Synergistic optimization of pore structure and hydrophilicity for an ultrathin, high-safety composite diaphragm...

Reducing diaphragm thickness is an effective approach for enhancing alkaline water electrolysis (AWE) performance. However, this thickness reduction often compromises the gas-blocking capability of the diaphragm. This study presents a convenient and cost-effective pore-modification strategy for fabricating ultrathin AWE composite diaphragms. Through the incorporation of sodium carboxymethyl cellulose (CMC) and regulation of the polysulfone (PSU)/ZrO₂ composition via a facile blending method, composite diaphragms with a continuous sponge-like structure and excellent hydrophilicity were prepared. The optimized CMC₂Z₈₃ composite diaphragm exhibited excellent gas-blocking performance. Additionally, the diaphragm had an ultralow area resistance (∼0.07 Ω cm² in 30 wt% KOH) and a high bubble-point pressure (∼3.67 bar) despite its small thickness (∼220 µm). The AWE cell with commercial electrodes achieved a high current density of 2.2 A cm ^-2 at 2.0 V in 30 wt% KOH at 80 °C and maintained a low anodic hydrogen content of 0.09% at 0.2 A cm^-2. Notably, the short-stack system equipped with the CMC₂Z₈₃ diaphragm maintained stable operation under dynamic conditions for 30 d (∼720 h). The low-cost fabrication process and excellent performance of the CMC-ZrO₂/PSU series diaphragms highlight their strong potential for industrial AWE applications.