The difference in voltage between the two MEA stacks , is applied across the external load. The hydrogen circulates continuously inside the JTEC heat engine and is never consumed. The current flow through the two MEA stacks , and the external load is the same. Specifically, in the JTEC heat engine, a hydrogen pressure differential is applied across each MEA stack , with a load attached, thereby producing a voltage and current as hydrogen passes from high pressure to low pressure.
The electron current is directed to the external load as electrons are stripped from the protons as they pass through the membrane , which is a proton conductive membrane PCM. More particularly, on the high pressure side of MEA stack and the low pressure side of MEA stack , hydrogen gas is oxidized resulting in the creation of protons and electrons.
The pressure differential at the high temperature end forces the protons through the membrane causing the electrodes to conduct electrons through an external load, while the imposition of an external voltage forces protons through the membrane at the low temperature end. On the high pressure side of MEA stack and the low pressure side of MEA stack , the protons are reduced with the electrons to reform hydrogen gas. Unlike conventional fuel cells, in which the hydrogen exiting the MEA stack would encounter oxygen and react with it producing water, there is no oxygen or water in the JTEC system.
This process can also operate in reverse. The reverse process is rather similar to that of using a MEA stack to electrolyze water, wherein water molecules are split and protons are conducted through the PCM, leaving oxygen behind on the water side. Hydrogen is often supplied at a high pressure to a pure hydrogen reservoir via this process.
In the JTEC, using hydrogen as the ionizable gas i. Hirschenhofer et al. The voltage generated by the MEA stack is thus given by the Nernst equation. The voltage is linear with respect to temperature and is a logarithmic function of the pressure ratio.
For example, referring to FIG. The working fluid in the JTEC is compressed in the low temperature electrochemical cell by supplying current at a voltage that is sufficient to overcome the Nernst potential of the low temperature cell , thereby driving hydrogen from the low pressure side of the membrane to the high pressure side.
On the other hand, the working fluid is expanded in the high temperature electrochemical cell as current power is extracted under the Nernst potential of the high temperature cell Electrical current flow is generated as hydrogen expands from the high pressure side of the membrane to the low pressure side.
As in any thermodynamic engine employing a working fluid and consistent with the nature of compressible gas, in the JTEC, a greater amount of work electricity is extracted during high temperature expansion than the work electricity input required for the low temperature compression.
The difference in heat energy input to the engine to maintain constant temperature during high temperature expansion versus the heat energy removed to maintain constant temperature during low temperature compression is provided as the difference in electrical energy output by the high temperature expansion process versus that consumed by the low temperature compression process.
Consistent with the Nernst equation, the high temperature cell will have a higher voltage than the low temperature cell. Since the current I is the same through both cells , , the voltage differential means that the power generated through the expansion of hydrogen in the high temperature cell is higher than that of the low temperature cell This voltage differential provides the basis for the JTEC engine.
Operation of the JTEC is generally similar to any other engine. For example, in a typical jet engine, the compressor stage pulls in air, compresses the air, and supplies the compressed air to the combustion chamber.
The air is then heated in the combustion chamber and expands through the power stage. The power stage couples shaft work back to the compressor stage, in order to maintain a continuous supply of compressed air. The difference in work generated by the power stage and that consumed by the compressor stage is the net work output by the engine.
However, the primary difference between such conventional engines and the JTEC is that such conventional engines utilize a turbine i. The thermodynamic states 1 through 4 are identical at the respective identified points in FIGS. As shown in FIG. The temperature of the hydrogen is maintained nearly constant by removing heat Q L from the PCM during the compression process. The membrane is relatively thin i. From state 2, the hydrogen passes through the recuperative, counterflow heat exchanger and is heated under approximately constant pressure to the high-temperature state 3.
The heat needed to elevate the temperature of the hydrogen from state 2 to 3 is transferred from hydrogen flowing in the opposite direction through the heat exchanger At the high-temperature, high-pressure state 3, electrical power is generated as hydrogen expands across the MEA stack from the high-pressure, high-temperature state 3 to the low-pressure, high-temperature state 4. Heat Q H is supplied to the thin film membrane to maintain a near constant temperature as the hydrogen expands from high-pressure state 3 to low-pressure state 4.
From state 4 to state 1, the hydrogen flows through the recuperative heat exchanger , wherein its temperature is lowered by heat transfer to hydrogen passing from state 2 to 3. The hydrogen is pumped by the low-temperature MEA stack from state 1 back to high-pressure state 2 as the cycle continues. However, some challenges have been encountered with developing a JTEC that is suitable for widespread use, particularly for systems that use hydrogen as the working fluid.
