Rapid Solid‐State Gas Sensing Realized via Fast K+ Transport Kinetics in Earth Abundant Rock‐Silicates

Here we report on the discovery of a novel fast potassium super stoichiometric silicate, with fully earth‐abundant nominal chemical composition of K 2+ x Mg 1− x /2 SiO 4 , which exhibits near superionic K + conductivity, up to 5 × 10 −5 S cm −1 at room temperature. Fast K + conduction is attributed to a high Continuous Symmetry Measure value in K‐polyhedrons, coupled with a low packing ratio of Corner‐Sharing‐framework. This is the first time that such a high conductivity is measured by a rock‐silicate formed only by abundant metal ions. K 2+ x Mg 1− x /2 SiO 4 displays excellent stability under air and humidity, which renders it a very promising candidate for economical fabrication of electrochemical devices such as potentiometric gas sensors. We demonstrated this by fabricating a gas sensor for SO 2 detection, as the first demonstration of type III potentiometric gas sensors using K + conductors. At 500 °C and SO 2 concentrations in the range of 0–10 ppm, the sensor exhibited high sensitivities (69–72 mV dec −1 ), robust signal output (220 mV for 2 ppm of SO 2 ), fast response times (1–6 min), and excellent stability in ambient condition.