1. Review of United States fuel-cell patents issued from 1860 to 1947
2. A. Marko and K. Kordesch, U.S. Pat. 2615932, Oct. 28, 1952.
3. A. Marko and K. Kordesch, U.S. Pat. 2699598, Feb. 16, 1954.
4. E. Justi, U.S. Pat. 2860175, Nov. 11, 1958.
5. E. Justi, H.-J. Thuy, and A. Winsel, U.S. Pat. 2912478, Nov. 10, 1959.