Fe azaphthalocyanine unimolecular layers (Fe AzULs) on carbon nanotubes for realizing highly active oxygen reduction reaction (ORR) catalytic electrodes

A new class of Pt-free catalysts was designed that included molecular iron phthalocyanine (FePc) derivatives, namely, iron azaphthalocyanine (FeAzPc) unimolecular layers (Fe AzULs) adsorbed on oxidized multiwall carbon nanotubes (oxMWCNTs). FeAzPcs were dissolved in organic solvents such as dimethyl sulfoxide (DMSO), and catalytic electrodes modified with molecularly adsorbed FeAzPcs were successfully prepared. The optimized composition of the catalytic electrodes was determined, and the electrodes exhibited superior activity for the oxygen reduction reaction (ORR) and better durability than conventional FePc catalytic electrodes and commercial Pt/C due to the electron-withdrawing properties of the pyridinic nitrogen in FeAzPcs. The catalytic electrodes that were molecularly modified with FeAzPcs have higher activities than those composed of FeAzPc crystals and oxMWCNTs. To the best of our knowledge, among all of the conventional catalysts based on modified MWCNTs and oxMWCNTs, this catalyst exhibits the highest activity. Unlike other Pt-free catalytic electrodes, the Fe AzUL catalytic electrodes can be prepared by low-cost processing without pyrolysis and are therefore promising catalytic electrode materials for applications, such as polymer electrolyte fuel cells and metal–air batteries.