Syntheses, Characterizations And Hydrogen Storages Properties Of Nanomental-doped ZIF-8/Go Composites

In this paper, a series of mental-organic frameworks (ZIF-8)/graphene oxide (GO) supported Pt, Pd and NiPt nanoparticles (NPs) with different loading amounts were obtained via in-situ method of ZIF-8/GO with metal salt solution followed by a reduction treatment. Powder X-ray diffraction, Fourier transform infrared spectra, scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, inductively coupled plasma-emission spectroscopy, and nitrogen adsorption-desorption measurements were employed to investigate the physical and chemical properties of as-prepared samples. The porosities were investigated using the gas adsorption/desorption analyzer. In addition, hydrogen capacities and hydrogen storage mechanisms of composites at 77 K and 298 K were discussed.(1) The Pt,Pd and NiPt particles in the corresponding composites have average diameters of about 4.5,4.6 and 4.2-5.1 nm, respectively. All metal-doped ZIF-8/GO composites maintain the host framework of pure ZIF-8, although their specific surface areas were significantly reduced.(2) At 77 K the introduction of metal catalysts into the ZIF-8/GO matrix does not favor the hydrogen adsorption performance. In contrast, the adsorption properties carried out at ambient temperature (298 K) resulted in dramatically improved storage capacities, by factors of 3.8-11.8 (Pt-doped ZIF-8/GO),7.9-12.6 (Pd-doped ZIF-8/GO) and 2.3-3.8 (NiPt-doped ZIF-8/GO) times over pristine ZIF-8 at the hydrogen pressure of 860 mmHg. This enhancement is mainly attributed to the spillover mechanism by metal catalysts into the ZIF-8/GO support.(3) In Pt-doped ZIF-8/GO and Pd-doped ZIF-8/GO systems,the effect of catalysts dispersion and content on the level of hydrogen storage was also explored, which showed that the composites with the most homogeneous metal distribution and moderate loading amount would display the highest hydrogen adsorption performance.(4) In NiPt-doped ZIF-8/GO system,Notably, the Pt seems to be the best adsorbent for hydrogen storage because of the higher catalytic reactivity of platinum than nickel.