UC San Diego

The development of self-power electronics has attracted wide-spread attention owing to their potential applications in internet of things (IoT), nanorobotics, health monitoring, wireless communications, etc. However, the harvested energy resources (solar energy, thermal energy, radio frequency energy, etc.) are normally intermittent and unpredictable, so suitable energy storage devices that can store collected energies and have a stable are in high demand. Supercapacitors typically show a high-power density and an extended cycling life (>10,000 cycles) that perfectly fit the requirement of self-powered electronics. However, their practical applications are limited by the low energy densities and significant self-discharge problem. To enhance the performance of the supercapacitors, we demonstrated the electro-deposition of an open-shell conjugated polymer with reduced graphene oxide achieves electrodes with capacitance up to 186 mF cm−2 (372 F cm−3). The extended delocalization within the synthesized polymer stabilizes the redox states and facilitates a 3 V wide potential window, while the hierarchical composite electrode structure promotes ultrafast kinetics. The micro-supercapacitor shows a high-power density of 227 mW cm−2 with an energy density of 10.5 μWh cm−2 and stability of 84% capacitance retention after 11,000 cycles. These attributes allow operation at 120 Hz for fast charging and alternating current (AC) line filtering applications, which may be suitable to replace bulky electrolytic capacitors or serve as high-endurance energy storage for wireless electronics. Beyond the electrode material development, a novel supercapacitor configuration, structural supercapacitor was also developed to enhance the energy density of the whole device. A novel gradient structural electrolyte was designed for structural supercapacitor to balance its ionic conductivity and mechanical strength. By combining this electrode-electrolyte system, a structural supercapacitor that can replace the metallic chassis of transportation vehicles to provide extra electricity was fabricated. The structural supercapacitor was shaped into the hull of a model boat with a solar energy harvesting system, and it achieved both a high electrochemical and mechanical strength compared to its monofunctional counterparts. The demonstration was a promising prototype to show that structural energy storage can complement energy harvesting system to make electronics more energy-autonomous, requiring less maintenance cost if we have billions of electronics that can have operated on self-recharge. In addition, to enhance the efficiency of the self-powered electronics, an ion-exchange mechanism was also developed to suppress the self-discharge problem of energy storage units of self-powered electronics. This design increases the charging efficiency of the device and prevents the loss of stored energy during standby. It was demonstrated to work with radio frequency energy-harvesting circuits and showed the potential to serve as an energy reservoir for wireless electronic applications.