Ge-based hybrid composites from Ge-rich zeolites as highly conductive and stable electronic materials

Abstract

© 2019 American Chemical Society. Ge-containing zeolites were used as precursors for the synthesis of highly conductive and stable hybrid electronic materials by postsynthetic thermal treatment of the crystals in the presence of an olefin. Treating the as-prepared Ge zeolites in 1-butene at 700 °C formed a graphitic matrix within and outside the crystals due to the thermal degradation of the organic structure-directing agent inside the pores and the polymerization of the olefin. Importantly, these conditions forced Ge out of the framework, leading to the collapse of the crystalline structure and subsequent formation of metallic Ge nanoparticles distributed either as small, well-dispersed nanoparticles within the silica matrix or larger carbon-coated core-shell Ge@C nanoparticles on the external surface of the carbon-silica composite. Varying the zeolite topology influenced the size of the Ge@C nanoparticles, with those obtained using the multipore zeolite ITQ-22 (IWW, 12 × 10 × 8 rings) featuring smaller sizes (30-60 nm) than those obtained with the large-pore zeolite ITQ-33 (ITT, 18 × 10 × 10 rings) (80-120 nm), where the lack of diffusional limitations increased metal sintering rates. The zeolite topology also influenced the final carbon content and dispersion of the Ge nanoparticles. The best performing Ge-based hybrid material was obtained by thermal treatment of ITQ-22 (Si/Ge = 4) at 700 °C in 1-butene. Unlike Ge-free hybrid controls, an ITQ-22 (Si/Ge = 4) sample treated at 700 °C in 1-butene showed a conductivity value of ∼2 S/m (measured at 1 V), which is in the range of a commercially available graphene. The simple methodology presented here is an alternative route for the efficient preparation of highly stable Ge-based hybrid composites with excellent conductivity for potential use as high-capacity electrodes.