Synthesis of cobalt sulfide–NC composite catalyst assisted by polyaniline as nonprecious electrocatalyst for oxygen reduction reaction

Abstract

The scarce, expensive Pt is the preferred catalyst for the oxygen reduction reaction (ORR) in metal–air batteries or fuel cells. In this study, a composite catalyst consisting of cobalt sulfide and polyaniline (PANI) was utilized for optimal ORR kinetics. Cobalt sulfide catalysts were prepared at different temperatures, the optimal cobalt sulfide catalyst was coated with PANI, and the coated catalyst was annealed to form a core–shell cobalt sulfide@NC composite catalyst. Structural characterization was performed via X-ray diffraction (XRD) and Raman spectroscopy, scanning electron microscopy, and high-resolution transmission electron microscopy (HR-TEM) were conducted to characterize the catalyst morphology. CoS-160 exhibited a flower-like structure; CoS-180, containing Co₉S₈, exhibited both flower-like and sheet structures; and CoS-200 exhibited a sheet structure. With an increase in temperature, XRD and Raman spectroscopy verified the formation of Co₉S₈, serving as ORR active sites, in CoS-180 and CoS-200. HR-TEM indicated that the Co₉S₈-x@NC catalysts had a core–shell structure. Among them, Co₉S₈–180@NC had the highest graphitization degree, and total nitrogen, pyridinic N, graphitic N contents, resulting in the highest onset potential, limiting current density and the lowest Tafel slope for ORR in alkaline media among the catalysts. In an accelerated stress test, a performance degradation of less than 1 % was observed, and a chronoamperometry test demonstrated a current retention rate of 95.49 %.