Synthesis and characterization of metal oxide-carbon nanocomposites for energy conversion and storage

Abstract

Heterogeneous composites of metal oxides and low dimensional carbon nanomaterials were fabricated through chemical synthesis and their structural and optical properties were analyzed and applied to solar cells, photovoltaic chemical cells and super capacitors. Chemically surface-modified zinc oxide graphene quantum dots were synthesized and inverted solar cells were fabricated using them. Quantum dot monolayers play a multifunctional role as surface modification, sub-photosensitive and electron transport layers, increasing energy conversion efficiency due to improved interfacial properties and efficient charge transfer. We demonstrate the in-situ chemical synthesis and their properties of multilayer graphene shells on the surface of zinc oxide core nanoparticles for the photoelectrochemical cell. The stable oxygen bridge bonds between the zinc oxide core and the oxygen-related functional groups on the multilayer graphene shells facilitate the efficient photoinduced charge separation. The efficient electron transfer between the zinc oxide core and the multilayer graphene shell resulted in the significant improvement of the photocatalytic activity and the photoelectrochemical response. Simultaneously, the photocorrosion of ZnO was prevented by having the oxygen bridge bonds between the ZnO and MLG which suppressed the photo-generated holes oxidizing the surface oxygen atoms on ZnO, and in turn the holes are consumed by photocatalytic reaction. We demonstrate the in-situ chemical synthesis and their properties of the core (active material)/shell (conductive material) type $Co_3O_4$/graphene quantum dots (QDs) for energy storage. The stable oxygen bridge bonds between the $Co_3O_4$ core and the oxygen-related functional groups on the graphene shells facilitate the efficient charge/discharge performance. The efficient electron transfer process between the $Co_3O_4$ core and the graphene shell lead to an improvement in the electrochemical activity. The excellent performance of the $Co_3O_4$/G QDs electrode is attributed to the significant improvement of the electrochemical activity, without conductive additives, due to the presence of metal oxide QD covered by graphene shells which leads to the good electrical properties.