9S8) nanocrystals as electrocatalytic interlayers for the reutilization of polysulfide in lithium-sulfur batteries

Accelerating the Catalytic Conversion of Polysulfides in Lithium-Sulfur Batteries from Both the Cathode and the Separator Perspectives

Lithium-sulfur (Li-S) batteries have a high theoretical energy density and are regarded to be an ideal choice for the next generation of electrochemical energy storage systems. However, their practical application is hindered by several bottlenecks, including the insulating nature of sulfur and its discharge products (Li2S2/Li2S), the shuttling behavior of intermediate polysulfides, and slow redox reactions. Herein, we propose a highly efficient bimetallic selenide electrocatalyst featuring a hollow porous core-shell spherical structure, which serves as both a cathode host and a modified separator coated on a commercially available polypropylene separator to address the above issues. The bimetallic selenide enhances cathode conductivity, and its unique hollow porous core-shell spherical structure provides rapid ion transport channels, along with ample spatial confinement for lithium polysulfides. Additionally, the abundant reactive sites on the bimetallic selenides exhibit high intrinsic electrocatalytic activity, accelerating polysulfide conversion and improving redox kinetics. Density functional theory calculations indicate that bimetallic selenides interact more strongly with polysulfides and present lower reaction barriers compared to those of their sulfide counterparts. Consequently, these bimetallic selenide materials demonstrate superior rate performance and cycling stability in Li-S batteries, achieving an impressive lifespan of 1400 cycles with a minimal decay rate of 0.030% per cycle at 1.0 C. This work provides unique insights into enhancing the performance of transition metal compounds in Li-S batteries.

Enhancement of ammonia synthesis via electrocatalytic reduction of low-concentration nitrate using co-doped MIL-101(Fe) nanostructured catalysts

In the domain of electrocatalytic NO3- reduction (NO3-RR) for the treatment of low-concentration nitrate-containing domestic or industrial wastewater, the conversion of NO3- into NH4+ holds significant promise for resource recovery. Nevertheless, the central challenge in this field revolves around the development of catalysts exhibiting both high catalytic activity and selectivity. To tackle this challenge, we design a two-step hydrothermal combine with carbonization process to fabricate a cobalt-doped Fe-based MOF (MIL-101) catalyst at 800 °C temperatures. The aim was to fully leverage cobalt's demonstrated high selectivity in NO3- electroreduction and enhance activity by promoting electron transfer through the d-band of Fe. The results indicate that the synthesized catalyst inherits multiple active sites from its precursor, with the co-doping process optimized through the topological properties of the MOF. Elemental analysis and oxidation state testing were employed to scrutinize the fundamental characteristics of this catalyst type and comprehend how these features may influence its efficiency. Electrochemical analysis revealed that, even under conditions of low NO3- concentration, the Cox@MIL-Fe catalyst achieved an impressive nitrate conversion rate of 98 % at -0.9 V vs. RHE. NH4+ selectivity was notably high at 87 %, and the by-product NO2- levels remained at a minimal threshold. The Faradaic efficiency for NH4+ reached 74 %, with ammonia yield approaching 0.08 mmol h-1 cm-2. This study furnishes indispensable research data for the design of Fe-based electrocatalysts for nitrate reduction, offering profound insights into the modulation of catalysts to play a pivotal role in the electroreduction of nitrate ions.

High-Entropy Metal Oxide-Coated Carbon Cloth as Catalysts for Long-Life Li-S Batteries

Lithium-sulfur (Li-S) batteries with high specific energy density, low cost, and environmental friendliness of sulfur have been regarded as a competitive alternative to replace lithium-ion batteries. However, the shuttle effect and the sluggish conversion rate of lithium polysulfides (LiPSs) have seriously limited the practical application of Li-S batteries. Herein, high-entropy oxides grown on the carbon cloth (CC/HEO) are synthesized by a simple and ultrafast solution combustion method for the sulfur cathode. The as-prepared composites possess abundant HEO active sites for strong interaction with LiPSs, which can significantly promote redox kinetics. Besides, the carbon fiber substrate not only ensures high electrical conductivity but also accommodates large volume change, leading to a stable sulfur electrochemistry. Benefiting from the rational design, the Li-S batteries with CC/HEO as cathode skeleton exhibits good cyclability with a capacity decay rate of 0.057% per cycle after 1000 cycles at 2 C. More importantly, the Li-S batteries with 4.3 mg cm-2 high sulfur loading can still retain a high capacity retention of 78.2% after 100 cycles.

Cobalt Nitride Nanoparticles Encapsulated in N-Doped Carbon Nanotubes Modified Separator of Li-S Battery Achieving the Synergistic Effect of Restriction-Adsorption-Catalysis of Polysulfides

Although lithium-sulfur (Li-S) batteries have broad market prospects due to their high theoretical energy density and potential cost-effectiveness, the practical applications still face serious shuttle effects of polysulfides (LiPSs) and slow redox reactions. Therefore, in this paper, cobalt nitride nanoparticles encapsulated in nitrogen-doped carbon nanotube (CoN@NCNT) are prepared as a functional layer for the separator of high-performance Li-S batteries. Carbon nanotubes with large specific surface areas not only promote the transport of ions and electrons but also weaken the migration of LiPSs and confine the dissolution of LiPSs in electrolytes. The lithiophilic heteroatom N adsorbs LiPSs by strong chemical adsorption, and the CoN particles with high catalytic activity greatly improve the kinetics of the conversion between LiPSs and Li2S2/Li2S during the charge-discharge process. Due to these advantages, the battery with CoN@NCNT modified separator has superior rate performance (initial discharge capacity of 834.7 mAh g-1 after activation at 1 C) and excellent cycle performance (capacity remains 729.7 mAh g-1 after 200 cycles at 0.2 C). This work proposes a strategy that can give the separator a strong ability to confinement-adsorption-catalysis of LiPSs in order to provide more possibilities for the development of Li-S batteries.

MoP quantum dots based multifunctional efficient electrocatalyst for stable and long-life flexible lithium-sulfur batteries

The commercialization of lithium-sulfur (Li-S) batteries is challenging, owing to factors like the poor conductivity of S, the 'shuttle effect', and the slow reaction kinetics. To address these challenges, MoP quantum dots were decorated on hollow carbon spheres (MoPQDs/C) in this study and used as an efficient lithium polysulfides (LiPSs) adsorbents and catalysts. In this approach polysulfides are effectively trapped through strong chemisorption and physical adsorption while simultaneously facilitating LiPSs conversion by enhancing the reaction kinetics. MXene serves as a flexible physical barrier (MoPQDs/C@MXene), further enhancing the confinement of LiPSs. Moreover, both materials are conductive, significantly facilitating electron and charge transfer. Additionally, the flexible MoPQDs/C@MXene-S electrode offers a large specific surface area for sulfur loading and withstand volume expansion during electrochemical processes. As a result, the MoPQDs/C@MXene-S electrode exhibits excellent long-term cyclability and maintains a robust specific capacity of 992 mA h g-1 even after 800cycles at a rate of 1.0C (1C = 1675 mA g-1), with a minimal capacity decay rate of 0.034 % per cycle. This work proposes an efficient strategy to fabricate highly efficient electrocatalysts for advanced Li-S batteries.