Fabricating a Functionalized Polyoxometalate with ZIF-8: AComposite Material for Water Oxidation in a Wide pH Range

摘要

Designing an efficient oxygen evolution reaction(OER) electrocatalyst is a challenging task because molecularoxygen is essential to sustain life. Herein, we have synthesized andstructurally characterized a {Bi(OH2)2}3+-functionalized Kegginpolyoxometalate (POM) compound, K5Bi(H2O)2SiW11O39middot13H2O(K51middot13H2O). Keeping in mind that the {Bi(OH2)2}3+species on the surface of the POM has the potential to act as anactive site for electrocatalytic water oxidation, we encapsulated thefunctionalized Keggin POM anion Bi(OH2)2SiW11O395-insidethe cavities of a well-known zeolitic-type framework material ZIF-8, a zinc imidazole-containing metal-organic framework, becausecompoundK51middot13H2Oper seis water-soluble and unstable in theoxidation window of water oxidation. The resulting host-guest-type composite material H5Bi(H2O)2SiW11O39@ZIF8 (H51@ZIF8) functions as an efficient electrocatalyst for water oxidation.Detailed electrochemical analyses have established that the title OER catalyst,H51@ZIF8, works in a wide pH window, ranging fromalkaline pH 13.0 to neutral pH 7.0 through an acidic pH 4.0. Diverse controlled experiments have been performed to infer that thebismuth-aqua complex is the functional site responding to the OER, with a catalytic turnover frequency of 1.24, 5.90, and 0.93 s-1of pH 13.0, pH 7.0, and pH 4.0 solutions, respectively, at the respective overpotentials of 375.0 mV vsthe reversible hydrogenelectrode (RHE), 585.21 mV (vsthe RHE), and 830.10 mV (vsthe RHE).