Role of Oxygen Vacancy Defects in the Electrocatalytic Activity of Substoichiometric Molybdenum Oxide

Mesoporous α-MoO3–x combined with poly(diallyldimethylammonium chloride)–functionalized reduced graphene oxide (PDDA–rGO) is introduced as an inexpensive and efficient oxygen reduction reaction (ORR) catalyst. The mesoporous catalysts are wrapped by conductive rGO sheets via an electrostatic interaction induced by a PDDA polyelectrolyte. The thermal interaction of PDDA with MoO3 efficiently reduces the metal oxide to MoO3–x at 400–600 °C, creating a surface oxygen vacancy. Through a combination of density functional theory and experiments, the role of the surface oxygen vacancy sites in the ORR activity of MoO3–x is identified. For the first time, all the energy barriers against ORR are calculated at each step for MoO3 with no oxygen vacancies and MoO3–x with surface oxygen vacancies. It is shown that the presence of an Mo4+‐vO•• oxygen vacancy site on the surface significantly reduces the energy barriers against ORR in the reaction pathways. An overpotential of 0.86 V (vs a reversible hydrogen electrode)...