逆向電透析藍色能源轉換(或滲透能源轉換)是一種能將儲存在海水和河水間濃度梯度差化學勢能利用離子選擇薄膜來收集之新穎技術，然而，目前對離子選擇薄膜的研究仍存在離子選擇性、離子通量差和電阻高等問題。為了提高離子選擇性，過去報導了數種基於層狀二維材料堆疊而成之次奈米孔洞薄膜；然而，這些二維奈米片堆疊而成的離子擴散路徑過長，導致系統離子通量較差，進而使這些基於層狀二維材料的離子選擇薄膜能實現的功率輸出仍然有限。為了解決這個問題，我們開發了兩種新型二維金屬有機框架(metal organic framework，簡稱MOF)所組成之複合薄膜，包括(i)二維Ti3C2Tx MXene和二維Cu-TCPP MOF複合薄膜（在此稱為MXCT）、與(ii)芳綸奈米纖維(aramid nanofiber，簡稱ANF)和二維Cu-TCPP MOF複合薄膜（在此稱為 AMOF），此兩薄膜與在水溶液中極不穩定的傳統 Cu-TCPP MOF薄膜相比，由於所設計分子之間存在強氫鍵，在電解質溶液中皆具有高穩定性，也驗證此兩類以二維MOF材料為基準之複合薄膜在藍色能源轉換應用上深具潛力。得益於二維Cu-TCPP MOF奈米片中豐富且有序的次奈米離子通道，我們驗證此兩種複合薄膜皆具有比獨立式Ti3C2Tx MXene 薄膜和 ANF 薄膜具有更高離子選擇性、離子傳輸通量、和更低的電阻，通過混合人工海水和河水(50倍NaCl濃度梯度)，MXCT和AMOF皆分別可實現高達8.12和10.1 W/m2的驚人高滲透功率輸出密度，此兩數值皆明顯高於商業基準(5 W/m2)，並且優於過去文獻中報導過的所有最先進離子選擇性薄膜。此外，我們也驗證MXCT和AMOF均顯示出連續 7 天收集滲透能源的高穩定性，展示出長期運行實際應用的潛力。上述成果證明了基於二維Cu-TCPP MOF所組成之複合薄膜在高選擇性和高性能藍色滲透能源發電中具有高應用前景。

Chemical potential energy stored in a concentration gradient between seawater and river water can be harvested using an ion-selective membrane, and this reverse electrodialysis-based technique is also called the blue energy conversion (or osmotic energy conversion). However, the current investigations of ion-selective membranes suffer from poor ion selectivity, inferior ionic flux and high resistance. To enhance up ion selectivity, sub-nanometer-scale pore membranes based on several types of the two-dimensional (2D) materials have been reported. However, the power output achieved from these 2D material-based membranes is still limited because of the inferior ionic flux caused by the tortuous interlayer ion diffusion pathway. To resolve this issue, we develop two novel types of 2D metal-organic framework (MOF) based composite membranes, including (i) 2D Ti3C2Tx MXene and Cu-TCPP MOF (named as MXCT) and (ii) aramid nanofibers (ANF) and 2D Cu-TCPP MOF (named as AMOF). In contrast to the conventional Cu-TCPP membrane which is unstable in aqueous solution, both the 2D Cu-TCPP composite membranes exploited are highly stable in salty solutions due to the existence of strong hydrogen bonding between engineered molecules. This indicates the potential use of these 2D MOF composites as blue energy conversion membranes. Benefiting from abundant, ordered sub-nm ion channels in 2D Cu-TCPP nanosheets, both the 2D MOF composite membranes show much higher ion selectivity, higher ionic flux, and lower resistance than the pure free-standing Ti3C2Tx MXene and ANF membranes. By mixing artificial seawater and river water (50-fold NaCl gradient), the amazingly high osmotic power densities up to 8.12 and 10.1 W/m2 can be achieved for the MXCT and AMOF, respectively. Both of these two values are apparently higher than the commercial benchmark (5 W/m2) and outperform all of the state-of-the-art ion-selective membranes reported in the literatures. In addition, both the 2D MOF composite membranes (MXCT and AMOF) reveal high stability in harvesting osmotic energy for continuous 7 days, demonstrating the potential of long-term operation for practical application. These works demonstrate the promising utilization of 2D Cu-TCPP MOF composite membranes for highly selective and high-performance osmotic power generation.

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