Re-Investigation of Cobalt Porphyrin for Electrochemical Water Oxidation on FTO Surface: Formation of CoOx as Active Species

The use of cobalt porphyrin complexes as efficient and cost-effective molecular catalysts for water oxidation has been investigated previously. However, by combining a set of analytical techniques (electrochemistry, ultraviolet-visible spectroscopy (UV-vis), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and synchrotron-based photoelectron spectroscopy (SOXPES and HAXPES)), we have demonstrated that three different cobalt porphyrins, deposited on FTO glasses, decompose promptly into a thin film of CoOx on the surface of the electrode during water oxidation under certain conditions (borate buffer pH 9.2). It is presumed that the film is composed of CoO, only detectable by SOXPES, as conventional techniques are ineffective. This newly formed film has a high turnover frequency (TOF), while the high transparency of the CoOx-based electrode is very promising for future application in photoelectrochemical cells.