Polyhedral Oligomeric Silsesquioxane (POSS)-crosslinked Phosphonated Polybenzimidazole High-temperature Proton Exchange Membrane with Synergistic Physical Confinement and Chemical Anchoring★

doi:10.6023/A26060195

Abstract

Phosphoric acid-doped polybenzimidazole (PA/PBI) is one of the most promising electrolyte materials for high-temperature proton exchange membrane fuel cells (HT-PEMFCs). However, it suffers from severe phosphoric acid leakage and excessive membrane swelling under high doping levels, which critically impair long-term stability. To address this challenge, this work proposes a synergistic strategy combining “physical confinement” and “chemical anchoring”. An epoxy-functionalized polyhedral oligomeric silsesquioxane (epoxy-POSS) was employed as a rigid crosslinking node to construct a three-dimensional crosslinked network with hydroxyl-containing polybenzimidazole (OHPBI). Meanwhile, a phosphonic acid-containing small molecule, 4-hydroxyphenyl dihydrogen phosphate (HDP), was introduced to achieve stable phosphoric acid anchoring and to build efficient proton transport pathways. The effects of the crosslinked network and phosphonic acid groups on membrane structure and performance were systematically investigated. The results show that the EP10 membrane achieves a phosphoric acid uptake of 261% while exhibiting a swelling ratio as low as 112%, demonstrating an excellent balance between high acid loading and dimensional stability compared to pristine OHPBI. Under anhydrous conditions at 180 ℃, the EP10 membrane exhibits a proton conductivity of 101.9 mS•cm^-1 with an activation energy as low as 13.3 kJ•mol^-1. The single-cell peak power density reaches 1.013 W•cm^-2, approximately twice that of pristine OHPBI. Cold-start thermal cycling and accelerated stress tests further confirm the excellent operational stability of the membrane under dynamic conditions. These results demonstrate that the dual synergistic strategy based on epoxy-POSS crosslinking and phosphonic acid immobilization provides a viable route toward high-performance and durable high-temperature proton exchange membranes.

Key words: high-temperature proton exchange membrane, polybenzimidazole, polyhedral oligomeric silsesquioxane (POSS), phosphonic acid immobilization, crosslinking

Cite this article

Weiyi Jin, Yi Tang, Tianqi Yang, Ziheng Huang, Chenliang Gong. Polyhedral Oligomeric Silsesquioxane (POSS)-crosslinked Phosphonated Polybenzimidazole High-temperature Proton Exchange Membrane with Synergistic Physical Confinement and Chemical Anchoring^★[J]. Acta Chimica Sinica, 2026, 84(10): 1554-1562.

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Fig. & Tab. 7

Figure 1. Schematic diagram of the structure and proton transport of EPX crosslinked membranes

Figure 2. FT-IR spectrum (a) and enlarged view (b), XRD (c), and gel content (d) of the pristine OHPBI membrane and EPX crosslinked membranes

Figure 3. (a~e) SEM surface morphologies, (f~j) cross-sectional SEM images, and (k~n) P element surface mappings, from left to right corresponding to EP0, EP5, EP10, EP15, and EP20 membranes

Figure 4. PA uptake and swelling ratio of the pristine OHPBI membrane and EPX crosslinked membranes (a), phosphoric acid retention at 80 ℃, 40% RH (b) and 160 ℃, 0% RH (c)

Figure 5. Thermal stability (a), oxidative stability (b), and mechanical properties before (c) and after (d) PA immersion of the pristine OHPBI membrane and EPX crosslinked membranes

Figure 6. Proton conductivity of OHPBI membrane and EPX cross-linked membranes under unhumidified conditions at 100~180 ℃ (a), Arrhenius plot (b), single-cell performance at 180 ℃ under unhumidified and backpressure-free conditions with a gas flow rate of 200 mL•min-1 (c), cold-start thermal cycling test in galvanostatic mode, initiating when the cell temperature reaches 70 ℃ with a current density of 0.2 A•cm-2 and continuously heating to 160 ℃ (d), and accelerated stress test at 160 ℃ in potentiostatic mode with the voltage decreasing from 1.0 V to 0.1 V at a rate of 25 mV•min-1 (e); comparison of EP10 membrane with representative HT-PEMs in recent years (f)

样品	OHPBI (mmol)	环氧POSS (mmol)	HDP (mmol)	X ^a/mol%
OHPBI	0.3	—	—	0
EP0	0.3	0.012	—	0
EP5	0.3	0.012	0.015	5
EP10	0.3	0.012	0.03	10
EP15	0.3	0.012	0.045	15
EP20	0.3	0.012	0.06	20

Table 1. Composition of each component in the preparation of OHPBI and EPX crosslinked membranes

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物理限域与化学锚定协同的笼型聚倍半硅氧烷(POSS)交联膦酸化聚苯并咪唑高温质子交换膜^★