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Abstract

Supercapacitor miniaturization is highly sought after due to the considerable demand for portable, flexible, and wearable microscale electronics. Constructing supercapacitor devices in micro- and nano-scale dimensions, however, poses significant conceptual and technical challenges. We report an in-plane nickel–ruthenium/ruthenium-oxide (NiRu/RuO₂) nano-supercapacitor fabricated by the focused ion beam (FIB) technique. The FIB-patterned nano-supercapacitor exhibits interdigitated microscale electrodes separated by extremely small, 100 nm, spacings and a thin (200 nm) electrodeposited NiRi/RuO₂ layer. An aqueous device exhibited high areal capacitance (10.5 mF cm⁻²) at high scan rates, low equivalent series resistance (0.047 Ω cm²), good capacitance retention, and a power density of 625 mW cm⁻² with an energy density of 0.8 μW h cm⁻². A NiRu/RuO₂ nano-supercapacitor containing a polymer gel electrolyte was also prepared, demonstrating the practical applicability of the technology. Notably, the FIB-fabricated NiRu/RuO₂ nano-supercapacitor featured high frequency response and alternating current (AC)-line filtering capabilities, making the device the smallest supercapacitor AC line-filter reported. The new FIB-fabricated NiRu/RuO₂ nano-supercapacitor design may open new avenues in nano- and micro-scale energy storage, power conditioning, and AC line filtering.