Anion Exchange Membranes with 1D, 2D and 3D Fillers: A Review

Abstract

Hydroxide exchange membrane fuel cells (AEMFC) are clean energy conversion devices that are an attractive alternative to the more common proton exchange membrane fuel cells (PEMFCs), because they present, among others, the advantage of not using noble metals like platinum as catalysts for the oxygen reduction reaction. The interest in this technology has increased exponentially over the recent years. Unfortunately, the low durability of anion exchange membranes (AEM) in basic conditions limits their use on a large scale. We present in this review composite AEM with one-dimensional, two-dimensional and three-dimensional fillers, an approach commonly used to enhance the fuel cell performance and stability. The most important filler types, which are discussed in this review, are carbon and titanate nanotubes, graphene and graphene oxide, layered double hydroxides, silica and zirconia nanoparticles. The functionalization of the fillers is the most important key to successful property improvement. The recent progress of mechanical properties, ionic conductivity and FC performances of composite AEM is critically reviewed.

Keywords: AEMFCs; LDH; MOF; carbon dots; carbon nanotubes; graphene oxide; silica; zirconia.

Figure 1

(a) Number of publications and (b) number of citations on the topic “composite anion exchange membranes” (from ISI Web of Science 2021).

Figure 2

TEM images of (a) halloysite nanotubes and (b) quaternized halloysite nanotubes. Reproduced with permission from Ref. [23].

Figure 3

Effect of MWCNT addition in PVA on DMAFC performance at 30 °C (anode: 2 M MeOH in 6 M KOH, flow rate of 5 mL min⁻¹; cathode: humidified O₂, flow rate of 100 mL min⁻¹). Reproduced with permission from Ref. [24].

Figure 4

Synthesis of ionic liquids functionalized CNTs (IL-(M;B)@CNT). Reproduced with permission from Ref. [34].

Figure 5

Preparation of LDH coated carbon nanotubes (LDH@CNTs). Reproduced with permission from Ref. [42].

Figure 6

Conductivity measurements at 60 °C as a function of RH% of membranes after treatment at 25 °C in 2 M KOH for 24 h. Reproduced with permission from Ref. [37].

Figure 7

Hydroxide conductivity variations vs. time of TC-PPO and hybrid membranes with ASU-LDH at 30 °C. Reprinted with permission from Ref. [45]. Copyright (2018) American Chemical Society.

Figure 8

Comparison between conventional and novel MEAs. (a) Polarization and power–density curves; (b) constant current discharge curves (O₂, current density 700 mA cm⁻²). Reproduced from Ref. [77] with permission from The Royal Society of Chemistry.

Figure 9

Modification process of GO via free radical polymerization-grafting with a b-VIB group. Reproduced with permission from Ref. [87].

Figure 10

SEM images (A) and fiber diameter distribution (B) of QPPO–SiO₂; optical photographs of nanofiber mats (C) and membrane (D) after hot-press. Reproduced with permission from Ref. [102].

Figure 11

Effect of exposure to (1.5 M VO₂⁺ + 3 M H₂SO₄) at 30 °C on sulfate ion conductivity of QPEK-C and QPEK-C/10–40 wt% TMSP-TMA⁺ composite membranes. Reproduced with permission from Ref. [110].

Figure 12

DMFC curves of QPVA/10 wt% Al₂O₃ composite membrane with various fuels (4 M KOH + x M CH₃OH) at 25 °C and in ambient air. Reproduced with permission from Ref. [111].

Figure 13

DBFCs performances for CoOOH⁻ functionalized and pristine membranes. V (a) and power density (b) as a function of discharge current density at 30 °C. Reproduced with permission from Ref. [128].

Figure 14

Synthesis of ion-exchange polymer (PVBTAH) inside the porous network of ZIF-8. Reprinted with permission from Ref. [133]. Copyright (2014) American Chemical Society.

Figure 15

Synthesis of CDs and QCDs. Reproduced with permission from Ref. [139].