具濃差之奈米流道離子傳輸及其在能源開發應用之探討

Abstract

在過去大部分奈米流道離子傳輸的研究中，奈米流道兩側之電解液濃度皆相同，且皆假設奈米流道兩側連接於大儲槽。而在實際應用場合，奈米流道需連接至一定大小之流道或儲槽，且兩側之電解液可能具有濃度差異及流速。鑑於過去對此方面之研究較少，本研究擬針對此進行奈米流道離子傳輸特性進行實驗及理論探討。由於離子交換膜可視為奈米流道之組合，在實驗探討方面本研究擬利用離子交換膜替代奈米流道，探討之參數包括電解液之濃度比、流速、以及酸鹼值等對電流-電位曲線之影響。此外，電解液流動空間大小因影響濃度極化之邊界層厚度，故其對電流-電位曲線之影響，亦加以探討。在理論探討方面，則以單一奈米流道及連接之微米流道為物理模型，探討在流體流動、電遷移、分子擴散影響下，由計算所得之電流-電位曲線了解離子之傳輸特性，並與實驗結果驗證。當具有濃差之電解液直接接觸或以一離子交換膜分隔時，可建立一電位差，並可利用其建立一逆滲析發電裝置，其架構及原理與上述之奈米流道電流-電位曲線之反向操作。因此，本計畫擬將建立之實驗裝置及理論模式延伸至建立一以濃差為驅動力之發電裝置，並探討電解液之濃度比、流速、以及酸鹼值、流動空間大小，以及用以電子傳輸之氧化還原劑濃度等對發電效率之影響。

Most of the previous studies on the ion transport through nanochannels focused on thesituation that nanochannel is connected with large reservoirs filled with electrolyte. The bulkconcentrations of the electrolyte are equal and motionless. In practical applications,nanochannel must be connected with finite-sized channel for flow supply. Under such case,the electrolytes on both ends of nanochannel may have different bulk concentration andvelocity. In the proposed project, we will focus on exploring more understanding on theeffects of concentration gradient and electrolyte flow on the ion transport through thenanochannel. The effects of electrolyte concentration ratio, flow velocity, pH value, and sizeof electrolyte compartment on the current-voltage curve will be examined both experimentallyand numerically to identify the ion transport characteristics. For the experiments, the ionexchange membrane will be employed to emulate the nanochannel array while single chargednanopore will be used in the physical domain.As the electrolytes with different concentrations are brought in contact or separated by ionexchange membrane, an electric potential is established. Based on the reverse electrodialysis,electricity can be harvested from this electric potential. The electricity generation based onreverse electrodialysis is the reversed operation as the current-voltage measurement describedabove. Therefore, the experimental setup and numerical model built will be extended toconstruct an electricity harvesting device based on reverse electrodialysis. The effects ofelectrolyte concentration ratio, flow velocity, pH value, size of electrolyte compartment, andconcentration of redox couples used for electron transport on the electricity generationefficiency will be examined both experimentally and numerically.