Localized covalent crosslinking of poly(p-terphenyl pyridine) by radial 1,3,5-tricarbazolylbenzenes for preparation of high-temperature proton exchange membranes

Abstract

High-temperature proton exchange membranes (HT-PEMs) with excellent swelling resistance are highly desirable to promote the safety, reliability and durability of fuel cells. Herein, we propose poly (p-terphenyl co 1,3,5-tri (9H-carbazol-9-yl) benzene pyridine) polymers (PTP/x%TCB, x refers to the crosslinking degree) featuring locally high-density crosslinking network structure. These crosslinked membranes exhibit the same solubility as that corresponded pristine membranes in commonly used organic solvents. This is different from the prepared membranes with the conventional crosslinking networks. Moreover, the prepared PTP/x%TCB membranes preserve sufficient free volume for phosphoric acid (PA) doping and ion conduction as proved by free volume fraction of the membrane. The volume swelling ratio of PTP/2%TCB membrane decreases by 50 % compared to that of the PTP membrane having the same PA uptake of 206 wt%. This indicates that the locally high-density crosslinking structure can effectively inhibit the plasticizing effect of the doped PA. The acid-doped PTP/2%TCB membrane delivers a proton conductivity of 123 mS cm⁻¹ at 160°C. This membrane-based H₂/O₂ fuel cell exhibits a peak power density of 972 mW cm⁻² and a specific power of 1620 mW mg⁻¹ (Pt loading: 0.6 mg cm⁻²) without backpressure. Additionally, more fuel cell demonstrations with backpressure of 2.5 bar for both anode and cathode, as well as durability test at different current densities with start-stop cycling operation are made.