Mass-loading independent electrocatalyst with high performance for oxygen reduction reaction and Zn-air battery based on Co-N-codoped carbon nanotube assembled microspheres

Although carbon materials have shown large potential as efficient electrocatalysts for oxygen reduction reaction (ORR), their practical performance with high energy density and power density is difficult to maintain under high mass-loading due to the compact restacking that seriously hinders mass/charge diffusion. To overcome this issue, we demonstrate the design and synthesis of hierarchical Co-N-codoped carbon nanotube hollow microspheres (CNT HMSs) with high disperse, large surface area and uniform mesopores, which effectively guarantees the high electrochemical activity and stability towards ORR even under high mass-loading. As a result, the power density of Zn-air battery based on CNT HMS gradually enhances from 52.8 to 183.8 mW cm(-2) with a good linear relationship when the mass-loading increases from 1.5 (traditional used for most reported works) to 6.0 mg cm(-2), indicating a well-preserved catalytic activity with high mass-loading. In addition, the long-term stability (10 h) test illustrates that monodisperse morphology and uniform size distribution of CNT HMS have been well maintained, while the referent carbon particles show serious agglomeration and obvious increased particle size. This suggests a much enhanced stability of CNT HMS compared with traditional particles, which offers large opportunity for the practical applications in metal-air batteries or fuel cells.