High efficient and non-precious metal electrocatalysts for oxygen evolution reactions (OER) and oxygen reduction reactions (ORR) are at the heart of key renewable-energy technologies. Nevertheless, developing highly-active bi-functional catalysts at low cost for both OER and ORR still remains a huge challenge. In this paper, Co3O4 nanocrystals embedded in N-doped mesoporous graphitic carbon layer/multiwalled carbon nanotubes (MWCNTs) hybrids are prepared by a facile carbonization and subsequent oxidation process of MWCNTs-based metal-organic framework (MOF). As a result, in alkaline media, the hybrid material catalyzes OER with an onset potential of 1.50 V (vs reversible hydrogen electrode) and over-potential only of 320 mV to achieve a stable current density of 10 mA cm -2 for at least 25 h. The same hybrids also exhibit similar catalytic activity but superior stability to commercial 20 wt% Pt/C catalyst for ORR, making it a high-performance cheap bi-catalyst for both OER and ORR. The design concept of nonmetal-doped and precious-metal-free electrocatalysts from MOF can be extended to fabricate other novel, stable and easy to use catalyst system for advanced applications.

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The results indicated that obesity was associated with the risk of gastric cancer, especially for males and among non-Asians. Both overweight and obesity were associated with the risk of gastric cardia cancer.