Poly(triphenylene-piperidine) membranes reinforced by carboxy intrinsic microporous polymers towards high output power at low phosphoric acid levels for HT-PEMFC

To address the inferior mechanical properties associated with high phosphoric acid (PA) content, a rigid microporous polymer containing carboxyl groups (cPIM) was incorporated into poly (triphenylene-piperidine) (PTP) matrix to prepare composite membranes (PTP-xcPIM) for high-temperature proton exchange membrane fuel cells (HT-PEMFCs). Compared to the original membrane (PTP/PA), the PTP-xcPIM/PA reinforced membranes exhibited improved mechanical properties (13–17 MPa) and higher proton conductivity (>90 mS cm−1@180 °C) at a similar PA content. After assembling into a single HT-PEMFC, the reinforced composite membrane could achieve a high output power of over 1000 mW cm−2. The addition of the microporous layer to the composite membranes significantly increased the PA retention due to its siphoning effect on PA. Especially, PTP-10cPIM/PA retained 57.64% of PA after 100 h at 60 °C and 50%RH, while PTP/PA retained only 52.11% in the same harsh environment. These phenomena imply that the strategy of introducing rigid microporous polymers containing functional groups can lead to the simultaneous enhancement on the PA retention capacity and proton conductivity at low PA doping levels, and effectively avoid the "trade-off" effect between the mechanical properties and the output performance.