An Ionic Diode Covalent Organic Framework Membrane for Efficient Osmotic Energy Conversion

Abstract

Heterogeneous membranes that exhibit an ionic diode effect are promising candidates for osmotic energy conversion. However, existing heterogeneous membranes lack molecular-level designed ion channels, thereby limiting their power densities. Here, we demonstrate ionic diode covalent organic framework (COF) membranes with well-defined ion channels, asymmetric geometry and surface charge polarity as high-performance osmotic power generators. The COF diode membranes are comprised of heterojunctions combining a positively charged ultrathin COF layer and a negatively charged COF layer supported by a porous COF nanofiber scaffold, exhibiting an ionic diode effect that effectuates fast unidirectional ion diffusion and anion selectivity. Density functional theory calculations reveal that the differentiated interactions between anions and COF channels contributed to superior I− transport over other anions. Consequently, the COF diode membranes achieved high output power densities of 19.2 and 210.1 W m–2 under a 50-fold NaCl and NaI gradient, respectively, outperforming state-of-the-art heterogeneous membranes. This work suggests the great potential of COF diode membranes for anion transport and energy-related applications.

Designing Nanofluidic Diode from a Hybrid‐Bilayer Covalent Organic Framework: Molecular Simulation Investigation

“…In a recent study, two oppositely charged COFs (TpPa-SO3Na and TpEB) with hundreds of nanometers were used to form an ionic diode and a rectification ratio ≈13 was achieved. [31] Finally, we should note that the COFs are considered to be treated as rigid. Despite the fact that such a treatment is commonly utilized in simulation studies, [28,29] framework flexibility is not taken into account.…”

“…[ 30 ] After the submission of the current study, an ionic diode COF membrane was reported by comprising two oppositely charged COFs (TpPa‐SO 3 Na and TpEB) and demonstrated efficient osmotic energy conversion. [ 31 ]…”

“…[30] After the submission of the current study, an ionic diode COF membrane was reported by comprising two oppositely charged COFs (TpPa-SO 3 Na and TpEB) and demonstrated efficient osmotic energy conversion. [31] It is worthwhile to note that the concept of nanofluidic diodes was introduced over two decades ago. [32] However, the underlying mechanism at a sub-nm scale remains obscure.…”

Monolayer-Assisted Surface-Initiated Schiff-Base-Mediated Aldol Polycondensation for the Synthesis of Crystalline sp2 Carbon-Conjugated Covalent Organic Framework Thin Films

“…Data are for C2DPs, 7 PyPa-SO 3 H/SANF, 28 bulk COF, 16 BDA-TAM, 58 monolayer COF, 59 and TpEB@TpPa-SO 3 Na. 60 Journal of the American Chemical Society selectivity coefficient decreases with the increase of the salinity gradient, which is mainly caused by the decrease of the Debye length with the increase of salt solution concentration. Encouraged by the high conductance, fast ion transport channels, and extremely stable frame structure of the resultant sp 2 c-COF films, the TFPT−TMT was selected to further fabricate an osmotic power generator in varied working environments at pH = 7, pH = 10, and pH = 14 with 50-fold NaCl salinity gradient.…”

“…(f) The permeable power generation performance of the TFPT−TMT membrane is compared with that of the imine-linked COF membrane reported recently. Data are for C2DPs,7 PyPa-SO 3 H/SANF,28 bulk COF,16 BDA-TAM,58 monolayer COF,59 and TpEB@TpPa-SO 3 Na 60.…”