1. G. Grüneberg, W. Wicke, E. Justi, British Patent GB994448 (1961) also equivalent French Patent FR1321373 (1961).
2. G. Goebel, B.D. Struck, W. Vielstich, in: W. Vielstich (Ed.), English translation by D.J.G. Ives, Fuel Cells—Modern Processes for the Electrochemical Production of Energy, Wiley/Interscience, New York, 1965, pp. 374–376, ISBN: 0471906956.