Pseudocapacitive Storage in Molybdenum Oxynitride Nanostructures Reactively Sputtered on Stainless-Steel Mesh Towards an All-Solid-State Flexible Supercapacitor.

Abstract

Exploiting pseudocapacitance in rationally engineered nanomaterials offers greater energy storage capacities at faster rates. The present research reports a high-performance Molybdenum Oxynitride (MoON) nanostructured material deposited directly over stainless-steel mesh (SSM) via reactive magnetron sputtering technique for flexible symmetric supercapacitor (FSSC) application. The MoON/SSM flexible electrode manifests remarkable Na⁺-ion pseudocapacitive kinetics, delivering exceptional ≈881.83 F g^-1 capacitance, thanks to the synergistically coupled interfaces and junctions between nanostructures of Mo₂N, MoO₂, and MoO₃ co-existing phases, resulting in enhanced specific surface area, increased electroactive sites, improved ionic and electronic conductivity. Employing 3D Bode plots, b-value, and Dunn's analysis, a comprehensive insight into the charge-storage mechanism has been presented, revealing the superiority of surface-controlled capacitive and pseudocapacitive kinetics. Utilizing PVA-Na₂SO₄ gel electrolyte, the assembled all-solid-state FSSC (MoON/SSM||MoON/SSM) exhibits impressive cell capacitance of 30.7 mF cm^-2 (438.59 F g^-1) at 0.125 mA cm^-2. Moreover, the FSSC device outputs a superior energy density of 4.26 µWh cm^-2 (60.92 Wh kg^-1) and high power density of 2.5 mW cm^-2 (35.71 kW kg^-1). The device manifests remarkable flexibility and excellent electrochemical cyclability of ≈91.94% over 10,000 continuous charge-discharge cycles. These intriguing pseudocapacitive performances combined with lightweight, cost-effective, industry-feasible, and environmentally sustainable attributes make the present MoON-based FSSC a potential candidate for energy-storage applications in flexible electronics.