For example, hydrogen leakage through small defects in the conduit system may occur due to the small size of the hydrogen molecule. In particular, hydrogen leakage can occur at the joints of the interconnects for the conduit couplings between the high-temperature cell and the low-temperature cell. Specifically, unlike conventional fuel cells, where the open circuit voltage can be greater than 1V, the Nernst voltage from the hydrogen pressure differential across a MEA stack is in the range of only about 0.
As such, many cells will have to be connected in series to achieve useful output voltage levels. Further, in order to achieve efficient energy conversion, the membranes must have high diffusion barrier properties, because diffusion of working fluid such as hydrogen gas under the pressure differential across the membrane results in reduced electrical output and efficiency.
The membranes utilized must also have good ion conductivity. However, known and available membrane materials that have good ion conductivity, such as Nafion manufactured by the DuPont Corp. Conversely, known and available membrane materials that have high molecular diffusion barrier properties generally have relatively low ionic conductivity, and use of such materials would result is high system impedance and high polarization losses. As such, large membrane areas are needed in order to keep current density at a minimum so as to minimize resistive polarization losses.
However, the cell will have low internal impedance if the ion conduction cross-sectional area of the membrane is too large. Accordingly, there is a need for a practical way of using available high barrier, low conductivity membrane materials to provide a thermo-electrochemical heat engine that can approximate a Carnot equivalent cycle, that can operate over a wide range of heat source temperatures, and that eliminates the reliability and inefficiency problems associated with mechanical engines.
The solid state heat engine of the present invention fulfills this need. One embodiment of the present invention relates to a co-sintered or fused, high density MEA stack or electrochemical cell configured to electrochemically expand or compress an ionizable working fluid.
The MEA stack is a multi-layered structure of alternating thin electrodes and membranes. The membranes are preferably non-porous and conductive of ions of the working fluid. The membranes are a high diffusion barrier to the working fluid that has not been ionized. The electrodes are preferably porous and include additives to promote electronic conductivity and a catalyst to promote the desired electrochemical reactions.
In one embodiment, the MEA stack is preferably made of ceramic materials and has a co-sintered structure. In another embodiment, the MEA stack is preferably made of polymeric materials and has a fused structure. Co-sintering or fusing of the components of the MEA stack allows for a practical construction of a large membrane area within a relatively small volume, while avoiding the complications and challenges associated with construction of individual cells and then making individual interconnects including flow manifolds, seals and electrical connections.
The electrochemical cells or MEA stacks of the present invention also preferably operate on pressure differentials. I have also surprisingly discovered that in-plane flow of the working fluid within thin electrodes enables construction of MEA stacks having high energy conversion density. This is unexpected, considering that existing fuel cell art teaches against in-plane flow of reaction fluids within thin electrodes. Specifically, existing fuel cell art teaches that electrodes should be thin, but that flow through the electrode should be perpendicular to the ion conductive membrane i.
In operation, working fluid enters an MEA stack through one of the porous electrodes and releases electrons to that electrode as its ions enter and are conducted through the membrane. The electrons are routed through an external circuit to the other electrode on the opposite side of the membrane. The ions are conducted through the membrane and exit the electrode on the opposite side. The working fluid is reconstituted as its ions exit the membrane and recombine with the electrons.
The thin electrodes and membranes are stacked at high density in alternating sequence with each other, such that adjacent MEA stacks share a common electrode. More particularly, the high density MEA stacks of the present invention are preferably configured such that each membrane is sandwiched by a pair of electrodes, with one of the electrodes of the pair being positioned on the high pressure side of the membrane and the other electrode of the pair being positioned on the low pressure side of the membrane.
In another embodiment, the present invention relates to a thermo-electrochemical converter, preferably configured as a JTEC, direct heat to electricity engine having a monolithic co-sintered ceramic structure or a monolithic fused polymeric structure. The co-sintered ceramic structure or fused polymeric structure preferably includes a heat exchanger and first and second high density MEA stacks of the structure described above.
Twenty years ago, he patented the idea for the Johnson Thermo-Electrochemical Converter JTEC , a device that turns waste heat into useable electricity at an unprecedented and unheard of efficiency. His idea worked on the white board- all of the chemistry and physics and equations bore him out, but the materials to make it feasible were not yet available.
With the huge advances in Material Science in the last decade, his bold idea is now a reality. In , Dr. The expansion of the working fluid through the first MEA stack generates electricity. The second high density MEA stack is preferably connected to a heat sink and functions to pump the working fluid from a low pressure to a high pressure.
