흐름전극(Flow-electrode) 기반 축전식 염분차 발전에 대한 연구

Abstract

The development of renewable energy is becoming more and more important due to the increase of environmental regulations as well as the reduction of fossil fuels. Renewable energy using natural resources such as sunlight, wind, rain, ocean, geothermal, biological organisms and etc. is classified as solar power, wind power, hydraulic, ocean, geothermal, biomass and waste-to-energy and etc. Recently, research about ocean energy such as wave power, tidal power, salinity-gradient power and temperature-gradient power are actively being conducted. In particular, ocean energy has many advantages as follows: unlimited use of seawater resources, environmental friendly, economical process, no greenhouse gas emissions. In addition, salinity-gradient power benefits by continuously production energy. It is predictable, and it can be used effectively on-site unlike solar and wind power. The salinity difference between seawater and fresh water, which can be used as a renewable power source, generates a potential difference between ion selective membranes. As a kind of salinity-gradient power generation, this technology is a salinity gradient power system that is applied to flow-electrode. Such a system has many advantages. The capacitive salinity-gradient power system based on flow-electrode is economical because it needs only one pair of ion exchange membranes. Moreover, the resulting power cost is low or than pressure-retarded osmosis and reverse electrodialysis. In addition, it is environmentally friendly process because there is no chemical waste. In this study, a salinity-gradient power system based on flow-electrode capacitive deionization (FCDi) concept was set-up. It was optimized with regard to concentration of the NaCl solution and flow rates of the flow-electrode and feed water, resulting in the maximum power. When the flow rates of flow-electrode in 3.5 wt% NaCl solution and distilled water as feed water were 25 and 3 mL/min, respectively, the maximum continuously power was 0.28 W per unit area. In addition, it was confirmed that long-term operation can produce electrical power (0.22 W/m2). Electrochemical impedance spectroscopy was also performed to analyze the electrochemical properties including capacitance and resistance of the flow-electrode in either static or flow state. An equivalent circuit was constructed from a Nyquist diagram as well. Therefore, the system of capacitive salinity-gradient power based on FCDi has the potential to be a new technology to harvest concentrated energy with an environmentally friendly and sustainable method.