Design of efficient ZIF-derived nitrogen and sulfur co-doped nanocarbons toward oxygen reduction through host-guest reactions

摘要

Carbon-based metal-free catalysts have emerged as a promising class of candidates to replace the precious metal catalysts for oxygen reduction reaction (ORR). Herein, an efficient nitrogen (N) and sulfur (S) co-doped nanocarbon electrocatalyst has been fabricated from ZIF-8 via strong host-guest chemical reactions, which involve disassembly-reassembly of ZIF-8 initiated by a reactive S-containing molecule of Ls (Ls = 4-(thiophen-2-yl) pyrimidine-2-thiol). In this case, Ls molecule with a strongly coordinative thiol group not only provides the S-heteroatoms but also rebuilds ZIF-8 to generate the precursor of Ls@ZIF-8, in which Ls exists in the form of Zn2+-Ls coordination assembly. This method renders homogeneous inclusion of S-source into ZIF-8 while maintaining the initial morphology of ZIF-8. By tuning the amount of Ls and annealing temperature, the optimal nitrogen and sulfur co-doped nanocarbon (designated as N-S-C-1) exhibits uniform N and S doping with an exceptionally high surface area (1658.8 m(2)/g) and pore volume (3.27 cm(3)/g), hierarchical porous structure as well as high electronic conductivity. In the alkaline electrolyte, N-S-C-1 achieves a comparable ORR activity to the benchmark Pt/C catalyst, but a better methanol tolerance and electrochemical stability.