Superior dual mode electrochemical sensing of NH3 using Ni2+ doped CuO anode with lanthanum gallate based electrolyte

Abstract

Lanthanum gallate based electrochemical sensor was investigated in amperometric and potentiometric modes. A constant bias voltage of + 1 V was applied at CuO based electrode with respect to a fixed lanthanum strontium cobaltite (LSC55) electrode for detecting 3–40 ppm NH3 in base gas (5% O2 + N2) from 300 ℃ to 650 ℃ with the aim for exhaust gas application. CuO electrode composition with Ni2+ doping was studied and sensor with 2 mol% Ni2+ doped CuO exhibited highest sensitivity of 2124 µA/decade and 338 mV/decade at 550 ℃ in amperometric and potentiometric modes respectively. Using electron paramagnetic resonance (EPR) spectroscopy, the reason for the highest sensing performance due to the formation of efficient active sites for this specific doping of CuO was ascertained. Incidentally, all the sensors were found reproducible in sensing, fast in operation. The electrochemical sensor could detect concentration of NH3 as low as 3 ppm even at temperature 300 ℃ because of high ionic conductivity of the electrolyte and the electrode performances. Influence of biasing, preferential electrochemical reactions at the electrode-electrolyte interfaces and oxygen pumping current through the electrolyte confirmed the mechanism of sensing. High selectivity for ammonia detection with respect to others coexisting gases was observed. High sensitivity in both the sensing modes with minimum sensing down to 3 ppm NH3 makes the developed sensor a promising candidate for exhaust gas application.