A practical one-electrode electrochemical methodology for tracking catalyst reconstruction in NiFe-Prussian blue...

Efficient and durable alkaline oxygen evolution reaction (OER) catalysts are essential for large-scale water electrolysis, yet the dynamic reconstruction of precatalysts into their true active phases remains difficult to track with simple, broadly accessible tools. Here, we use NiFe Prussian blue analogues (NiFe-PBA) grown on nickel foam (NF) as a model system to develop a practical, fully sequential one-electrode workflow that correlates structural evolution with electrochemical kinetics during the OER. NiFe-PBA/NF electrodes with varying Ni : Fe stoichiometries are synthesized hydrothermally and optimized for OER performance, identifying NiFe-PBA 1 : 1/NF as the best-performing composition. A continuous one-electrode protocol is then applied to the same physical electrode, enabling us to monitor reconstruction and kinetic stabilization under realistic operating conditions. Post-OER analysis reveals substantial disruption of the NiFe-PBA framework, amorphization, and increased Ni³⁺/Fe³⁺ and oxyhydroxide species, consistent with the formation of a NiFeOOH-like active phase. By directly linking these structural and surface-chemical changes to the observed kinetic improvements, this study clarifies the role of NiFe-PBA as an electrochemically transformable precursor to NiFeOOH and demonstrates a simple, accessible one-electrode approach for tracking catalyst reconstruction and active-phase evolution in alkaline OER.