Microporous poly(aryl piperidinium) hydroxide exchange membranes with multi-directional branched structure for high...

Area of Science:

• Materials Science
• Electrochemistry
• Polymer Chemistry

Background:

• Hydroxide exchange membranes (HEMs) are critical components in hydroxide exchange membrane fuel cells (HEMFCs) for energy conversion.
• Existing HEMs face challenges balancing ionic conductivity with mechanical and chemical stability.
• Octaphenylcyclotetrasiloxane (OCSi) offers a unique structural motif for designing advanced HEMs.

Purpose of the Study:

• To synthesize and characterize novel multi-directional branched HEMs incorporating OCSi.
• To investigate the structure-property relationships of these OCSi-based HEMs.
• To evaluate the performance and durability of the developed HEMs in H₂/O₂ fuel cells.

Main Methods:

• Synthesis of quaternized poly(octaphenylcyclotetrasiloxane-terphenyl-piperidinium) (QPOCSi-TP-2) membranes.
• Characterization of membrane morphology, ionic conductivity, mechanical strength, and chemical stability.
• Fabrication and testing of H₂/O₂ fuel cells utilizing the synthesized QPOCSi-TP-2 membrane.

Main Results:

• The QPOCSi-TP-2 membrane exhibited high ionic conductivity (152.9 mS cm^-1 at 80 °C) due to continuous OH^- conducting channels.
• Demonstrated excellent mechanical stability (76.5 MPa tensile strength) and outstanding chemical stability (1500 h in 5 M NaOH at 80 °C).
• Achieved a peak power density of 1.26 W cm^-2 in H₂/O₂ cell tests and low voltage degradation (1.02 mV h^-1) over 120 h operation.

Conclusions:

• The OCSi structure effectively enhances ionic conductivity and mechanical/chemical stability in HEMs.
• QPOCSi-TP-2 membranes show significant promise for high-performance and durable hydroxide exchange membrane fuel cells.
• This study presents a viable strategy for overcoming key limitations in current HEM technology.