This work identifies coordination topology as a design variable for balancing activity and stability without changing chemical composition. More broadly, the all-octahedral design of Tri-Co₃O₄ may guide coordination-topology engineering in other transition-metal oxides with mixed coordination environments or accessible polymorphs with different polyhedral connectivity. This approach could tune active-site populations and lattice stability without adding new elements, although the preferred coordination geometry and operando phase stability must be evaluated for each oxide under acidic OER conditions. Because Tri-Co₃O₄ is a metastable phase, possible surface amorphization or partial phase conversion under prolonged acidic polarization should be considered. Operando such as XRD, XAS, and Raman measurements in PEMWE cells combing the post-operation electron microscopy are needed to distinguish retention of the trigonal bulk structure from surface reconstruction. Scaling the vacuum-assisted molten-alkali route will also require uniform precursor-KOH mixing, heat and mass transfer, vacuum conditions, and alkali removal while preserving phase purity across larger batches. Beyond powder synthesis, scale-up from the reported 1 × 1 cm² cell presents additional challenges. Large-area electrodes require uniform catalyst loading and ionomer distribution, controlled thickness and porosity, and low interfacial resistance. The metastable phase must also be retained during ink preparation, coating, and hot pressing. Large-area PEMWE tests are needed to determine whether current distribution and water and gas transport affect long-term performance under device-relevant conditions.