Graphitic-N induced asymmetric charge distribution of carbon sites accelerates O2 activation for efficient oxygen reduction reaction.

Developing resource-abundant and sustainable metal-free carbon-based efficient oxygen reduction reaction (ORR) electrocatalysts is essential for the practical application of zinc-air batteries (ZABs). Unfortunately, the actual active sites and fundamental catalytic mechanism remain ambiguous and warrant further investigation. Herein, we develop a facile method for the preparation of highly graphitic nitrogen-doped hollow porous carbon nanospheres (denoted as NPHSs) to boost ORR. In-situ spectroscopy and DFT collectively show that the increment of graphitic nitrogen content can improve the degree of electron delocalization and accelerate the electron transport rate to effectively break the highly inert conjugated electronic structure of C sites, thereby promoting the formation of OOH* to reduce the reaction energy barrier. Therefore, the fabricated NPHSs with optimal graphitic nitrogen content exhibit excellent ORR activity, outstanding long-term stability, and high methanol tolerance in alkaline medium. Furthermore, the NPHSs-assembled liquid rechargeable ZABs deliver high power density, large specific capacity, and superior cycling stability. This work offers a new perspective for electronic modification of high-efficiency metal-free carbon-based electrocatalysts in energy-related fields.