Metal-organic frameworks derived flower-like Co_3O_4/nitrogen doped graphite carbon hybrid for high-performance sodium-ion batteries

In this work, a novel flower-like cobalt-based metal organic frameworks(MOFs) self-assembled by Co^(2+) and nicotinic acid have been designed and synthesized. After a simple annealing treatment, Co_3O_4 nanoparticles in-situ decorating on nitrogen doped graphite carbon-sheet(Co_3O_4/NC) were obtained. The resultant Co_3O_4/NC hybrid with unique flower-like structure and ration combination of Co_3O_4 nanoparticles and nitrogen doped graphite carbon, endowing the hybrid with enhanced electrical conductivity,short ion diffusion pathways and rich porosity to the materials, which can largely alleviate the problems of Co_3O_4 such as inferior intrinsic electrical conductivity, sluggish ion kinetics and large volume change upon cycling. When evaluated as anode material for sodium-ion batteries(SIBs), the Co_3O_4/NC hybrid exhibits satisfied reversible capacity(213.9 mAh g^(-1) after 100 cycles at 0.1 A g^(-1) ), excellent rate capability(145.4 m Ah g^(-1) at 2 A g^(-1) and 130.1 mAh g^(-1) at 4 A g^(-1) ) and robust long-term cycling stability(120.1 m Ah g^(-1) after 2000 cycles at 0.5 A g^(-1) ), showing great potential for high-performance SIBs.

Synergistic effect of metallic nickel and cobalt oxides with nitrogen-doped carbon nanospheres for highly efficient oxygen evolution

The most energy-inefficient step in the oxygen evolution reaction(OER), which involves a complicated four-electron transfer process, limits the efficiency of the electrochemical water splitting. Here, well-defined Ni/Co3O4 nanoparticles coupled with N-doped carbon hybrids(Ni/Co3O4@NC) were synthesized via a facile impregnation-calcination method as efficient electrocatalysts for OER in alkaline media. Notably, the impregnation of the polymer with Ni and Co ions in the first step ensured the homogeneous distribution of metals, thus guaranteeing the subsequent in situ calcination reaction, which produced well-dispersed Ni and Co3O4 nanoparticles. Moreover, the N-doped carbon matrix formed at high temperatures could effectively prevent the aggregation and coalescence, and regulate the electronic configuration of active species. Benefiting from the synergistic effect between the Ni, Co3O4, and NC species, the obtained Ni/Co3O4@NC hybrids exhibited enhanced OER activities and remarkable stability in an alkaline solution with a smaller overpotential of 350 m V to afford 10 m A cm-2, lower Tafel slope of 52.27 m V dec-1, smaller charge-transfer resistance, and higher double-layer capacitance of 25.53 m F cm-2 compared to those of unary Co3O4@NC or Ni@NC metal hybrids. Therefore, this paper presents a facile strategy for designing other heteroatom-doped oxides coupled with ideal carbon materials as electrocatalysts for the OER.