As one important component of sulfur cathodes, the carbon host plays a key role in the electrochemical performance of lithium-sulfur (Li-S) batteries. In this paper, a mesoporous nitrogen-doped carbon (MPNC)-sulfur nanocomposite is reported as a novel cathode for advanced Li-S batteries. The nitrogen doping in the MPNC material can effectively promote chemical adsorption between sulfur atoms and oxygen functional groups on the carbon, as verifi ed by X-ray absorption near edge structure spectroscopy, and the mechanism by which nitrogen enables the behavior is further revealed by density functional theory calculations. Based on the advantages of the porous structure and nitrogen doping, the MPNC-sulfur cathodes show excellent cycling stability (95% retention within 100 cycles) at a high current density of 0.7 mAh cm −2 with a high sulfur loading (4.2 mg S cm −2 ) and a sulfur content (70 wt%). A high areal capacity (≈3.3 mAh cm −2 ) is demonstrated by using the novel cathode, which is crucial for the practical application of Li-S batteries. It is believed that the important role of nitrogen doping promoted chemical adsorption can be extended for development of other high performance carbon-sulfur composite cathodes for Li-S batteries.

Nitrogen-Doped Mesoporous Carbon Promoted Chemical Adsorption of Sulfur and Fabrication of High-Areal-Capacity Sulfur Cathode with Exceptional Cycling Stability for Lithium-Sulfur Batteries

The commercialization of fuel cells, such as proton exchange membrane fuel cells and direct methanol/formic acid fuel cells, is hampered by their poor stability, high cost, fuel crossover, and the sluggish kinetics of platinum (Pt) and Pt-based electrocatalysts for both the cathodic oxygen reduction reaction (ORR) and the anodic hydrogen oxidation reaction (HOR) or small molecule oxidation reaction (SMOR). Thus far, the exploitation of active and stable electrocatalysts has been the most promising strategy to improve the performance of fuel cells. Accordingly, increasing attention is being devoted to modulating the surface/interface electronic structure of electrocatalysts and optimizing the adsorption energy of intermediate species by defect engineering to enhance their catalytic performance. Defect engineering is introduced in terms of defect definition, classification, characterization, construction, and understanding. Subsequently, the latest advances in defective electrocatalysts for ORR and HOR/SMOR in fuel cells are scientifically and systematically summarized. Furthermore, the structure-activity relationships between defect engineering and electrocatalytic ability are further illustrated by coupling experimental results and theoretical calculations. With a deeper understanding of these complex relationships, the integration of defective electrocatalysts into single fuel-cell systems is also discussed. Finally, the potential challenges and prospects of defective electrocatalysts are further proposed, covering controllable preparation, in situ characterization, and commercial applications.

Defect Engineering for Fuel‐Cell Electrocatalysts

Heteroatom-doped carbon materials (HDCMs) have been widely studied as some of the most prominent material candidates for use in a wide range of applications, such as batteries, supercapacitors (SCs), and the oxygen reduction reaction (ORR) Over the past few years, various metal-free heteroatom-doped carbon composites have been developed via integrating different heteroatoms into carbon with different nanostructures, from single-atom doping (N, P, B, S, etc) to multiple heteroatom doping (N/P/S, N/S/B, etc) For the first time, this review comprehensively analyzes the relevant features of HDCMs used in batteries, SCs, and the ORR, and provides guidance for the design of more efficient materials By controlling the content and types of heteroatom-containing reagents, not only the physical and chemical properties of the material can be adjusted, but also the specific surface area and pore volume can be increased via controlling the morphology, thereby enhancing the electrochemical performance of the material Subsequently, this review summarizes the developments and the history of HDCMs, including synthesis methods, the relationship between doping (doping position and content) and performance, reaction mechanisms, and evaluations of systems In addition, the important role of oxygen doping is raised and discussed, to remind researchers not to ignore the role of oxygen in improving material properties Finally, future developments and challenges relating to key technologies in this thriving field are also discussed in this report

Untangling Respective Effects of Heteroatom-doped Carbon Materials in Batteries, Supercapacitors and ORR to Design High-Performance Materials

Heterogeneous catalysis plays an important role in modern industries. Exploring catalysts with high efficiency, low-cost and high stability is an important issue for the research of heterogeneous c...

Defect chemistry in heterogeneous catalysis: recognition, understanding and utilization

Electromagnetic (EM) wave absorbing materials play an increasingly important role in modern society for their multi‐functional in military stealth and incoming 5G smart era. Dielectric loss EM wave absorbers and underlying loss mechanism investigation are of great significance to unveil EM wave attenuation behaviors of materials and guide novel dielectric loss materials design. However, current researches focus more on materials synthesis rather than in‐depth mechanism study. Herein, comprehensive views toward dielectric loss mechanisms including interfacial polarization, dipolar polarization, conductive loss, and defect‐induced polarization are provided. Particularly, some misunderstandings and ambiguous concepts for each mechanism are highlighted. Besides, in‐depth dielectric loss study and novel dielectric loss mechanisms are emphasized. Moreover, new dielectric loss mechanism regulation strategies instead of regular components compositing are summarized to provide inspiring thoughts toward simple and effective EM wave attenuation behavior modulation.