Electrical power is consumed by the compression process and the heat of compression is rejected. The co-sintered or fused heat engine preferably further comprises a conduit system including at least one high pressure flow channel, and more preferably a plurality of high pressure flow channels, which couple the flow of the working fluid between high pressure electrodes of the first high density MEA stack to high pressure electrodes of the second high density MEA stack, such that the connected high pressure electrodes are essentially at the same pressure.
The conduit system preferably further includes at least one low pressure flow channel, and more preferably a plurality of low pressure flow channels, which couple the flow of the working fluid between the low pressure electrodes of the first high density MEA stack to the low pressure electrodes of the second high density MEA stack, such that the connected low pressure electrodes are essentially at the same pressure.
The high pressure electrodes within each high density MEA stack are preferably electrically connected to each other. Similarly, the low pressure electrodes within each high density MEA stack are preferably electrically connected to each other. As such, the electrically connected high density MEA stacks function as a single membrane electrode assembly having a large area and a Nernst voltage that is a function of the stacks' temperature and the pressure differential across the membranes.
In one embodiment, sections of the high pressure channels and sections of the low pressure channels are preferably in physical contact with each other, and thus have a high interface area and thermal conductivity so as to facilitate effective heat transfer between working fluid in a high pressure channel and working fluid in a low pressure channel.
The heat exchanger of the co-sintered or fused heat engine preferably functions as a recuperative heat exchanger to recuperate heat from working fluid leaving the high temperature MEA stack by coupling it to working fluid flowing to the high temperature MEA stack. Providing such a recuperative heat exchanger in combination with a heat source and heat sink coupled to the high and low temperature electrochemical cells i.
In one embodiment, wherein the MEA stacks operate as part of an engine, the heat source to which the first MEA stack is coupled is preferably at an elevated temperature relative to the temperature of the heat sink to which the second MEA stack is coupled.
As such, the higher temperature MEA stack i. The voltage generated by the high temperature MEA stack is high enough to overcome the Nernst voltage of the low temperature MEA stack and have sufficient voltage left over to power an external load connected in series.
In another embodiment, in which the MEA stacks operate as part of a heat pump application, the first MEA stack is preferably coupled to a heat source that is at a reduced temperature and the second MEA stack is preferably coupled to a heat sink that is at an elevated temperature relative to the heat source of the first MEA stack. Working fluid is expanded at a low temperature in the first MEA stack as the heat of expansion is extracted from the low temperature heat source.
Working fluid is compressed at a high temperature in the second MEA stack, and the heat of compression is rejected at the elevated temperature.
An external power source is connected in series with the low temperature MEA stack in order to provide a combined voltage that is high enough to overcome the Nernst potential of the high temperature MEA stack and thereby drive the compression process therein. The following detailed description of preferred embodiments of the present invention will be better understood when read in conjunction with the appended drawing. For the purposes of illustrating the invention, there is shown in the drawing an embodiment which is presently preferred.
It is understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown. In the drawings:. Certain terminology is used in the following description for convenience only and is not limiting. The elements or components identified by these terms, and the operations thereof, may easily be switched. Referring to the drawings in detail, wherein like numerals indicate like elements throughout the several views, FIGS.
In one embodiment, where components of the high density MEA stack are made of ceramic materials, the MEA stack 10 , and more particularly each of the flat components of the stack 10 as described in detail hereinafter , is produced by co-sintering. Co-sintering is a known, low cost procedure for shaping ceramic materials, and more particularly for the fabrication of thin i.
Co-sintering technology can be used to produce a wide variety of controlled morphologies, from highly porous to fully dense microstructures. The co-sintering process is well known to those skilled in the art. Generally, starting powders of different natures, and more particularly starting ceramic powders, are incorporated and mixed together with an aqueous medium to form a slurry, and the slurry is then cast into green tapes using a tape casting method.
Tape casting also allows for stacking the cast green tapes to obtain a multilayered final product i. More particularly, multiple coating layers of green ceramic material may be cast or screen printed onto each other to form a layered structure which is ultimately sintered to form a MEA stack.
For a given powder, the sintering behavior of the cast green tapes, and hence the final microstructure of the sintered layers, depends on the arrangement and particle sizes, dispersion and homogeneity of the starting ceramic powder particles in the slurry. Consequently, the slurry formulation is a very important step in the shaping process. Preferably, the slurry is composed of a mixture of several organic and inorganic compounds. The organic components preferably include a binder, a dispersant, a plasticizer, and, in the case of organic tape casting, a solvent.
