Synergistic Control of Structural Disorder and Surface Bonding Nature to Optimize the Functionality of Manganese Oxide as an Electrocatalyst and a Cathode for Li-O2 Batteries.

An efficient way to improve the electrocatalyst and Li-O2 battery performances of metal oxide is developed by an exquisite synergistic control over structural disorder and surface bonding nature. The effects of amorphous nature and surface chemical environment on the functionalities of metal oxide are systematically investigated with well-crystalline and amorphous MnO2 nanocrystals with/without surface anchoring of highly oxidized iodate clusters. The amorphous MnO2 nanocrystal containing anchored iodate clusters shows much better performance as an oxygen evolution electrocatalyst and cathode catalyst for Li-O2 batteries than both iodate-free amorphous and well-crystalline homologues, underscoring the remarkable advantage of simultaneous enhancement of structural disorder and surface electron density. In situ X-ray absorption spectroscopic analysis demonstrates the promoted formation of double (MnO) bond, a critical step of oxygen evolution reaction, upon amorphization caused by the poor orbital overlap inside highly disordered crystallites. The beneficial effects of iodate anchoring and amorphization on electrocatalyst functionality are attributable to the alteration of surface bonding character, stabilization of Jahn-Teller active Mn3+ species, and enhanced charge transfer of interfaces. The present study underscores that fine-tuning of structural disorder and surface bonding nature provides an effective methodology to explore efficient metal oxide-based electrocatalysts.