Electrogenerated hydrophilic carbon nanomaterials with tailored electrocatalytic activity

Abstract

This work investigates the influence of the type of buffer electrolyte used in the generation of Electrochemical Hydrophilic Carbon (EHC) on their physical-chemical properties and electrocatalytic activity. The EHC nanomaterials were prepared in three different biological buffers, phosphate, glycine and citrate buffers (EHC@phosphate, EHC@glycine, EHC@citrate) and their surface properties were fully characterized by AFM, XPS and Raman. The EHC nanomaterials drop cast onto a glassy carbon electrode were electrochemically characterized in [Fe(CN)6]3-/4- and [Ru(NH3)6]3+/2+ redox probes solutions, and their electrocatalytic activity was investigated towards hydrogen peroxide and oxygen reduction reactions (ORR) in a phosphate buffer solution. It was found that the nature of buffer electrolyte strongly influences the surface chemical state of the EHC materials, disorder degree in the hexagonal sp2 carbon network and oxygen functional groups, affecting both the EHC electrocatalytic activity towards the ORR and H2O2 reduction reaction. The most catalytic material for the ORR was EHC@citrate, whereas EHC@glycine showed the highest oxygen conversion (n ≅ 2.7 to 3). Moreover, it was shown that the content of oxygen singly bonded to carbon correlates strongly with the number of electrons transferred. A very singular behaviour in the electrochemical reduction of hydrogen peroxide was observed on EHC@glycine, qualitatively interpreted as an autocatalytic reaction. In contrast, a blocking-like effect was depicted on EHC@phosphate. These results must have an important impact in the development of materials with peroxidase-like activity and in the design of O2 sensors with non-sensitivity to H2O2.