Hybrid energy source composed of a metal-air battery and a fuel cell

Abstract

The invention relates to an energy source comprising a metal-air battery and a hydrogen fuel cell. The metal-air battery and the hydrogen fuel cell are connected to one another by a fluid connection means. The metal-air battery has a foam anode. The effect of parasitic corrosion at the foam anode is utilized in order to introduce the hydrogen formed thereby into the hydrogen fuel cell. In addition, the invention is directed to a system comprising an energy transducer and the energy source according to the invention. Furthermore, the invention relates, in further aspects, to uses of the energy source according to the invention in a Bayer process in the context of aluminium production and in stationary, semistationary and / or dynamic applications.

Description

[0001] HYBRID ENERGY SOURCE FROM A METAL-AIR BATTERY AND A FUEL CELL

[0002] DESCRIPTION

[0003] The invention relates to an energy source comprising a metal-air battery and a hydrogen fuel cell. The metal-air battery and the hydrogen fuel cell are connected to each other by a fluid connection. The metal-air battery has a foam anode. The effect of parasitic corrosion on the foam anode is utilized to introduce the resulting hydrogen into the hydrogen fuel cell.

[0004] Furthermore, the invention is directed to a system comprising an energy converter and the energy source according to the invention. Furthermore, in further aspects, the invention relates to uses of the energy source according to the invention in a Bayer process in the context of aluminum production and stationary, semi-stationary, and / or dynamic applications.

[0005] Background and state of the art

[0006] The current state of technology offers a very broad spectrum of energy sources, each dedicated to a variety of applications. The use of energy sources, such as conventional batteries, has become an integral part of everyday life. Other energy sources and / or their use are still the subject of ongoing research and development. In addition to research and development issues, economic interests as well as environmental and climate considerations are also playing an increasingly important role in the provision of modern energy sources.

[0007] In the automotive industry, the lithium-ion battery (often abbreviated to Li-ion battery) is the most widely used technology in battery-electric vehicles (BEVs). Through continuous development, its gravimetric energy density, practically achievable at the cell level, is currently between 100 and 200 Wh / kg (watt-hours per kilogram), approximately one-tenth that of conventional fuels (see Girishkumar et al. (2010)).

[0008] Heavy batteries and short ranges are the result. Furthermore, lithium extraction is energy-intensive and ecologically and socially questionable. Light metal-air batteries, such as aluminum-air and magnesium-air, but also zinc-air batteries, are energy storage devices with a high gravimetric energy density. They use ambient oxygen as a reactant, enabling an open cell design and thus reducing the weight of the battery, which consequently enables longer ranges (see Armand & Tarascon (2008)).

[0009] The particularly high theoretical energy densities of magnesium and aluminum-air batteries (Mg / O26800 Wh / kg (Zhang, Tao & Chen (2014)), Al / O28100 Wh / kg (Elia et al. (2016)) illustrate the enormous potential of this technology compared to Li-ion batteries.

[0010] Light metal-air batteries consist of a light metal anode, an electrolyte, and a gas diffusion electrode (GDE) as the cathode. The anode is oxidized in the electrolyte, and the cathode is reduced. The electrons released in the anode can be used on their way to the cathode via an external load.

[0011] The electrochemical reaction within the magnesium-air and aluminum-air battery can be represented as follows (Rahman, Wen & Wang (2013)):

[0012] Magnesium-air battery:

[0013] Anode: 2 Mg + 4 OH- - 2 Mg (OH)2+ 3 e- (potential of E o = - 2.69 V)

[0014] Cathode: O2+ 2 H2O + 4 e- 4 OH' (potential of Eo = 0.40 V)

[0015] Total: 2 Mg + O2+ 2 2 Mg (OH)2(potential of E ges = 3.09 V)

[0016] Aluminum-air battery:

[0017] Anode: 2 Mg + 4 OH- Al (OH)4' + 3 e- (potential of E o = - 2.34 V)

[0018] Cathode: O2+ 2 H2O 4 OH- (potential of E o = 0.40 V)

[0019] Total: 4 AI + 3 O2 + 6 H2O -> 4 AI (OH)3(Potential of Eg e s = 2.74 V)

