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Vanadium oxides are potential anode materials for sodium-ion batteries, however, their application is limited for their rate capability and cycle life. Herein, hollow spheres of Co-doped V 2 O 3 enveloped in N-doped carbon (Co-V 2 O 3 @NC) are prepared through a hydrothermal step with the following sintering process. The hollow spherical structure supplies short distance and large area for fast ion transfer kinetics, which also provides voids to ease the volume expansion. The strong coupling between Co-V 2 O 3 nanoparticles and carbon layer constitutes a solid structure that enhances the conductivity and keeps electrode integrity. Co-doping introduces plenty of active sites for surface capacitance behavior and accelerates charge transfer. On account of the benefits, Co-V 2 O 3 @NC exhibits excellent Na+ storage properties as anode, including high capacity of 338.5 mAh g−1 at 0.1 A g−1, stable cycling capability of 240 mAh g−1 after 1000 cycles at 1 A g−1, and excellent rate performance. This work describes the importance of constructing specific structured materials for advanced anodes. [Display omitted] • Hollow spheres of Co-doped V 2 O 3 enveloped in N-doped carbon are prepared. • Hollow structure accelerates ion transfer kinetics and buffers volume expansion. • Co-doping provides sites for surface-controlled sodium storage. • Carbon coating improves conductivity and benefits electrode integrity. • High-performance sodium storage performances are acquired. [ABSTRACT FROM AUTHOR]

Heterostructure fabrication is believed to acquire promoted charge transfer and improved surface storage contribution, thus obtaining high-performance anodes for sodium-ion batteries. Herein, the simultaneous phosphatization and selenization of polydopamine functionalized ZIF-67 is adopted to engineer N-doped carbon coated Co(PO 3) 2 /CoSe 2 heterostructure. The hetero-interface with plenty of surface sites is activated with large surface reaction and fast sodium ion transport dynamics. The multiphase synergism and carbon coating layer assure high conductivity and structural stability. The designed sample delivers impressive anode performance, exhibiting a high sodium storage capacity of 333.4 mAh g−1 at 0.1 A g−1 and 192.7 mAh g−1 after 1000 cycles at 2 A g−1. This simple and reasonable method can be utilized to construct other transition metal based heterostructures with multiphase synergism for the application of advanced anodes. [Display omitted] • N-doped carbon coated Co(PO 3) 2 /CoSe 2 heterostructure is prepared. • Heterostrucrue favors surface-controlled pseudocapacitive sodium storage. • N-doped carbon shell enhances conductivity and keeps electrode integrity. • Multiphase synergism benefits electrochemical kinetics and structure stability • Large/fast sodium storage properties with excellent stability are obtained. [ABSTRACT FROM AUTHOR]

• Heterogeneous Co@CoO encapsulated in P, N co-doped carbon fibers is prepared. • Synergism between Co and CoO is beneficial to improve OER. • PNC fiber benefits charge transfer and catalysis stability. • Low overpotentials of 289 (KOH) and 371 (PBS) mV at 10 mA cm−2 for OER. Heterostructured materials favoring synergism, efficient charge transfer, and abundant active sites have aroused enormous interests for water electrolysis. Here heterogeneous Co@CoO encapsulated in P, N co-doped carbon nanofibers supported on carbon cloth (Co@CoO-PNC/CC) has been prepared to pursue attractive synergism for the application of pH-tolerant catalyst for oxygen evolution reaction (OER) in both alkaline and neutral solutions. The prepared Co@CoO-PNC/CC exhibits advanced OER performances, generating a current density of 10 mA cm−2 at overpotential of 289 mV in alkaline media and 371 mV in neutral media. The high OER activity can be assigned to the synergistic effect of abundant active sites and enhanced charge transfer between Co and CoO, as well as the specific P, N co-doped carbon nanofiber architecture. [ABSTRACT FROM AUTHOR]