Constructing immobilized H3PO4 network in nanosized ZSM-5 zeolitic framework achieves high proton conductivity after acceleration acid leaching test

Abstract

In the midst of demand for the high and stable anhydrous proton conducting membrane for the high-temperature polymer electrolyte membrane fuel cells (HT-PEMFCs), phosphoric acid (PA)-doped polybenzimidazole (PBI) is positioned as one of the most promising candidates. The key to develop the PA-PBI is to address the issue of phosphoric acid leaching, which causes significant performance deterioration. Here we introduced the nanosized ZSM-5 zeolite which plays the role of the rigid cage for confining H3PO4 to the PBI, and then evaluated by utilizing the acceleration acid leaching test (ALT) to put long-term operation in perspective. The ZSM-5 not only retain the high degree of PA after ALT, but also constructs the efficient proton conducting channel derived by the chemically-immobilized H3PO4 in pore channel. After ALT, PBI electrolyte membrane with 5 wt% of ZSM-5 exhibited 2.8 × 10−5 S cm−1 of proton conductivity at 150 °C anhydrous condition, which is three orders higher magnitude than pure PBI (1.1 × 10−8 S cm−1). Furthermore, H2/O2 HT-PEMFC single-cell constructed with PBI/5%ZSM-5 displayed an excellent maximum power density of 387 mW cm−2 at 150 °C anhydrous conditions, even after the ALT. The results indicate the possible improvement of the long-term stability of the fuel cell by utilizing readily available ZSM-5.