Electric Field-Controlled Ion Transport In TiO₂ Nanochannel

On the basis of biological ion channels, we constructed TiO₂ membranes with rigid channels of 2.3 nm to mimic biomembranes with flexible channels; an external electric field was employed to regulate ion transport in the confined channels at a high ionic strength in the absence of electrical double layer overlap. Results show that transport rates for both Na⁺ and Mg²⁺ were decreased irrespective of the direction of the electric field. Furthermore, a voltage-gated selective ion channel was formed, the Mg²⁺ channel closed at −2 V, and a reversed relative electric field gradient was at the same order of the concentration gradient, whereas the Na⁺ with smaller Stokes radius and lower valence was less sensitive to the electric field and thus preferentially occupied and passed the channel. Thus, when an external electric field is applied, membranes with larger nanochannels have promising applications in selective separation of mixture salts at a high concentration

Balancing Osmotic Pressure of Electrolytes for Nanoporous Membrane Vanadium Redox Flow Battery with a Draw Solute

Vanadium redox flow batteries with nanoporous membranes (VRFBNM) have been demonstrated to be good energy storage devices. Yet the capacity decay due to permeation of vanadium and water makes their commercialization very difficult. Inspired by the forward osmosis (FO) mechanism, the VRFBNM battery capacity decrease was alleviated by adding a soluble draw solute (e.g., 2-methylimidazole) into the catholyte, which can counterbalance the osmotic pressure between the positive and negative half-cell. No change of the electrolyte volume has been observed after VRFBNM being operated for 55 h, revealing that the permeation of water and vanadium ions was effectively limited. Consequently, the Coulombic efficiency (CE) of nanoporous TiO₂ vanadium redox flow battery (VRFB) was enhanced from 93.5% to 95.3%, meanwhile, its capacity decay was significantly suppressed from 60.7% to 27.5% upon the addition of soluble draw solute. Moreover, the energy capacity of the VRFBNM was noticeably improved from 297.0 to 406.4 mAh remarkably. These results indicate balancing the osmotic pressure via the addition of draw solute can restrict pressure-dependent vanadium permeation and it can be established as a promising method for up-scaling VRFBNM application

Proton-Selective Ion Transport in ZSM‑5 Zeolite Membrane

The ionic ZSM-5 zeolite membranes were investigated for proton-selective ion separation in electrolyte solutions relevant to redox flow batteries. The zeolite membrane achieved exceptional selectivity for proton over V⁴⁺ (VO²⁺), Cr²⁺, and Fe²⁺ via size-exclusion at the zeolitic channel openings, and remarkably low area specific resistance resulted from its hydrophilic surface, copious extraframework protons, and micron-scale thickness. The ZSM-5 membrane, as a new type of ion separator, demonstrated substantially reduced self-discharge rates and enhanced efficiencies for the all-vanadium and iron–chromium flow batteries as compared to the benchmark Nafion membrane. Findings of this research show that ionic microporous zeolite membranes can potentially overcome the challenge of trade-off between ion selectivity and conductivity associated with conventional polymeric ion separators