Effects of CoFe2O4 electrode microstructure on the sensing properties for mixed potential NH3 sensor

Mixed potential ammonia sensors based on 5YSZ (ZrO2 doped 5 mol% Y2O3) were prepared, with ferrite CoFe2O4 as sensing electrode material. Co-sintering of electrode and electrolyte has been realized. Sensors with different electrode microstructure characterized by Environmental Scanning Electron Microscope (ESEM) were made by different sintering process, and its influences on the sensors' performance were investigated. The co-sintered sensor, with a porous three dimensional network structure electrode and great adhesion with electrolyte, exhibits the largest response (about 81 mV for 320 ppm NH3) and the highest NH3 sensitivity (55 mV/decade) with the response time (8-10 s) and recovery time (10-12 s) at 450 °C, it also shows satisfying NH3 selectivity compared with NOx, and O2 has few influence on the sensor responses. The enhancement of the NH3 sensitivity may owe to the porous three dimensional network structures, which is beneficial to adsorption and diffusion of the target gas, and better bonded interface between the electrode and electrolyte also provides more quantity of triple-phase boundary (TPB).