Anion Exchange Membranes for Fuel Cells: State‐of‐the‐Art and Perspectives

Abstract

Technological developments showed that fuel cells are effective sources of power for medium-to large-scale backup power and vehicular applications (e.g., automobiles and buses). [4] In particular, fuel-cellpowered electric vehicles have a longer driving range and shorter refueling time than rechargeable battery-powered vehicles. For example, Toyota has reported that its hybrid fuel cell vehicle can drive up to 830 km powered by 5 kg of H 2 at a pressure of less than 700 bar. [5,6] In this Perspective, we analyze progress in the development of fuel cells fabricated from polymer electrolyte membranes, which run at relatively low temperature (60-90 °C), start up fast, and are portable, and have thus drawn much attention for their potential commercial applications. [7] Proton exchange membrane fuel cells (PEMFCs) have proven successful for transportation and power generation applications, owing to their high power output, compact design, and lightweight cells. Their high performance is due to their use of Nafion, a sulfonated tetrafluoroethylene-based fluoropolymer-copolymer with outstanding chemical stability [8] and excellent proton (H + ) conductivity. [9] PEMFCs' high power output has been demonstrated in stationary, portable, and high-demand devices, and in consumer vehicles. [10][11][12] However, PEMFC membranes and catalysts are expensive, and this has hindered the broader adoption of PEMFC technology by the market. Specifically, PEMFC stacks (i.e., combinations of multiple PEMFCs) are expensive due to their requirement for platinum-group metal (PGM) catalysts and fluorocarbon membranes, which account for 40% and 11% of a cell's cost, respectively, and translate to high vehicle prices. [13,14] As a result, manufacturers are attempting to meet market demand for cheaper PEMFCs by lowering their content of PGM catalysts (or eschewing PGM catalysts entirely) and avoiding their use of fluorocarbon membranes. As an alternative to the use of H + in ion transport, the corresponding redox reactions of hydroxide (OH − ) ions have received attention. Fuel cells with OH − -transporting membranes are termed anion exchange membrane fuel cells (AEMFCs). The working principles of AEMFCs are slightly different from those of PEMFCs, but their overall redox bases are the same. In an AEMFC, water and oxygen are fed into the cathode for reduction to OH − , which then travel through the AEM to the anode to meet the fuel, H 2 , which is oxidized to generate electricity, with water as a byproduct. [15][16][17][18] In contrast to PEMFCs, AEMFCs use cationic Fuel cell technology is a clean way of generating energy and should enable carbon neutrality. However, although traditional proton exchange membrane fuel cells (PEMFCs) have made a commercial impact, their high cost hinders their wider adoption. Fuel cells that use anion exchange membranes (AEMs) are a promising alternative to PEMFCs, as they can achieve the same performance at a lower cost. In this Perspective, recent trends in the fabrication of polymer-based high-performance AEM...

Molecular-Level Control over Oxygen Transport and Catalyst–Ionomer Interaction by Designing Cis–Trans Isomeric Ionomers

“…5 Polymer electrolytes used as the anion exchange membrane (AEM) and electrode binder play a critical role in the overall performance of AEMFCs. 6,7 The past few decades have witnessed substantial progress in the development of AEMs and AEMFC catalysts. However, systematic studies of the ionomer binders in the catalyst layers (CLs) are rarely touched (Figure S4; there has been increasing research interest in AEMs and especially electrochemical catalysts in the past decade, while studies on ionomer binders are inadequate).…”

“…Anion exchange membrane fuel cells (AEMFCs) have been priority advocated in the past decades, as their superior oxygen reduction reaction (ORR) kinetics enables the use of nonprecious metal catalysts under an alkaline environment. − Nevertheless, the performance of AEMFCs remains a significant technical hurdle for their commercialization . Polymer electrolytes used as the anion exchange membrane (AEM) and electrode binder play a critical role in the overall performance of AEMFCs. , The past few decades have witnessed substantial progress in the development of AEMs and AEMFC catalysts. However, systematic studies of the ionomer binders in the catalyst layers (CLs) are rarely touched (Figure S4; there has been increasing research interest in AEMs and especially electrochemical catalysts in the past decade, while studies on ionomer binders are inadequate).…”

Polyfluorenes Bearing N,N-Dimethylpiperidinium Cations on Short Spacers for Durable Anion Exchange Membranes

“…Operating under alkaline conditions avoids the very corrosive environments of the corresponding acidic systems, which require the use of expensive and rare metals for corrosion protection and catalysis. One of the most critical components of both AEMFCs and AEMECs is the anion exchange membrane (AEM) which significantly affects the durability and performance of the systems . AEMs usually consist of a polymer backbone tethered with suitable cationic groups having hydroxide (OH – ) as counterions .…”

Efficient Synthesis of High-Performance Anion Exchange Membranes by Applying Clickable Tetrakis(dialkylamino)phosphonium Cations

“…Anion exchange membranes (AEMs) are used in fuel cells and electrolyzers as the core components for selective ion conduction. The development of high-performance AEMs is critical for the commercialization of these electrochemical devices [ 3 ]. High-performance AEMs should have the following requirements: (1) Proper mechanical and physical properties: An AEM should be a thin film that is not too brittle, nor too soft.…”

“…The conductivity of some commercial products has already reached or exceeded 100 mS cm −1 at 60 [ 5 ]. However, the majority of reported AEMs are based on quaternary ammonium (QA) ion structures and simple imidazolium (IM) ions [ 3 ], most of which are prone to degradation under alkaline conditions. The degradation of cations is the main reason for the loss of conductivity.…”