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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.

1393wileyonlinelibrary.com the practical applications of SIBs have been hamstrung by the lack of suitable anode materials to host Na + , which has a larger radius than that of Li + . Graphite with a highly ordered structure is considered to be not suitable to accommodate Na + because Na hardly forms staged intercalation compounds with graphite. [ 2 ] Twodimensional layered metal sulfi des (LMSs) with analogous structures to graphite, such as MoS 2 , [ 3 ] WS 2 , [ 4 ] SnS, [ 5 ] and SnS 2 , [ 6 ] have been reported as potential electrode materials for SIBs. The open framework of these types of materials allows Na + to insert reversibly with acceptable mobilities. However, the further application of 2D LMSs is impeded by their inherent limitations. First, these semiconductor metal sulfi des have inherently low electronic conductivity, which affects their electrochemical performances for Na + storage. Second, owing to the high surface energy and interlayer van der Waals attractions, [ 7 ] these thermally unstable 2D nanomaterials have a tendency to restack to minimize the surface energy. Furthermore, the signifi cant volume change and mechanical stress as a concomitant of sodium-ion insertion and extraction can induce the failure of the electrode and the loss of contact between active materials and the current collector, resulting in poor cycling stability.Graphene has established itself as a promising candidate to circumvent these challenges. For example, WS 2 /graphene, [ 4 ] SnS/graphene, [ 5b ] and SnS 2 /graphene [ 6 ] nanocomposites have already been successfully applied as anode materials for SIBs, showing a synergistic effect for sodium-ion storage, including improved capacity, rate capability, and cycling stability. In these reports, it is generally recognized that the enhanced electrochemical performances are attributed to the good electronic conductivity and mechanical resilience of graphene as 2D conformal building blocks for these layered sulfi des. However, a fundamental understanding of the exact interaction mechanism between LMSs and graphene for improving Na + storage performance is still not clear. The heterointerface between LMSs and graphene has been proven to contribute to novel properties and new functionalities that cannot be achieved by individual constituting materials. [ 8 ] Therefore, investigations Graphene has been widely used as conformal nanobuilding blocks to improve the electrochemical performance of layered metal sulfi des (MoS 2 , WS 2 , SnS, and SnS 2 ) as anode materials for sodium-ion batteries. However, it still lacks in-depth understanding of the synergistic effect between these layered sulfi des and graphene, which contributes to the enhanced electroactivity for sodium-ion batteries. Here, MoS 2 /reduced graphene oxide (RGO) nanocomposites with intimate two-dimensional heterointerfaces are prepared by a facile one-pot hydrothermal method. The heterointerfacial area can be effectively tuned by changing the ratio of MoS 2 to RGO. When used as anode materials for sodiu...

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.

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.