Nickel containing polyoxometalates incorporated in two different metal-organic frameworks for hydrogen evolution reaction

Abstract Nickel containing polyoxometalates (POMs) K6NiSiW11O39·15H2O (1), K5NiPW11O39. 15H2O (2), K6NiGeW11O39·15H2O (3) are encapsulated in two different metal-organic frameworks (MOFs), i.e. MIL-100 (Fe) (a) and UIO-67 (b). As a result, six POM-MOF composites i.e. [H6NiSiW11O39]0.24[Fe3C18H7O14]·14H2O (1a), [H5NiPW11O39]0.23[Fe3C18H7O14]·14H2O (2a), [H6NiGeW11O39]0.26[Fe3C18H7O14]·14H2O (3a), [H6NiSiW11O39]0.20 [Zr6O4(OH)5.4][C14H8O4]5.3.15H2O (1b), [H5NiPW11O39]0.19[Zr6O4(OH)5.4] [C14H8O4]5.3·14H2O (2b), [H6NiGeW11O39]0.19[Zr6O4(OH)5.4] [C14H8O4]5.3·13H2O (3b) are fabricated and characterized via various analytical techniques. These composites are utilized as catalysts in photochemical and electrochemical hydrogen evolution reactions (HER). In photochemical experiments, 1a, 1b, 2a, 2b, 3a and 3b produced 9.2, 8.5, 11, 32, 45 and 30 µmols of hydrogen respectively; whilst generated a current density of 24, 17, 32, 80, 46 and 112 µA, respectively during electrochemical catalysis. Striking results of the detailed study show that when POM 3 is embedded in MIL-100 (Fe), it produces 45 µmols of H2 compared to when embedded in UIO-67 (30 µmols).