Fast Response, Highly Sensitive and Selective Mixed-Potential H₂ Sensor Based on (La, Sr)(Cr, Fe)O_3-δ Perovskite...

A planar mixed-potential type sensor consisting of La_0.8Sr_0.2Cr_0.5Fe_0.5O_3-δ sensing electrode, yttria-stabilized zirconia solid electrolyte, and Pt reference electrode was developed for H₂ detection. The sensor showed high and repeatable response with a value of -143.6 mV for 1000 ppm of H₂ at 450 °C. The sensor response varied linearly or logarithmically with the hydrogen concentration in the range of 20-100 ppm and 100-1000 ppm of H₂, respectively. The response/recovery time generally decreased with increasing concentration and temperature, and reached almost steady above 300 ppm of H₂. Response time as short as 4 s and recovery time of 24 s were attained at 450 °C for 500 ppm. The sensor exhibited excellent selectivity to hydrogen against interference of CH₄, C₃H₈, CO, NO₂, and NH₃. The mixed-potential mechanism was assessed by electrochemical measurements, and the sensing behavior was discussed in relation to the reaction kinetics. The excellent H₂ sensing performance for concentrations above 100 ppm is ascribed to the high electrocatalytic activity of the perovskite electrode to H₂ oxidation. The inferior performance for lower H₂ concentrations may be related with slow gas diffusion in the electrode.