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

Hydroxide exchange membranes (HEMs) are important materials for energy conversion devices in hydroxide exchange membrane fuel cells (HEMFCs). This study details a series of multi-directional branched HEMs containing octaphenylcyclotetrasiloxane (OCSi). The OCSi structure allows for the establishment of continuous OH − conducting channels within the membrane while addressing the prevailing trade-off between ionic conductivity and size/mechanical stability. Thanks to the formation of fine microphase-separated morphologies, the quaternized poly(octaphenylcyclotetrasiloxane-terphenyl-piperidinium) (QPOCSi-TP-2) membrane has high conductivity (152.9 mS cm −1 at 80 °C), excellent mechanical stability (tensile strength of 76.5 MPa) and outstanding chemical stability (1500 h in 5 M NaOH at 80 °C). In H 2 /O 2 cell tests at 80 °C, the peak power density of the QPOCSi-TP-2 membrane reaches 1.26 W cm −2 . During 120 h of operation at 100 m A cm −2 , the voltage degradation rate of the cell is 1.02 mV h −1 .