鹽濃差度梯度產生的滲透能：孔道表面波形設計的影響及修正後的電動模型對離子尺寸和介電效應的研究

Abstract

近年來，學術研究對於鹽濃差發電的興趣日益增長，這種創新方法利用鹽水和淡水間的鹽度差異，讓離子通過奈米孔道時產生電力。先前的理論研究主要集中在內表面光滑的奈米孔道上。從鹽度梯度中成功提取滲透壓能源的關鍵在於奈米孔道的離子選擇性能。這要求奈米孔道材料與水溶液接觸的表面具有適當的表面電荷，並且奈米孔的尺寸應當與電雙層的尺寸匹配。 第一章中，為了提升奈米流體滲透壓發電的性能，我們研究了四種具有獨特波形內表面設計（方形、鋸齒形、三角形和正弦波）的圓柱形奈米孔道。此研究聚焦於探討系統濃度效應和固液界面幾何特性對發電表現的影響。我們證明了波形孔道內表面的存在引入了新的變數，這些變數對奈米流體系統的整體性能產生重大影響。在波形孔道內表面的最佳振幅下，提高波形頻率顯著改善了滲透電流、擴散電位、最大功率和最大效率。這些研究成果已經發表在Physical Chemistry Chemical Physics journal上。 然而，目前的研究主要依賴標準的泊松-能斯特-普朗克（Poisson-Nernst-Planck, PNP）模型，該模型過於簡化離子為點電荷，並忽略了如離子的有限大小、波恩能（Born energy）和介電能等關鍵因素。在第二章中，為了修正這些遺漏，我們採用了一種將溶液介電常數視為濃度函數的觀點，並為每種離子引入了修改後的化學勢能，從而提出了一種修改後的PNP模型。該模型全面考慮了離子的體積效應、波恩力和介電力。我們的研究旨在描述標準PNP模型和修改後PNP模型之間的差異，包括系統性能如電流、擴散電位、最大功率和最大效率等方面。通過這一探討，我們提供了電動力學現象的新見解，揭示了由奈米孔內離子分佈引發的現象。

In recent scholarly inquiries, there has been a growing interest in salinity gradient power, an innovative method exploiting the disparity in salinity between brine and fresh water to generate electricity via nanopores. Previous theoretical studies in this field based mainly on nanopores having a smooth inner surface. The successful operation of osmotic power derived from salinity gradients hinges on the ion-selective properties of the nanopore. This necessitates that the surface of the nanofluidic material in contact with the salt solution carries an appropriate charge, and that the dimensions of the nanofluidic channels align with those of the electrical double layer (EDL). In Chapter 1, to enhance the performance of nanofluidic osmotic power, we investigated four types of cylindrical nanopore, each has a unique waveform wall design (square, sawtooth, triangle, and sine waves). This study focused on elucidating the influence of bulk salt concentration and geometric characteristics at the solid-liquid interface. We demonstrated that the presence of a waveform wall introduces new variables that have a significant impact on the overall performance of a nanofluidic osmotic power system. At the optimal amplitude of the waveform wall, raising waveform frequency can improve remarkably the osmotic current, diffusion potential, maximum power, and maximum efficiency. These research findings have been published in the Physical Chemistry Chemical Physics journal. However, prevalent studies predominantly rely on the standard Poisson-Nernst-Planck (PNP) model, which oversimplifies ions as point charges and neglects crucial factors such as the finite size of ions, Born energy and dielectric energy differences. In Chapter 2, to rectify these oversights, we adopt a perspective that considers solution permittivity as a concentration-dependent function and introduce a modified chemical potential for each ionic species, leading to the formulation of a modified PNP model. This model comprehensively accounts for ion steric effects, Born, and dielectric forces. Our investigation aims to delineate disparities between standard and modified PNP models, encompassing system performance such as current, diffusion potential, maximum power, and maximum efficiency. Through this rigorous examination, we offer novel insights into the electrokinetic phenomenon, shedding light on profound phenomena arising from ion distribution within nanopores.