Density functional theory study of the adsorption of oxygen molecule on iron phthalocyanine and cobalt phthalocyanine

Abstract

Iron phthalocyanine (FePc) and cobalt phthalocyanine (CoPc) molecules have been studied in the past as possible catalysts for oxygen reduction reactions. In this work, density functional theory (DFT) computation results of oxygen molecule (O2) adsorption on FePc and CoPc molecules are reported. For O2 on FePc, both end-on and side-on configurations are found to be energetically favourable but the end-on adsorption configurations are more stable than the side-on configurations. Moreover, our results predicted that compared to those in the end-on configuration, the adsorbed O2 molecules in the side-on configuration have weaker O–O bonds, which led us to believe that the side-on configurations would be more active in catalysing oxygen reduction reaction. In contrast, we found that only end-on configurations are energetically stable for O2 on CoPc. Based on our DFT calculation results and the corresponding experimental observations, we postulate that on the surface of transition metal phthalocyanine catalyst molecules the side-on adsorption of O2 molecules could promote four-electron oxygen reduction process while the end-on adsorption of O2 molecules would facilitate two-electron oxygen reduction process.