Zinc Oxide/Reduced Graphene Oxide Composites and Electrochemical Capacitance Enhanced by Homogeneous Incorporation of Reduced Graphene Oxide Sheets in Zinc Oxide Matrix

Abstract

ZnO/reduced graphite oxide composites were synthesized using a two-step method in which KOH reacts with Zn(NO3)2 in the aqueous dispersions of graphite oxide (GO) to form a Zn(OH)2/graphite oxide precursor, followed by thermal treatment in air. It was found that the dispersion of reduced graphene oxide (rGO) sheets within composites was key for achieving an excellent capacitive performance of the samples. However, the mass ratio of ZnO to rGO determined whether rGO sheets within composites were dispersed or agglomerated. The composite achieved homogeneous incorporation of rGO sheets within the ZnO matrix when the mass ratio of ZnO to rGO was equal to 93.3:6.7. This composite, in which the weight percent of rGO was only 6.7%, appeared in the SEM images to be almost entirely filled with rGO sheets coated by ZnO and exhibited high specific capacitance and excellent cycling ability. Furthermore, the sheets overlapped to form a three-dimensional network structure, through which electrolyte ions easily access the surface of the rGO or electrochemical active sites. The homogeneously incorporated rGO sheets were shown to provide 128% enhancement in specific capacitance compared with 135 F g−1 for pure zinc oxide samples. Also, the unexpected phenomena involved in the experimental processes are discussed in detail.

Reduced graphene oxide decorated with in-situ growing ZnO nanocrystals: Facile synthesis and enhanced microwave absorption properties

“…As displayed in Figure 2 shows the XRD patterns of the RGO/ZnO composites before and after thermal treatment. On the XRD pattern of the composites before thermal treatment, the diffraction peak appears at 2θ=10.5° corresponding to the (001) plane of GO [35]. The peak is intense and sharp demonstrating the complete oxidation of…”

“…Recently, it was proved to be an ideal candidate for microwave absorbption application on account of its light weight, semiconductive properties and large scale synthesis that can be easily realized [29,30]. Because of the unique properties of RGO and ZnO as well as the synergistic effect between them, their composites have been investigated for many uses, such as photocatalyst [31][32][33], photoluminescence [34], supercapacitor [35], sensors [36,37] and so on.…”

The Electrochemical Behavior of Zinc Oxide/Reduced Graphene Oxide Composite Electrode in Dopamine

“…Theoretically (002) peak of rGO is expected to appear in the XRD diffractogram of ZnO/rGO. However, it cannot be observed in the corresponding compositions (Figure 2b), indicating that the surfaces of rGO are fully covered by ZnO [21]. Hence, the diffraction peaks are mainly from the up-layer ZnO phase in the ZnO/rGO compositions.…”

“…The SEM image of GO showing that the oxidation of graphite after treated with modified Hummers' method caused a visible change in their morphology, or it has a wrinkled appearance with multiple folds. This wrinkled aspect can be explained by the oxidation process to promote the admission of hydroxyl groups and epoxy groups, known as functional groups [21]. The formation of ZnO on the surface of graphene layer is indicated by the microsphere-like hierarchical structures after the GO is undergoes reduction by Zn(NO 3 ) 2 .…”

Down-top nanofabrication of binary (CdO)_x&nbsp;<br />(ZnO)_1-x&nbsp;nanoparticles and their antibacterial activity

“…26,27 Similarly, hexagonal ZnO is a II-VI composite semiconductor made of the metallic element zinc (II) and the non-metallic element oxygen (VI). 28 Thus, many ZnO semiconductor materials have shown availability of notable characteristics that has encouraged many applications to exploit these features. This structure has been used as the standard hexagonal crystal structure and classified as an n-type semiconductor with 3.27 eV-3.50 eV direct band gaps.…”