An exhaust post-treatment device (2) for a vehicle (4) for reducing nitrogen oxides present in the exhaust gases (20) of the vehicle (4) by supply of liquid reducing agent (18) to the exhaust gases (20) in an exhaust pipe (32). The device (2) locally warms a surface (31) within the exhaust pipe (32) by a Peltier element (6) by using thermal energy from the exhaust gases (20) to vaporize liquid reducing agent (18) which reaches the surface (31), thereby avoiding the formation of deposits of reducing agent within the exhaust pipe (32). Also a method for post-treatment of exhaust gases from vehicles with an exhaust post-treatment device (2) including a Peltier element (6).