Performance and degradation behavior of carbonyl Fe – MoS2 composite as anode material in Fe-air batteries

Abstract

The two technical limitations of iron-air batteries are: (1) Hydrogen evolution reaction (HER) and (2) Passivation. HER account for low charging efficiency while passivation in Fe-air batteries account for its inability to fully discharge at a high rate due to the formation of iron hydroxide. As a result of this, many studies has been dedicated to inhibit these problems. Just like in recent literature, the enhancement of Fe-air anode for commercialization is not trivial. With high purity carbonyl Fe–MoS2 composites electrode and the influence of 2 mM Na2S additives in 6 M KOH electrolyte solution and 1.88 wt % polyacrylic acid as the gelling agent, we have demonstrated a high performance carbonyl Fe anodes comprising of 3 wt % MoS2 (F3M), 5 wt % MoS2 (F5M), and 10 wt % MoS2 (F10 M) additives in Fe anodes. The result of the various electrodes characterized via field emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD) reveals a distinct surface morphology that correspond to fundamental crystallographic growth patterns. Additionally, Energy dispersive spectroscopy (EDS) and SEM mapping affirms that both the Fe and additive (weight (Wt. %) and atomic percent (At. %)) were well dispersed in the electrode. According to Tafel test, F3M, F5M, and F10 M exhibits corrosion inhibition efficiency of 51.2%, 21.1% and 5.6% respectively. Thus, the corrosion rate decreased in the order of bare Fe > F10 M > F5M > F3M. While drastic capacity retention drops occur in the bare Fe electrode around 300th cycle, we were able to regenerate the battery back to full capacity via our choice of additives (F3M). During regeneration at 800th cycles, the capacity retention of F3M, F5M and F10 M electrodes were 97%, 93%, and 76% respectively. Therefore, in conjunction with the unique structure and synergistic effect that characterizes two excellent anode materials, F3M is best choice for a high-performance Fe-air battery due to its excellent performance, low side effects (corrosion and passivation), low float current, superior capacity retention and efficiency during cycling compare to F5M and F10 M.