[0020] One of the challenges with light metal-air batteries is so-called parasitic corrosion, which refers to the formation of hydrogen during battery discharge. Some of the electrons released during oxidation at the anode locally reduce water to hydrogen instead of leaving the anode through the external circuit (see, for example, Egan et al. (2013), Cho et al. (2015), and Zhang, Tao & Chen (2014)). This means that electrical charge is lost to an external consumer. Impurities, particularly iron, copper, and nickel, can enhance hydrogen formation because they act like local cathodes for hydrogen formation. Secondary aluminum is therefore not yet suitable as an anode material, so that high-purity materials (>99.99) are predominantly used as anode material, both in their pure form and as the basis for an alloy. This, however, enormously increases the energy and cost requirements for production.Added to this is the limited number of suppliers and thus the limited availability of high-purity lightweight metal materials. The current state of the art states that the practical energy density is between a few hundred and a few thousand Wh / kg, depending on the load and voltage level (Fan, Lu & Leng (2015), Ma et al. (2011). This often lies significantly below the often-quoted rule of thumb of one-third of the theoretical energy density. Handling the escaping and highly flammable hydrogen poses a further challenge.

[0021] Yu, Sha et al. (2020) concerns investigations into the electrochemical properties of a metal-air battery. In particular, an aluminum-air battery with a foam anode comprising aluminum is described. The corrosion behavior and electrochemical performance of the foam anode of the aluminum-air battery are investigated. A combination of the aluminum-air battery with a foam anode and a hydrogen fuel cell is not mentioned in the teachings of Yu, Sha et al. (2020).

[0022] Another energy source known in the state of the art is the fuel cell. Hydrogen fuel cells, in particular, are a mature technology that is already being used reliably in many areas. Hydrogen is introduced at the anode side and ambient air at the cathode side. At the anode, molecular hydrogen (H2) is converted into hydrogen nuclei (H +The electrons are split into two groups: protons (or protons) and electrons. The protons migrate through an electrolyte membrane, which is permeable only to them, to the oxygen side. The electrons migrate from the anode through an electrical conductor to the cathode. This current flow can, for example, drive an electric motor. On the cathode side, oxygen, electrons, and IT ions combine to form H2O, or water (Ehret (2018)).

[0023] Polymer electrolyte fuel cells (PEM), for example, are used both in stationary applications and in BEVs due to their high power density and load flexibility (e.g., acceleration and deceleration in vehicles). With operating temperatures of approximately 80°C, they are also used as heat sources. However, hydrogen must be generated in advance and provided under strict safety conditions, especially in mobile applications. Increased energy consumption and the associated costs make it difficult for this technology to compete with conventional fossil fuels – despite CO2-free operation.

[0024] Approaches to using a combination of a metal-air battery and a hydrogen fuel cell as an energy source are also known in the state of the art.

[0025] JP 2012248529 A discloses a system comprising a battery that generates hydrogen as a result of a reaction during charging and / or discharging, and a hydrogen fuel cell. The system is designed such that the hydrogen fuel cell can use the hydrogen generated in the battery for its own operation. Furthermore, electrical charges or currents for operating the system can be drawn from both the battery and the hydrogen fuel cell.

[0026] KR 20150067485 A discloses a system comprising a metal-air battery and a hydrogen fuel cell. The hydrogen fuel cell of the system disclosed in KR 20150067485 A is supplied with hydrogen produced in the metal-air battery. Water produced as a result of the operation of the hydrogen fuel cell is, in turn, used for the metal-air battery. The metal-air battery can contain, in particular, lithium, aluminum, magnesium, zinc, or vanadium. Furthermore, a battery management system (BMS) can be used in combination with the system.

[0027] Wang et al. (2013) discloses a hybrid energy source comprising two half-cells, namely an aluminum-air cell and an H2-air cell. Both half-cells are electrochemically connected. Furthermore, the two half-cells are embedded in an alkali-resistant polymer or polymer block. The polymer was prepared using 3D rapid prototyping. An aluminum plate located at the bottom of the polymer block serves as the anode for the aluminum-air cell and as a hydrogen source for the hydrogen-air cell, utilizing the hydrogen produced at the aluminum anode through parasitic corrosion.

