The secret of the magic gourd(I): biomass from various organizations of ourds as a sustainable source for high-performance supercapacitors

The classic cartoon “Calabash Brothers” describes a story of seven brothers born from a magic gourd uniting to defeat powerful enemies. In order to explore the secret of the magic gourd, several transition metals were used to synthesize metal silicates (C-MSi) by planted gourd leaves (GLs) and then the C-MSi materials were used to fabricate supercapacitor electrodes and devices with superior electrochemical performance. By integrating theoretical calculations and experimental results, the supercapacitor electrodes and devices obtained from the combination of transition metals with amorphous carbon exhibit superior electrochemical performance. In detail, in the three-electrode system, the NaOH etched materials (C-MSi) exhibited better electrochemical performance (for instance, as for C-CdSi, 607 F g⁻¹ at 0.5 A g⁻¹ and the capacitance retention of 98.2% after 10,000 cycles) than the unetched ones (i-C-MSi). Hybrid supercapacitor (HSC) devices also achieve very excellent electrochemical properties. Take C-CdSi//AC as an example, the areal specific capacitance with 691 mF cm⁻² at 2 mA cm⁻², the energy density with 5.04 Wh m⁻² at the power density of 22.2 W m⁻² and the cycle stability with 87.3% after 6,000 cycles. This approach is very versatile and was also applied to produce many hierarchically structured metal-silicate materials of other biomass precursors, including roots, vines, flowers, fruits and seeds of the planted gourds. Thus, it is a potential way to prepare transition metal silicates using biomaterials for the enhancement of electrochemical performance and improvement of energy storage and conversion. Also, this paper preliminarily reveals the secret of the magic gourd.