Boosting the Supercapacitive Performance via Incorporation of Vanadium in Nickel Phosphide Nanoflakes: A High-Performance Flexible Renewable Energy Storage Device

Developing an efficient capacitive matrix along with the emergence of battery-type characteristics is the key priority function to attain high-performance asymmetric supercapacitors (ASCs). The rational design of metal-rich transition metal phosphides with a remarkable electrochemical activity and rich valence state possesses an efficient approach to overcome their limitation toward the low-rate capability with poor cycle life against metal deficient counterparts for their practical application. Herein, the metal-rich porous vanadium-doped nickel phosphide (V-Ni₁₂P₅) nanoflakes have been synthesized via a one-step solvothermal method. The as-synthesized electrode delivers a high specific capacity of 1455 F g–¹ at a current density of 1 A g–¹, and the corresponding assembled ASC device delivers a maximum energy density of 38.41 Wh kg–¹ at a power density of 626.48 W kg–¹ as well as long term cycling stability with 76.3% capacitive retention after 11,000 cycles. The assembled four sets of 1 × 1 cm² devices in series designed with the help of a flexible carbon cloth matrix can light a red LED for 3 min and can rotate a 3 V home-designed windmill device for 1 min with in situ charging via a 6 V standard silicon solar panel illuminated by 50 W street light for 1 min. The flexible device can retain its invariant capacitive performance under rigorous twisting and bending at variable angles of 0, 90, and 135°. The significant enhancement (∼60%) of electrochemical activity for doped systems is mainly attributed to the generation of partial positive polarity on the metal centers and thereby induces strong adhesion of electrolytes under prolonged operation. Hence, this present work demonstrates the excellent capability of V-Ni₁₂P₅ nanoflakes toward the realistic drive of renewable energy conversion, unveiling the booming technology toward reliable high-performance hybrid energy-storage systems.