Iron-air batteries are well known in the art, and taught, for example, by Chottiner, in U.S. Pat. No. 4,152,489. These batteries can utilize air as an oxidant reactant. The air contacts an electrode made of an outer hydrophobic membrane, laminated to an active hydrophilic layer. The electrode layers can contain carbon particles, catalyst, low oxygen overvoltage material, such as WC, and binder, pasted into a fiber metal plaque. These batteries usually contain an iron fuel electrode, immersed in potassium hydroxide electrolyte, and disposed between a set of air electrodes.
The iron electrode can contain a mixture of iron oxides, for example Fe.sub.2 O.sub.3 and Fe.sub.3 O.sub.4, with reaction promoting compounds and dispersing agents, pasted into diffusion bonded, nickel-plated steel plaques, as taught by Seidel, in U.S. Pat. No. 3,849,198. The iron electrode can also be self-supporting, and contain sintered metallic iron particles coated with a metal sulfate, such as MgSO.sub.4, as taught by Buzzelli et al. in U.S. Pat. No. 4,132,547. Because they operate at about 25.degree. C. and have a very high energy-to-density ratio, they have been considered in the past as a power source for electrically run automobiles.
Fuel cells of the phosphoric acid, molten carbonate, and solid oxide type are also well known power sources, although they operate at a much higher temperature than an iron-air battery, usually, from about 150.degree. C. to 1100.degree. C. Coal gasification processes are also well-known means to produce electrical energy, as taught, for example, by Archer et al., in U.S. Pat. No. 3,804,606. Fuel cells have been suggested to be used to provide heat to a wide variety of systems, including large fluidized bed coal gasification reactors, where coal char is fed into the reactor, along with air or oxygen and steam, and heat is generated along with valuable combustible gases, such as CO and hydrogen, as taught by Gorin, in U.S. Pat. No. 2,581,651.
In Gorin, the coal gasification reactor heat of combustion is kept at about 760.degree. C., which is below maximum operating temperature, so as to be at a temperature less than the operating range of the fuel cell which receives part of the combustion heat. The fuel cell also generates heat, which helps to maintain the coal combustion. The CO and hydrogen from the gasification furnace, along with air or oxygen are used as reactants for the fuel cell. Such a process, however, loses some efficiency because there are many highly technical problems associated with maintaining a fuel cell within a gasification reactor. What is needed is an even more efficient, and simpler method of converting coal to electrical energy.