Molten-Salt-Assisted Synthesis of 3D Holey N-Doped Graphene as Bifunctional Electrocatalysts for Rechargeable Zn-Air Batteries

Development of efficient bifunctional oxygen electrocatalysts is urgently needed for high-performance rechargeable Zn-air batteries. However, sluggish oxygen reduction reaction/oxygen evolution reaction (ORR/OER) kinetics and poor mass transport are two key issues that hinder the performance of Zn-air batteries. Herein, a facile strategy is reported to prepare 3D holey N-doped graphene (3D HNG) with the aid of molten salts for boosting the performance of ORR/OER-driven Zn-air batteries. The as-prepared HNG shows a hierarchical porous framework structure with a 1:1 ratio of pyridinic to graphitic N. Owing to the matched N catalytic active sites and the special pore structure, 3D HNG displays super bifunctional electrocatalytic activity toward both ORR and OER. Specifically, rechargeable Zn-air batteries fabricated with this electrocatalyst show excellent discharge capacity, rechargeability, and round-trip efficiency. Density functional theory (DFT) computations further reveal that armchair-graphitic N and zigzag-pyridinic N are more favorable for ORR and OER, respectively. By combining these two components, the mixed structure displays the lowest overpotentials of 0.47 and 0.36 V for ORR and OER, respectively, comparable to the theoretical values of Pt and RuO2. This work provides a new strategy for optimizing N-doped carbon materials for bifunctional oxygen electrocatalysts.