Room-Temperature Defect Chemistry in Functional Oxides

Although the defect chemistry and transport of protons in oxides has been relatively well studied at elevated temperature, still little is known on the proton defect chemistry at room temperature. In this talk, I am going to focus on the defect chemical equilibrium and interfacial kinetics that involves proton charge transfer in oxides. The understanding is obtained by using well-controlled thin film model systems. Firstly, I will show our recent work on a prototypical perovskite oxide NdNiO₃ (NNO). High proton concentration, up to 1 proton per unit cell, can be incorporated to NNO by hydrogenation, which can induce drastic changes in lattice constant and electronic conductivity.¹ We also show that the incorporated protons can be converted to oxygen vacancies by thermochemical dehydration process.² Secondly, I will discuss the kinetics of hydrogen incorporation reaction at both oxide/electrolyte interfaces and in the bulk. The co-existence of interfacial pseudo-capacitance-like and bulk battery-like charge storage is found in oxides that incorporate protons.³ Overall, our work shows the intricacy of room-temperature protonic defect chemistry that can be utilized to control the functionality of oxides as well as to tune charge storage mechanisms.

1. H. Chen, Q. Lu et al., Nano Lett., 22 (2022), 8983-8990
2. H. Chen, Q. Lu et al., JMCA 12 (2024), 23658-23669
3. L. Wei, Q. Lu et al., JMCA 146 (2024), 24167–24176