基於pH可調節奈米通道之鹽濃差發電:幾何形狀的影響

Abstract

鹽濃差發電係由海水與淡水之間的化學能轉換成電能，於近年來備受關注。 第一章節中，我們主要探討濃度、以及三種不同形狀:子彈型、圓錐型與喇叭型之pH可調節奈米孔道對發電的影響。喇叭型奈米孔道因電雙層顯著地重疊，而擁有最好的離子選擇性。子彈型奈米孔道隨著曲率的改變，在發電上表現出局部極大值的情況。此研究成果已發表於Electrochimica Acta。 第二章節中，我們在一個pH可調節的漏斗型奈米孔道中，發現了違背常理的發電行為：普通來說，當奈米通道表面帶電越高的時候，能夠增強離子選擇性，進而達到更好的鹽濃差發電。然而在實驗的結果中顯示，表面帶電越高的時候，鹽濃差發電會隨著表面帶電增加而減少。這個發現在考慮通道表面的具有羧基官能基的數值模擬結果支持下，證實了表面帶電的增加，大幅地增強了離子極化現象，但是削弱通道兩端的有效濃度差，進而降低了鹽濃差發電。以上所獲得的結果提供了在鹽濃差發電裝置的設計上必要的資訊，也藉由實驗與理論的結合，證實了高表面帶電的奈米孔道中，特異的發電行為。此研究成果將投稿於國際期刊。

Salinity gradient power, which converts a difference in salinity between brine and fresh water into electricity, has received more and more attention in the recent years. In Chapter 1, the performance of power generation in a nanochannel having a pH-regulated surface is examined, with focus on the influence of the bulk salt concentration, and three types of nanochannel shape: bullet-shaped, conical, and trumpet-shaped nanochannels. Because of the significant electric double layer overlapping, the trumpet-shaped nanochannel has the best ion selectivity. As the ratio of (nanochannel length/curvature radius) varies, the maximum power generated from a bullet-shaped nanochannel has a local maximum. The above results were published in Electrochimica Acta. In Chapter 2, it has been long believed that to archive high-performance osmotic power, the highly charged channel materials should be exploited so as to enhance the ion selectivity. Herein, we report counterintuitive surface-charge-density-dependent osmotic power in a single funnel-shaped nanochannel, violating the previous fact. For a highly charged nanochannel, the performance of osmotic power decreases with a further increase in surface charge density. This observation is strongly supported by the rigorous model where the equilibrium chemical reaction between protons and carboxyl functional groups on the channel wall was taken into account. The modeling result proves that a significant increase in the surface charge density of nanochannel amplifies the effect of ion concentration polarization, thus weakening the effective salinity ratio across the channel and undermining the osmotic power generation. The results gathered from experiments and simulations help us to better understand the mechanisms of osmotic power in the nanochannel and provide desirable information for designing salinity gradient power devices. The above results will be submitted to the international journal.