Investigation of IrRuOx-Based Porous Transport Electrodes as a Function of Post-Treatments

This study examines the effects of post-treatment annealing (argon, vacuum, air; 200–500 °C) on electrodeposited IrRuOx porous transport electrodes (PTEs) using X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS). The aim is to investigate how these treatments influence the material's composition, structure, and their respective impact on electrochemical properties. Electrochemical testing reveals atmosphere-dependent pathways: argon annealing improves stability up to 400 °C but produces Ir enrichment and heterogeneity at 500 °C that degrades performance; air annealing stabilizes oxidized species at 200 °C but yields larger activity and stability losses by 300 °C; and vacuum annealing at 200 °C preserves activity while improving stability. XPS characterization focuses on the analysis of Ir 4f, Ru 3d, and O 1s regions. For Ir 4f and Ru 3d spectra, simple metrics that didn’t involve fitting are explored, whereas for O 1s, deconvolution strategies are evaluated and a six-component model is adopted. In many cases, simple XPS metrics, binding energy (BE) and full width at half maximum (FWHM), capture trends that correlate with catalytic activity and stability, while detailed fitting is necessary to resolve complex oxygen speciation in other cases. Additionally, XPS-derived metrics are correlated with electrochemical performance using principal component analysis (PCA), highlighting patterns within a complex dataset. These results advance our understanding of XPS analysis of Ir-based catalysts, emphasize the importance of thorough and careful analysis, and highlight opportunities for combining simple metrics with multivariate analysis for the development of more efficient materials.