Activating Inert Crystal Face via Facet‐Dependent Quench‐Engineering for Electrocatalytic Water Oxidation

Abstract Developing a facile strategy to activate the inert crystal face of an electrocatalyst is critical to full‐facet utilization, yet still challenging. Herein, the electrocatalytic activity of the inert crystal face is activated by quenching Co 3 O 4 cubes and hexagonal plates with different crystal faces in Fe(NO 3 ) 3 solution, and the regulation mechanism of facet‐dependent quench‐engineering is further revealed. Compared to the Co 3 O 4 cube with exposed {100} facet, the Co 3 O 4 hexagonal plate with exposed {111} facet is more responsive to quenching, accompanied by a rougher surface, richer defect, and more Fe doping. Theoretical calculations indicate that the {111} facet has a more open structure with lower defect formation energy and Fe doping energy, ensuring its electronic and coordination structure is easier to optimize. Therefore, quench‐engineering largely increases the catalytic activity of {111) facet for oxygen evolution reaction by 13.2% (the overpotential at 10 mA cm −2 decreases from 380 to 330 mV), while {100} facet only increases by 7.6% (from 393 to 363 mV). The quenched Co 3 O 4 hexagonal plate exhibits excellent electrocatalytic activity and stability in both zinc–air battery and water‐splitting. The work reveals the influence mechanism of crystal face on quench‐engineering and inspires the activation of the inert crystal face.