Understanding 2D Nanoflake-like Heterostructures for Energy Storage and Conversion Applications at the Atomic Level

Introduction: The conversion and storage of solar energy into chemical fuel hold promise to meet the increasing demand for global energy and ensure a permanent renewable energy supply for the future. As promising candidates... [ view full abstract ]

Introduction:
The conversion and storage of solar energy into chemical fuel hold promise to meet the increasing demand for global energy and ensure a permanent renewable energy supply for the future. As promising candidates for energy storage and energy conversion, 2-D materials have drawn plenty of researchers´ attention. Despite such a wide spectrum of research on the optimization of nanostructures in various 2D materials, precise relationship between the materials´ structure and physical and chemical properties remains elusive.
Methods:
Hydrothermal method, electrodeposition etc.. Field emission scanning electron microscope (SEM), transmission electron microscopy (TEM), scanning transmission electron microscopy-electron energy loss spectroscopy (STEM-EELS, with a high angle annular dark field (HAADF)) and geometric phase analyses (GPA).
Result:
Honeycomb-like hematite nanoflakes/branched polypyrrole nanoleaves heterostructures with a 3D complex structure have been synthesized and employed as high-performance negative electrodes for asymmetric supercapacitors application. Besides, the core-shell MoO2/MoS2 nanoflakes have been synthesized via a step by step process and are utilized as photocathode for water splitting application.
Discussion:
The detailed TEM-STEM characterization and deep EELS chemical analysis at the nanoscale has been combined to elucidate the mechanisms underlying the formation and morphology evolution of core-branch Fe2O3@PPy heterostructures. In addition, we have studied the mechanism of converting MoO2 nanoflakes into 2D free-standing MoS2 electrode by sulfurization process for water splitting. In this way, the atomic resolution aberration corrected HAADF STEM reveals the sulfurization mechanism in an unprecedented detail, together with EELS chemical maps.