Maximizing Ion Permselectivity in MXene/MOF Nanofluidic Membranes for High‐Efficient Blue Energy Generation

Abstract

Both ion permeability and selectivity of membranes are crucial for nanofluidic behavior. However, it remains a long‐standing challenge for 2D materials to balance these two factors for osmotic energy harvesting. Herein, the MXene/metal–organic framework (MOF) hybrid membranes are reported to realize efficient ion‐permselective nanofluidic system, leading to high‐performance osmotic power generator. In the system, zeolitic imidazolate framework‐8 (ZIF‐8) is deposited onto the MXene surface and intercalated between the MXene nanosheets by electropolymerization approach. The angstrom‐sized windows of ZIF‐8 layer act as ion selectivity filters, endowing the membrane with high cation selectivity by size effect. The intercalation of ZIF‐8 crystals, reduces the interspacing of MXene, therefore, not only enhancing the ion permeability by shortening the ion transport pathway through the membrane, but also further improving the selectivity by increasing the overlap effect of electric‐double layer. The maximum power density reaches up to 48.05 W m−2 under 500‐fold salinity gradient with a high permeability (1263.3 A m−2), and a high selectivity of 0.906 at 50‐fold is obtained. This study provides a facile method to fabricate nanofluidic 2D membranes with both high ion permeability and selectivity for water nexus energy conversion.

Vacancy Engineering for High-Efficiency Nanofluidic Osmotic Energy Generation

“…Meanwhile, the maximum power density reached 9.7, 5.91, and 3.84 W m −2 under testing areas of 0.03, 1, and 5 mm 2 , respectively (Figure S18b). Such a size effect on the power density widely exists in the previous reports, 31,32 which could be attributed to the stronger ion concentration polarization caused by pore−pore interactions under a large membrane size. 4 The stability of the V-NbP membrane was tested by an H cell configuration in Figure S9.…”

Interfacial Super-Assembly of Intertwined Nanofibers toward Hybrid Nanochannels for Synergistic Salinity Gradient Power Conversion

“…7−9 This worldwide blue energy can be gathered by nanofluidic systems with cation-or anion-exchange nanochannels using membrane technologies, such as pressureretarded osmosis (PRO) 10 and reverse electrodialysis (RED). 11,12 Among them, RED attracts significant attention as it can directly transform the electrochemical potentials into electrical energy, and its applications are closely related with the nature of the ion exchange nanochannel membranes. 13−17 In recent years, various ion exchange nanochannel membranes with enhanced ion selectivity and high mass flux, such as single-layer MoS 2 nanopores, 18 mesoporous carbon/anodic aluminum oxide (AAO), 19 ordered mesoporous silica/AAO, 20 heterogeneous MXene/PS-b-P2VP, 21 polyamide modified graphene oxide/AAO, 22 polymer polystyrenesulfonate (PSS) incorporated metal organic framework (MOF)/AAO, 23 bacterial cellulose nanofiber/GO, 24 and sulfonated poly(ether ketone)/AAO/polypyrrole composite membrane 25 devices.…”

“…Owing to the exhaustion of traditional nonrenewable resources and increasingly severe global environmental problems, it is necessary to strike a better balance between energy security, environmental protection, and economic development. − As an abundant, sustainable, renewable, and stable energy resource, salinity gradient energy between the seawater and river water, which is also known as “blue energy”, can be harvested. − In theory, 0.8 kW of energy can be produced from every cubic meter water since the chemical potential differences are constructed with the salt concentration differences, which is almost comparable with the hydrostatic pressure energy that is harvested from a 280 m high water column. − This worldwide blue energy can be gathered by nanofluidic systems with cation- or anion-exchange nanochannels using membrane technologies, such as pressure-retarded osmosis (PRO) and reverse electrodialysis (RED). , Among them, RED attracts significant attention as it can directly transform the electrochemical potentials into electrical energy, and its applications are closely related with the nature of the ion exchange nanochannel membranes. − In recent years, various ion exchange nanochannel membranes with enhanced ion selectivity and high mass flux, such as single-layer MoS 2 nanopores, mesoporous carbon/anodic aluminum oxide (AAO), ordered mesoporous silica/AAO, heterogeneous MXene/PS- b -P2VP, polyamide modified graphene oxide/AAO, polymer polystyrenesulfonate (PSS) incorporated metal organic framework (MOF)/AAO, bacterial cellulose nanofiber/GO, and sulfonated poly­(ether ketone)/AAO/polypyrrole composite membrane have been explored to assemble into salinity gradient power conversion devices. However, not only the competition of selectivity and permeability but also the instability and high cost of these nanochannel membranes have led to the low power density and further limit their realistic scale-up applications. , Thus, it is still necessary to develop a new type of nanochannel membrane through designing and controlling the characteristics of the nanomaterials to handle these practical challenges. , …”

Promoting osmotic energy conversion through fluorinated nanochannel membranes with large-scale exfoliation and low transmission resistance

“…30 Zhou et al used intercalated ZIF-8 to shorten the transport pathway of ions in a MXenes membrane and obtained a ∼3.9 kΩ internal resistance and high output power density. 31 Wu et al and Wen et al showed that PVMs 16 and holey GO 17 nanosheets can be reconstituted as low-resistance nanochannels, respectively. Tam et al and Wen et al realized the reduction of transport resistance by enlarging the nanochannel space through bulky cellulose nanocrystals (CNC) 22 and cellulose nanofibers (CNF), 23 respectively.…”