MoO<sub>2</sub> as a Propitious “Pore-Forming Additive” for Boosting the Water Oxidation Activity of Cobalt Oxalate Microrods
Sourav Ghosh, Harish Reddy Inta, Sagar Ganguli, Gouri Tudu, Heramba V. S. R. M. Koppisetti, Venkataramanan Mahalingam
Abstract
The electrocatalytic oxygen evolution reaction (OER) demands an efficient catalyst with low overpotential, rapid kinetics, and long-term stability. Herein, we demonstrate the activity of molybdenum oxide (MoO2)-embedded cobalt oxalate (CoC2O4·2H2O) nanostructures for the OER process. The excellent performance of the microrod-like MoO2/CoC2O4·2H2O composite is reflected in just 330 mV overpotential for 10 mA/cmgeo2, low Tafel slope (78 mV/dec), 90% faradaic efficiency, and 24 h stability in 1.0 (M) KOH. The as-prepared electrocatalyst requires a significantly lower overpotential wrt CoC2O4·2H2O. Incorporation of MoO2 elegantly modified the textural property, such as surface area and porosity, of the as-prepared material. Furthermore, MoO2/CoC2O4·2H2O was found to follow the proton-decoupled electron-transfer mechanism for electrocatalyzing OER. Postcatalytic characterization revealed the electrochemical transformation of a one-dimensional (1-D) MoO2/CoC2O4·2H2O microrod into a sheetlike two-dimensional α-Co(OH)2/CoOOH during alkaline OER. Interestingly, postcatalytic X-ray photoelectron spectroscopy, inductively coupled plasma, and energy-dispersive X-ray spectroscopy analyses suggest MoO2 etching from the material, leading to exposure of a higher number of electrochemically active sites that otherwise lay inactive because of their presence in the bulk. Both CoC2O4·2H2O- and MoO2/CoC2O4·2H2O-integrated 1-D nanostructures showed an ∼0.01 s–1 turnover frequency value at 400 mV overpotential. We believe that the enhancement in geometrical electrocatalytic activity is not due to the direct participation of MoO2 in catalysis but due to its electrochemical etching, which makes a higher number of catalytically active sites accessible to the electrolyte. This study conveys the in situ electrochemical activation strategy through etching of pore additive for the alkaline OER process.