Sodium-Salt-Promoted Growth of Self-Supported Copper Oxides with Comparative Supercapacitive Properties

In this work, we developed a facile hydrothermal system to synthesize self-supported copper oxides with different nanostructures. In this system, we used copper foam as both the substrate and the copper source, and selected a wide range of sodium salts to serve as directing agents, promoting the formation of copper oxide with different nanostructures. We first show that, at 30 mM of sodium fluoride, we can successfully grow nanocubes on the copper foam substrate that comprise both CuO and Cu2O. Such a mixed composition is unique among the investigated salts. However, if a lower concentration of NaF or a different salt is used, Cu2O nanocrystals of different structures, such as nanoplatelets or irregular particles, can be obtained. When these samples were tested in supercapacitors, they demonstrated contrasting pseudocapacitive properties where the initial mixed Cu2O/CuO nanocube sample demonstrated a very stable reversible capacitance of about 400 mF cm(-2) for 1600 cycles. This is significantly higher than that for the other samples, as well as advantageous compared to other copper-oxide-based electrode materials. The impedance analysis suggested that such a performance could be attributed to the low diffusion resistance of this sample.