Anode Preparation Strategies for the Electrocatalytic Oxidation of Water Based on Strong Interactions between Multiwalled Carbon Nanotubes and Cationic Acetylammonium Pyrene Moieties in Aqueous Solutions

Abstract

A strategy is reported for the immobilization of iridium-based water oxidation catalyst 3 onto fluorine-doped tin oxide (FTO) anodes evaluated for the electrocatalytic oxidation of H2O. The strategy is based on noncovalent π–π interactions between multiwalled carbon nanotubes (MWCNTs) and the cationic acetylammonium pyrene moiety (Pyr+) covalently attached to a NHC IrCp*Cl2 catalytically active center (NHC=N-heterocyclic carbene, Cp*=C5Me5). The dispersive properties of the Pyr+ moiety in compound 3 leads to the formation of stable MWCNT dispersions in aqueous solutions. In addition, the MWCNT/3 assembly shows activity in the Ce4+-driven oxidation of H2O. FTO/MWCNT/3 anodes show increased current densities when used as a working electrode for the electrocatalytic oxidation of H2O. At higher anodic polarizations initially high current densities were achieved; however, these currents prove to be non-sustained due to delamination and degradation of the catalytically active surface. The immobilization strategy is limited to applications below 1.4 V vs normal hydrogen electrode (NHE) as oxidation of the pyrene backbone is evident at higher potentials.