Complementary microscopy techniques applied for optimizing the structure and performance of graphene-based hybrids

To improve the performance of graphene and to extend its potential applications, one of the most effective efforts is to hybridize graphene with one or more metal/metal oxide nanocrystals (NCs). In this paper, we demonstrate the complementary techniques of X-ray diffraction, high resolution electron microscopy (HREM), energy-dispersive X-ray spectroscopy (EDX), and energy-filtered transmission electron microscopy (EFTEM), which enables us to optimize the synthetic conditions, improve the quality of attached NCs, and tailor the performance of graphene-based hybrids for green energy related applications. Specifically, we explored the EFTEM technique to characterize two graphene-based composites. For the first sample of graphene/CoOx, we present how the oxygen elemental map can identify that the oxidization of attached cobalt NCs most likely occurred during post treatments, rather than during the solvothermal reaction; for the second sample of graphene/(Mn, Co, Ni)Ox, we demonstrate how two-dimensional elemental mapping can differentiate the distribution of Mn, Co, and Ni on the surface of graphene. The results indicate that the EFTEM technique can supply very valuable and indispensable information, which contributes to comprehensive evaluation of structure and performance of graphene based hybrids.