An electrochemical ammonia sensor based on NiCo2O4/γ-MnO2 modified ionic liquids

Accurate and rapid ammonia detection is critical for environmental monitoring and clinical diagnosis of chronic kidney disease. Herein, a highly sensitive room-temperature ionic liquid (RTIL) in electrochemical ammonia sensor based on a Pt-Ru electrode was developed for detecting ammonia concentrations ranging from 0 to 100 ppm. To achieve prolonged operational life and stability, 1-(2-hydroxyethyl)-3-methylimidazolium tetrafluoroborate ([HOETMIM][BF 4 ]) was utilized as the electrolyte. Nickel cobaltite (NiCo 2 O 4 ) and γ-MnO 2 were synthesized separately via hydrothermal methods. The effects of modified ionic liquids on the sensor’s performance were investigated by incorporating different mass fractions of NiCo 2 O 4 and γ-MnO 2 . Comprehensive analyses, including X-ray diffraction (XRD), scanning electron microscopy (SEM), Mapping, energy-dispersive spectroscopy (EDS), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS), confirmed the successful and rational synthesis of the samples. The ammonia sensing performance of the ILs/NiCo 2 O 4 /γ-MnO 2 sensor was studied at room temperature (25°C) using constant potential polarization (it) and electrochemical impedance spectroscopy (EIS) techniques. The testing data demonstrated that the optimized ILs/NiCo 2 O 4 /γ-MnO 2 sensor(5 wt% composite, 1:1 mass ratio) exhibited good sensitivity of 0.10 ± 0.02 μA/ppm, a limit of detection(LOD) of 1 ± 0.2 ppm, and a limit of quantification(LOQ) of 3 ± 0.5 ppm. The response and recovery times show clear difference among different sysrems: pure IL system exhibited 510 s/530 s, 5 wt% composite modified system achieved 12.22 s/3.6 s, and the fastest recorded values in batch tests were 17 s/14.5 s. Compared to traditional ionic liquid sensors, the ILs/NiCo 2 O 4 /γ-MnO 2 sensor demonstrated a significant improvement in ammonia sensing performance, with a selectivity ratio > 10 against common interfering gases.