Apparatus and method for heating a device for exhaust gas after-treatment

An apparatus for heating an exhaust gas after-treatment unit in a vehicle has, as a drive source, both a combustion engine and an electric motor. The apparatus includes: a honeycomb body configured for exhaust gas to flow therethrough, the honeycomb body having a hollow, through which hollow the exhaust gas flows; and at least one electric heating element arranged in the hollow so as to heat the honeycomb body. The honeycomb body includes a plurality of metal foils stacked one on top of the other, which metal foils form between them a plurality of flow channels, through which a flow can pass along an axial direction, wherein the hollow of the honeycomb body extends in a radial direction, in which the at least one heating element is accommodated.