Performance and DRT Analysis of Surface Decorated Spinel-Oxide Electrodes for Mixed-Potential Type Ammonia Gas Sensor

The solid-electrolyte based electrochemical gas sensors appeared as the most promising sensing technology for the in-situ quantification of exhaust pollutants. At present, high sensitivity and selectivity supplemented by suitable long-term stability is the bottleneck challenge for these technologies to commercialize. In present work, highly sensitive and ammonia (NH 3 ) selective mixed-potential gas sensors were developed using surface decorated CuFe 2 O 4 (CFO) spinel oxide electrodes. The CFO–NiO composite SE delivered a maximum response of −62 mV to 80 ppm ammonia, supported by a sensitivity of -70 mV/dec. at 650 ℃. By a thorough analysis of response behavior and I–V characteristics, the sensing mechanism was found to be based upon the mixed-potential model complying to the reaction-rate limited Butler–Volmer NH 3 oxidation kinetics. Finally, the DRT analysis of impedance spectra confirmed that the overall polarization resistance was invariable of the mass-transport processes and solely governed by the extent of interfacial redox reactions proceeding at the triple-phase boundaries (TPB), determining the electrode potential of the sensor. Moreover, the high sensitivity, selectivity, and excellent stability without a degradation over five months, validated the suitability of these sensors to be a potential candidate for in-situ ammonia quantifications in industrial and automotive applications.