Self-supported iron-doped nickel oxide multifunctional electrodes for highly efficient energy storage and overall water-splitting uses

Caused by complex synthesis processes, slow diffusion rates, and the formation of undesired nanostructures, it is tedious to produce a high-quality nickel oxide (NiO) electrodes for potential energy storage and water splitting applications. This paper introduces a novel chemical technique for producing self-supported iron-doped NiO electrodes having a high concentration of oxygen vacancies by utilizing different iron-based salts i.e. iron nitrate, iron chloride, iron ammonium sulfate, iron fumarate, and iron sulfate salts. After examining physical properties, the electrochemical energy storage and water splitting measurements were performed where iron nitrate precursor-mediated self-supporting Fe-NiO electrode confirms the optimum performance. Specifically, it exhibits a specific capacitance (SC) of 3302.5 Fg⁻¹ at a current density of 5 Ag⁻¹. The as-fabricated Fe-NiO-A//Bi₂O₃ asymmetric supercapacitor has a broad voltage range of 1.5 V, a remarkable volumetric-energy-density of 98.2 W hkg⁻¹ at a power density of 900 Wkg⁻¹, and a long-lasting cycling life with 92.6 % capacity retention after 5000 cycles at a current density of 15 Ag⁻¹. A bifunctional Fe-NiO//Fe-NiO electrocatalyst demonstrates a current density of 10 mA cm⁻² and remarkable long-term durability of 75 h without any degradation while operating at an ultra-low cell voltage of only 1.51 V, specifying importance of self-supported Fe-doped NiO electrodes for electrochemical energy storage and water splitting applications.