Construction of Core-Shelled Covalent/Metal-Organic Frameworks for Oxygen Evolution Reaction.

Oxygen evolution reaction (OER) is the half-reaction in zinc-air batteries and water splitting. Developing highly efficient catalysts toward OER is a challenge due to the difficulty of removing four electrons from two water molecules. Covalent organic frameworks (COFs) provide the new chance to construct the highly active catalysts for OER, because they have controlled skeletons, porosities, and well-defined catalytic sites. In this work, core-shell hybrids of COF and metal-organic frameworks (MOFs) have first demonstrated to catalyze the OER. The synergetic effects between the COF-shell and MOF-core render the catalyst with higher activity than those from the COF and MOF. And the catalyst achieved an overpotential of 328 mV, with a Tafel slope of 43.23 mV dec in 1 m KOH. The theoretical calculation revealed that the high activity is from the Fe sites in the catalyst, which has suitable binding ability of reactant intermediate (OOH), and thus contributed high activity. This work gives a new insight to designing COFs in electrochemical energy storage and conversion systems.