Room-temperature superprotonic conductivity in COOH-functionalized multicomponent covalent organic frameworks

TL;DR

A new type of material with carboxylic acid groups shows high proton conductivity at room temperature, which could be useful for energy applications.

Contribution

The first general strategy to achieve superprotonic conductivity in COOH-functionalized COFs without additives.

Findings

COOH-functionalized COFs achieved proton conductivity of 10−2 S cm−1 at room temperature.

H-bonding between COOH groups and water enabled efficient proton transport via Grotthuss mechanism.

COFs outperformed similar frameworks without COOH groups by up to three orders of magnitude.

Abstract

In solid materials, the development of hydrogen bonding (H-bonding) networks within pores is crucial for efficient proton conductance. In this study, a chemically stable carboxylic acid-functionalized, quinoline-linked 2D microporous covalent organic framework (COF) (Qy-COOH) was synthesized using the Doebner multicomponent reaction (MCR) and compared to a similar framework lacking the –COOH functionality (Qy-H), prepared via an MC Domino reaction. The proton conductivity of the –COOH-functionalized MCR-COF was significantly enhanced, reaching 10−2 S cm−1, attributed to strong H-bonding interactions between water molecules and the dangling –COOH groups within the COF pores. In contrast, the analogous Qy-H framework exhibited a much lower proton conductivity of 10−5 S cm−1, while an imine-based COF showed only 10−6 S cm−1. This work represents the first demonstration of a general strategy to achieve efficient proton conduction in a class of layered 2D –COOH-functionalized COFs, offering superprotonic conductivity without requiring additives at room temperature. The MCR-COF design approach provides a promising pathway for developing highly stable and high-performance proton-conducting materials.

A –COOH-functionalized COF synthesized via the multicomponent Doebner reaction shows high proton conductivity from room to elevated temperatures. Dangling –COOH groups form H-bonded water networks, enabling Grotthuss proton hopping without dopants.

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