Vertically Aligned Niobium Nanowire Arrays for Fast-Charging Micro-Supercapacitors

Planar micro-supercapacitors are attractive for system on chip technologies and surface mount devices due to their large areal capacitance and energy/power density compared to the traditional oxide-based capacitors. In the present work, a novel material, niobium nanowires, in form of vertically aligned electrodes for application in high performance planar micro-supercapacitors is introduced. Specific capacitance of up to 1 kF m⁻² (100 mF cm⁻²) with peak energy and power density of 2 kJ m⁻² (6.2 MJ m⁻³ or 1.7 mWh cm⁻³) and 150 kW m⁻² (480 MW m⁻³ or 480 W cm⁻³), respectively, is achieved. This remarkable power density, originating from the extremely low equivalent series resistance value of 0.27 Ω (2.49 µΩ m² or 24.9 mΩ cm²) and large specific capacitance, is among the highest for planar micro-supercapacitors electrodes made of nanomaterials.

Fast-charging micro-supercapacitors are made from vertically aligned niobium nanowire arrays. Thanks to the high electrical conductivity of the nanowires, the micro-supercapacitor exhibits a very small characteristic relaxation time constant of 8.4 ms. With 1 m sulfuric acid, cycling rates of up to 300 V s⁻¹ are achieved while with 1-ethyl-3-methylimidazolium tetrafluoroborate an operating voltage of up to 4 V is obtained.

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