Comparison of Two New Substituted Iron Phthalocyanines as Electrocatalysts for the Oxygen Reduction and Hydrazine Oxidation Reaction

Abstract

In this work, two newly synthesized iron phthalocyanines (FePc's), with de-activating substitutents, iron(II) 2,9,16,23-tetra-tert-butyl-phthalocyanine (FePc(tBu)4), and its' naphthalocyanine derivative, iron(II) 2,11,20,29-tetra-tert-butyl-2,3-naphthalocyanine (FeNpPc(tBu)4), were evaluated as both oxygen (O2) reduction, and hydrazine (N2H4) oxidation electrocatalysts in acidic as well as basic media, respectively. Their UV-Vis spectra were compared, followed by surface wave cyclic voltammograms in a N2 purged acidic electrolyte. Their activities were compared to those of the unsubstituted or baseline FePc using rotating disk electrode (RDE), rotating ring disk electrode (RRDE) and cyclic voltammetry (CV) techniques. The resulting Tafel and Koutecky-Levich analyses confirmed the predicted activities towards both reactions to be FePc > FePc(tBu)4 > FeNpPc(tBu)4. However, a change in the FeNpPc(tBu)4 O2 reduction reaction (ORR) mechanism, as well as its' low activity towards N2H4 oxidation was also observed, demonstrating unexpected electronic and steric effects.