Hierarchically porous metal-free carbon with record high mass activity for oxygen reduction and Zn-air batteries

Abstract

Improving the mass activity of metal-free carbon materials for oxygen reduction is more practically meaningful for developing energy devices (e.g., metal air batteries), but remains a great challenge. Here we proposed a facile strategy to produce metal-free carbon materials (termed HPNSC) with record-high mass activity based on a new robust β-cyclodextrin polymer network. This designed robust network can not only act as a self-template to create a hierarchically porous structure with a very large electrochemically active surface area (ECSA) of 429 m² g⁻¹, but can also serve as a self-sponsored network-anchored heteroatom doping source leading to a high intrinsic activity of 8.14 × 10⁻³ mA cm⁻². The affluent mass-transport-favoring mesopores and macropores in HPNSC contribute to 83% of its ECSA, which affords a record mass activity of 35 mA mg⁻¹@0.85 V among metal-free carbon catalysts which is nearly two times higher than that of Pt/C in alkaline media. Furthermore, a primary zinc air battery using HPNSC displays a high peak power density of 144 mW cm⁻² (110 mW cm⁻² for the state-of-the-art Pt/C) and a high energy density of 1007 W h kg_Zn⁻¹, which is the highest value among metal-free catalysts. Importantly, HPNSC also delivers higher activity and better stability in a rechargeable zinc air flow battery compared with the benchmark Pt/C.