One attractive suggestion is based on harvesting the potential produced in different steps of metabolism in living systems [2]. Basic principles remain the same in all such models. One of them is to tap the oxidative phosphorylation path, and the other one is to use the photosynthetic mechanism. There are a few more novel systems suggested by other schools: (a) calcium pumps in biological systems by Ernesto Carafoli of Swiss Federal Institute of Technology, Zurich, (b) constructing cells from bacteriorhodopsin of the purple membranes of certain bacteria by Lester Packer of the University of California at Berkeley, United States, and

Figure 1.4 Gaseous battery (hydrogen fuel cell).

(c) isolated energy-rich compounds, i. e., iron-sulfur proteins, ATP, and so forth, suggested by many other authors [3].