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 electrocatalysts, 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.