Other additives, such as wetting agents, defoamers, and pore formers if porosity is desired in the final microstructure may also be used to form the slurry. An example of a ceramic powder for formation of a high temperature MEA stack as discussed in more detail hereinafter 10 is yttrium doped barium cerate Y:BaCeO 3. After casting, the stacked cast tapes are allowed to dry. The tapes may be allowed to air dry for a predetermined period of time or may be passed through a drier to accelerate drying.
Select organic components may remain in the green tapes after drying. The tapes are then heated to elevated temperatures to effect sintering of the cast green tapes. The organic components which remained after drying are sacrificial materials that are removed when the tapes are heated for sintering.
As such, the remaining organic components give rise to pores and flow passages which remain during the subsequent sintering treatment. The sintered layers of the MEA stack 10 are thus formed. In another embodiment, where components of the high density MEA stack are made of polymeric materials, the MEA stack 10 , and more particularly each of the flat components of the stack 10 as described in detail hereinafter , is produced by a fusing process.
The various types of fusing processes are well known to those skilled in the art. In another type of fusing process, the polymeric components may be assembled together in a series of hot pressing steps wherein a layer is added and hot pressed in place with each step.
The MEA stack 10 comprises overlapping layers of alternating electrodes 23 and membranes 22 arranged in a high density stacked configuration. The membranes 22 are preferably ion conductive membranes or proton conductive membranes having a thickness on the order of approximately 0.
More particularly, the membranes 22 are preferably made from a proton conductive material, and more preferably a polymer proton conductive material or a ceramic proton conductive material.
However, it will be understood by those skilled in the art that any material, and preferably any polymer or ceramic material, which demonstrates a similar proton conductivity over a broad temperature range may be used to form the membranes The polymer or ceramic membrane material 22 preferably forms a high barrier to molecular working fluid flow and provides for effective containment of the working fluid.
The use of different materials for the various components i. Accordingly, the electrodes 23 are preferably comprised or formed of the same material as the membranes However, the electrodes 23 are preferably porous structures, while the membranes 22 are preferably non-porous structures.
Because the same basic material composition is preferably used for the electrodes 23 as for the bulk membrane 22 material structure, the high thermal stresses that would otherwise occur under the extreme temperatures encountered during co-sintering or fusing to form the MEA stacks 10 and in many end-use applications during operation of the MEA stacks 10 are eliminated or at least reduced. In one embodiment, the porous electrodes 23 may be doped or infused with additional material s to provide electronic conductivity and catalytic material, in order to promote oxidation and reduction of the working fluid.
The length 28 of the MEA stack 10 is preferably between approximately 0. The width depth into the drawing of the MEA stack 10 is preferably between approximately 1 cm and cm.
However, it will be understood by those skilled in the art that the dimensions of the MEA stack 10 may vary and be selected as appropriate depending on the application in which the MEA stack 10 is to be used.
Given the low ion conductivity of known and available ceramic materials which may be used to form the membranes 22 and the low Nernst voltage levels generated at reasonable operating temperatures and pressures by these ceramic membrane materials, high membrane surface areas are desirable within the MEA stack Resistive losses associated with high current density, as protons are conducted through the membranes, could otherwise represent a significant reduction in output voltage and thereby efficiency.
Accordingly, the MEA stack 10 has a high density of overlapping electrodes 23 and membranes 22 , which yields a very high membrane to electrode interface area within a relatively small stack volume, with the ion conductive material of the membranes 22 comprising the bulk structure of the MEA stack More particularly, the bulk area of the MEA stack 10 is occupied by a plurality of the membranes It will be understood that the bulk area within a particular stack 10 will depend on the number of membrane 22 and electrode 23 layers, as well as the respective thicknesses of such layers, within a given unit of stack height.
In one embodiment, the plurality of membranes 22 are surrounded by an external housing 21 , which may be made of the same or of a different material as the membranes The MEA stack 10 further comprises a conduit system including at least one low pressure conduit 37 represented by dashed lines in FIG.
Preferably, the conduit system includes a plurality of low pressure conduits 37 and a plurality of high pressure conduits A supply of an ionizable gas, preferably hydrogen, is contained within the conduit system as the working fluid.
The low pressure conduits 37 direct the flow of the working fluid e. The low pressure conduits 37 and high pressure conduits 38 define low and high pressure sides of the MEA stack The high pressure side of the MEA stack 10 may be at a pressure of as low as 0.
