Branched naphthalene ring-containing polybenzimidazole membranes for high-temperature fuel cells and alkaline electrolytic waters

The ionic conductivity of polymers exerts a profound influence on the operational efficiency of energy conversion devices. Elevated conductivity efficiently mitigates ohmic resistance, thus optimizing the overall functionality of these systems. Previous research has demonstrated that incorporating naphthalene rings into polybenzimidazole (PBI) molecular structures confers exceptional oxidative stability to the material. In this work, low−content large 3D structures and highly rigid adamantane structures are introduced as branching points into the naphthalene−containing PBI, enabling it to absorb more electrolytes while improving dimensional stability. Specifically, upon phosphoric acid (PA) absorption, the branched 1.0Ad−NPBI membrane exhibited a proton conductivity of up to 155.8 mS cm⁻¹. In an H₂−O₂ fuel cell (0.6 mg cm⁻² Pt), it achieved a peak power density of 1022.4 mW cm⁻² at 180 °C. After absorbing KOH solution, its hydroxide ion conductivity reached 176.7 mS cm⁻¹, and it delivered a current density of 5.4 A cm⁻² at 2.0 V in alkaline electrolytic water (AWE) cells (in 6 M KOH, at 80 °C). It confirms that branching is a very suitable strategy for improving the performance of PBI.