Investigation of Hydroxyl Proton Diffusion in Ceramic Proton Conductors Revealed by In Situ Raman Spectroscopy

Proton ceramic fuel cells are one of the most promising and efficient clean energy conversion technologies that can reduce the operating temperature of fuel cells to lower than 600 °C. An emerging type of perovskite ceramics with "intrinsic oxygen vacancies", such as BaSc_1–xMo_xO_3–δ (BSM), exhibit preeminent proton conductivity at lower than 300 °C. The high proton conductivity of these materials is proposed to be due to high proton concentration and high proton diffusion coefficient with reduced proton trapping. However, research on the impact of their microstructural and chemical properties on proton diffusion remains insufficient. We investigate the chemical environment and diffusivity of hydroxyl protons in BSM, using in situ Raman spectroscopy at different temperatures in humid atmospheres. In our previous work, we have investigated the chemical environment and performance of surface adsorbed water species including hydroxyl protons, demonstrating that this approach can facilitate a deeper understanding of the proton transport mechanisms [1]. The H₂O/D₂O isotope exchange behavior is studied through the changes of O–H and O–D stretching vibrations. Comparison between the proton diffusion coefficient from conductivity (D_σ) and tracer diffusion coefficient (D*) from H/D isotope exchange reveals the mobility and conduction mechanism of hydroxyl protons in BSM. Moreover, the impact of proton trapping effects on proton transport is discussed, through comparing the O–H stretching vibrations in perovskite ceramics with different dopant types. This research provides an in-depth understanding for the development of high-performance proton-conducting ceramic materials with minimal proton trapping effects.

Reference:
1. Z. Zhao, R. Wang, D. Han, X. Ling, Q. Chen, Molecular and Dissociative Adsorbed Water Concentration and Surface Protonic Conduction in Nanocrystalline TiO₂. Small 2406826 (2024) https://doi.org/10.1002/smll.202406826.