S/N codoped carbon nanotubes as an efficient ORR electrocatalyst for zinc–air batteries

Abstract

The development of low-cost non-noble metal ORR catalysts has important practical significance for the development of fuel cells and metal–air batteries. In this work, an S/N codoped carbon nanotube was prepared as an efficient ORR catalyst, and its performance is almost comparable to that of commercial Pt/C. We use concentrated nitric acid to oxidize carbon nanotubes to produce more oxygen-containing groups on their surface and treat these oxygen-containing groups with the Lawesson reagent to obtain a precursor containing sulfur. Then, a S/N codoped ORR catalyst can be obtained by pyrolysis with urea (S/N/CNT). The results show that the S/N codoping strategy can indeed change the charge distribution of carbon nanotubes, create more active sites, and improve the catalytic performance of the ORR. In 0.1 M KOH, the onset potential and half-wave potential of S/N/CNT are 1.04 V and 822 mV, respectively, which are close to those of Pt/C (1.04 V and 815 mV). S/N/CNT is a standard 4-electron reaction system, the electron transfer number is about 3.88–3.91 from 0.2 V to 0.8 V, and has good methanol tolerance. Compared with Pt/C-based Zn–air batteries, S/N/CNT-based Zn–air batteries display a higher galvanostatic discharge capacity as well as a desirable stability in 6 M KOH and 0.2 M Zn(OAc)₂ alkaline electrolyte. The ZABs fabricated using air electrodes containing S/N/CNT demonstrate good performance, with a high open-circuit potential (1.39 V) and a large peak power density (123 mW cm⁻²).