Highly efficient Co3O4/Co@NCs bifunctional oxygen electrocatalysts for long life rechargeable Zn-air batteries

Rational design and synthesis of high-performance bifunctional oxygen electrocatalysts are in high demand for metal air batteries. Herein, Co3O4/Co nano-heterojunctions tailored in nitrogen-doped porous graphitized carbon frameworks (Co3O4/Co@NCs) are synthesized via annealing Co-based metal-organic-frameworks (Co-based MOFs). This structure for electrocatalysts with a combination of mixed metallic Co species and encapsulating porous graphitized carbon offers an efficient charge/mass transport environment. In addition, the Co3O4/Co nano-heterostructured interfaces serve as efficient reactive sites to enhance oxygen electrocatalysis. Furthermore, the strong binding forces between nanoparticles and carbon frameworks through Co-N covalent bonds prevent the loss of nanoparticles from the electmcatalysts, providing outstanding durability. Consequently, Co3O4/Co@NCs surpasses the performance of noble-metal catalysts with a positive half-wave potential of 0.92 V (vs. reversible hydrogen electrode, RHE) for the oxygen reduction reaction and a low potential of 1.55 V at 10 mA cm 2 for the oxygen evolution reaction. Impressively, our assembled zinc-air batteries using Co3O4/Co@NCs as the rechargeable air electrode exhibit superior charge-discharge performance and ultra-stable cyclability with almost no increase in polarization even after 600 h (10 mA cm(-2)), possessing great potential for practical application in next-generation rechargeable batteries.