Hierarchical Porous Carbon Derived from Coal Tar Pitch Containing Discrete Co-Nx-C Active Sites for Efficient Oxygen Electrocatalysis and Rechargeable Zn-Air Batteries

Coal tar pitch (CTP), as a byproduct of the rich, low-cost, high-carbon yield coal industry, is expected to achieve high value-added and comprehensive utilization. The oxygen reduction reaction is the cornerstone of both fuel cells and zinc-air batteries (ZABs). Herein, as a proof-of-concept application, the activated CTP (ACTP) first used as carbon source through cobalt/nitrogen reengineering is demonstrated to be an effective and straightforward strategy for fabrication of high-performing hierarchical porous carbons (Co/N-HPCs). The as-prepared Co/N-HPC150/800 with a large specific surface area of 2076.58 m(2) g(-1) exhibits superior electrocatalytic properties for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in terms of a half-wave potential of 0.85 V (vs RHE) for ORR and an onset potential of 1.42 V (vs RHE) for OER, respectively, in 0.1 M KOH, superior to commercial Pt/C catalyst. Notably, we have experimentally shown that Co/N-HP150/800 as the air electrode for zinc-air battery demonstrates a high discharge peak power density achieving 425 mW cm(-2), a current density of 291 mA cm(-2) at a voltage of 1 V, and a long cycling stability beyond 250 h at 10 mA cm(-2). Moreover, the obtained rechargeable Zn-air battery exhibits a low discharge-charge voltage gap and long cycle life (2100 cycles with 10 min per cycle). The outstanding electrocatalytic properties are attributed to the unique hierarchical pore structures as well as coupling effects originated from cobalt doping and trace nitrogen-containing active sites from aqueous ammonia, which largely facilitates the charge transfer and enhances the stability of rechargeable ZABs. It opens a new and viable way for realizing the high value-added utilization of CTP.