A bi-guanidinium bridged polysilsesquioxane composite membrane was fabricated for the first time, which showed impressive hydroxide conductivity and decent alkali-stability. Its direct borohydride fuel cell yielded a peak power density of 321 mW cm−2 at ca. 700 mA cm−2 and 40 °C, which is to our knowledge the highest ever achieved with an anion exchange membrane (AEM). The cell could discharge at 200 mA cm−2 for 50 h with voltage maintained at 0.76 V. The strong basicity and resonance of bi-guanidinium cations are the enabling factor for the good membrane properties and fuel cell performance. This work provides a new strategy for non-ammonium AEM fabrication, and the synthetic chemistry involved can possibly extend for fabricating versatile AEMs with similar structure.
