3D nanoporous-structured Gold/Copper on microelectrode arrays for enhanced gas sensing in room temperature ionic liquids

Abstract

Microelectrode arrays offer higher current density and lower ohmic drop due to increased radial diffusion, making them particularly advantageous for electroanalytical applications, especially for the trace detection of analytes. Additionally, the informed design of microelectrodes can significantly improve current response. In this work, we present unique three-dimensional (3D) nanoporous structures of gold/copper on recessed microelectrode arrays (10 µm in diameter, 91 electrodes) for the voltammetric detection of oxygen and sulfur dioxide gases in a room-temperature ionic liquid. The fabrication of these 3D nanoporous structures involves the electrodeposition of co-metals, followed by chemical dealloying. Gold and copper were co-deposited into the microholes, followed by the selective removal of copper through chemical dealloying resulting in 3D cauliflower-like structures with numerous nanopores. These structures exhibited a 34-fold increase in electroactive surface area (ESA) compared to the unmodified arrays. The modified sensors were tested for their response to oxygen and sulfur dioxide gases in 1‑butyl‑1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ([C₄mpyrr][NTf₂]). A linear working range of 10–100 % vol. O₂ and 10–200 ppm SO₂ was achieved, with limits of detection of 1.1 % vol. O₂ and 1.0 ppm SO₂, respectively. The enhanced ESA significantly improved the performance of the sensors, resulting in a 191-fold increase in detection currents for oxygen and a 50-fold increase for sulfur dioxide compared to the recessed arrays. This work clearly demonstrates that integrating 3D nanoporous structures on microelectrode arrays significantly enhances surface area, leading to outstanding sensitivity and improved performance for gas sensing applications.