Mechanosynthesis of pseudocapacitive MnCO3 and CoCO3 electroactive materials

Abstract

• Ball milling is a cost-effective, one-step, and solvent-free approach to preparing electrode materials and shows advantages such as no use of heat treatment, harmful solvents, long processes, and high energy consumption required by the common methods such as solvothermal, sol–gel, hydrothermal, and precipitation. • Functional materials applied in supercapacitors can be produced via planetary ball milling. • Transition metal carbonates and nanocomposite were mechanochemically synthesized without additional process. • MnCO 3 and CoCO 3 resulted in excellent performance in 1 M KOH electrolyte. • High storage, remarkable rate capability, and outstanding capacitance retention were achieved. Transition metals are known for their enormous potential as electrode materials for supercapacitor applications, however anhydrous carbonate minerals, namely Mn-carbonate, and Co-carbonate, are less explored and exhibit competitive energy storage performance compared to oxide and hydroxide forms. For the first time, MnCO 3 (Rhodochrosite), CoCO 3 (Spherocobaltite) and MnCo mixture (Mn 1-x Co x CO 3 ) were synthesized via mechanochemistry by a one-pot approach and used to prepare pseudocapacitive electrode materials for electrochemical energy storage. In this work, these materials were tested in alkaline electrolyte, and the morphological and structural features of the materials were examined using SEM (Scanning Electron Microscope), Transmission Electron Microscopy (TEM) and X-ray Diffraction (XRD). The surface composition was studied by X-ray photoelectron spectroscopy (XPS). After milling, the microstructures showed an increase in dislocations and microstrains in their crystal lattices which influenced the electrochemical performance. The crystallinity of the carbonate materials was also affected by grinding. In 1 M KOH electrolyte, milled MnCO 3 evidenced the highest specific capacitance (354.3 F/g at 1.0 A/g), while milled CoCO 3 , revealed impressive capacitance retention of 94.8 % after 20000 continuous charge–discharge cycles at 10 A/g. Interestingly, the composite (Mn-Co)CO 3 evidenced superior rate capability (58.8 %) and enhanced capacitance retention under cycling compared to the individual cobalt and manganese carbonates. The results evidence the excellent electrochemical behavior of Mn and Co carbonates prepared by a simple, low-cost, and green route and prove their potential as electroactive electrode materials for electrochemical energy storage applications, particularly pseudocapacitors.

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