[0028] However, there is a need for optimization regarding the energy yield of the hybrid energy source disclosed in Wang et al. (2013). Particularly in light of its potential use as an energy source for means of transportation, such as cars, the required efficiency is not achieved. Furthermore, the energy source disclosed in Wang et al. (2013) exhibits structural inflexibility due to the embedding of the half-cells in the polymer block. Therefore, there is a need to optimize known energy sources in the state of the art.

[0029] Object of the invention

[0030] The objective of the invention was to eliminate the disadvantages of conventional energy sources known from the prior art. In particular, the energy source should enable a higher energy yield. Furthermore, the energy source should be cost-effective and conserve natural resources. Furthermore, the energy source should be versatile in its application.

[0031] Summary of the invention

[0032] The object of the invention is achieved by the independent claims. Preferred embodiments of the invention are disclosed in the dependent claims.

[0033] In a first aspect, the invention preferably relates to an energy source comprising a metal-air battery and a hydrogen fuel cell, characterized in that the metal-air battery has a foam anode and a fluid connection means is present between the metal-air battery and the hydrogen fuel cell, so that hydrogen produced at the foam anode by parasitic corrosion can be introduced into the hydrogen fuel cell.

[0034] The energy source according to the invention has proven to be particularly advantageous in a number of aspects.

[0035] It is a surprising advantage that the efficiency of the energy source is particularly high due to the use of parasitic corrosion at the foam anode of the metal-air battery. As discussed above, parasitic corrosion is characterized by the formation of hydrogen at the anode. This can occur, for example, through a chemical reaction with water from the electrolyte. Using aluminum as a foam anode, for example, parasitic corrosion can be described by the reaction equation

[0036] AI + 3 H2O + OH- - 3 / 2 H2+ AI(OH)-4.

[0037] Viewed in isolation, parasitic corrosion is a detrimental effect for the metal-air battery, since electrons released at the anode are consumed for local oxidation to hydrogen, which could, however, be used for the electrical load. In the context of the invention, however, the inherently detrimental effect of hydrogen formation due to parasitic corrosion is utilized to be introduced into the hydrogen fuel cell and utilized there. Since the foam anode has a porous structure, a larger surface area is available that can be used for hydrogen formation.

[0038] Accordingly, a higher proportion of hydrogen can also be introduced into the hydrogen fuel cell from the metal-air battery. The inventors arrived at the solution to the inventive problem through long and intensive research efforts. It was by no means obvious to provide a metal-air battery with a foam anode in combination with a hydrogen fuel cell and to utilize the effect of parasitic corrosion as a hydrogen source for the hydrogen fuel cell. The prior art taught the use of anodes in metal-air batteries that are associated with low hydrogen production. For example, high-purity anode materials were typically used to keep hydrogen production low. In the context of the invention, however, high hydrogen production at the anode of the metal-air battery is important, which is brought about by the use of the foam anode.In particular, the extremely high hydrogen production is due to the larger surface area of ​​the foam anode. The fluid coupling agent transfers the high proportion of hydrogen produced by the parasitic corrosion effect from the foam anode of the metal-air battery into the hydrogen fuel cell.

[0039] While pure or ultra-pure anode materials make it possible to keep hydrogen production at a low level, these are associated with high and complex costs and measures. In particular, the production of pure or ultra-pure materials is process-inefficient. Advantageously, the inefficiency aspects associated with pure or ultra-pure anode materials are eliminated by the preferred energy source. Thus, even less pure anode materials can be used for the foam anode, which enables high hydrogen production and, in turn, is beneficial for the operation of the hydrogen fuel cell.

