Evidence for the formation of cobalt porphyrin-quinone complexes stabilized at carbon-based surfaces toward the design of efficient non-noble-metal oxygen reduction catalysts

The interaction of electropolymerized Co(III)TAPP (polyCoTAPP) films with adsorbed resorcinol on glassy carbon (GC) and with surface quinone functionalities on aerogel carbon (AEC) were studied using reflection UV-visible spectroscopy and X-ray photoelectron spectroscopy. A red shift of the Soret band and the appearance of new Q bands appearing after adsorption of resorcinol on a GC/polyCoTAPP film was interpreted as being due to change of the metalloporphyrin electronic structure. The photoelectron depth profiles for an AEC/polyCoTAPP film showed that the cobalt ion is mostly in the Co(III) state at the outer layers of the film, while the amount of cobalt ion in the formal +2 state gradually increases in the inner film layers. This seems to indicate the formation of charge-transfer complexes between the metalloporphyrin and reduced quinone functionalities on the AEC surface. Understanding the nature of metalloporphyrin/porous carbon structures is an important step toward the design of reliable and low-cost non-noble-metal oxygen reduction catalytic electrodes and their application in fuel cells and batteries.