Redox behavior of ferrocene-methanol encapsulated in hydrophobic nanotubes

Abstract

The remarkable ability of hybrid imogolite nanotubes (Imo-CH₃) to efficiently encapsulate various small molecules coupled with their wall polarization, could make them potentially attractive for energy applications (battery, supercapacitor, photocatalysis…). To explore these potentialities, a first step is to understand the behavior of electroactive confined molecules inside the nanotube. Here, ferrocene methanol (FcMeOH) was encapsulated inside Imo-CH₃ of two different average lengths. The goal of this work is to assess whether the wall polarization has an influence on the redox behavior of the confined molecules. The adsorption isotherms of FcMeOH in the two types of nanotubes were determined. They exhibit an unusual S-shape, which is explained by the co-adsorption of FcMeOH and water followed by a wetting transition. The nanotubes can be loaded with up to 0.8 mmol·g⁻¹ (21 mAh·g⁻¹) of FcMeOH. An oxidation current from the encapsulated FcMeOH was measured in the case of the shorter nanotubes. However, electron transfer mechanisms are not affected by the wall polarization of the hybrid imogolite, implying that the electron transfer to the electrode probably occurs along the nanotube axis rather than by intra-wall tunneling.