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Developing stable but high active metal-nitrogen-carbon (M-N-C)-based hard carbon anode is a promising way to be the alternatives to graphene and blank hard carbon for sodium-ion batteries (SIBs), requiring the precise tailoring of the electronic structure for optimizing the Na+ intercalation behavior, yet is greatly challenging. Herein, Fe-N-C graphitic layer-encapsulating Fe3C species within hard carbon nanosheets (Fe-N-C/Fe3C@HCNs) are rationally engineered by pyrolysis of self-assembled polymer. Impressively, the Fe-N-C/Fe3C@HCNs exhibit outstanding rate capacity (242 mAh·g−1 at 2,000 mA·g−1), which is 2.1 and 4.2 times higher than that of Fe-N-C and N-doped carbon (N-C), respectively, and prolonged cycling stability (176 mAh·g−1 at 2,000 mA·g−1 after 2,000 cycles). Theoretical calculations unveil that the Fe3C species enhance the electronic transfer from Na to Fe-N-C, resulting in the charge redistribution between the interfaces of Fe3C and Fe-N-C. Thus, the optimized adsorption behavior towards Na+ reduces the thermodynamic energy barriers. The synergistic effect of Fe3C and Fe-N-C species maintains the structural integrity of electrode materials during the sodiation/desodiation process. The in-depth insight into the advanced Na+ storage mechanisms of Fe3C@Fe-N-C offers precise guidance for the rational establishment of confinement heterostructures in SIBs. [ABSTRACT FROM AUTHOR]

Electrocatalytic CO2 reduction to CO is a sustainable process for energy conversion. However, this process is still hindered by the diffusion-limited mass transfer, low electrical conductivity and catalytic activity. Therefore, new strategies for catalyst design should be adopted to solve these problems and improve the electrocatalytic performance for CO production. Herein, we report a multiscale carbon foam confining single iron atoms prepared with the assistant of SiO2 template. The pore-enriched environment at the macro-scale facilitates the diffusion of reactants and products. The graphene nanosheets at the nano-scale promote the charge transfer during the reaction. The single iron atoms confined in carbon matrix at the atomic-scale provide the active sites for electrocatalytic CO2 reduction to CO. The optimized catalyst achieves a CO Faradaic efficiency of 94.9% at a moderate potential of −0.5 V vs. RHE. Furthermore, the performance can be maintained over 60 hours due to the stable single iron atoms coordinated with four nitrogen atoms in the carbon matrix. This work provides a promising strategy to improve both the activity and stability of single atom catalysts for electrocatalytic CO2 reduction to CO. [ABSTRACT FROM AUTHOR]