Reversible Fe Magnetic Moment Switching in Catalytic Oxygen Reduction Reaction of Fe-Phthalocyanine Adsorbed on Ag(110)

The consequences of the evolution of the active site in the oxygen reduction reaction catalyzed by iron phthalocyanine (FePc) submonolayers deposited on the Ag(110) surface are explored. The capacity of reversibly and sharply switching the magnetic state of FePc molecules by chemical means is conclusively evidenced by X-ray magnetic circular dichroism (XMCD) at the Fe L2,3 absorption edge. In the molecular oxygen-dosed phase, oxygen intercalates between the molecule and the surface, thereby switching the Fe magnetic moment from a nearly negligible (mTot exp ≈ 0.26(1) μB) to an order of magnitude larger value (mTot exp ≈ 2.1(2) μB). Moreover, the characteristic XMCD spectrum undergoes a crossover from metallic to oxidized Fe(III)-like line shape, in accordance with an oxygen-induced decoupling of the molecular electronic states from the underlying metal surface. The FePc acts as a reversible bifunctional chemical− magnetic switch at the atomic monolayer scale.