Microwave-assisted dry synthesis of hybrid electrode materials for supercapacitors: Nitrogen-doped rGO with homogeneously dispersed CoO nanocrystals

In this research work, we have applied a dry microwave (MW) strategy to synthesize uniformly sized CoO nanocrystals homogeneously dispersed on the basal plane of nitrogen-doped reduced graphene oxide nanosheets (N-rGO NSs). The MW treatment is an ultra-fast process for exfoliation and in-situ reduction of graphite oxide and simultaneous decomposition of the cobalt precursor. The results show that during the MW-assisted synthesis process, the graphite oxide is exfoliated, reduced and combined with the available nitrogen from the precursor to form N-rGO NSs. Simultaneously; the Co ions react with oxygen functionalities on surface of N-rGO NSs to form CoO (N-rGO@CoO) nanocrystals. These processes, when combined, effectively prevented the aggregation of the CoO nanocrystals and the re-stacking of the N-rGO layers. The resulting N-rGO@CoO nanocomposites exhibited unique surface morphology and electrochemical performance for supercapacitor (SC) applications. As the SC electrode, the nanocomposite delivered high specific capacitance (744.1 F/g at 5 mV/s) and excellent cyclic stability (91.3 % over 5000 cycles). Thus, the MW-processing method proved to be a rapid, effective, and simple approach for single step synthesis of doped rGO-metal oxide electrodes for SC applications.