Pristine and Modified Porous Membranes for Zinc Slurry–Air Flow Battery

Abstract

The membrane is a crucial component of Zn slurry–air flow battery since it provides ionic conductivity between the electrodes while avoiding the mixing of the two compartments. Herein, six commercial membranes (Cellophane™ 350PØØ, Zirfon®, Fumatech® PBI, Celgard® 3501, 3401 and 5550) were first characterized in terms of electrolyte uptake, ion conductivity and zincate ion crossover, and tested in Zn slurry–air flow battery. The peak power density of the battery employing the membranes was found to depend on the in-situ cell resistance. Among them, the cell using Celgard® 3501 membrane, with in-situ area resistance of 2 Ω cm2 at room temperature displayed the highest peak power density (90 mW cm−2). However, due to the porous nature of most of these membranes, a significant crossover of zincate ions was observed. To address this issue, an ion-selective ionomer containing modified poly(phenylene oxide) (PPO) and N-spirocyclic quaternary ammonium monomer was coated on a Celgard® 3501 membrane and crosslinked via UV irradiation (PPO-3.45 + 3501). Moreover, commercial FAA-3 solutions (FAA, Fumatech) were coated for comparison purpose. The successful impregnation of the membrane with the anion-exchange polymers was confirmed by SEM, FTIR and Hg porosimetry. The PPO-3.45 + 3501 membrane exhibited 18 times lower zincate ions crossover compared to that of the pristine membrane (5.2 × 10−13 vs. 9.2 × 10−12 m2 s−1). With low zincate ions crossover and a peak power density of 66 mW cm−2, the prepared membrane is a suitable candidate for rechargeable Zn slurry–air flow batteries.

Anion Exchange Membranes Incorporating Multi N-Spirocyclic Quaternary Ammonium Cations via Ultraviolet-Initiated Polymerization for Zinc Slurry-Air Flow Batteries

“…The cell assembled with the PPO-6CH 2 -3x membrane exhibited an excellent maximum power density (153 mW/cm 2 ), which is higher than that of the cell assembled with the PPO-6CH 2 -2x (137 mW/cm 2 ) membrane due its higher OH – ion conductivity. The peak power density obtained is much higher than that of the cells employing commercial porous membranes . However, the cell was further optimized here, with the addition of an ionomer inside the electrode, which improves the electrochemical reaction kinetics.…”

“…The peak power density obtained is much higher than that of the cells employing commercial porous membranes. 23 However, the cell was further optimized here, with the addition of an ionomer inside the electrode, which improves the electrochemical reaction kinetics. Furthermore, the power density attained is one of the highest values reported for Zn-air batteries employing AEMs.…”

“…Furthermore, the power density attained is one of the highest values reported for Zn-air batteries employing AEMs. As summarized elsewhere, 19 various Zn-air batteries employing different AEMs, such as FAA-3-based AEM (Fumatech) (9.8 mW/cm 2 ), 69 AEM based on poly(vinyl alcohol)/guar hydroxypropyltrimonium chloride (50 mW/ cm 2 ), 70 QA-functionalized nanocellulose/graphene oxide AEM (44 mW/cm 2 ), 71 A201 tokuyama (33 mW/cm 2 ), 71 PPO− MPY (70 mW/cm 2 ), and ion-selective ionomer (PPO-3.45)coated Celgard 3501 membrane (66 mW/cm 2 ) 23 have been reported to show much lower peak power densities when compared to our membranes. It should be emphasized, however, that these tests were conducted under various operating conditions.…”

“…The utilization of porous membranes in Zn-air batteries has been reported to result in considerable Zn­(OH) 4 2– ion crossover, resulting in loss of capacity and blockage of air electrode by the formed ZnO particles ( ). To reduce the Zn­(OH) 4 2– ion crossover, various porous membrane modification strategies, including ion-selective polymer coating − and nanoparticle filling, have been attempted. These, on the other hand, have been linked to a decrease in ionic conductivity.…”

Mathematical Description of the Increase in Selectivity of an Anion-Exchange Membrane Due to Its Modification with a Perfluorosulfonated Ionomer

“…The electrostatic interactions between the −SO − 3 fixed groups of the PFSI and −N + (CH 3 ) 3 groups of the substrate membrane facilitate the penetration of the PFSI into macropores. When the PFSA solution is poured on the top of the membrane, it penetrates into it under the action of the gravitational and electrostatic forces, while the viscosity forces delay this penetration [68]. Over time, the solution fills the available pores and stops seeping through the membrane, so that some of it forms a film on the top side of the membrane.…”