Anion Exchange Composite Membranes Composed of Quaternary Ammonium-Functionalized Poly(2,6-dimethyl-1,4-phenylene oxide) and Silica for Fuel Cell Application

Robust anion exchange membranes based on ionic liquid grafted chitosan/polyvinyl alcohol/quaternary ammonium functionalized silica for polymer electrolyte membrane fuel cells

In this study, 1-bromohexyl-1methylpiperidinium bromide (Br-6-MPRD) ionic liquid grafted quaternized chitosan (QCS) and polyvinyl alcohol (PVA) blends were composited with glycidyl trimethyl ammonium chloride (GTMAC) quaternized silica (QSiO2) at different dosages. Glutaraldehyde (GA) crosslinked the membranes and then processed into hydroxide form with an aqueous potassium hydroxide solution. The resultant IL-QCS/PVA/QSiO2 membranes exhibit significantly improved ionic conductivity, moderate water absorption and swelling ratio compared with the pristine IL-QCS/PVA anion exchange membrane (AEM). Among them, the hydroxide ion conductivity and power density of IL-QCS/PVA/QSiO2-7 membrane can reach up to 78 mS cm-1 at 80 °C and 115 mW cm-2 at 60 °C respectively. In addition, IL-QCS/PVA/QSiO2 membranes have excellent thermal, mechanical, and chemical stabilities, which can meet the application requirements of AEM for fuel cells.

Molecular Dynamics Study on the Effect of Cyclic Conducting Moieties on Poly(2,6-dimethyl-1,4-phenylene oxide) Anion Exchange Membranes

We investigate PPO quaternized with different azoles (five-membered heterocyclic compounds) with a different odd number of Nitrogen atoms (1N-pyrrole, 3N-1,2,3-triazole, and 5N-pentazole) to form pyrrolium-PPO(py-PPO), 1,2,3,-triazolium-PPO(tri-PPO) and pentazolium-PPO(pen-PPO) AEMs, using molecular dynamics (MD) simulations to compare and evaluate their OH- transport via the vehicular mechanism. OH- diffusivity at the hydration level λ = 12 is 3.10 × 10-10 m2/s, 1.92 × 10-10 m2/s m2/s, and 1.91 × 10-10 m2/s for py-PPO, tri-PPO, and pen-PPO, respectively. This trend is due to the shorter distance between adjacent groups of py-PPO (7.5 Å) leading to an efficient hydroxide transport than tri-PPO (7.8 Å) and pen-PPO (8.1 Å) at λ = 12. Also, this trend is justified by the smaller average number of clusters for py-PPO (1.2), smaller than tri-PPO(2.0), and pen-PPO (1.5) at λ = 12, which suggests better connectivity and hence better conductivity.

Heterogeneous Anion-Exchange Membranes with Enhanced Ion Conductivity for Continuous Electrodeionization

In this study, the optimal fabrication parameters of a heterogeneous anion-exchange membrane (AEM) using an ionomer binder are investigated to improve the performance of continuous electrodeionization (CEDI) for producing ultrapure water. Poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) is selected as the base material for preparing the ionomer binder and quaternized to have various ion exchange capacities (IECs). The optimal content of ion-exchange resin (IER) powder according to the IEC of the ionomer binder is then determined through systematic analyses. In conclusion, it is revealed that a heterogeneous AEM with optimal performance can be fabricated when the IEC of the ionomer binder is lowered and the content of IER powder is also lower than that of conventional heterogeneous membranes. Moreover, crosslinked quaternized PPO (QPPO) nanofiber powder is used as an additive to improve ion conductivity without deteriorating the mechanical properties of the membrane. The membrane fabricated under optimal conditions exhibits significantly lower electrical resistance (4.6 Ω cm2) despite a low IER content (30 wt%) compared to the commercial membrane (IONAC MA-3475, 13.6 Ω cm2) while also demonstrating moderate tensile strength (9.7 MPa) and a high transport number (ca. 0.97). Furthermore, it is proven that the prepared membrane exhibits a superior ion removal rate (99.86%) and lower energy consumption (0.35 kWh) compared to the commercial membrane (99.76% and 0.4 kWh, respectively) in CEDI experiments.

Recent Developments on Bioinspired Cellulose Containing Polymer Nanocomposite Cation and Anion Exchange Membranes for Fuel Cells (PEMFC and AFC)

Hydrogen fuel cell (FC) technologies are being worked on as a possible replacement for fossil fuels because they produce a lot of energy and do not pollute the air. In FC, ion-exchange membranes (IEMs) are the vital components for ion transport between two porous electrodes. However, the high production cost of commercialized membranes limits their benefits. Various research has focused on cellulose-based membranes such as IEM with high proton conductivity, and mechanical, chemical, and thermal stabilities to replace the high cost of synthetic polymer materials. In this review, we focus on and explain the recent progress (from 2018 to 2022) of cellulose-containing hybrid membranes as cation exchange membranes (CEM) and anion exchange membranes (AEM) for proton exchange membrane fuel cells (PEMFC) and alkaline fuel cells (AFC). In this account, we focused primarily on the effect of cellulose materials in various membranes on the functional properties of various polymer membranes. The development of hybrid membranes with cellulose for PEMFC and AFC has been classified based on the combination of other polymers and materials. For PEMFC, the sections are associated with cellulose with Nafion, polyaryletherketone, various polymeric materials, ionic liquid, inorganic fillers, and natural materials. Moreover, the cellulose-containing AEM for AFC has been summarized in detail. Furthermore, this review explains the significance of cellulose and cellulose derivative-modified membranes during fuel cell performance. Notably, this review shows the vital information needed to improve the ion exchange membrane in PEMFC and AFC technologies.

Imidazolium-Quaternized Poly(2,6-Dimethyl-1,4-Phenylene Oxide)/Zeolitic Imidazole Framework-8 Composite Membrane as Polymer Electrolyte for Fuel-Cell Application

Anion exchange membrane fuel cells (AEMFCs) are considered superior to their counterpart proton exchange fuel cells due to their many advantages. Both fuel cells use membranes as polymer electrolytes to improve fuel-cell properties and power output. This work evaluates a series of imidazolium-quaternized poly(2,6-dimethyl-1,4-phenylene oxide) (ImPPO) functionalized zeolitic imidazole framework-8 (ZIF-8) (ImPPO/ZIF-8) as anion exchange membrane (AEM) electrolytes in a direct methanol alkaline fuel cell. FTIR and 1H NMR were used to confirm the successful membrane fabrication. SEM and TGA were used to study the morphological and thermal stability properties of the ImPPO/ZIF-8 membranes. The AEMs obtained in this work had contact angles ranging from 55.27–106.73°, water uptake from 9–83%, ion exchange capacity (IEC) from 1.93–3.15 mmol/g, and ion conductivity (IC) from 1.02–2.43 mS/cm. The best-performing membrane, ImPPO/3%ZIF-8, showed a water uptake of up to 35% at 80 °C, a swelling ratio of 15.1% after 72 h, IEC of 4.06 mmol/g, and IC of 1.96 mS/cm. A power density of 158.10 mW/cm2 was obtained. This makes ZIF-8 a good prospect as a filler for enhancing membrane properties.