Enhancing water uptake and hydroxide ion conductivity of alkali fuel cell electrolyte membrane by layered double hydroxide

Novel hydroxide ion-conductive composite membranes were fabricated through incorporating coprecipitation-synthesized magnesium (Mg)–aluminum (Al)-type layered double hydroxides (LDHs) into a potassium hydroxide (KOH)-doped polybenzimidazole (PBI) membrane to improve the hydroxide ion conductivity for the application to alkali fuel cells. The addition of LDH was essential for improving the water affinity of the PBI–KOH membranes. Although the KOH uptake of the LDH-incorporated PBI membranes decreased with increasing amounts of LDHs in the water uptake test, thermal analysis showed that the water content in the membrane increased with increasing amounts of added LDHs. LDH-incorporated PBI membranes showed the high hydroxide ion conductivity and the reduced dependent of the humidity because of the high amount of adsorbed water and high ionic conductivity of LDHs. The alkaline fuel cell performance evaluation test showed that the prepared PBI–KOH membrane with 30 wt% LDH had the highest power output, exhibiting a maximum power density of 210 mW cm−1 at 80 °C, which is more than double that of the cell device without LDH. Improved performance due to the high-water adsorption and hydroxide ion conductivity was achieved by incorporating LDHs into the KOH-doped PBI membranes.