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.