Photoelectrochemical production of H ₂ O ₂ using polypyrrole doped with meso-tetra-(4-sulfonatophenyl)-porphyrin

The photoelectrochemical route has emerged as an attractive alternative to produce H 2 O 2 in a sustainable way since O 2 , H 2 O, solar energy and electricity (which can be obtained from a renewable energy source) are used as inputs. Currently, this route is in an early stage of research and several challenges must be overcome, mainly associated with the materials used as photoelectrodes in the process. In this study, polypyrrole coatings doped with the anionic porphyrin meso-tetra-(4-sulfonatophenyl)-porphyrin (TPPS) were electrochemically synthesized and their nucleation and growth mechanisms were studied. Then, the photoelectrochemical performance of the synthetized materials towards the oxygen reduction reaction (ORR) was examined by chronoamperometry tests and by measuring the H 2 O 2 produced. It was found that in an initial stage of the electrosynthesis the coatings present an instantaneous nucleation with three-dimensional growth. Besides, it was observed that the coatings perform as electrocatalysts for the ORR and that their performance depends on their thickness. Interestingly, it was shown that the insertion of cobalt into the photoelectrodes increases the photocurrent by 100% and the total current by 74%, but this increase is not reflected in a larger production of H 2 O 2 because the oxygen reduction does not take place via a two-electron pathway when cobalt is present. These results contribute to understanding the role of polypyrrole-based coatings in the photoelectrochemical process and also provide evidence on their stability.