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Rational designing of electrode materials having high surface area can accomplish the enhanced charge‐storing ability of the electrochemical energy storage devices. Therefore, the surface area of cobalt vanadium oxide (CVO) material is controlled by changing growth dynamics in successive ionic layer adsorption and reaction methods. Structural analysis confirms the formation of hydrous cobalt vanadium oxide nanoparticles (Co3V2O8⋅nH2O) thin film electrodes, and alteration in the surface area with change in growth dynamics is observed in Brunauer–Emmett–Teller analysis. The CVO1:1 thin film electrode prepared at optimal growth dynamics illustrates high specific capacitance (Cs) (capacity) of 793 F g−1 (396.7 C g−1) at 0.5 A g−1, respectively. Moreover, aqueous hybrid supercapacitor devices constructed using CVO1:1 as cathode exhibit high Cs of 133.5 F g−1 at 1.1 A g−1, specific energy (SE) of 47.7 Wh kg−1 with specific power (SP) of 0.90 kW kg−1. The solid‐state hybrid supercapacitor devices also offer high Cs of 102.9 F g−1 at 0.3 A g−1, SE of 36.6 Wh kg−1 at SP of 0.30 kW kg−1. In the SILAR approach, the dipping time plays a critical role in improving the surface area of the material and, consequently, electrochemical performance, as the current work amply indicates.

Recently, excellent electrochemical performance and good conductivity of transition metal phosphates (TMPs) have been obtained, assuring their potential as a cathode in hybrid supercapacitors. Also, amorphous, hydrous materials are supposed to be exemplary active materials for high-performing supercapacitors because of their unique porous structure, structural flexibility, and rich defects. Therefore, the present investigation describes a simple synthesis method for hydrous and amorphous cobalt phosphate thin-film preparation by the simple successive ionic layer adsorption and reaction (SILAR) method on flexible stainless steel (SS) substrate for supercapacitor application. The structural and morphological analyses reveal mesoporous, agglomerated nanoparticle-like, hydrous, and amorphous cobalt phosphate over the SS substrate. The mesoporous nanoparticles of cobalt phosphate material possess the uppermost specific capacitance of 1147 F g −1 and 630.7 C g −1 specific capacity at a 1 mA cm −2 current density. To demonstrate practical relevance, hybrid supercapacitor devices were assembled with cobalt phosphate and rGO (reduced graphene oxide) as cathode and anode electrodes, respectively. Furthermore, the assembled hybrid aqueous supercapacitor device (S-CP4//KOH//rGO) delivers 44.8 Wh kg −1 specific energy (SE) at a specific power (SP) of 4.8 kW kg −1 with 126 F g −1 specific capacitance. The accumulated all-solid-state hybrid supercapacitor device (S-CP4//PVA-KOH//rGO) achieved the uppermost 77 F g −1 specific capacitance and SE of 27.37 Wh kg −1 at SP of 1.5 kW kg −1 with an outstanding 94% capacitive retention over 5000 cycles. Such remarkable supercapacitive performance results demonstrate that the SILAR method is an easy synthesis process for the binder-free preparation of cathode based on hydrous, amorphous cobalt phosphate thin films for hybrid supercapacitor devices.

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Currently, amorphous, hydrous compounds are receiving much attention as an electrode in hybrid supercapacitors (SCs) as it offer extraordinary electrochemical efficiency because of disorder in structure and excellent electrochemical interface....