Dielectric Loss Mechanism in Electromagnetic Wave Absorbing Materials

The reasonable design of electrode materials for rechargeable batteries plays an important role in promoting the development of renewable energy technology. With the in-depth understanding of the mechanisms underlying electrode reactions and the rapid development of advanced technology, the performance of batteries has significantly been optimized through the introduction of defect engineering on electrode materials. A large number of coordination unsaturated sites can be exposed by defect construction in electrode materials, which play a crucial role in electrochemical reactions. Herein, recent advances regarding defect engineering in electrode materials for rechargeable batteries are systematically summarized, with a special focus on the application of metal-ion batteries, lithium-sulfur batteries, and metal-air batteries. The defects can not only effectively promote ion diffusion and charge transfer but also provide more storage/adsorption/active sites for guest ions and intermediate species, thus improving the performance of batteries. Moreover, the existing challenges and future development prospects are forecast, and the electrode materials are further optimized through defect engineering to promote the development of the battery industry.

Defect Engineering on Electrode Materials for Rechargeable Batteries.

Electrochemical CO2 reduction is a promising way to mitigate CO2 emissions and close the anthropogenic carbon cycle. Among products from CO2RR, multicarbon chemicals, such as ethylene and ethanol with high energy density, are more valuable. However, the selectivity and reaction rate of C2 production are unsatisfactory due to the sluggish thermodynamics and kinetics of C-C coupling. The electric field and thermal field have been studied and utilized to promote catalytic reactions, as they can regulate the thermodynamic and kinetic barriers of reactions. Either raising the potential or heating the electrolyte can enhance C-C coupling, but these come at the cost of increasing side reactions, such as the hydrogen evolution reaction. Here, we present a generic strategy to enhance the local electric field and temperature simultaneously and dramatically improve the electric-thermal synergy desired in electrocatalysis. A conformal coating of ∼5 nm of polytetrafluoroethylene significantly improves the catalytic ability of copper nanoneedles (∼7-fold electric field and ∼40 K temperature enhancement at the tips compared with bare copper nanoneedles experimentally), resulting in an improved C2 Faradaic efficiency of over 86% at a partial current density of more than 250 mA cm-2 and a record-high C2 turnover frequency of 11.5 ± 0.3 s-1 Cu site-1. Combined with its low cost and scalability, the electric-thermal strategy for a state-of-the-art catalyst not only offers new insight into improving activity and selectivity of value-added C2 products as we demonstrated but also inspires advances in efficiency and/or selectivity of other valuable electro-/photocatalysis such as hydrogen evolution, nitrogen reduction, and hydrogen peroxide electrosynthesis.

Accelerating CO2 Electroreduction to Multicarbon Products via Synergistic Electric-Thermal Field on Copper Nanoneedles.

Recycling spent lithium-ion batteries (LIBs) is an urgent task in view of the resource shortage and environmental concerns. Here, a facile ternary molten salt approach is presented for efficiently regenerating the LiNi0.5 Co0.2 Mn0.3 O2 (NCM523) cathode of spent LIBs. Such an approach involves the treatment of spent cathode powder in the ternary molten salt at a moderate temperature (400 °C) and subsequent annealing in oxygen. The Li loss and degraded phases in spent NCM that cause the capacity decay can be fully remedied after the regeneration process. As a result, the regenerated cathode delivers a reversible capacity of 160 mAh g-1 at 0.5 C with retention of 93.7% after 100 cycles and maintains a high capacity of 132 mAh g-1 at a high rate of 5 C. The electrochemical performance of regenerated NCM cathode is compared favorably to the fresh NCM cathode, which demonstrates the feasibility of the molten salt approach to directly regenerate spent NCM cathode.

A Ternary Molten Salt Approach for Direct Regeneration of LiNi0.5 Co0.2 Mn0.3 O2 Cathode.

Defect-rich graphene skin modified carbon felt as a highly enhanced electrode for vanadium redox flow batteries

Silicon suboxides (SiOx) have been widely concerned as a practical anode material for the next-generation lithium-ion batteries due to their relatively high theoretical capacity and lower volume change compared to silicon (Si). Nevertheless, traditional binder poly(vinylidene difluoride) (PVDF) still cannot hold the integrity of the SiOx particle due to its weak van der Waals force. Herein, a copolymer binder for SiOx microparticles is synthesized through a facile method of free radical polymerization between acrylamide (AM) and acrylic acid (AA). By adjusting the mass ratio of the AM/AA monomer, the copolymer binder can generate a covalent-noncovalent network with superior elastic properties from the synergistic effect. During electrochemical testing, the SiOx anode with the optimal copolymer binder (AM/AA = 3:1) delivered a reversible capacity of 734 mAh g-1 (two times that of commercial graphite) at 0.5C after 300 cycles. Thus, this work developed a green and effective strategy for synthesizing a water-soluble binder for Si-based anodes.

Chuankun Jia

Papers

Defect Engineering on Electrode Materials for Rechargeable Batteries.

Accelerating CO2 Electroreduction to Multicarbon Products via Synergistic Electric-Thermal Field on Copper Nanoneedles.

A Ternary Molten Salt Approach for Direct Regeneration of LiNi0.5 Co0.2 Mn0.3 O2 Cathode.

Defect-rich graphene skin modified carbon felt as a highly enhanced electrode for vanadium redox flow batteries

Random Copolymer Hydrogel as Elastic Binder for the SiOx Microparticle Anode in Lithium-Ion Batteries.