Boosted Oxygen Kinetics of Hierarchically Mesoporous Mo₂C/C for High-current-density Zn-air Battery

The high-current-density Zn-air battery shows big prospects in next-generation energy technologies, while sluggish O-2 reaction and diffusion kinetics barricade the applications. Herein, the sequential assembly is innovatively demonstrated for hierarchically mesoporous molybdenum carbides/carbon microspheres with a tunable thickness of mesoporous carbon layers (Meso-Mo2C/C-x, where x represents the thickness). The optimum Meso-Mo2C/C-14 composites (approximate to 2 mu m in diameter) are composed of mesoporous nanosheets (approximate to 38 nm in thickness), which possess bilateral mesoporous carbon layers (approximate to 14 nm in thickness), inner Mo2C/C layers (approximate to 8 nm in thickness) with orthorhombic Mo2C nanoparticles (approximate to 2 nm in diameter), a high surface area of approximate to 426 m(2) g(-1), and open mesopores (approximate to 6.9 nm in size). Experiments and calculations corroborate the hierarchically mesoporous Mo2C/C can enhance hydrophilicity for supplying sufficient O-2, accelerate oxygen reduction kinetics by highly-active Mo2C and N-doped carbon sites, and facilitate O-2 diffusion kinetics over hierarchically mesopores. Therefore, Meso-Mo2C/C-14 outputs a high half-wave potential (0.88 V vs RHE) with a low Tafel slope (51 mV dec(-1)) for oxygen reduction. More significantly, the Zn-air battery delivers an ultrahigh power density (272 mW cm(-2)), and an unprecedented 100 h stability at a high-current-density condition (100 mA cm(-2)), which is one of the best performances.