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

Jhon Puerres,John Hurtado,Pablo Ortiz,Mauro Díaz,María T Cortés

doi:10.3390/polym13040657

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.

Highlights

Water oxidation and oxygen reduction are one of the most important and challenging reactions in energy conversion
The cobalt porphyrin CoTPPS and its free-base porphyrin TPPS were entrapped in polypyrrole by electropolymerization
Photoelectrochemical and spectroscopic characterizations showed that CoTPPS and TPPS in PPy degrade under anodic conditions, which was reflected in the poor stability of the photocurrents during oxidation of the electron donor thiosulfate

Summary

Introduction

Water oxidation and oxygen reduction are one of the most important and challenging reactions in energy conversion In both cases, photoelectrochemistry has emerged as an attractive alternative that makes use of solar radiation to boost the electrochemical process [1,2,3]. The search for better performances in electrochemical and photoelectrochemical processes has led to the evaluation of alternative compounds such as porphyrins [9,10]. Photoelectrochemical investigations with these compounds are currently scarce In this field, an important point to consider about the use of porphyrins is their immobilization on conductive and semiconductor electrodes

Methods

Results

Conclusion