Enhancing proton exchange membrane water electrolysis performance: Impact of iridium oxide catalyst ink dispersing methodology

Iridium oxide (IrO₂) is the most successful catalyst for triggering oxygen revolution reactions in proton exchange membrane water electrolyzers (PEMWE). However, conventional ultrasonic methods for ink dispersion often result in ink instability, catalyst aggregation, and sedimentation. To address these issues, we investigate the effects of the dispersion type, treatment time, and ionomer-addition sequence on the catalytic performance. Ball-milling procedure prepares a more stable catalyst ink and achieves a larger electrochemical surface area (ECSA) than ultrasonic method. Extending the ball-milling time to 12 h improves the ink stability (absorbance change rate ∼0.6 % h⁻¹); however, over-processing causes the thickest catalyst layer, leading to an enhanced mass transport resistance. Moreover, treating an ionomer with IrO₂ causes the substitution of sulfonic acid groups by carboxylic acid groups and reduces the repulsive force in colloidal particles, resulting in poor ink stability, low proton conductivity, and small ECSA. Therefore, adding ionomer after ball milling is recommended for the preparation of a stable ink with high catalytic performance. The membrane electrode assembly prepared using this procedure exhibits an improved performance of 1.70 A cm⁻² at 1.7 V, compared with that prepared using ultrasonic methods. This work provides crucial guidance of ink preparation for large-scale production of PEMWEs.