Emerging Porous Solid Electrolytes for Hydroxide Ion Transport

Abstract

Anion exchange membrane fuel cells (AEMFCs) offer several advantages over proton exchange membrane fuel cells, such as the use of a non‐precious metal catalyst, but these cells suffer from various issues related to OH–‐conducting electrolytes, including low conductivity and the formation of K2CO3 salt. These issues need to be resolved for the widespread use of AEMFCs. Recently, many studies have focused on developing excellent ion‐conductive electrolytes using porous materials based on metal–organic and covalent organic frameworks. However, most of this research is biased toward proton‐conducting electrolytes; to the best of the authors’ knowledge, reviews addressing OH–‐conducting electrolytes using porous materials have not been reported thus far. This review discusses OH–‐conducting porous crystalline materials and their membranes in terms of different synthetic strategies, conduction mechanisms, and experimental modalities for the design and development of future anion conductive electrolytes in fuel cells.

Crystal Channel Engineering for Rapid Ion Transport: From Nature to Batteries

“…Due to the high structural stability, large amounts of OH − ions can be trapped into the pores of these robust porous frameworks, resulting in a high ionic conductivity. Moreover, the combination of porous materials with polymer matrix to produce composite membranes is an effective solution for the design of practical OH − ‐mediating electrolytes, in which a reduced swelling ratio, a high mechanical strength, and a high OH − conductivity even at a low ion ion‐exchange capacity (IEC), can be approached [36] . Another typical example is the separation of fluoride (F − ) ions for water defluoridation via synthetic F − channels.…”

“…For example, the efficient hydrate ion (OH − ) transport is essential for high‐performance alkaline fuel cells. Figure 3d summarizes typical MOFs and covalent organic frameworks (COFs) based OH − ‐conducting porous crystalline materials [36] . Due to the high structural stability, large amounts of OH − ions can be trapped into the pores of these robust porous frameworks, resulting in a high ionic conductivity.…”

Advance of click chemistry in anion exchange membranes for energy application

“…21 However, the exact value of hydroxide conductivity is still uncertain due to the following reasons: (i) the hydroxide conductivity may be influenced by its side reaction with carbon dioxide when the membrane is exposed to the atmosphere; (ii) the functional groups may degrade at alkaline conditions or high temperature. 22 Due to the harsh working condition of AEMFCs, the chemical stability of AEMs should be carefully taken into accounts. 23 Coates and co-workers have investigated the degradation mechanisms for 26 kinds of organic cations under alkaline conditions, which provides valuable support to the design of alkaline-stable AEMs in the future.…”

Promoted Type I and II ROS Generation by a Covalent Organic Framework through Sonosensitization and PMS Activation

“…Porous organic materials including covalent organic frameworks (COFs) and porous organic polymers have strong potential as multifunctional platforms for a wide range of applications such as gas adsorption and separation, catalysis, and ion conduction due to their large surface area and tunable functionality. − Interestingly, a well-defined pore environment can facilitate rapid transport of ROS, improving sensitizer efficiency . Moreover, their large surface areas can contain large amounts of O 2 gas and can deliver O 2 to oxygen-poor microenvironments, supporting ROS generation even under hypoxic conditions such as solid tumor cell microenvironments. , In particular, the COF is an excellent platform because it is suitable for analyzing fundamental ROS mechanisms based on crystalline systems.…”