Unraveling the Catalytic Mechanism of Rutile RuO₂ for the Oxygen Reduction Reaction and Oxygen Evolution Reaction in Li–O₂ Batteries

Because of the involvement of solid-state discharge product Li 2 O 2, how a catalyst works in nonaqueous lithium–oxygen batteries is yet to be determined, although the question has undergone fierce debate. In this work, we take an effective and widely used catalyst, rutile RuO 2, as a representative and studied its catalytic mechanism in lithium–oxygen batteries via ab initio calculations. For the oxygen reduction reaction (ORR), it is found that rutile RuO 2 can provide large adsorption energies toward LiO 2 and Li 2 O 2, thus resulting in high initial discharge voltages. Moreover, the normalized degree of unsaturation of surface oxygen is identified as a descriptor for the ORR catalytic activity. For the oxygen evolution reaction (OER), we propose that, in addition to the three-phase interface, the OER may also occur at the two-phase interface of Li 2 O 2 /RuO 2, where rutile RuO 2 provides pathways for the lithium ions while oxygen evolves from the exposed surfaces of Li 2 O 2 . Calculation results show that our proposed catalytic scenario is both thermodynamically and kinetically viable. Along with the charge process, the remaining Li 2 O 2 can be attracted to the catalytic surfaces spontaneously, which can effectively preserve the reaction interface.