Insight into efficient bifunctional catalysis: Oxygen reduction and oxygen evolution reactions using MWCNTs based composites with 5,10,15,20-tetrakis(3',5'-dimethoxyphenyl) porphyrinato cobalt(Ⅱ) and 5,10,15,20-tetrakis(3',5'-dihydroxyphenyl)porphyrinato cobalt(II)

摘要

Development of cost-effective, durable, and efficient bifunctional electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is still required for efficient fuel cells, metal-air-batteries, and water electrolysis. For that purpose we have prepared tetrakis(3',5'-dimethoxyphenyl)porphyrinato cobalt(II) (CoDMTPP) and 5,10,15,20tetrakis(3',5'-dihydroxyphenyl)porphyrinato cobalt(II) (CoDHTPP). Further, multi-walled carbon nanotubes (MWCNTs) based composites of CoDMTPP (MWCNTs-CoDMTPP) and CoDHTPP (MWCNTs-CoDHTPP) are also prepared and characterized through spectroscopy (UV-vis, FTIR, and XPS), microscopy (SEM, TEM with EDAX), X-ray diffraction, thermogravimetry, and electrochemical techniques. The materials, MWCNTs-CoDMTPP and MWCNTs-CoDHTPP are immobilized on glassy carbon (GC) electrodes, represented as GC/MWCNTs-CoDMTPP and GC/MWCNTs-CoDHTPP. They show efficient ORR activity in acidic, basic, and neutral (pH 7.0 buffer) mediums. Further, both of these electrodes exhibit significant OER activity in 0.1 M KOH, indicating the bifunctional activity in basic medium. Based on the kinetic studies, the presence of -OH in the CoDHTPP is found to enhance the ORR activity. The electrodes, GC/MWCNTs-CoDMTPP and GC/MWCNTs-CoDHTPP exhibit high methanol tolerance capacity. A very small change in onset potential of 12 mV at GC/MWCNTs-CoDMTPP and 3 mV at GC/MWCNTs-CoDHTPP electrodes are observed for the ORR after 3000 continuous potential cycles indicating the high operational stability of the modified electrodes. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.