Regulating the selective adsorption of OH* over the equatorial position of Co3O4via doping of Ru ions for efficient water oxidation reaction

Abstract

The fabrication of highly active and durable electrocatalysts for the oxygen evolution reaction (OER) in alkaline and acidic environments is highly desirable. Herein, Co based benzene tricarboxylic acid derived Co₃O₄ nanorods doped with Ru³⁺ ions (Ru-Co₃O₄) are reported as an efficient electrocatalyst for the OER in both alkaline and acidic media. The highly porous network and distortion by electronic structural modulation in Co₃O₄ after doping of Ru³⁺ ions provide more active sites and ease the penetration of electrolyte, thereby enhancing the electron transport over exposed active metal sites. Operando/in situ Raman and electrochemical impedance spectroscopy (EIS) studies further reveal that optimal doping of Ru³⁺ ions over Co₃O₄ allowed the OER with a low applied potential. Moreover, Ru-Co₃O₄ 15 delivers a lower overpotential of 292 and 365 mV to drive 10 mA cm⁻² current density in alkaline and acidic media. Also, Ru-Co₃O₄ 15 shows a high durability for 33 and 16.5 h in alkaline (1 M KOH) and acidic (0.5 M H₂SO₄) media, respectively, under potentiostatic conditions. The higher activity of Ru-Co₃O₄ 15 is further evident from the volcanic relationship between the electronic charge and current density at 1.55 V, which demonstrates that the catalyst (Ru-Co₃O₄ 15) will efficiently catalyze the OER by adhering to the Sabatier principle of ion adsorption at the ideal concentration of Ru³⁺ ions. Structural observation from density functional theory (DFT) reveals that after doping of Ru, the bond length between the Ru adjacent Co and O (Co–O) is increased (1.95 Å) compared to the Co–O bond in Co₃O₄ (1.92 Å). This favors the OER process by promoting the selective adsorption of OH⁻ ions in the equatorial position of the d_x²−y² orbital with the least amount of energy.