Voltage-driven metal exsolution from perovskite (ABO₃) cathodes is a promising strategy for developing high-performance solid oxide electrolysis cells (SOECs). However, the effect of B-site composition on the exsolution process remains unclear due to the lack of direct and in situ comparison of the key parameters influencing exsolution. Herein, a multi-electrode model cell with graded potential distribution was constructed using La_0.6Sr_0.4Co_xFe_1-xO_3-δ (x = 0.2, 0.4 and 0.6, denoted as LSCF28, LSCF46 and LSCF64) as cathodes. Coupled with in situ spatially resolved X-ray photoelectron spectroscopy (μ-XPS), the effect of Co/Fe ratios on voltage-driven exsolution behaviors was investigated under the same conditions. The in-situ and comparative characterization results reveal preferential exsolution of Co⁰ compared with Fe⁰ under applied voltage. Moreover, the overall metal exsolution rates and oxygen vacancy generation rates follow the order LSCF28 > LSCF46 > LSCF64, suggesting that the oxygen vacancy plays an important role in linking Co/Fe ratios to voltage-driven exsolution. This work provides mechanistic insights for optimizing SOEC electrodes and establishes an efficient in situ strategy for comparative studies of multiple material systems.

The dynamic evolution of surface electrochemical potential of the electrolyte plays a key role in the performance of solid-state electrochemical devices, while its real-time characterization remains challenging. Here, we visualize the dynamic evolution of the surface electrochemical potential on yttria-stabilized zirconia (YSZ) in a planar Au|YSZ|Au model cell, using spatially resolved photoelectron-based techniques including photoemission electron microscopy (PEEM) and micro-region X-ray photoelectron spectroscopy (μ-XPS). PEEM reveals two sequential reaction fronts in YSZ under cathodic polarization, corresponding to the evolution of the chemical potential of oxygen ions, with a faster propagation speed on the top surface and a slower one in the near-surface region. XPS measurements quantitatively reveal the time-dependent electric potential distribution across YSZ surface. COMSOL simulations confirm the presence of a stronger electric field at the top surface, particularly at the advancing reaction fronts, compared to the near-surface region. The critical role of the electric field in driving surface reactions is further supported by the enhanced reactions observed at the tips of the zigzag-shaped electrode edges. This work offers mechanistic insights into the coupling between electrochemical potential dynamics and electrolyte reactions.