Designing atomically dispersed metal catalysts for oxygen reduction reaction (ORR) is a promising approach to achieve efficient energy conversion. Herein, we develop a template-assisted method to synthesize a series of single metal atoms anchored on porous N,S-codoped carbon (NSC) matrix as highly efficient ORR catalysts to investigate the correlation between the structure and their catalytic performance. The structure analysis indicates that an identical synthesis method results in distinguished structural differences between Fe-centered single-atom catalyst (Fe-SAs/NSC) and Co-centered/Ni-centered single-atom catalysts (Co-SAs/NSC and Ni-SAs/NSC) because of the different trends of each metal ion in forming a complex with the N,S-containing precursor during the initial synthesis process. The Fe-SAs/NSC mainly consists of a well-dispersed FeN 4 S 2 center site where S atoms form bonds with the N atoms. The S atoms in Co-SAs/NSC and Ni-SAs/NSC, on the other hand, form metal−S bonds, resulting in CoN 3 S 1 and NiN 3 S 1 center sites. Density functional theory (DFT) reveals that the FeN 4 S 2 center site is more active than the CoN 3 S 1 and NiN 3 S 1 sites, due to the higher charge density, lower energy barriers of the intermediates, and products involved. The experimental results indicate that all three single-atom catalysts could contribute high ORR electrochemical performances, while Fe-SAs/NSC exhibits the highest of all, which is even better than commercial Pt/C. Furthermore, Fe-SAs/NSC also displays high methanol tolerance as compared to commercial Pt/C and high stability up to 5000 cycles. This work provides insights into the rational design of the definitive structure of single-atom catalysts with tunable electrocatalytic activities for efficient energy conversion.

shuttle effect of polysulfide. [3] The suppression of the polysulfide shuttle effect is the primary challenge that has hindered the development of lithium-sulfur batteries. The ideal sulfur cathode host should have: (i) a highly porous structure with interconnected architecture to encapsulate sulfur, (ii) strong capability to restrain soluble polysulfides, (iii) high electronic conductivity, and (iv) flexible but robust mechanical properties.Carbon materials with well-designed pore structures, such as mesoporous carbon [4] and carbon nanotubes, [5] have been utilized to restrain the migration of soluble polysulfides from the cathode. Carbon materials can effectively improve the electronic conductivity of sulfur cathodes, and the as-fabricated lithium-sulfur cells showed high specific capacities during the initial few cycles. However, there has been a serious decay of capacity during long-term cycling. It is mainly ascribed to the weak intrinsic interactions between nonpolar carbon and polar polysulfides intermediate, and the large volume expansion/extraction of sulfur compounds during the discharge/ charge processes. [6] The physical barriers provided by sequestration and adsorption in carbon materials can only slow down diffusion of lithium polysulfides out of cathodes in the shortto medium-term of cycling (<100 cycles). Additionally, weak interaction can cause the detachment and separation of lithium sulfides (Li 2 S x , 1 < x < 2, the fully discharged products), from carbon matrix, which will induce irreversible active mass loss and isolation of electrical contacts. Therefore, strong physical and chemical interactions between sulfur/lithium polysulfides and the host materials are crucial to suppress polysulfides shuttling effects and capacity decay. It has been discovered that surface functionalized host materials, such as reduced graphene oxides, [1] polar metal oxides (MnO 2 , [7] Ti 4 O 7[8] ), metal-organic frameworks (MOFs), [9] and metal carbide MXene, [10] showed much better properties because of their hydrophilic surfaces that can bind lithium polysulfides via polar-polar interactions.Recently, a large family of ternary metal carbides, nitrides, or carbonitrides has been successfully prepared. These are termed as "MXene" and are denoted as M n + 1 X n T x , where M is an transition metal such as Ti or V, X is C and/or N, and T is a surface termination group (e.g., O, OH, and F). [11] They have been emerged as brand-new 2D materials with potential applications as electrode materials. Owing to layered structure, high electronic conductivity, remarkable chemical durability, Crumpled nitrogen-doped MXene nanosheets with strong physical and chemical coadsorption of polysulfides are synthesized by a novel one-step approach and then utilized as a new sulfur host for lithium-sulfur batteries. The nitrogendoping strategy enables introduction of heteroatoms into MXene nanosheets and simultaneously induces a well-defined porous structure, high surface area, and large pore volume. The as-prepared nitrogen-dope...

