Photoelectrochemical Stability under Anodic and Cathodic Conditions of Meso-Tetra-(4-Sulfonatophenyl)-Porphyrinato Cobalt (II) Immobilized in Polypyrrole Thin Films

Abstract

Cobalt porphyrins have emerged as promising catalysts for electrochemical and photoelectrochemical applications because of their good performance, low cost and the abundance of cobalt in the earth. Herein, a negatively charged porphyrin meso-tetra-(4-sulfonatophenyl)-porphin (TPPS) was immobilized in polypyrrole (PPy) during the electro-polymerization, and then it was metallized with cobalt to obtain meso-tetra-(4-sulfonatophenyl)-porphyrinato cobalt (II) (CoTPPS) as a dopant in PPy. The coatings were evaluated as photoelectrodes towards thiosulfate oxidation and oxygen reduction. For comparison purposes, the photoelectrochemical behavior of ClO4−-doped polypyrrole films was also evaluated. Characterizations by chronoamperometry, UV-Vis spectroscopy and Raman spectroscopy showed that polypyrrole is stable under anodic and cathodic conditions, but CoTPPS and TPPS immobilized in PPy are degraded during the anodic process. Thus, decreases in photocurrent of up to 87% and 97% for CoTPPS-doped PPy and TPPS-doped PPy were observed after a 30-min chronoamperometry test. On the other hand, good stability of CoTPPS and TPPS immobilized in PPy was observed during photoelectrochemical oxygen reduction, which was reflected in almost constant photocurrents obtained by chronoamperometry. These findings are relevant to understanding the role of CoTPPS as a catalyst or pre-catalyst in photoelectrochemical applications such as water splitting. In addition, these results could pave the way for further research to include CoTPPS-doped PPy in the design of novel photocathodes.

Effect of Electrosynthesis Potential on Nucleation, Growth, Adhesion, and Electronic Properties of Polypyrrole Thin Films on Fluorine-Doped Tin Oxide (FTO)

“…Since the discovery of intrinsically conductive polymers (ICPs) by Shirakawa et al in the 1970s [ 1 ], significant efforts have been made to understand the properties of these materials that combine the characteristics of metals and plastics. Over time, potential applications have been investigated in several areas where ICPs perform as functional materials, for example, batteries [ 2 , 3 , 4 ], solar cells [ 5 , 6 , 7 ], electrochromic devices [ 8 , 9 , 10 ], sensors [ 11 , 12 , 13 ], and more recently in photocatalysis and photoelectrochemistry [ 14 , 15 , 16 , 17 , 18 ]. Commonly, the performance of ICPs is strongly related to their morphology, redox state, and structural order (chain arrangement and conjugation length) as these parameters influence the surface area, electronic, and optical properties of the polymers [ 19 , 20 ].…”