[0040] The preferred energy source also has the advantage that, among other things, the pore structure of the foam anode allows hydrogen production to be regulated, thus optimizing the efficiency of the energy source. For example, a higher proportion of hydrogen can be produced through parasitic corrosion, which is then fed into the hydrogen fuel cell as fuel, if the surface area of ​​the foam anode on the metal-air battery is increased. The surface area of ​​the foam anode is related to the pore structure. The pore structure of the foam anode includes the pore proportion, the type, shape, size, and / or distribution of the pores. Thus, the choice of pore structure also allows the surface area of ​​the foam anode, and therefore the amount of hydrogen that can be produced and thus also the amount of hydrogen to be fed into the hydrogen fuel cell to be adjusted.This also advantageously increases the service life of the hydrogen fuel cell, as more hydrogen can be made available as fuel. The amount of hydrogen generated through parasitic corrosion and introduced into the hydrogen fuel cell can be influenced not only by the pore structure, but also by the choice of foam anode material. As mentioned above, this can be regulated, in particular, by the purity of the foam anode material.

[0041] In addition, the preferred energy source has the advantage of being lower in mass. In particular, the pores of the foam anode, i.e. the empty areas of the foam anode which provide the pores, create areas in which no foam anode material is present. The pores or the missing material result in a lower mass than a solid material. Due to the lower mass, the preferred energy source is particularly well suited to a wide variety of applications. For example, the lower mass enables a greater range to be achieved when using the preferred energy source in means of transport. Furthermore, the lower mass is also advantageous in the distribution and supply of stationary applications. In itself, the preferred energy source is advantageously suited to stationary, semi-stationary and / or dynamic applications or devices, which will be discussed in more detail below.Another advantage is that the preferred energy source is functional regardless of which semipermeable membrane is used in the hydrogen fuel cell.

[0042] The components of the preferred energy source, comprising a metal-air battery, a hydrogen fuel cell, and a connecting agent, are cost-effective to acquire. Furthermore, the energy source according to the invention is not expensive to provide using the preferred components. Extremely rapid preparation of the energy source is possible, further increasing its efficiency.

[0043] In the context of the invention, the energy source refers to the device that can be provided by the metal-air battery and the hydrogen fuel cell, wherein a fluid connection means is present between the metal-air battery. Furthermore, the metal-air battery has a foam anode, wherein hydrogen generated locally by parasitic corrosion is introduced into the hydrogen fuel cell through the fluid connection means. The average person skilled in the art knows that both a metal-air battery and a hydrogen fuel cell can be evaluated as individual energy sources. However, the invention is directed to the combination of the metal-air battery and the hydrogen fuel cell. Therefore, the term "hybrid energy source" can also be used analogously for the energy source according to the invention.Therefore, the invention is also directed to a hybrid energy source comprising a metal-air battery and a hydrogen fuel cell, characterized in that the metal-air battery has a foam anode and a fluid connection means is present between the metal-air battery and the hydrogen fuel cell, so that hydrogen produced at the foam anode by parasitic corrosion can be introduced into the hydrogen fuel cell.

[0044] The hydrogen fuel cell is used to generate electricity from hydrogen (H2). Hydrogen is used as the fuel and oxygen (O2) as the oxidant. Oxidation takes place on the anode side. The hydrogen is oxidized at the anode and converted into cations. The ions migrate through the membrane separating the anode and cathode, while the electrons are carried to the cathode via the current flow. Reduction takes place on the cathode side. Oxygen, used here as the oxidant, is reduced at the cathode and converted into anions. These react directly with the hydrogen ions to form water.

[0045] A metal-air battery is a battery in which electrical energy is released from the chemical reaction of metals with oxygen. The oxygen is preferably obtained from the ambient air. As is usual, the metal-air battery has a cathode and an anode, with the cathode preferably being a gas diffusion electrode. The anode preferably has air contact. During discharging, oxygen from the air is reduced at the anode, and during charging, it is oxidized. This oxygen then combines with the metal ions, which are oxidized in the cathode and migrate through the electrolyte to the anode. In the context of the invention, the anode of the metal-air battery is a foam anode.

[0046] A foam anode is an anode designed as a foam. Since the anode is preferably made of metal, the foam anode is a metal foam. The foam anode has a porous structure. The foam anode is preferably essentially three-dimensional, i.e., has dimensions in length, width, and height.

