Dimensional engineering of carbon dots derived sulfur and nitrogen co-doped carbon as efficient oxygen reduction reaction electrocatalysts for aluminum-air batteries

The sluggish kinetics of oxygen reduction reaction (ORR) on the cathode limits the development of metal-air batteries and fuel cells. In this work, N, S doped carbon materials with one dimensional (1D) microrod, two dimensional (2D) nanosheet and three dimensional (3D) framework structures prepared using nitrogen-doped carbon dots as precursors are studied as electrocatalysts to improve the ORR performance. The carbon dots with the unique properties are crucial in forming the designed structure, and the formation mechanism of the dimensional carbon materials is revealed. The ORR performance is investigated in both alkaline and neutral electrolytes, and the results reveal that the two-dimensional N, S doped carbon nanosheets (2D N-S-CNS) show better ORR performance than the 1D or 3D counterparts, which is mainly attributed to the higher heteroatoms doping amount. In addition, the ORR performance of 2D N-S-CNS is comparable to that of Pt/C. To reveal the practical application, the carbon electrocatalysts are also studied in aluminum-air (Al-air) batteries, and the Al-air batteries based on 2D N-S-CNS display larger power density and higher working voltage than those with Pt/C in both KOH and NaCl electrolytes.