Monodisperse Metallic NiCoSe2 Hollow Sub-Microspheres: Formation Process, Intrinsic Charge-Storage Mechanism, and Appealing Pseudocapacitance as Highly Conductive Electrode for Electrochemical Supercapacitors

Highly conductive metal selenides are gaining prominence as promising electrode materials in electrochemical energy-storage fields. However, phase-pure bimetallic selenides are scarcely retrieved, and their underlying charge-storage mechanisms are still far from clear. Here, first a solvothermal strategy is devised to purposefully fabricate monodisperse hollow NiCoSe2 (H-NiCoSe2) sub-microspheres. Inherent formation of metallic H-NiCoSe2 is tentatively put forward with comparative structure-evolution investigations. Interestingly, the fresh H-NiCoSe2 does not demonstrate striking supercapacitive behaviors when evaluated for electrochemical supercapacitors (ESs). But it exhibits competitive pseudocapacitance of approximate to 750 F g(-1) at a rate of 3 A g(-1) with a high loading of 7 mg cm(-2) after approximate to 100 cyclic voltammetry (CV) cycles. With systematic physicochemical/electrochemical analyses, intrinsic energy-storage mechanism of the H-NiCoSe2 is convincingly revealed that the electrooxidation-generated biactive CoOOH/NiOOH phases in aqueous KOH over CV scanning, rather than the H-NiCoSe2 itself, account for the remarkable pesudocapacitance observed after cycling. An assembled H-NiCoSe2-based asymmetric device has delivered an energy density of approximate to 25.5 Wh kg(-1) with a power rate of approximate to 3.75 kW kg(-1), and long-span cycle life. More significantly, the electrode design and new perspectives here hold profound promise in enriching material synthesis methodologies and in-depth understanding of the complex charge-storage process of newly emerging pseudocapacitive materials for next-generation ESs.