iTechGuides is reader-supported. When you buy through links on our site, we may earn an affiliate commission. As an Amazon Associate I earn from qualifying purchases. Learn more
Nanofiltration has been studied as a way to improve the separator membranes in all-vanadium redox flow batteries. A 2011 study reported that membranes with smaller pore-size distributions had greater vanadium-ion/proton selectivity, and that cells using the prepared membranes performed comparably to commercialized Nafion. That is a promising research result, not proof that nanofiltration separators are widely used in batteries today.
What nanofiltration means for energy storage
Here, nanofiltration (NF) refers to a membrane approach investigated for redox flow batteries—not a general-purpose upgrade for every kind of energy-storage system. The directly relevant evidence concerns all-vanadium redox flow batteries (VRBs), which keep their energy-storing electrolytes in separate positive and negative compartments.
A separator sits between those compartments. It needs to restrict the movement of redox-active species from one side to the other while allowing charge-balancing ions to pass. Unwanted crossover can undermine battery operation; restricting ion movement too much can also impede the transport needed for the cell to work.
Free tools Windows power users keep installed
One-click scans. No signup required.
How pore-size exclusion can change transport
The 2011 study by Zhang and colleagues investigated NF membranes as an alternative to traditional ion-exchange membranes. Its proposed mechanism was pore-size exclusion: controlling the membrane’s pore-size distribution changes how readily different ions cross it, including vanadium ions and protons.
#1 Best Overall
The paper’s abstract states: “The results showed that membranes show increasing vanadium ion/proton (V/H) selectivity with decreasing pore size distribution.” In other words, the study reported greater selectivity as the pore-size distribution decreased. This is a relative-transport finding, not a quantified claim about how much a battery’s capacity, efficiency, or stored energy improves.
What the 2011 battery results establish
Zhang et al. reported that VRB cells assembled with their prepared NF membranes showed performance comparable to commercialized Nafion. The finding suggests that a pore-size-designed separator could be a viable research direction for this battery chemistry. It does not establish present-day commercial deployment, broad market adoption, or that every NF membrane would work as a battery separator.
The distinction matters because “nanofiltration” alone does not specify the membrane’s chemistry, transport properties, durability, or suitability for a particular electrolyte. A membrane made for water treatment should not be assumed to be compatible with a redox flow battery.
Why selectivity is only one part of the design
A battery separator must balance selective transport with the practical demands of cell operation. Reviews of redox-flow-battery membranes identify several relevant properties:
- Active-species crossover: how effectively the membrane limits redox-active material moving between electrolyte compartments.
- Ionic conductivity: whether charge-balancing ions can pass readily enough to support battery operation.
- Stability: whether the membrane can withstand the chemical and mechanical conditions it encounters.
- Electrolyte uptake and water uptake: how interaction with the electrolyte affects membrane behavior.
- Ion-exchange capacity: a membrane property relevant to ion transport.
- Sustainability and cost: practical considerations alongside electrochemical performance.
These are connected design trade-offs, not a single score. A separator that improves selectivity may still be unsuitable if it compromises conductivity, stability, or another requirement.
Why results may not transfer to other flow batteries
The reported NF result is specific to aqueous all-vanadium flow batteries. It should not be treated as proof of performance in non-aqueous redox flow batteries, where membrane design has additional chemistry-dependent constraints. A 2022 review identifies solvent uptake, ion transport, and redox-species permeability as critical factors for non-aqueous systems and describes high-performance membranes as an ongoing challenge.
Accordingly, membrane suitability has to be assessed for the battery’s operating chemistry. A promising result with vanadium and protons cannot establish performance with different solvents, electrolytes, or redox-active species.
The Tool Desk
Outbyte PC Repair FREERepair Windows errors before they cause bigger problemsFix Now →Outbyte Driver Updater FREEScan for outdated or missing drivers - takes under a minuteDriver Scan →How to interpret claims about NF separators
When evaluating a claim that nanofiltration improves energy storage, check what was measured and for which system. The evidence described here supports a specific reported selectivity trend and a cell-performance comparison in a 2011 VRB study. It does not provide a percentage improvement in energy storage, a current product ranking, or evidence of widespread commercial use.
For a meaningful comparison between an NF separator and an ion-exchange or other porous membrane, the relevant axes include vanadium-ion/proton selectivity, ionic conductivity, active-species crossover, chemical and mechanical stability, electrolyte uptake, operating chemistry, and cost. These are comparison criteria identified in membrane reviews, not a head-to-head ranking of products.
Quick Recap
Sources
- Zhang et al., “Nanofiltration (NF) membranes: the next generation separators for all vanadium redox flow batteries (VRBs)?,” Energy & Environmental Science, first published 1 April 2011.
- “Redox Flow Battery Membranes: Improving Battery Performance by Leveraging Structure–Property Relationships,” ACS Energy Letters, issue publication 8 January 2021.
- “Membranes for Redox Flow Battery Applications,” Membranes, 2012.
- “Membrane design for non-aqueous redox flow batteries: Current status and path forward,” Chem, published online 29 April 2022; issue dated 9 June 2022.
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.
