Recently, various energy transducers driven by the relative motion of solids and liquids have been demonstrated. However, in relation to the energy transducer, a proper understanding of the dynamic behavior of ions remains unclear. Moreover, the energy density is low for practical usage mainly due to structural limitations, a lack of material development stemming from the currently poor understanding of the mechanisms, and the intermittently generated electricity given the characteristics of the water motion (pulsed signals). Here, we verify a hypothesis pertaining to the ion dynamics which govern the operation mechanism of the transducer. In addition, we demonstrate enhanced energy transducer to convert the mechanical energy of flowing water droplets into continuous electrical energy using an electrolyte-insulator-semiconductor structure as a device structure. The output power per droplet mass and the ratio of generated electric energy to the kinetic energy of water drops are 0.149v mW·g·m·s and 29.8%, respectively, where v is the speed of the water droplet.
Activated carbons (ACs) were prepared by activation of coal tar pitch (CTP) in the range of 700°C-1000°C for 1-4 h using potassium hydroxide (KOH) powder as the activation agent. The optimal activation conditions were determined to be a CTP/KOH ratio of 1:4, activation temperature of 900°C, and activation time of 3 h. The obtained ACs showed increased pore size distribution in the range of 1 to 2 nm and the highest specific capacitance of 122 F/g in a two-electrode system with an organic electrolyte, as measured by a charge-discharge method in the voltage range of 0-2.7 V. In order to improve the performance of the electric double-layer capacitor electrode, various mixtures of CTP and petroleum pitch (PP) were activated at the optimal activation conditions previously determined for CTP. Although the specific capacitance of AC electrodes prepared from CTP only and the mixtures of CTP and PP was not significantly different at a current density of 1 A/g, the AC electrodes from CTP and PP mixtures showed outstanding specific capacitance at higher current rates. In particular, CTP-PP61 (6:1 mixture) had the highest specific capacitance of 132 F/g, and the specific capacitance remained above 90% at a high current density of 3 A/g. It was found that the high specific capacitance could be attributed to the increased micro-pore volume of ACs with pore sizes from 1 to 2 nm, and the high power density could be attributed to the increased meso-pore volume.
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