1：Experimental Design and Method Selection:

The study synthesized a hybrid electrocatalyst (BC1.5MN) using a solid-state reaction method to combine single and double perovskite structures for enhanced OER performance. Theoretical models include the OER mechanism involving four-electron charge-transfer steps on transition metal sites.

2：5MN) using a solid-state reaction method to combine single and double perovskite structures for enhanced OER performance. Theoretical models include the OER mechanism involving four-electron charge-transfer steps on transition metal sites. Sample Selection and Data Sources:

2. Sample Selection and Data Sources: Powders of BaCO3, Co3O4, MoO3, and Nb2O5 (analytical grade from Aladdin Industrial Corporation) were used as starting materials. Hybrid-WI and hybrid-PM samples were prepared for comparison via wet impregnation and physical mixing methods.

3：List of Experimental Equipment and Materials:

Equipment includes X-ray diffraction (XRD, Rigaku Smartlab 3 kW), high-resolution transmission electron microscopy (HRTEM, JEOL JEM-200CX), X-ray photoelectron spectroscopy (XPS, Kratos Axis Ultra DLD), BET analysis system, soft X-ray absorption spectroscopy (XAS at Dragon beam line, NSRRC), rotating disk electrode (RDE) equipment, CHI 760E bipotentiostat workstation, Ag/AgCl reference electrode, platinum wire counter electrode, carbon cloth working electrode. Materials include BaCO3, Co3O4, MoO3, Nb2O5, Co(NO3)2·6H2O, ethanol, KOH solution.

4：Experimental Procedures and Operational Workflow:

Synthesis involved mixing powders, ball milling, calcination at specified temperatures, and characterization. Electrochemical measurements were performed in a three-electrode cell with RDE, using O2-saturated 0.1 M KOH solution. Stability tests included chronopotentiometry and cyclic voltammetry.

5：1 M KOH solution. Stability tests included chronopotentiometry and cyclic voltammetry. Data Analysis Methods:

5. Data Analysis Methods: Data analysis involved calculating overpotential, mass activity, intrinsic activity, Tafel slopes, electrochemical double-layer capacitances, and using XPS and XAS for chemical state analysis.