Enhanced Potentiometric Hydrogen Sensing Response Based on the Ba_0.5Sr_0.5Co_1–yFe_yO_3–δ Electrode with Unusual Polarity

In this work, unusual potentiometric hydrogen sensing of mixed conducting Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3–δ was reported. Inspired by the unusual polarity, a dual sensing electrode (SE) potentiometric hydrogen sensor was fabricated by pairing Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3–δ with electronic conducting ZnO to enhance the hydrogen response. Hydrogen sensing measurements suggested that significantly higher response, larger sensitivity, and lower limit of detection (LOD) were achieved by the dual SE sensor when compared with the single SE sensor based on Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3–δ or ZnO. A high response of 97.3 mV for 500 ppm hydrogen and a low LOD of 2.5 ppm were obtained by the dual SE sensor at 450 °C. Furthermore, the effect of the Fe doping concentration in Ba_0.5Sr_0.5Co_1–yFe_yO_3–δ (y = 0.2, 0.5, and 0.8) on hydrogen sensing response was investigated. The potentiometric response values to hydrogen increased monotonically with increasing Fe doping concentration. With the Fe/Co atomic ratio increased from 0.25 to 4, the responses to 500 ppm hydrogen raised by 69.6 and 94% at 350 and 450 °C, respectively. The sensing behaviors of unusual Ba_0.5Sr_0.5Co_1–yFe_yO_3–δ may be ascribed to the predominant surface electrostatic effect. These results show that mixed conducting Ba_0.5Sr_0.5Co_1–yFe_yO_3–δ is desirable for developing high-performance dual SE hydrogen sensors.