[0047] The effect of parasitic corrosion has already been described above. For the sake of completeness, it should be mentioned that this effect refers to the unwanted hydrogen production that occurs locally at the anode of the metal-air battery. In and of itself, the effect of parasitic corrosion is considered detrimental to metal-air batteries. The local formation of hydrogen at the anode means that hydrogen is produced in an area or in the vicinity of the anode of the metal-air battery. This is caused by electrons released at the anode, which, instead of leaving the anode via the external circuit, locally reduce water to hydrogen.

[0048] In the context of the invention, it is intended to utilize the inherently detrimental effect of parasitic corrosion for the hydrogen supply of the hydrogen fuel cell. For this purpose, a fluid connection means is provided between the metal-air battery and the hydrogen fuel cell.

[0049] The fluid connection means refers to a device with which the gaseous hydrogen produced by parasitic corrosion is introduced from the metal-air battery into the hydrogen fuel cell. Accordingly, a fluid connection is established between the metal-air battery and the hydrogen fuel cell through the fluid connection means. A first end of the fluid connection means is preferably arranged in a vicinity of the foam anode of the metal-air battery. It may also be preferable to bring the first end of the fluid connection means into direct contact with the foam anode of the metal-air battery. A second end of the fluid connection means is preferably arranged in a vicinity of the anode of the hydrogen fuel cell. Furthermore, it may be preferable to bring the second end of the fluid connection means into direct contact with the anode of the hydrogen fuel cell.This allows the hydrogen to be oxidized at the anode of the hydrogen fuel cell.

[0050] In a further preferred embodiment, the energy source is characterized in that the foam anode comprises a material selected from a group comprising iron or a light metal, wherein the light metal is preferably selected from a group comprising zinc, magnesium, aluminum, compounds and / or alloys of said light metals.

[0051] The materials mentioned have advantageously proven to be particularly suitable for use in the foam anode of the metal-air battery for the preferred energy source.

[0052] In a preferred embodiment, the foam anode comprises iron as its material. If the foam anode comprises iron, it can also be referred to as an iron-air battery. Since iron is an element that occurs abundantly in nature, e.g., in the Earth's crust, it can advantageously be mined in particularly large quantities. Another advantage is that there will be no supply bottlenecks. Rather, there is a significant cost advantage, which is accompanied by considerable economic efficiency.

[0053] In a further preferred embodiment, the foam anode comprises a material comprising a light metal. The light metal is preferably selected from a group comprising zinc, magnesium, aluminum, compounds and / or alloys of the aforementioned light metals.

[0054] Zinc-air batteries are particularly cost-effective, environmentally friendly, and compact, which also translates to their preferred energy source. Magnesium-air batteries have a high capacity and also offer significant cost advantages due to the availability of sufficient magnesium. Aluminum-air batteries are characterized by a particularly high power density, which also translates to their preferred energy source.

[0055] Another particular advantage of using an aluminum-air battery is that secondary aluminum can be used for the foam anode. Secondary aluminum refers to aluminum that has been produced by remelting scrap. It is irrelevant whether this is new scrap from ongoing aluminum production or old scrap from previously used aluminum products (recycled). Since secondary aluminum is less pure than primary aluminum (aluminum produced from aluminum oxide, which in turn is extracted from the aluminum ore bauxite; the "primary" refers to the fact that the aluminum was produced directly from the raw material, i.e., in its purest form for the first time), it advantageously results in higher hydrogen production.

[0056] In addition, the materials mentioned are suitable for processes that can be used to produce a foam anode, such as additive processes, sintering, replication processes, extrusion, etc.

[0057] Using alloys and / or compounds of the listed materials for the foam anode, parasitic corrosion and thus the formation of hydrogen can be advantageously controlled. This advantageously reduces self-corrosion of the foam anode and increases the oxidation rate. Preferably, one or more alloy partners are used that have a lower melting temperature compared to the metal or light metal used, exhibit a higher nobility, are soluble in the electrolyte used, and / or have a high hydrogen overpotential, especially for aluminum for the foam anode.

[0058] In a further preferred embodiment, the energy source is characterized in that the foam anode has a purity level of between approximately 80 - 100%, preferably between approximately 97 - 99%, particularly preferably between approximately 99 - 99.9%, most particularly preferably of approximately 99.5%.

