Mn(III) and Fe(III) Porphyrin Complexes as Electrocatalysts for Hydrogen Evolution Reaction: A comparative study

In the present work, we carried out comparative studies on electrochemical reduction of proton to molecular hydrogen, i.e. 2H(+) + 2e -> H-2 using meso-tetrakis-(tetraphenyl)porphyrin iron(III) chloride [Fe(TPP)Cl] and meso-tetrakis(phenyl)porphyrin manganese(III) chloride [Mn(TPP)Cl] as electrocatalysts. Acetic acid (CH3COOH) was used as the proton source. Results suggest that the reduction of CH3COOH on the surface of vitreous carbon electrode (Ep = -1.8 V vs. Ag/AgCl in [Bu4N][BF4]-DMF) shifts to lower negative values in the presence of [Fe(TPP)Cl] and [Mn(TPP)Cl] (-1.6 and -1.3 V, respectively vs. Ag/AgCl). Analysis of peak current values indicated that [Fe(TPP)Cl] was more active (6 x) as compared to [Mn(TPP)Cl]. However, the [Mn(TPP)Cl]-catalyzed reduction process more swiftly (the potential is more positive than +30 mV).