Prospects for Alkaline Anion‐Exchange Membranes in Low Temperature Fuel Cells

Abstract

This article introduces the radical approach of applying alkaline anion-exchange membranes (AAEMs) to meet the current challenges with regards to direct methanol fuel cells (DMFCs).A review of the literature is presented with regards to the testing of fuel cells with alkaline membranes (fuelled with hydrogen or methanol) and also to candidate alkaline anionexchange membranes for such an application. A brief review of the directly related patent literature is also included. Current and future research challenges are identified along with potential strategies to overcome them. Finally, the advantages and challenges with the direct electrochemical oxidation of alternative fuels are discussed, along with how the application of alkaline membranes in such fuel cells may assist in improving performance and fuel efficiency. KeywordsLow temperature, Alkaline anion-exchange membrane, Direct methanol fuel cell, Polymer electrolyte fuel cell.

Highly Stable, Anion Conductive, Comb-Shaped Copolymers for Alkaline Fuel Cells

“…7,8 Alkaline fuel cells (AFCs) have received significant interest in recent years relative to acidic fuel cells, 9−14 because of advantages when operating under alkaline conditions, which include enhancement of the electrode reaction kinetics, especially at the cathode, and the catalysts are not subjected to corrosion at high pH. 9,12,13 Consequently, non-noble metals or inexpensive metal oxides can be used as catalysts to greatly reduce the cost of the device. 13−16 In addition, high energy density liquids and gases such as ethanol, hydrazine, and ammonia can be adopted as fuels.…”

Alkali resistant and conductive guanidinium-based anion-exchange membranes for alkaline polymer electrolyte fuel cells

“…Polymer electrolyte membrane fuel cells are attracting increasing attention as a clean energy generation technology due to their high energy conversion efficiencies, low local pollution levels, low noise and low maintenance costs [1]. Recently, fuel cells containing anion-exchange membranes (APEFCs) are gaining international recognition as they promise to overcome the disadvantages of Nafion-based proton exchange membrane fuel cells (PEMFCs) such as low CO tolerance, high electro kinetic over potentials, high fuel permeation and catalyst cost [2].…”

“…Recently, fuel cells containing anion-exchange membranes (APEFCs) are gaining international recognition as they promise to overcome the disadvantages of Nafion-based proton exchange membrane fuel cells (PEMFCs) such as low CO tolerance, high electro kinetic over potentials, high fuel permeation and catalyst cost [2]. The existence of an alkaline environment in APEFCs presents several advantages compared with PEMFCs: Enhanced cell efficiency, expanded range of the viable cathode catalysts and fuels, depressed fuel crossover and more facile fuel oxidation [1,[3][4][5][6][7]. These advantages increase the probability of reducing the costs of APEFCs compared to the better known PEMFCs.…”

“…Over the last 10 years, alkaline anion-exchange membranes (AAEM), the core component of APEFCs, have been extensively studied and considerable advances have been made [1,8]. Among the variety of methods used for AAEM synthesis, an important and common method is to modify an existing base polymer, such as poly(phthalazinon ether sulfone ketone) (PPESK) [9], polysulfone (PS) [10] and poly(ether ketone) (PEK) [11].…”

“…Typically, the AAEMs are synthesized via chloromethylation of the pristine polymers and subsequent exposure to trimethylamine (TMA) to form the desired benzyltrimethyl-type quaternary ammonium (QA) head-groups [9][10][11]. However, there are three potential disadvantages with the use of AAEMs: (1) The commonly used chloromethyl methyl ether, used for the chloromethylation step, is a carcinogen and highly harmful to human health (its use has been restricted since 1970s) [12]; (2) The poor stability of the QA head-groups (the most commonly encountered) in alkaline environments is caused by the attack on the quaternary ammonium groups by the strongly nucleophilic OH -anions via direct nucleophilic displacements, Hofmann elimination reactions, and/or minor side-reactions involving ylide-intermediates [1,[13][14][15]; (3) The lower ionic conductivities observed are due to the weak alkalinity of QA hydroxides (cf. the strong acidity of the perfluorosulfonic acid groups in PEMs) and resultant poor self-dissociation capability (e.g.…”