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HIGHLIGHTSNovel synthesis of aerogel-like porous MXene architectures Porous MXene architectures can effectively prevent the restack of MXene nanosheets Porous MXene demonstrated a high electroadsorption capacity MXene electrodes achieved a high capacitive deionization capacity

Sodium (Na) metal is one of the most promising electrode materials for next-generation low-cost rechargeable batteries. However, the challenges caused by dendrite growth on Na metal anodes restrict practical applications of rechargeable Na metal batteries. Herein, a nitrogen and sulfur co-doped carbon nanotube (NSCNT) paper is used as the interlayer to control Na nucleation behavior and suppress the Na dendrite growth. The N- and S-containing functional groups on the carbon nanotubes induce the NSCNTs to be highly "sodiophilic," which can guide the initial Na nucleation and direct Na to distribute uniformly on the NSCNT paper. As a result, the Na-metal-based anode (Na/NSCNT anode) exhibits a dendrite-free morphology during repeated Na plating and striping and excellent cycling stability. As a proof of concept, it is also demonstrated that the electrochemical performance of sodium-oxygen (Na-O ) batteries using the Na/NSCNT anodes show significantly improved cycling performances compared with Na-O batteries with bare Na metal anodes. This work opens a new avenue for the development of next-generation high-energy-density sodium-metal batteries.

Sodium-based batteries have attracted considerable attention and are recognized as ideal candidates for large-scale and low-cost energy storage. Sodium (Na) metal anodes are considered as one of the most promising anodes for next-generation, high-energy, Na-based batteries owing to their high theoretical specific capacity (1166 mA h g −1 ) and low standard electrode potential. Herein, an overview of the recent developments in Na metal anodes for high-energy batteries is provided. The high reactivity and large volume expansion of Na metal anodes during charge and discharge make the electrode/electrolyte interphase unstable, leading to the formation of Na dendrites, short cycle life, and safety issues. Design strategies to enable the efficient use of Na metal anodes are elucidated, including liquid electrolyte engineering, electrode/electrolyte interface optimization, sophisticated electrode construction, and solid electrolyte engineering. Finally, the remaining challenges and future research directions are identified. It is hoped that this progress report will shape a consistent view of this field and provide inspiration for future research to improve Na metal anodes and enable the development of high-energy sodium batteries.

The electron-withdrawing groups were selectively introduced onto the edge of g-C 3 N 4 nanosheets. The edge functionalization not only induces an upward bending that improves the adsorption of oxygen molecules but also promotes the separation of photo-generated electron-hole pairs. By using these nanosheets as the photocatalyst for water disinfection, Dan Wang and colleauges achieved a record-high efficiency toward the photo-disinfection of Escherichia coli under visible-light irradiation among all metal-free catalysts.

The practical applications of lithium metal anodes in high-energy-density lithium metal batteries have been hindered by their formation and growth of lithium dendrites. Herein, we discover that certain protein could efficiently prevent and eliminate the growth of wispy lithium dendrites, leading to long cycle life and high Coulombic efficiency of lithium metal anodes. We contend that the protein molecules function as a “self-defense” agent, mitigating the formation of lithium embryos, thus mimicking natural, pathological immunization mechanisms. When added into the electrolyte, protein molecules are automatically adsorbed on the surface of lithium metal anodes, particularly on the tips of lithium buds, through spatial conformation and secondary structure transformation from α-helix to β-sheets. This effectively changes the electric field distribution around the tips of lithium buds and results in homogeneous plating and stripping of lithium metal anodes. Furthermore, we develop a slow sustained-release strategy to overcome the limited dispersibility of protein in the ether-based electrolyte and achieve a remarkably enhanced cycling performance of more than 2000 cycles for lithium metal batteries.