Developing non-platinum catalysts for the oxygen reduction reaction (ORR) has become urgent for electrochemical energy devices. Herein, we synthesize N-doped hollow carbon nanospheres (N-HCNs) which only contain active pyridinic-N and graphitic-N by using polystyrene spheres and aniline as the corresponding template and precursor. The electrochemical measurements show that N-HCNs possess superior ORR electrocatalytic activity (half-wave potential is 15 mV higher than that of the precious Pt/C electrocatalyst), durability and anti-toxicity to Pt/C in alkaline media. Simultaneously, N-HCNs also reveal comparable ORR activity and superior stability to Pt/C in acidic media. Such high ORR performance can be ascribed to their hierarchical porous structure, ultra-high specific surface area, plenty of edge defects and high contents of active N atoms. It is noteworthy that when used as the catalyst for the air electrode of zinc–air batteries, N-HCNs present a higher power density and a larger operating voltage than Pt/C at the same discharge current density.

Two-electron oxygen reduction reaction (ORR) catalysts are essential for the electrosynthesis of hydrogen peroxide (H₂O₂). MXenes, a rising family of two-dimensional (2D) transition metal carbides, have been extensively studied for energy storage and (photo)electrocatalysis due to their rich chemical compositions and tunable electronic structures. In this work, three representative MXenes of Ti₃C₂T_x, V₂CT_x, and Nb₂CT_x were selected for H₂O₂ electrosynthesis and we found that MXenes are inherent two-electron ORR catalysts with high H₂O₂ selectivity. In addition, this work critically evaluates their electrocatalytic activity and stability. Interestingly, Nb₂CT_x catalyst maintains better electrocatalytic activity and higher stability for a long time test, although the stability of Ti₃C₂T_x and V₂CT_x catalysts is poor owing to the metal dissolution property of Ti and V in alkaline media. Moreover, the assembled device based on Nb₂CT_x catalyst presents a high H₂O₂ production and a rapid organic dye decoloration ability.