Disentangling flocculation and sedimentation dynamics in IrOx catalyst inks: Role of pre-mixing process in interfacial structure evolution and long-term dispersion stability

초록

The long-term dispersion stability of catalyst inks is critical for achieving high-performance catalyst layers for polymer electrolyte membrane water electrolysis (PEMWE), as it is closely linked to the formation of catalyst-ionomer interfacial structures that govern the uniformity and functionality of the catalyst layer. However, the influence of pre-mixing dynamics on the evolution of interfacial structures, flocculation-sedimentation behavior, and ionomer-adsorption characteristics of catalyst inks has not yet been clearly elucidated. Herein, we employ a real-time multiwavelength optical analytical method to quantitatively investigate how pre-mixing processes influence the interfacial stabilization and long-term dispersion behavior of IrOx nanoparticles. Wavelength-dependent stability index studies revealed that sonication and planetary mixing effectively suppressed reaggregation by inducing aggregate disintegration and facilitating the more uniform adsorption of ionomers onto IrOx surfaces through highly efficient mixing. These interfacial effects contributed to the formation of more homogeneous colloidal structures and enhanced dispersion stability. Notably, planetary mixing improved the near-IR stability index by 71.8% and maintained the smallest average particles and stable zeta potential compared to the conventional process. This is attributable to the disintegration of flocculated particles via high-shear pretreatment and reflocculation inhibition due to the formation of a more uniform catalyst-ionomer interfacial network. These findings provide new insights into the role of pre-mixing processes in governing the catalyst-ionomer interfacial structures and their impact on the long-term stability of PEMWE catalyst inks.

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