Effect of catalyst loading on hydrogen storage capacity of ZIF-8/graphene oxide doped with Pt or Pd via spillover

In this work, a series of zeolitic imidazolate framework (ZIF-8)/graphene oxide (GO) supported Pt or Pd nanoparticles (NPs) with different loading amounts were obtained via a simple liquid impregnation 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 Pt and Pd particles in the corresponding composites have average diameters of about 4.5 and 4.6 nm, respectively. All metal-doped ZIF-8/GO composites maintained the host framework of pure ZIF-8, although their specific surface areas were significantly reduced. The introduction of metal catalysts into the ZIF-8/GO matrix does not favor the hydrogen adsorption performance at 77 K due to the physisorption mechanism. In contrast, the adsorption isotherms at 298 exhibited dramatically improved storage capacities, by factors of 3.8-11.8. (Pt-doped ZIF-81GO) and 7.9-12.6 (Pd 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/G0 support. More importantly, 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. (C) 2016 Elsevier Inc. All rights reserved.