摘要
最近的实验表明,在聚合物支撑的石墨烯上移动水滴可以在石墨烯中产生电压.为了揭示基底、石墨烯和离子水在发电中的作用,我们对水/石墨烯/基底界面进行了多尺度的分析和模拟,发现被基底上表面偶极吸引到石墨烯表面的离子会驱动石墨烯中的电荷重新分布,从而在水/石墨烯/基底界面处形成由石墨烯中的镜像电荷、吸附在石墨烯表面的离子以及溶液中的反离子组成的三电层结构.当水滴在石墨烯表面移动时,动态形成的三电层前端动边界驱动着石墨烯中的电荷形成电流.采用Langmuir吸附理论,结合第一性原理计算,确定了三电层中的离子浓度,并且估计了每个被吸附的离子可在石墨烯中拖动的电荷量.由此,得到了产生的电流与离子浓度、水滴移动速率、石墨烯厚度和基底上的偶极密度、偶极矩之间的关系式,且与实验测量结果吻合.该研究结果表明,控制基底上的表面偶极(密度和大小)可优化水伏发电器件的性能并促进其实际应用.
Recent experiments have demonstrated that moving water droplets on polymer-supported graphene can generate electric voltages in graphene.Here,we perform a multi-scale analysis on the mechanism of the generated voltages on the basis of an interplay among the substrate,graphene and ionic water.We find that the attraction of ions in water by substrate dipoles drives charge redistribution in graphene,forming an electric triple layer(ETL)at the water/graphene/substrate interface,made of an ion layer fixed on graphene,an image charge layer in graphene and a counterion layer in water.As a droplet moves on graphene,dynamic formation of the ETL at its front end drives a flow of charge in graphene.Using Langmuir adsorption theory combined with ab initio calculations,we determine the ion concentration in the ETL and estimate the amount of charge that each ion can draw in graphene.Then,the electric current in graphene is formulated in terms of ion concentration,droplet velocity,graphene thickness and density of substrate dipoles,which well reproduces experimentally measured currents in graphene.These results underscore the importance of tailoring substrate dipoles in optimizing the performance of devices for water energy harvesting and promoting practical applications.
作者
张宏波
张助华
郭万林
Hongbo Zhang;Zhuhua Zhang;Wanlin Guo(State Key Laboratory of Mechanics and Control of Mechanical Structures,Key Laboratory for Intelligent Nano Materials and Devices of Ministry of Education,and Institute of Nanoscience,Nanjing University of Aeronautics and Astronautics,Nanjing 210016,China)
基金
supported by the National Key Research and Development Program of China (2019YFA0705400)
the National Natural Science Foundation of China (11772153 and22073048)
the Natural Science Foundation of Jiangsu Province(BK20190018)
the Fundamental Research Funds for Central Universities (NJ2020003, NZ2020001, NP2019301, NJ2019002 and NC2018001)
a Project Funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions
