Achieving 1060 mW cm⁻² with 0.6 mg cm⁻² Pt Loading Based on Imidazole‐Riched Semi‐Interpenetrating Proton Exchange Membrane at High‐Temperature Fuel Cells

Abstract Enhancing phosphoric acid (PA) doping in polybenzimidazole (PBI) membranes is crucial for improving the performance of high‐temperature proton exchange membrane fuel cells (HT‐PEMFCs). However, excessive PA uptake often leads to drawbacks such as PA loss and compromised mechanical properties when surpassing PA capacity of PBI basic functionality. Herein, a new strategy that integrates high PA uptake, mechanical strength, and acid retention is proposed by embedding linear PBI chains into a crosslinked poly(N‐vinylimidazole) (PVIm) backbone via in‐situ polymerization. The imidazole (Im)‐riched semi‐interpenetrating polymer network (sIPN) membrane with high‐density nitrogen moieties, significantly enhancing the PA doping degree to 380% shows an excellent conductivity (0.108 S cm⁻¹). Meanwhile, the crosslinking structure in the sIPN membrane ensures adequate mechanical properties, low hydrogen permeability, and a relatively low swelling ratio. As a result, the single cell based on the membrane achieves the highest power density of 1060 mW cm⁻² with a low Pt loading (0.6 mg cm⁻²) up to now and exhibits excellent fuel cell stability.