Electrokinetic Power Generation Systems For Environmental Energy Harvesting

Energy is an important material foundation for the development of society,people’s living quality and protecting national security.With the rapid consumption of traditional energy,the situation of energy and environmental pollution is becoming more severe.It is of great significance to develop advanced energy conversion technologies for environmental energy harvesting.Besides,the rapid growth of personal and mobile electronics for applications in communication,health care,and environmental monitoring has caused significant challenges on powering of these electronic devices.Electrokinetic power generation(EPG)based on electrical double layer(EDL)in micro/nano channels has attracted great attention in recent years.Owing to its extremely simple structure,tiny volume,high reliability and environmentally friendly characteristics,EPG may open up a new prospect for energy harvesting of practical applications and being used for mobile electronics powering.Basing on this technology,novel electrokinetic energy conversation systems were proposed and their working performance were theoretically and experimentally studied.The main research content and conclusions of this work include:(1)The output performance of pressure driven electrokinetic generator was investigated comprehensively by establishing physical model and mathematic model.We found that the surface charge density,pressure difference,solution concentration and the size of the micro/nano channel had significant effect on the output performance.When the surface charge density is increased,the streaming current is increased and the streaming potential is decreased.The output electric power is first increased and then decreased.When the pressure difference is increased,the solution velocity is increased and all of the streaming current,streaming potential and the output power are increased.In low concentration,all of the streaming current,streaming potential,output power and conversion efficiency are maximal owing to the overlap of EDL.They remain constant as solution concentration increasing until EDL is detached and begin to decrease.When the diameter of channel is increased,all of the streaming current,streaming potential and output power are increased.Because the input power is increased at the same time as the diameter increasing,the conversion efficiency first increases and then decreases as the diameter increasing.The experimental results by an anodic aluminum oxide(AAO)nanoporous membrane with an effective sectional diameter of 1.5 mm indicated that the maximum output power can reach up to 0.25 mW and the conversion efficiency is 9%.(2)A novel thermally driven electrokinetic generation system is proposed and its working performance is theoretically and experimentally studied.By investigating with two typical micro/nano-porous media(nickel oxide wick and AAO),we found that the system has a good current-potential curve and performs well.The output electric power can be enhanced up to 50 nW(wick experiment),which is three order of magnitude higher than traditional single channel generators.The system can convert low grade heat energy(5 ℃ temperature difference in 20 ℃environment)into electrical energy continuously and steadily,which could be used for self-powered electronic devices(AAO experiment).(3)A novel water microjet array system based on electrokinetic phenomenon is proposed for electric power and hydrogen generation.The output performance is investigated by using a 572 pores stainless steel nozzle with pore radius of 8 μm and thickness of 60 μm fabricated by ultrashort-pulse laser drilling method.Experimental results show that the streaming current is up to 1268 nA,the open-circuit voltage is up to 85 kV,the corresponding hydrogen productivity is 35 mL/(m2·h).The maximum output electric power is 38 mW corresponding a remarkable power density as high as 1.39×106 W/m2.The maximum efficiency is obtained to be 4.73%,which can be further promoted by optimizing the device design.This system provides a new method for generating hydrogen and could be used in electrostatic painting and electrophoresis applications.(4)A novel electrokinetic generation system based on multi-energies synergy is proposed for multiple environmental energy harvesting.Experimental results indicate that this system exhibits excellent energy collecting ability.Even at indoor environment(T=14 ℃,RH =35%),the open-circuit voltage can reach 7 mV with nature liquid evaporation on the top of a home-made experimental apparatus with diameter of 2.5 cm.The output electricity can be increased with wind velocity,temperature or light intensity increasing.This system is of promising potential in environmental energy development.