Preferably, the high pressure side of the MEA stack 10 is maintained at a pressure of approximately psi. The low pressure side of the MEA stack 10 may be at a pressure of as low as 0. Preferably, the low pressure side of the MEA stack is maintained at a pressure of approximately 0. A preferred pressure ratio of the high pressure side to the low pressure side is 10, The electrodes 23 in each MEA stack 10 are alternatingly coupled to the high pressure and low pressure conduits 38 , 37 , respectively, such that each membrane 22 is sandwiched between a first electrode 23 supplied by a high pressure conduit 38 and a second electrode 23 supplied by a low pressure conduit Accordingly, each membrane 22 is preferably situated between a high pressure electrode 23 b and a low pressure electrode 23 a , such that each membrane 22 has a high pressure side and a low pressure side.
The one sea trial proved that even though the engine ran well it was underpowered. When it was raised the Ericsson cycle engine was removed and a steam engine took its place. Ericsson designed and built a very great number of engines running on various cycles including steam, Stirling, Brayton, externally heated diesel air fluid cycle. He ran his engines on a great variety of fuels including coal and solar heat. Ericsson also was the inventor of the screw propeller for ship propulsion, in the USS Princeton.
Inventor breaks through again -- Beyond Super Soaker : Atlantan's energy game-changer earns honors. He holds about patents, many of them in that arcane spot where chemistry, electricity and physics cross into the marketplace. And his latest invention appears to do the impossible: generating electricity with no fuel and no moving parts. Even among the geniuses who gathered to honor him and his new thermo-electrochemical converter at a Breakthrough Awards banquet in Manhattan this month, the Atlanta scientist's new invention was ignored when his most famous device was revealed.
Johnson, 59, doesn't mind if he's better known for watery mayhem than rocket science. A billion dollars could buy most of a Galileo mission. Johnson's share he licensed the Soaker's design to Larami, later bought by Hasbro won him the financial independence to pursue his own ideas, which is how the Johnson Thermo-electrochemical Converter system -- JTEC for short was born. Using heat to force ions out of a hydrogen cell, the JTEC "is just a stunning insight," said Jerry Beilinson, deputy editor of Popular Mechanic s magazine, which honors innovators in its current issue and sponsors the Breakthrough Awards.
Beilinson groups Johnson with other great synthesists of science, including Henry Ford and Thomas Edison. He also points out that Johnson, a native of Mobile, flourished in a somewhat hostile environment. In his governor stood up for segregation in Alabama, standing in the schoolhouse door.
Five years later, Johnson, a high school senior, finished building a remote-controlled robot with a reel-to-reel tape player for a brain and jukebox solenoids controlling its pneumatic limbs. The door wasn't exactly blocked, but no other black high schools participated in the event.
On the strength of Linex, Williamson won. Teachers predicted Johnson would go far. His robots went even farther. He also helped design the Cassini robot probe that flew million miles to Saturn. In , just before the Super Soaker made him wealthy, Johnson moved to Atlanta. In , he began working in earnest on the JTEC. You don't know what's there, but you sure want to explore it to find out.
Johnson's device can potentially work with even modest temperature differentials -- say, between body heat and ambient air -- to power implanted medical devices such as pacemakers. If successful, at high heat it would generate Con Edison-scale output. It also would run backward for refrigeration purposes: put in electricity to generate heat loss for, say, wearable air conditioning. Paired with a parabolic solar array to generate heat, it would create virtually limitless emission-free power.
This energy game-changer comes from unlikely quarters: a renovated factory on a formerly bleak stretch of Decatur Street. In addition to his workshop, he hosts a high school robotics team sponsored by the Black Men of Atlanta and donates office space for the Georgia Alliance for Children, of which he is the chairman. On a recent weekday, Johnson, impeccable in head-to-toe khaki, conducts a tour of the workshop, moving among shiny stainless steel deposition chambers and glove boxes where scientists can manipulate delicate materials isolated in a pure argon atmosphere.
Here the two dozen employees of his privately owned concern work on several projects at once, developing solid-state batteries and lithium-air batteries. At one station Bill Rauch is working on solid-state batteries. Rauch says every now and then Johnson has a get-together at his Ansley Park home for the employees; they swim in the pool and squirt each other with off-the-shelf Super Soakers.
Then Johnson comes out with a prototype water weapon not available to the public. He crushes the opposition.
Johnson's interest in thermal engines and heat pumps led to experiments using water vapor instead of Freon as a compressible liquid, which led, oddly enough, to the birth of the Super Soaker. His work with batteries led to an interest in generating electricity electrochemically, instead of mechanically, which led to the JTEC. The JTEC completes the loop between heat pumps and batteries.
It;s freshman chemistry, said Karl Littau, a material scientist at Palo Alto Research Center, a California nursery for high-tech innovation. Most electricity is generated using heat to power a mechanical device, such as a piston or a turbine. The JTEC uses heat to force ions through a special membrane.
0コメント