Progress of Alkaline Anion Exchange Membranes for Fuel Cells: The Effects of Micro-Phase Separation

Abstract

Compared with that of proton exchange membrane fuel cells (PEMFCs), alkaline anion exchange membrane fuel cells (AEMFCs) with alkaline anion exchange membranes (AEMs) as electrolytes are attracting increased attention due to their potential use as non-precious catalysts. As one of the key components of AEMFCs, an ideal AEM must possess high hydroxide conductivity, good thermal stability, sufficient mechanical stability, and excellent long-term durability at elevated temperatures in an alkaline environment. Until now, a large number of AEMs with various chemical structures and properties have been prepared, and studied in detail, and it has been found that the microphase separation structure greatly affected the performance of AEMs. This minireview provides recent progress made of AEMs with hydrophilic/hydrophobic microphase separation structure. The hydroxide conductivity, alkaline stability, and mechanical properties of AEMs could be improved due to the formation of hydrophilic/hydrophobic microphase separation in the membranes. The relationship among the microphase separation, the chemical structure of the polymers, and the performance of membranes has been discussed in detail. This article attempts to give an overview of some key factors for the future design of novel AEMs with excellent performance such as high conductivity and improved chemical stability.

On the evolution of sulfonated polyphenylenes as proton exchange membranes for fuel cells

“…6 This review does not include the growing field of research focused on anion exchange membranes, for which comprehensive reviews also exist. 34,35,36 For clarity and comparison, we categorize the diverse number of sulfonated polyphenylene (SPP) variants into generalized classes: (i) linear, (ii) kinked, (iii) side-chain sulfonated, (iv) postsulfonated phenylated, and (v) pre-sulfonated phenylated, as shown in Table 1. Commercialization of sulfonated polyphenylenes (SPP)s has been several decades in the making, starting with the early work of G. Goldfinger on linear poly(p-phenylene)s, 74,75 and W. Ried, [76][77][78] as well as J. K. Stille, [79][80][81] on phenylated polyphenylenes in the late 1940s to early 1970s, to the first ever reported post-sulfonation of a phenylated polyphenylene in 1972, 82 through to reinforced SPPs produced by Ionomr Innovations, Inc., announced in 2020, 83,84 as illustrated in the timeline shown below (Figure 3).…”

“…Timeline for evolution of sulfonated polyphenylenes. 28,29,30,36,[71][72][73][74][75][76][77][78][79] Corresponding authors from each publication are named.…”

Nanocomposite Anion Exchange Membranes with a Conductive Semi-Interpenetrating Silica Network

“…Formation of the composite membrane. A quantity of 0.12 mL of the previous solution, containing 6.0 × 10 −5 mol of TMSP and 2.0 × 10 −5 mol of AEAPS was added to 8 mL of PSU-TMA solution (0.05 M in DMSO, 4.0 × 10 −4 mol) and heated at 60 • C for 30 min. The transparent and uniform solution was transferred into a Petri dish and heated at 90 • C for 12 h in an oven.…”

“…Anion exchange membranes (AEM) are extensively investigated for their well-known advantages when used in electrochemical devices, including the absence of noble metal catalysts for the oxygen reduction reaction in fuel cells [ 1 , 2 , 3 , 4 , 5 , 6 ]. However, the drawbacks of these ionomeric materials limit their extensive use and the replacement of proton exchange membranes in commercial devices [ 7 , 8 ].…”

Silica Containing Composite Anion Exchange Membranes by Sol–Gel Synthesis: A Short Review

“…Anion exchange membranes (AEM) are important materials for applications in energy and in the environment [ 1 , 2 , 3 , 4 ]. In electrochemical energy technologies, they are used as ion-conducting separators between the electrode compartments physically impeding the mixture of electrolyte solutions in redox flow batteries [ 5 , 6 , 7 , 8 , 9 , 10 ] or gases (hydrogen and oxygen) in anion exchange membrane fuel cells (AEMFC) and water electrolyzers [ 11 , 12 , 13 , 14 ]. In this case, the major requirements are a high ionic conductivity in order to reduce as much as possible the Ohmic drop during current flow; and a low permeability to reactants, i.e., electrochemically active ions in a redox flow battery or a low hydrogen and oxygen permeability in AEMFC.…”