The effects of Cu-content on Mg2CuxFe1O3.5+x electrodes for YSZ-based mixed-potential type NH3 sensors

Yttria-stablized zirconia (YSZ)-based mixed-potential type NH3 sensors using Mg2CuxFe1O3.5+x mixed metal oxides (x=0, 0.25, 0.50, 1) as sensing electrode material were fabricated for ammonia (NH3) detection at different working temperatures (T=350 °C, 400 °C, 450 °C, 500 °C). The Mg2CuxFe1O3.5+x electrodes were characterized by X-Ray Diffraction (XRD), Environmental Scanning Electron Microscope (ESEM), Energy Dispersive Spectrometer (EDS) and the Brunauer–Emmett–Teller (BET) method. The effects of Cu-content on phase composition, microstructures, NH3 response performances and electrochemically catalytic-activity of Mg2CuxFe1O3.5+x electrodes were discussed. Magnesium copper oxide (Mg0.78Cu0.22O) may be a functional phase that improved NH3 sensitivity of Mg2CuxFe1O3.5+x electrodes, but magnesium dicopper oxide (Cu2MgO3) played an opposite role as a suppressive phase. The Mg2Cu0.25Fe1O3.75 electrode exhibits the biggest response (about 267 mV for 200 ppm of NH3), the highest NH3 sensitivity (220 mV/decade NH3) and the highest electrochemically catalytic-activity may be attributed to its suitable Cu-content for functional phase (Mg0.78Cu0.22O) with higher NH3 adsorptivity, which can absorb more NH3 to the triple-phase boundary (TPB) for the electrochemically reaction.