High-performance noble metal-free gas sensors are crucial for widespread applications in various areas. Non-Nernstian electrochemical sensors have attracted tremendous attention, but are limited by the high cost and low efficiency of Pt electrode. Moreover, responses from different electrodes usually have the same polarity, degrading the sensor performance. Here we report a reverse response on a series of mixed ionic-electronic conductors (MIECs). Exemplary SrFe0.5Ti0.5O3-δ (SFT50) perovskite shows excellent H2 sensing properties, including high sensitivity and selectivity, humidity resistance, and long-term stability. Strikingly, the response is positive, as opposed to the usual one. Such an unusual response is ascribed to the change of the surface electrostatic potential due to the gas chemical reaction, which outcompetes traditional mechanisms, thereby reversing the response polarity. A conceptual noble-metal-free sensor with dual oxide electrodes of opposite polarity is designed by substituting SFT50 for the benchmark Pt, achieving a 1.5-2.0× increase in H2 response, sensitivity, and selectivity and a low limit of detection of 16 ppb. The ideal unity of excellent sensing and unusual polarity for MIECs can be used to optimize the performance of a variety of conventional sensors while reducing the cost. Our findings provide new insights into electrochemical gas sensing and offer a facile approach for developing low-cost high-performance gas sensors.
Keywords: electrochemical; gas sensor; mixed conductor; perovskite; potential.