[0059] The purity level indicates the content of inclusions that influence the properties of the foam anode. Inclusions can refer to foreign materials, for example. For hydrogen fuel cells, the more impure the foam anode, the more hydrogen is produced or converted. For metal-air batteries, on the other hand, a higher purity level results in more electrical energy. These specifications have proven advantageous in that they allow for a compromise between hydrogen conversion and available electrical energy.

[0060] Advantageously, the purity level of approximately 80-100% covers a particularly large number of materials, especially alloys, that can preferably be used for the foam anode in the context of the invention. Recycled material, e.g., recycled aluminum, can also advantageously be used for the foam anode of the metal-air battery.

[0061] In another preferred embodiment, the foam anode has a purity of between 97 and 100%. This preferred proportion has proven to be a particularly good compromise between the hydrogen content produced and the available electrical energy. In particular, the preferred purity of between 97 and 100% ensures particularly optimal, long-lasting operation of the energy source.

[0062] Terms such as essentially, approximately, etc. preferably describe a tolerance range of less than ± 20%, preferably less than ± 10%, even more preferably less than ± 5%, and especially less than ± 1%. Terms such as essentially, approximately, etc. always disclose and include the exact value stated.

[0063] In a further preferred embodiment, the energy source is characterized in that the foam anode has an average web thickness of between approximately 0.1 - 5 mm, preferably between approximately 0.1 - 1 mm, particularly preferably between approximately 0.1 - 0.5 mm, most particularly preferably of approximately 0.3 mm.

[0064] In the context of the invention, webs refer to sections of the foam anode that border the pores. The average web thickness preferably refers to the mean value of the web thickness.

[0065] In general, the physical, particularly mechanical, properties of the foam anode are determined by the density, porosity, pore size, and / or web thickness, particularly by their interrelationships. These web thicknesses have proven advantageous in that they impart sufficient stability to the foam anode for the context of the invention. Thus, the robustness of the foam anode is advantageously increased, allowing for the provision of a particularly low-vibration energy source. At the same time, these web thicknesses make it possible to impart a structure to the pores that provides a particularly large surface area and thus allows for the production of more hydrogen.

[0066] In a further preferred embodiment, the fluid connection means is a hose.

[0067] A hose is advantageously inexpensive to purchase and easy to adapt to provide a fluidic connection between the hydrogen fuel cell and the metal-air battery. This allows the hose to be bent to individual requirements and easily shortened and / or lengthened. Thus, the use of a hose favors the use of the preferred energy source. Furthermore, the flexibility of hoses is advantageous for the preferred energy source, allowing for flexibility, for example, to accommodate pressure fluctuations and thus ensure long-term functional reliability.

[0068] Furthermore, additional components, which particularly promote the reliability of the preferred energy source's operation, can be easily incorporated into a hose. The energy source preferably has a pressure monitoring device. The pressure monitoring device is particularly preferably located on the fluid connection device, preferably on the hose. This allows the pressure of the hydrogen, which is gaseous and transferred to the hydrogen fuel cell, to be monitored. If unsuitable pressure values ​​are found, measures can be taken to ensure continued functionality of the energy source.

[0069] In a further preferred embodiment, the energy source is characterized in that the energy source has a fluid control unit, wherein the fluid control unit is present on the connecting means, between the connecting means and the air-metal battery and / or between the connecting means and the hydrogen fuel cell, wherein the fluid control unit is preferably selected from a group comprising a gas-permeable and liquid-tight membrane, a valve and / or a first pump.

[0070] A fluid control unit is a component of the energy source that allows the flow itself and / or flow parameters of the hydrogen from the metal-air battery into the hydrogen fuel cell to be regulated. This advantageously ensures optimal introduction of hydrogen into the hydrogen fuel cell. For example, the flow rate and / or the amount of hydrogen supplied can be optimized. Thus, the use of a fluid control unit can also improve the operation of the energy source. This is due, among other things, to the fact that parameters for introducing hydrogen into the hydrogen fuel cell can also influence the functionality of the energy source.

