Hydrogels Doped with Inorganic Ammonium Chloride Salt for Fuel Cell Applications

Introduction: Inorganic ammonium salts, such as ammonium chloride (NH4Cl), can form electrolytes due to their protonated ammonium ions acting as proton carriers. This study investigates the use of NH4Cl-doped polyacrylamide hydrogel as a flexible proton conductor for fuel cell applications. Methods: A freestanding hydrogel membrane was fabricated through in situ polymerization of ethylene glycol dimethacrylate and acrylamide within aqueous NH4Cl. The hydrogel';s mechanical and conductive properties were characterized, and it was assembled into a fuel cell to evaluate its performance. Results: The NH4Cl-doped hydrogel exhibited a fracture tensile stress of 90 kPa at 462% elongation. The conductivity measurements, which varied with temperature, revealed that proton conduction primarily followed a vehicle mechanism, showcasing an impressive ionic conductivity of 119 mS cm?¹. The fuel cell achieved a maximum power density of 31.9 mW cm?², marking a solid performance. Discussion: The "structure-performance" relationship of inorganic ammonium salt-doped hydrogels is clarified through multi-scale characterization. The dual influence mechanism of NH4 + concentration on proton conduction has been revealed. The developed HGA-n material combines excellent mechanical strength and proton conductivity, and its power density provides a new option for gel electrolytes used in fuel cells. Conclusions: A flexible proton conductor is prepared by doping ammonium chloride (NH4Cl) into polyacrylamide hydrogel for the first time and is successfully assembled into a fuel cell. This work demonstrates a novel approach for utilizing inorganic ammonium salts in electrochemical applications, offering a promising route for developing flexible proton-conducting materials for fuel cells.