Electrokinetic Proton Transport in Triple (H+/O2−/e−) Conducting Oxides as a Key Descriptor for Highly Efficient Protonic Ceramic Fuel Cells - Seong - 2021 - Advanced Science - Wiley Online Library:
In this regard, we employ the isotope exchange diffusion profile (IEDP) method in which deuterium was used as a tracking indicator of proton diffusion via time-of-flight secondary ion mass spectrometry (ToF-SIMS).[8] This strategy enables to precisely evaluate the proton tracer diffusion coefficient (D*H) analysis of triple conducting oxide, PrBa0.5Sr0.5Co1.5Fe0.5O5+δ (PBSCF), excluding the interactions of oxide ions and electrons. The proton diffusion coefficient value of PBSCF at 550 °C (D*H, 1.04 × 10−6 cm2 s−1) is two orders of magnitude higher than its oxygen diffusion coefficient at 590 °C (D*O, 1.9 × 10−8 cm2 s−1). The D*H of PBSCF shows higher value than D*O of typical mixed ionic and electronic conductors (MIECs) such as Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF), PrBaCo2O5+δ (PBCO), GdBaCo2O5+δ (GBCO), La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF), and La0.6Sr0.4CoO3−δ (LSC) (1.63 × 10−9–3.01 × 10−11 cm2 s−1) at 550 °C. Furthermore, we have successfully obtained the surface exchange coefficient of a proton (k*H) in the value of 2.60 × 10−7 cm s−1. Based on the outstanding proton kinetics of PBSCF, the excellent electrochemical performance is obtained in practical PCFC condition (e.g., 0.42 W cm−2 at 500 °C). In this study, we introduce an innovative way to quantify proton kinetic properties (D*H and k*H) of TCOs being significant indicator for characterizing the electrochemical behavior of proton and the mechanism of electrode reactions.
