Oxygen- and proton-transporting open framework ionomer for medium-temperature fuel cells.

Area of Science:

• Electrochemistry
• Materials Science
• Chemical Engineering

Background:

• Medium-temperature proton exchange membrane fuel cells (MT PEMFCs) offer advantages over low-temperature counterparts but suffer from ionomer dehydration and gas transport issues at 100°C–120°C.
• Nafion ionomers, crucial for proton conduction, can dehydrate at higher temperatures, limiting fuel cell efficiency.

Purpose of the Study:

• To develop novel ionomers that improve water retention and proton conductivity in MT PEMFCs.
• To overcome gas transport limitations in MT PEMFCs operating at elevated temperatures.
• To enhance the performance of MT PEMFCs using a bio-inspired approach.

Main Methods:

• Synthesized α-aminoketone-linked covalent organic framework (COF) ionomers.
• Interwove COF ionomers with Nafion to create composite membranes.
• Tested the performance of MT PEMFCs incorporating the COF-Nafion membranes at 105°C with H₂ and air fuel.
• Evaluated proton and oxygen transport properties.

Main Results:

• The COF ionomers, inspired by osmolytes, act as "breathable" proton conductors by leveraging synergistic hydrogen bonding to retain water.
• Enhanced hydration and proton transport were observed, alongside reduced oxygen transport resistance.
• MT PEMFCs with COF-Nafion achieved peak power density of 18.1 W/mg_Pt and rated power density of 9.5 W/mg_Pt, representing significant increases (101% and 187%) compared to control cells.

Conclusions:

• The developed COF ionomers effectively address water management and gas transport challenges in MT PEMFCs.
• This novel material significantly boosts fuel cell performance, demonstrating a promising strategy for advancing high-temperature fuel cell technology.
• The bio-inspired design offers a pathway to more durable and efficient proton exchange membrane fuel cells.