In situ NAP-XPS and electrochemical impedance characterisation of La_0.31Sr_0.58Ti_0.97Ni_0.03O_3-δ thin film model electrodes

La_xSr_0.9-xTi_yNi_1-yO_3-δ (LSTN) has been proposed as a promising group of mixed ionic-electronic (MIEC) perovskites for solid oxide fuel- and electrolysis cell applications. In this study, thin film as-prepared (before redox treatment) La_0.31Sr_0.58Ti_0.97Ni_0.03O_3-δ (LSTN3) pulsed laser deposited (PLD) electrodes were characterised electrochemically and using <i>in situ</i> near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) at different H₂/H₂O ratios and electrode potentials at 650 °C. The electrochemical activity of LSTN3|gas surface increased with water content in a hydrogen environment. Ti XPS spectra revealed rutile-like coordinated Ti surface termination of LSTN3 and Ti³⁺/Ti⁴⁺ ratio changes in the surface layer as a function of oxygen activity in LSTN3. Change in the kinetics of the electrochemical process at ~0.3 V in H₂ with 1.6% H₂O was observed and explained as oxidation of exsolved Ni. La and Sr XPS spectra were independent of polarisation and depended only on water content in the gas. The changes in La(OH)₃ concentration at the surface (influenced by water content in the gas) match with the changes in the electrochemical activity.