Influence of nickel exsolution on the electrochemical performance and rate-determining stages of hydrogen oxidation on Sr1.95Fe1.4Ni0.1Mo0.5O6-δ promising electrode for solid state electrochemical devices

Highlights: • Sr_1.95Fe_1.4Ni_0.1Mo_0.5O_6–δ oxide as symmetrical electrode for SOFCs was investigated. • The key role of hydrogen presence in ambient for metal particles formation is showed. • Effect of nickel exsolution on performance of Sr_1.95Fe_1.4Ni_0.1Mo_0.5O_6–δ was studied. • Exolution of nickel leads to a change in the mechanism of HOR. • Symmetrical SOFC with Sr_1.95Fe_1.4Ni_0.1Mo_0.5O_6–δ electrodes was tasted. -- Abstract: The paper presents new results of the studies of a promising electrode material Sr_1.95Fe_1.4Ni_0.1Mo_0.5O_6–δ (SFNM) for solid state electrochemical application. It is shown that the SFNM phase is stable at pO₂ = 10^–20 atm at 800 °C. Exsolution of Fe particles was observed after heat treatment of SFNM in 5% H₂ + Ar. After heat treatment of SFNM in wet hydrogen, the exsolution of Ni–Fe particles was observed. The electrochemical activity of the SFNM electrode is found to be higher than of the undoped Sr_1.95Fe_1.5Mo_0.5O_6–δ (SFM) oxide in both oxidative and reductive conditions. It was shown for the first time that the pathway of hydrogen oxidation reaction on SFNM and SFM electrodes fundamentally differs, while the pathway of oxygen reduction reaction on both electrodes is the same. It was established for the first time that the exsolution of Fe-Ni particles in an SFNM electrode leads to an increase in the rate of dissociation of adsorbed hydrogen on the electrode surface. During the tests of the fuel cell with 300 μm LaGaO₃-based supporting electrolyte and SFNM electrodes a maximum power density of about 0.5 W cm^–2 at 800 °C under wet hydrogen / air condition was obtained.