Sensor element, gas sensor, and sensor element manufacturing method

A method of manufacturing a sensor element for detecting a particular gas present in a measurement object gas, the sensor element having a first electrode disposed on a solid electrolyte layer;

• a second electrode serving as a counter electrode to the first electrode and disposed on the solid electrolyte layer;
• and at least one porous layer which intervenes between the outside and one of the first and second electrodes such that the measurement object gas introduced from the outside to the one electrode passes through the porous layers,
• wherein the at least one porous layer is a catalyst layer supporting particles of one or more noble metals selected from the group consisting of Pt, Pd, and Rh, and
• wherein the method comprises;
• a permeation step of causing a noble metal salt solution containing ions or particles of the noble metal to permeate the porous layer to serve as the catalyst layer;
• and
• a heat treatment step of conducting a heat treatment of the porous layer which the noble metal salt solution has permeated in an inert atmosphere or a substantially inert atmosphere containing oxygen in an amount of 2,000 mass ppm or less, at a temperature equal to or higher than the thermal decomposition temperature of a component of the noble metal salt solution.