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

Abstract 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 NiCoSe 2 (H‐NiCoSe 2 ) sub‐microspheres. Inherent formation of metallic H‐NiCoSe 2 is tentatively put forward with comparative structure‐evolution investigations. Interestingly, the fresh H‐NiCoSe 2 does not demonstrate striking supercapacitive behaviors when evaluated for electrochemical supercapacitors (ESs). But it exhibits competitive pseudocapacitance of ≈750 F g −1 at a rate of 3 A g −1 with a high loading of 7 mg cm −2 after ≈100 cyclic voltammetry (CV) cycles. With systematic physicochemical/electrochemical analyses, intrinsic energy‐storage mechanism of the H‐NiCoSe 2 is convincingly revealed that the electrooxidation‐generated biactive CoOOH/NiOOH phases in aqueous KOH over CV scanning, rather than the H‐NiCoSe 2 itself, account for the remarkable pesudocapacitance observed after cycling. An assembled H‐NiCoSe 2 ‐based asymmetric device has delivered an energy density of ≈25.5 Wh kg −1 with a power rate of ≈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.