Incorporation and electrocatalytic activity towards O₂ reduction of electrodeposited graphene/Eu³⁺ coatings

Graphene and its derivatives, such as graphene oxide (GO), have been vastly investigated in the past few decades. Its unique features such as high electron mobility and large surface area justify its extensive use as a component in electrocatalytic systems. Obtaining graphene coatings can be achieved by several electrodeposition methods, such as the well-Investigated electro-reduction. Moreover, we have recently discovered that GO coatings can also be obtained by direct electro-oxidation. GO sheets can be combined by electropolymerization of the phenol edge groups. Ether or carboxylic edge groups are formed, depending on the applied potential. These coatings are characterized by a lower O/C ratio and a higher content of C=C bonds (compared to GO). This process extends the aromatic conjugation system of the graphene oxide sheets, which results in coatings with a highly conductive nature.

Based upon the high coordination number of lanthanide ions and their ability to bind oxygen functional groups, we incorporated Eu³⁺ ions in graphene oxide coatings. The combined coatings were examined using a variety of electrochemical, spectroscopic and microscopic methods. Cyclic voltammetry was conducted for the coatings in order to establish their ability to catalyze O₂ reduction in 0.1M KOH. The best performance was obtained for the reduced-GO/Eu³⁺ coatings: O₂ peak potential was observed at –0.23 V as compared to -0.29 V vs. Ag/AgCl for electropolymerized- GO/Eu³⁺.