Combination cell

#Utility system electric loads vary from hour to hour, day to day, and from season to season. These load variations result in typical annual electric utility system load factors ranging from about 50 to 70 percent. Utility system generating capacity is installed to meet the system's annual peak daily load requirements with a certain degree of reliability. Therefore, the amount of total installed generating capacity is generally in the range of 15 to 25 percent higher than the system's peak day load demand. Because of the difference between the variations in the system load profile and the generation capacity reserve margin at any time, a portion of a system's baseload installed generating capacity may be unused during off-peak or light load periods. This availability of off-peak base-load generating capacity makes electric energy storage concepts attractive to utilities because of the potential savings which could result from storing low cost base-load off-peak energy for use in supplying peak load requirements. The benefits of electrochemical energy storage devices are expected to be realized more fully in conjunction with nuclear power plants which are designed as base load plants for optimal economy of operation rather than with base-load fossil fuel plants whose fuel supply is limited, unstable and increasing in cost as lower sulfur content fuel is needed to meet air pollution control requirements.

#Off-peak energy storage requirements have been met in the past by the use of hydroelectric pumped water storage on electric utility systems. Lack of acceptable sites for future pumped storage systems has increased the desirability of developing alternative off-peak energy storage systems. Electrochemical energy storage systems are potentially attractive for future use in electric utility systems. The two general types of electrochemical systems being considered are: rechargeable chemical batteries (e.g., lithium sulfur and lead-acid batteries) and hydrogen systems. One type of hydrogen system is based on a water electrolysis subsystem to generate hydrogen, a metal hydride subsystem to store hydrogen, and a hydrogen/air (oxygen) fuel cell subsystem. The electrolyzer/fuel cell combination (two separate devices) with hydrogen, and possibly oxygen, storage constitutes an off-peak energy storage system. This use of a fuel cell is distinguished from a reformed-type fuel cell operating on fossil fuels as a source of hydrogen to generate peaking power.

#The water battery or reversible electrolyzer of the present invention is distinguished from the above hydrogen system in that the same hardware or device is used to perform both the water electrolysis and the fuel cell functions within a closed system recycling the water and gases between the device and their storage facilities. The general concept of using a single device for off-peak energy storage is not new. The term "regenerative (hydrogen-oxygen) fuel cell" has been used to describe several different concepts that were variations of fuel cell technology for space applications: a single electrolyzer/fuel cell device with internal gas storage, separate electrolyzer and fuel cell devices in a common unit with internal gas storage, separate water electrolysis and fuel cell subsystems with external gas storage.

#FIG. 1 is a front sectional view, largely schematic, of a typical combination cell according to the present invention.

#FIG. 2 is a similar view of alternative forms of some of the components and arrangements in FIG. 1.

#FIG. 3 is an enlargement of the portion labelled 3 in the cell of FIG. 1.

#A typical combination water electrolyzer and fuel cell 10 according to the present invention for selectively storing and supplying energy while in a substantially fixed position comprises a pan 11, 11' held in a substantially horizontal position, an aqueous electrolyte 12 held within the pan, means communicating with a supply of hydrogen 13 and forming a container 14, 14' for the hydrogen within the pan 11, a nonporous hydrogen diffusion negative electrode 15, 15' positioned within the pan 11 and having one surface 16, 16' in contact with the electrolyte 12 and an opposite surface 17, 17' communicating with the hydrogen, means communicating with a supply of oxygen 18 and furnishing the oxygen to a region 19 contiguous with the exposed surface 20 of the electrolyte 12, a porous positive electrode 21, 21' in contact with the electrolyte 12 and having a thin substantially flat major portion 22, 22' adjacent and substantially parallel to the upper surface 20 of the electrolyte 12 with a substantial portion of the surface 40, 42; 40', 42' of the positive electrode 21 contacted by electrolyte 12 and adjacent an interface 23, 23' of the electrolyte 12 and the oxygen, and means 41, 41', 44, 44' (with a switch 24) for connecting the electrodes 15, 21; 15', 21' selectively either to a source of direct current 25 for charging the cell 10 or to an electric load circuit 26 for using the energy stored in the cell 10 when charged.

#A typical cell 10 comprises also an insulating member 27 fitting onto the upper portion of the cell 10 and shaped to hold another such cell, and at least one additional such cell 10, each held by the insulating member 27 of the cell beneath it. Also typically included are means 13 (with connecting means 28 thereto) for storing in a first confined region 14, 14' the supply of hydrogen, including that produced during charging, and means 18 (with connecting means 29 and a housing 30) for storing in a second confined region 19 the supply of oxygen, including that produced during charging; means 18 (may include conventional manual or automatic pressure controls) for maintaining the partial pressure of the oxygen in the second confined region 19 at about 5 to 3000 psia; and means, such as a fan 31 and a heat exchanger 32 (may include conventional manual or automatic temperature controls), for maintaining the temperature of the electrolyte at least at about 100.degree. C.

#As shown in FIGS. 1 and 3, the negative electrode 15 typically comprises a thin member 33 on a porous support 34 held in a substantially horizontal position to form, with the bottom portion 35 of the pan 11, the container 14 for the hydrogen within the pan 11, and with the upper surface 16 of the thin member 33 supporting the electrolyte 12. Another typical form of the negative electrode, as shown in FIG. 2, comprises a thin tube 15' immersed in the electrolyte 12 and with the inside of the tube 15' comprising the means communicating (via the connecting means 28) with the supply of hydrogen 13 and forming the container 14' for the hydrogen within the pan 11. Typically the tube 15' comprises a thin conductive outer layer 37 on a porous tubular support 38, and the pan 11 has an insulating inner surface 39 that supports the tube 15'. The surface 16, 16' of the negative electrode 15, 15' in contact with the electrolyte 12 typically comprises a corrosion resistant alloy consisting essentially of a major amount of palladium and a minor amount of silver, typically about 10 to 45 percent by weight of silver and the balance palladium. Other corrosion resistant, electrically conductive materials, such as iron, nickel, and their alloys, also may be used. The negative electrode 15, 15' typically comprises a conductive layer 33, 37 about 0.2 to 80 micrometers thick in contact with the electrolyte 12 on a porous support 34, 38 in contact with the hydrogen.