Wagner officially retired in 1966 but from 1967 to 1977 was a Scientific Member of the Max Planck Institute in Göttingen, continuing to contribute to publications. Many modern inventions based on solid-state technology and semiconductor fabrication, used in devices such as solar energy conversion have been developed with the aid of Wagner's theories. Some examples of solid state electrochemical devices are typically, fuel cells, batteries, sensors and membranes.
Wagner died on 10 December 1977 in Göttingen.