Ligand regulation to prepare an Fe, N, S tri-codoped hollow carbon electrocatalyst for enhanced ORR performance and Zn–air batteries

Abstract

It is significant to explore high-efficiency, low-cost, and stable electrocatalysts for the oxygen reduction reaction (ORR) to substitute the precious metal platinum in electrochemical energy conversion devices. Materials with an Fe–N_x center are considered as promising catalysts to achieve this. Herein, a feasible SiO₂–ZnCl₂ template strategy is used to obtain nitrogen–sulfur–Fe co-doped periodic porous hollow carbon by calcining the Fe-based complexes with different ligands (1,10-phenanthroline, 2,2-bipyridine, and 1,2-dicyanobenzene). Owing to the introduction of the SBA-15 template and pore-forming agent ZnCl₂, the as-prepared materials possess a large specific surface area (SSA) and a well-defined hollow structure. Most importantly, different ligands have a crucial effect on the nitrogen content of the obtained materials, which in turn directly affects the metal active sites of ORR. The appropriate selection of 1,10-phenanthroline as the ligand creates abundant Fe–N_x active sites after the pyrolysis process. Therefore, the optimal hollow carbon (denoted as Z-CNS-Fe) derived from the complex of Fe²⁺ and 1,10-phenanthroline exhibits better ORR performance with a half-wave potential of 0.880 V, which is 30 mV higher than that of commercial Pt/C (0.850 V). Beyond this, Z-CNS-Fe shows long-term stability and superior tolerance to methanol crossover. In addition, when Z-CNS-Fe was applied as the cathode of a primary Zn–air battery, the obtained metal–air cell provided a power density as high as 141 mW cm⁻², which exceeded that of commercial Pt/C (114 mW cm⁻²). The high open-circuit voltage and satisfactory durability also indicate its potential practical applicability.