Quantifying protons in triple conducting perovskite-type oxides via laser-induced breakdown spectroscopy – A comparative validation approach

Proton-conducting oxides are promising materials for renewable energy technologies - e.g. as electrolytes and electrodes in solid oxide cells or membranes for hydrogen purification. Particularly relevant for these applications are perovskites, which can accommodate high concentrations of protons in their crystal structure. However, quantifying the proton concentration is challenging under reducing conditions, OH uptake and oxygen loss occur simultaneously, causing compensating weight changes. Thus, attributing weight changes directly to OH uptake is not possible without complementary techniques for validation. Here, we focus on quantifying the proton concentration in the triple conducting perovskite-type oxide BaFe_0.85Y_0.15O_3–δ (BFY) under various oxidation and protonation states. To do so, we introduce an alternative analytical method, which is capable of direct proton detection in perovskites and well-suited for in-situ quantification: Laser-induced breakdown spectroscopy (LIBS). This technique analyses characteristic emissions from the plasma generated by UV-laser irradiation of the material. Validation of results involved gravimetry and Fourier-transform infrared spectroscopy (FT-IR). While gravimetry was used to determine the proton concentration under special experimental conditions, FT-IR spectroscopy was used to distinguish the protons – located in the perovskite structure in the form of ${\left(\mathrm{OH}\right)}_O^{•}$ point defects - from molecular water (e.g. at the surface). The results underscore the reliability of LIBS for the quantification of bulk protons in perovskite-type oxides, positioning it as a valuable alternative to conventional methods.