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+xMg_1−x/2SiO₄, 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+xMg_1−x/2SiO₄ 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 SO₂ detection, as the first demonstration of type III potentiometric gas sensors using K⁺ conductors. At 500 °C and SO₂ 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 SO₂), fast response times (1–6 min), and excellent stability in ambient condition.