Tunable Supercapacitor Materials Derived from Hydrochar/Gold Nanograpes

Since electrode materials play a crucial role in the performance of supercapacitors, the design of architectures based on carbon nanocomposites can enhance the electrochemical performance based on the synergistic effect between the components. Here, we have devised a facile synthetic route for the preparation of a C/Au nanocomposite, denoted as carbon/gold nanograpes (C/Au NGs), based on the hydrothermal polymerization of glucose-stabilized gold nanoparticles. Carbonization/activation of the C/Au NGs at 500 °C yields microporous carbon nanospheres containing several Au nanoparticles, giving a high volumetric capacitance. However, this volumetric capacitance suffers a dramatic drop at fast charge/discharge rates. When heating the C/Au NGs at 700 °C, the Au nanoparticles melt and flow out of the carbon nanospheres, altering the micropore structure of the C/Au NGs shells, and recrystallize at the surface, while some nanoclusters containing only a few Au atoms remained homogeneously dispersed within the pore network of the carbon shell. These nanostructural changes result in an increase in the ionic transport rates across the carbon shell as well as a lowering of the resistance, thus increasing the volumetric capacitance in aqueous acidic solutions and showing a remarkable improvement in the capacitance retention.