Small-sized Ni(1 1 1) particles in metal-organic frameworks with low over-potential for visible photocatalytic hydrogen generation

Abstract

The development of an advanced co-catalyst is critical for improving the efficiency of the photocatalytic hydrogen evolution reaction. Noble metals (such as Pt) have been identified to be the most active co-catalyst for this reaction since they exhibit significantly low over-potential. However, their low-abundance, high cost, its scale-up setup usage is impeditive. Here, we reported that high efficient small-sized nickel particles embedded in the frameworks of MOF-5 as a co-catalyst with low over-potential for visible photocatalytic hydrogen evolution. The electrochemical measurements showed a low over-potential of −0.37V, which have the similar over-potential as Pt@MOF-5. Such low over-potential is attributed to their high dispersion (41.8%), small-sized nickel particles (∼9nm), and high specific surface area of MOF-5 (2973m2/g). As evidenced by electrochemical impedance spectra (EIS) measurements, Ni nanoparticles with exposed (111) facet were more benefited the electrons transfer from MOF-5 than that of (200) facet one. In addition, Ni@MOF-5 exhibited the larger transient photocurrent and longer fluorescence lifetime. These results led to the high photocatalytic activities and stability for hydrogen evolution sensitized by Eosin Y (EY) over Ni@MOF-5. The rate of hydrogen evolution reached 30.22mmolh−1g−1[Ni] (at pH 11) over Ni@MOF-5 irradiated under visible light irradiation (λ≥420nm) in 2h. The apparent quantum efficiency (AQE) of 16.7% over EY-Ni@MOF-5 was achieved at 430nm. MOF-5 might promote the photogenerated electrons transfer from excited EY to the hydrogen evolution active sites (Ni), and consequently enhance photocatalytic hydrogen evolution efficiency.