Surface decorated spinel-oxide electrodes for mixed-potential ammonia sensor: Performance and DRT analysis

[Display omitted] •Novel, cost-effective, and high-performance surface decorated spinel-oxide electrode for a mixed-potential ammonia sensor.•The DRT analysis was employed for the first time to investigate the multistep relaxation processes during sensor operation.•The mixed-potential was solely governed by the interfacial redox reactions at the TPB rather than mass-transport processes.•The sensor displayed excellent sensitivity, selectivity, and exceptional stability over five months. The mixed-potential gas sensors appeared as the most promising sensing technology for the in-situ quantification of exhaust pollutants due to their simple configuration, low-cost, and thermochemical stability. Presently, high sensitivity and selectivity supplemented by long-term stability is the bottleneck challenge for these sensors to commercialize. Herein, highly sensitive and ammonia (NH3) selective mixed-potential gas sensors were developed using surface decorated CuFe2O4 (CFO)–MOX (M = Sn, Ni, Zn) composite sensing electrodes (SE). The CFO–NiO SE enriched of the surface oxygen vacancies produced a maximum response of −62 mV to 80 ppm NH3, supported by excellent sensitivity at 650 ℃. The comprehensive analysis of the response behavior and current-voltage (I–V) characteristics verified the sensing mechanism to be based upon the mixed-potential model conforming to the reaction-rate limited Butler–Volmer NH3 oxidation kinetics. Finally, the distribution of relaxation times (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). Moreover, the high sensitivity, selectivity, and exceptional stability over five months substantiate the suitability of the presented sensor as a potential candidate for in-situ ammonia quantifications in industrial and automotive applications.