Publication date: 10th April 2024
Triggering topotactic phase transitions by adjusting oxygen stoichiometry while maintaining the cation framework is recognized as an effective method for tuning functional oxide properties. This phase engineering can significantly alter the ligand field around metal cations and modify the electronic structure of oxides, potentially influencing (electro-)catalytic properties. Phase engineering is particularly relevant for tuning oxygen incorporation/evolution reactions (OIR/OER), crucial for energy conversion devices, especially solid oxide fuel/electrolysis cells (SOFC/SOECs). However, detailed case studies of mechanistic understanding of phase-dependent electro-catalytic activity, especially for oxygen exchange reactions at elevated temperature, have been rare. To tackle this challenge, in this presentation, we will show that crossing phase boundaries can lead to entirely different mechanisms of oxygen incorporation/evolution reactions, using a simple yet generalizable binary oxide, PrOx, as a model system.[1] We identify phase boundaries in PrOx, the threshold oxygen chemical potential triggering the phase transition, by measuring the electrochemical quantity of chemical capacitance. We found that the chemical capacitance reaches a maximum at the phase boundary. We also investigated the kinetics of oxygen exchange reactions, including incorporation and evolution, depending on the direction of applied biases. Surprisingly, crossing the phase boundary causes a drastic change in the reaction order concerning the pressure of the oxygen gas phase. The oxygen exchange kinetics show a strong dependence on the oxygen partial pressure for the oxygen-poor phase of PrOx, while for the oxygen-rich phase, the exchange kinetics are almost insensitive to the amount of available oxygen molecules. Therefore, we conclude that our findings pave the way towards a deeper understanding of phase-specific kinetics and reaction mechanisms for a variety of electrochemical interfaces.
This work was supported by funding from the Research Center for Industries of the Future, and School of Engineering Dean Special Projects Fund (SOE-DSPF), Westlake University, and by the National Natural Science Foundation of China (NSFC, Grant No. 52202148). This work used shared facilities at the Instrumentation and Service Centers for Physical Science (ISCPS) of Westlake University. Part of the work was performed at Beamline 02B of the Shanghai Synchrotron Radiation Facility, which is supported by ME2 project from the National Natural Science Foundation of China (Grant No. 11227902).
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