This work investigates the impact of tetrabutylammonium (TBA⁺) cations within Nafion on polycrystalline (pc) Pt as a model system to understand their influence on ORR activity using rotating disk electrode experiments. We demonstrate the promotive kinetic effects of TBA⁺- Nafion formulations through variations in the Tafel slope, with Nafion (68 mV/dec) being slightly higher compared to TBA⁺-Nafion (62 mV/dec), and an increased O₂ mass transport current density for TBA⁺-Nafion compared to Nafion alone. Potentiostatic electrochemical impedance spectroscopy reveals that TBA⁺- Nafion films exhibit lower O₂ mass transport resistance (111.6 ohm) compared to Nafion alone (188.8 ohm) at 0.7 V RHE, further corroborating ORR polarization data
Ex situ X-ray photoelectron spectroscopy (XPS) indicates that Nafion undergoes greater degradation on Pt pc disks after ORR compared to TBA⁺- Nafion films, where the ionomer remains intact. Morphological analysis via atomic force microscopy infrared spectroscopy reveals distinct swelling dynamics between TBA⁺- Nafion and Nafion films post-reaction. In addition, ionomer film stability varies within the TBA⁺- Nafion system, where spectroscopically, Nafion chemical signatures remain consistent across the Pt interface. In contrast, Nafion films without TBA⁺ exhibit varied spectroscopic features, indicating ionomer inhomogeneity and dynamic changes after ORR. Pt stability was evaluated using inductively coupled plasma mass spectrometry, which revealed no Pt dissolution in TBA⁺-Nafion films (baseline dissolution), whereas Nafion films exhibited a Pt dissolution rate of 0.15 ng cm⁻² s⁻¹. Interestingly, while Pt dissolution is often correlated with increased oxide formation, both ex situ XPS and in situ X-ray absorption spectroscopy (XAS) indicate greater oxide features in the presence of TBA⁺. These oxide species are attributed to oxygenated adsorption states associated with ORR, suggesting a favorable microenvironment for enhanced reaction kinetics.
Altogether, these findings provide insight into how electrode-ionomer interactions influence activity, mass transport, and material stability under operating conditions. By systematically investigating well-defined electrocatalyst-ionomer interfaces, this study establishes a framework for optimizing PEMFC catalyst inks and demonstrates how TBA⁺ can modulate Pt surface structure to promote ORR electrocatalysis.