PORPHYRIN NANORODS MODIFIED GLASSY CARBON ELECTRODE SURFACE FOR OXYGEN REDUCTION REACTION CATALYSIS

Abstract

Meso-tetra-(4-sulphonatephenyl) porphyrin (TPPS), iron(III) meso-tetra-(4-pyridyl) porphyrin (FeTPyP), and platinum(II) meso-tetra-(4-pyridyl) porphyrin (PtTPyP), were synthesized and characterized. These molecules were used to fabricate porphyrin nanorods by electrostatic self-assembly of two oppositely charged molecules consisting TPPS-FeTPyP (HT-Fe) and TPPS-PtTPyP (HT-Pt). The ground state absorption spectra and transmission electron microscopic images of the nanostructures were obtained. The porphyrin nanorods (PNR) were used to modify glassy carbon electrodes and were characterized in buffer solution of pH 2 by cyclic voltammetry and electrochemical impedance. The PNR-modified GCE were used for catalytic reduction of O2 in 0.1 M H2SO4 and kinetics of the oxygen reduction reaction (ORR) on these electrodes were studied using rotating disk electrodes modified. The onset potential for HT-Pt GCE was 0.009 V up till -0.60 V with two distinct peaks at -0.157V (ip = 33.4 µA) and -0.582 V (ip= 75.4 µA) and a very broad weak peak indicating slow electron transfer process occurred at around -0.328 V (ip= 53.0 µA). While with HT-Fe GCE an onset potential of -0.02 V with peaks at -0.155 V (ip = 32.3 µA), -0.434 V (ip = 105 µA) and -0.624 V (ip = 127 µA).  The rotating disk electrode studies of this did not yield the typical diffusion plateau-like wave, however the multiple peaks of current-potential curves. This has been previously reported due to different active site on the bare GCE. Keywords: Porphyrin nanorods, Modified electrodes, ORR Catalysis