Non‐trivial Contribution of Carbon Hybridization in Carbon‐based Substrates to Electrocatalytic Activities in Li‐S Batteries

Abstract

Appling an electrochemical catalyst is an efficient strategy for inhibiting the shuttle effect and enhancing the S utilization of Li-S batteries. Carbonbased materials are the most common conductive agents and catalyst supports used in Li-S batteries, but the correlation between the diversity of hybridizations and sulfur reduction reaction (SRR) catalytic activity remains unclear. Here, by establishing two forms of carbon models, i.e., graphitic carbon (GC) and amorphous carbon (AC), we observe that the nitrogen atom doped in the GC possesses a higher local charge density and a lower Gibbs free energy towards the formation of polysulfides than in the AC. And the GC-based electrode consistently inherits considerably enhanced SRR kinetics and superior cycling stability and rate capability in Li-S batteries. Therefore, the function of carbon in Li-S batteries is not only limited as conductive support but also plays an unignorable contribution to the electrocatalytic activities of SRR.

Bimetal‐Organic Framework Nanoboxes Enable Accelerated Redox Kinetics and Polysulfide Trapping for Lithium‐Sulfur Batteries

“…However, the sluggish redox kinetics and adverse shuttling effect of LiPSs lead to the inferior Coulombic efficiency, poor rate capability, and limited lifespan in Li−S batteries. To tackle the above issues, numerous carbon‐based materials, transition metal oxides and sulfides have been widely employed as sulfur hosts to immobilize LiPSs and facilitate their conversion kinetics [5–14] . However, most of these sulfur hosts suffer from the relatively poor conductivity and limited active adsorption sites, resulting in low sulfur utilization, slow reaction kinetics, and rapid capacity decay.…”

“…To tackle the above issues, numerous carbon-based materials, transition metal oxides and sulfides have been widely employed as sulfur hosts to immobilize LiPSs and facilitate their conversion kinetics. [5][6][7][8][9][10][11][12][13][14] However, most of these sulfur hosts suffer from the relatively poor conductivity and limited active adsorption sites, resulting in low sulfur utilization, slow reaction kinetics, and rapid capacity decay. Constructing novel sulfur hosts with well-designed catalytic active sites is highly desirable for advanced LiÀ S batteries but remains as a grand challenge.…”

Finding the Ideal Electrocatalyst Match for Sulfur Redox Reactions in Li-S Batteries

“…In our recent work, we proposed that the hybridization of the C−C bonds in the carbon support plays a crucial role in the electronic structure of catalytically active centers and indirectly influences the activity of the electrocatalyst toward SRR. 24 Using nitrogen-doped graphite carbon (GC) and amorphous carbon (AC) as models and combining theoretical calculations with electrochemical tests, we discovered that if the carbon atoms adjacent to the active center (N atom) are sp 2 hybridized, the localized charge density of the active catalytic center is effectively enhanced (Figure 10a) and the Gibbs free energy during the SRR is lower. Experimentally, we synthesized two groups of N-doped carbon catalysts and verified their degree of carbon hybridization from their XPS C 1s spectra (Figure 10b) and XAS.…”

Intrinsic Carbon Defects in Nitrogen and Sulfur Doped Porous Carbon Nanotubes Accelerate Oxygen Reduction and Sulfur Reduction for Electrochemical Energy Conversion and Storage

“…Carbon-based materials have been widely investigated as both ORR and SRR catalysts and gained more focus owing to their good conductivity, flexible structural tailorability, and curtailed cost. 18,19 However, pristine bulky carbon materials show poor catalytic activity due to a low specific surface area and weak adsorption affinity to oxygen and sulfur. The electrochemical performance of carbon-based materials can be greatly boosted by morphology and type of active site engineering, such as construction of nanoscale architectures and incorporation of defects.…”

“…Incorporation of effective electrocatalysts in cathodes can optimize the adsorption/desorption of reactant/product species, reduce the activation energy of the reduction reactions, and expedite the electrochemical kinetics during the reduction processes. − Although platinum (Pt)-based materials are the most effective commercialized ORR electrocatalysts, , their large-scale application is limited by the scare reserves and exorbitant price; hence, high-performance and cheap ORR electrocatalysts are urgently needed. Carbon-based materials have been widely investigated as both ORR and SRR catalysts and gained more focus owing to their good conductivity, flexible structural tailorability, and curtailed cost. , However, pristine bulky carbon materials show poor catalytic activity due to a low specific surface area and weak adsorption affinity to oxygen and sulfur. The electrochemical performance of carbon-based materials can be greatly boosted by morphology and type of active site engineering, such as construction of nanoscale architectures and incorporation of defects. − Carbon-based materials with various nanostructures of high specific surface area and large pore volume, including nanosheets, , nanoscrolls, nanofibers, , nanotubes, − nanorods, hollow nanospheres, − nanocubes, nanocages, etc., have been constructed to expose more active sites, accommodate more reactants and products, and facilitate mass transfer.…”