Leveraging Prolonged Electrochemical Activation of Cobalt Phosphate in HER and Its Interfacial Effects in OER for Water Electrolysis

Dynamic electrochemical activation, enabling precise tuning of material properties to generate efficient electrocatalysts, is rarely explored for the hydrogen evolution reaction (HER). Hence, materials exhibiting structural evolution and consequent activity enhancement under cathodic potentials are highly desirable as tunable platforms for developing efficient HER electrocatalysts. Herein, for the first time, we unravel β‐Co(OH) 2 as a prolonged activation‐enabled phase that evolves under cathodic potential. Strategically employing Co 3 (PO 4 ) 2 as an alkaline‐responsive precursor for β‐Co(OH) 2 and activating through a steady‐state technique generated an efficient electrocatalyst that attained −10 mA/cm 2 at 114 ± 8 mV, which is ~156 mV less than its preconditioned analog. Comparative electrocatalytic analysis of Co 3 (PO 4 ) 2 ‐derived β‐Co(OH) 2 against its conventional counterpart unveils the governing influence of the phosphate precursor in enhancing the time‐dependent performance boost. The OER activity of the material was rationally tuned by heterostructure engineering of Co 3 (PO 4 ) 2 with Ag 3 PO 4 via a room‐temperature route. The evolved active phase, CoOOH/Ag 2 O, attained 10 mA/cm 2 at 240 mV overpotential, surpassing the individual counterparts. The material exhibited a Faradaic efficiency of 97 ± 2% following the PDET mechanism. The ~100 h durability of electrode materials, coupled with their efficient performance in overall water splitting (10 mA/cm 2 at 1.65 V, 75 h stability), underscores their practical viability.