Facile synthesis, spectroscopy and electrochemical activity of two substituted iron phthalocyanines as oxygen reduction catalysts in an acidic environment

Two substituted iron phthalocyanine macrocycles were synthesized and evaluated as oxygen reduction electrocatalysts in an acidic, or proton exchange membrane (PEM) fuel cell-like, environment. The non-noble, transition metal macrocycles iron(II) 2,9,16,23-tetra-tert-butyl-phthalocyanine (FePc(tBu)4), and iron(II) 2,11,20,29-Tetra-tert-butyl-2,3-naphthalocyanine (FeNpPc(tBu)4) were made via a facile synthesis. Successful synthesis was confirmed using UV–Vis spectroscopy as well as matrix-assisted laser desorption/ionization time of flight (MALDI-TOF) mass spectroscopy. These two substituted iron phthalocyanines were characterized using cyclic voltammetry (CV) and their electrocatalytic activities towards the oxygen reduction reaction (ORR) were evaluated using rotating disk electrode (RDE) techniques. The ORR activities of these substituted iron phthalocyanines were compared to those of the unsubstituted species, iron(III) phthalocyanine (FePc). The RDE trace of FeNpPc(tBu)4 indicates a 2 electron ORR mechanism, whereby O2 is reduced mainly to H2O2. This is in contrast to FePc, FeNpPc and FePc(tBu)4, which exhibit predominantly 4 or mixed 2 and 4, electron ORR mechanisms.