A catalytically active layer that is used, for example, as an electrode for a solid electrolyte-based sensor element of a gas sensor for determining a gas component in a gas mixture. The catalytically active layer includes a metallic component, that includes a noble metal in the form of platinum, rhodium, and/or palladium, and additionally a base metal. At least a portion of the originally present base metal is replaced by cavities in the metallic component.