Visualizing dynamic evolution of surface electrochemical potential on solid-state electrolyte via spatially resolved photoelectron measurements

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.