# Achieving ultra-low oxygen transport resistance of fuel cells by microporous covalent organic framework ionomers

## TL;DR

This paper introduces a new type of ionomer using covalent organic frameworks to significantly reduce oxygen transport resistance in fuel cells, improving efficiency with ultra-low platinum usage.

## Contribution

The development of COF ionomers that create sub-nm porous structures to enhance oxygen transport and reduce platinum loading in fuel cells.

## Key findings

- COF ionomer electrodes reduce oxygen transport resistance by 96.4% compared to polymer electrodes.
- With ultra-low Pt loading, COF ionomer electrodes achieve a peak power density three times higher than polymer electrodes.
- The sub-nm porous structures improve platinum utilization and oxygen diffusion efficiency.

## Abstract

Research on ultra-low platinum (Pt)-loaded fuel cells is essential for reducing costs and advancing hydrogen fuel cell commercialization. However, oxygen diffusion resistance remains a major challenge, limiting the oxygen reduction reaction and fuel cell efficiency. To address this challenge, a stable colloidal dispersion of polymer-grafted covalent organic framework (COF) ionomers has been developed. These COF ionomers enhance hydroxide conductivity and oxygen transport by creating a sub-nm porous structure on the catalyst surface, while also dispersing catalyst particles and stabilizing the three-phase interface. Compared to polymer electrodes, COF ionomer electrodes reduce oxygen transport resistance by 96.4%. With ultra-low Pt loading (60 μg cm−2), COF ionomer electrodes achieve a peak power density of 0.78 W cm−2, three times higher than that of polymer electrodes. This study presents a promising alternative for the development of more efficient ionomers with low oxygen transfer resistance in fuel cells.

COF ionomers form sub-nm porous structures on the catalyst surface, which shorten the oxygen diffusion path to the catalyst and enhance the utilization efficiency of platinum-based catalysts.