The use of battery-driven equipment and appliances has been steadily increasing, while also increasing the demand for safe, efficient and high-performance power supplies. An electric energy storage device called supercapacitor has recently been considered as a practical and even better energy storage device, which can replace the currently widely used energy storage devices such as lithium ion batteries. The charging and discharging speed of the supercapacitor is faster, and the continuous working time is longer, so it can be used for various applications such as regenerative braking of vehicles and wearable electronic devices.
However, despite the great potential of supercapacitors, there are still some shortcomings that prevent their widespread use. One of the main problems is the low energy density, that is, the energy stored per unit area is insufficient. At the beginning, scientists tried to use organic solvents as the electrolyte of supercapacitors (as a conductive medium) to solve this problem and increase the generated voltage (note that in energy storage devices, the square of the voltage is proportional to the energy density). However, organic solvents are expensive and have low electrical conductivity. Therefore, scientists believe that perhaps water electrolytes will be better. Since then, the development of high-efficiency supercapacitor components equipped with water electrolytes has become a central research topic in this field. Takeshi Kondo, a scientist who has recently made a research breakthrough, said: "If a non-flammable, non-toxic and safe water electrolyte can be used to make a high-performance supercapacitor, the supercapacitor can be integrated into wearable devices and other devices, bringing benefit."
Dr. Kondo collaborated with the Tokyo University of Science team and the Japanese chemical company Daicel Corporation to explore the possibility of using boron-doped nanodiamond as the electrode of supercapacitors, which are conductive materials in batteries or capacitors , It connects the electrolyte to the external wires to deliver current out of the system. The research team chose the electrode material based on the recognition that boron-doped diamond has a wide potential window, which can keep high energy storage equipment stable for a long time. Dr. Kondo said: "We believe that if conductive diamond is used as the electrode material, a large voltage can be generated in the water-based supercapacitor."
Scientists have used a technique called microwave plasma-assisted chemical vapor deposition (MPCVD) to fabricate such electrodes and verify their performance through testing. They found that in a two-electrode system containing aqueous sulfuric acid electrolyte, the voltage generated by such electrodes is much higher than that of traditional batteries, so the energy and power density of supercapacitors will also be much higher. In addition, they also found that even after 10,000 charge and discharge cycles, the electrode is still very stable.
After success, the scientists went on to explore whether this electrode material would have the same performance if the electrolyte was turned into a saturated sodium perchlorate solution. As we all know, saturated sodium perchlorate solution can generate higher voltage than traditional sulfuric acid electrolyte. In fact, the device has generated a higher voltage. Therefore, as Dr. Kondo said: "Boron-doped nanodiamond electrodes are very useful for water-based supercapacitors, and such supercapacitors are suitable for high-speed charging and discharging high-energy storage devices."