A Mononuclear Co < sup > II < /sup > Coordination Complex Locked in a Confined Space and Acting as an Electrochemical Water-Oxidation Catalyst: A "ship-in-a-Bottle" Approach

Abstract

Preparing efficient and robust water oxidation catalyst (WOC) with inexpensive materials remains a crucial challenge in artificial photosynthesis and for renewable energy. Existing heterogeneous WOCs are mostly metal oxides/hydroxides immobilized on solid supports. Herein we report a newly synthesized and structurally characterized metal-organic hybrid compound [{Co3(μ3-OH)(BTB)2(dpe)2} {Co(H2O)4(DMF)2}0.5]n·n H2O (Co-WOC-1) as an effective and stable water-oxidation electrocatalyst in an alkaline medium. In the crystal structure of Co-WOC-1, a mononuclear CoII complex {Co(H2O)4(DMF)2}2+ is encapsulated in the void space of a 3D framework structure and this translationally rigid complex cation is responsible for a remarkable electrocatalytic WO activity, with a catalytic turnover frequency (TOF) of 0.05 s-1 at an overpotential of 390 mV (vs. NHE) in 0.1 m KOH along with prolonged stability. This host-guest system can be described as a "ship-in-a-bottle", and is a new class of heterogeneous WOC.