Simultaneous Determination of Elemental Iridium and Platinum Loadings on Catalyst Coated Membranes Using a Niton <scp>XL3t</scp> X‐Ray Fluorescence Analyser

ABSTRACT Iridium and platinum have adjacent atomic numbers that account for the proximity of their x‐ray transition energies and thus the overlapping peaks in their x‐ray fluorescence spectra. This presents a challenge for the quantitative elemental analysis of IrO 2 ⋅2H 2 O‐Pt binary catalyst coatings, especially where the ‘Fundamental Parameter’ method is unavailable, as in the Niton XL3t energy dispersive x‐ray fluorescence analyser. Therefore, we studied the spectral resolution of the Lα, Lη and Lβ peaks for Ir and Pt as recorded on a Niton XL3t to identify the optimal regions of interest. These ROIs were used to measure a set of discrete Ir and Pt standard samples—in which the elemental loadings were derived from the mass and formulation of the catalyst coatings—for constructing correlation graphs to enable the conversion of x‐ray intensity data (cps μA −1 ) to elemental loading (mg cm −2 ). These correlation data were fitted to a quadratic regression. The overall measurement uncertainty for the elemental loadings was determined by combining the residual standard error in the quadratic regression with the uncertainty for the elemental loadings used in the construction of the correlation graph, yielding ±0.07 mg cm −2 for Ir (ROI: 9.00–9.18 keV) and ± 0.04 mg cm −2 for Pt (ROI: 9.36–9.65 keV). The quadratic functions and their corresponding ROIs were programmed into the analyser to measure a set of IrO 2 ⋅2H 2 OPt binary standard samples. This revealed a strong agreement between the elemental loadings as displayed on the analyser and those derived from the mass and formulation of these standard samples.