# 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.

## Key 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.