▎ 摘　　要

Highly efficient electrocatalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) have been regarded as the core elements in a wide range of renewable energy technologies. Surface engineering of the electrocatalysts is one of the most popular strategies to improve their catalytic activity. Herein, we, for the first time, designed an advanced bi-functional electrocatalyst for the ORR and OER by simultaneously etching and doping a cobalt sulfides-graphene hybrid with NH3-plasma. The graphene supported Co9S8 nanoparticles were prepared (denoted as Co9S8/G) first, followed by the NH3-plasma treatment, which could not only lead to nitrogen doping into both Co9S8 and graphene, but also partially etch the surface of both Co9S8 and graphene. The heteroatom doping could efficiently tune the electronic properties of Co9S8 and graphene, and the surface etching could expose more active sites for electrocatalysis, which can contribute significantly to the enhanced electrocatalytic performance for ORR and OER. The electrochemical results revealed that the etched and N-doped Co9S8/G shows excellent ORR activity, which is close to that of the commercial Pt/C catalyst, and great OER activity. The strategy developed here provides a novel and efficient approach to prepare hybrid bi-functional electrocatalysts for ORR and OER.