[0071] Thus, it may be preferred for the fluid control unit to be in the form of a membrane that is gas-permeable and liquid-tight. This advantageously enables the introduction of hydrogen into the hydrogen fuel cell while simultaneously avoiding the introduction of the electrolyte of the metal-air battery. This is particularly advantageous because the electrolyte could potentially trigger further chemical reactions that could reduce the performance of the hydrogen fuel cell and thus also of the preferred energy source. These reactions are advantageously avoided by using a gas-permeable and liquid-tight membrane. Such a membrane can, for example, but without limitation, comprise a hydrophobic and microporous material, for example PTFE (polytetrafluoroethylene) with micropores.

[0072] Preferably, a valve can also be used as a fluid control unit. The flow of hydrogen can be regulated by means of the valve. If necessary, it is also possible to stop the flow of hydrogen. This can be particularly useful during maintenance, for example for carrying out cleaning and / or repairs. Preferably, a first pump is present as the fluid control unit. For gaseous fluids, i.e. also hydrogen, which is relevant for the invention, one also speaks of a blower or a compressor. The blower allows a flow without any appreciable pressure. The compressor compresses the hydrogen to a higher pressure. The first pump can be used, in particular, to regulate the speed at which the hydrogen is conveyed.

[0073] In a preferred embodiment, the first pump is a peristaltic pump. With a peristaltic pump, the hydrogen is forced through by an external mechanical deformation of the hose. This advantageously enables particularly precise dosing of the hydrogen to be introduced into the hydrogen fuel cell. Furthermore, a substantially uniform and shock-free transport of the hydrogen is enabled, thus achieving optimal introduction into the hydrogen fuel cell. Thus, long-lasting and reliable operation of the preferred energy source is possible.

[0074] In a further preferred embodiment, the energy source is characterized in that the metal-air battery and the hydrogen fuel cell are present as separate components, wherein the separate components are preferably mounted spatially separated from one another.

[0075] The fact that the metal-air battery and the hydrogen fuel cell are present as separate components preferably means that the energy source can be constructed in multiple pieces. In particular, an operative connection between the metal-air battery and the hydrogen fuel cell is established in the form of a fluidic connection via the fluid connection means. Preferably, there is no electrical connection between the metal-air battery and the hydrogen fuel cell.

[0076] Preferably, the metal-air battery and the hydrogen fuel cell are mounted spatially separated from each other. Thus, they are preferably not located in a spatially fixed separation, in particular not in a housing.

[0077] The expression “spatially separated” can preferably mean that the metal-air battery and the hydrogen fuel cell are present in separate spatial units. In particular, a spatially separated installation of the metal-air battery and the hydrogen fuel cell can mean that they are not positioned within one spatial section, but in different spatial sections. Furthermore, a spatially separated installation of the metal-air battery and the hydrogen fuel cell can preferably mean that they are not positioned in one (single) or the same housing. In particular, a spatially separated installation can mean that the metal-air battery and the hydrogen fuel cell are each present in one, i.e., in different housings.

[0078] Advantageously, by separating the components of the preferred energy source, mutual thermal influence and / or chemical correlation effects can be avoided. Thermal influence preferably refers to the effect of heat that the hydrogen fuel cell can have on the metal-air battery, or vice versa. Hydrogen fuel cells, for example, have a temperature of approximately 80°C, so the effect of such a comparatively high temperature is prevented by separating the components. Chemical correlation effects refer to chemical reactions and / or products that could adversely affect the operation of the preferred energy source. Furthermore, the separate design is advantageous in that if a component fails or degrades in performance, it can be replaced more easily.This, in turn, has the advantage of significantly facilitating the interaction of the latest developments of the respective components through exchange and / or combination. Spatially separated installation is also advantageous in that it provides greater flexibility regarding the arrangement of the metal-air battery and the hydrogen fuel cell in a limited installation space, e.g., in a passenger car. Thus, the separate design, in particular, offers a multitude of advantages for the preferred energy source, which were not expected in their entirety, so that the technical effect can be considered synergistic.

[0079] In a further preferred embodiment, the energy source is characterized in that the hydrogen fuel cell is connected to a heat conductor, preferably a heat exchanger.

[0080] In the context of the invention, a heat conductor refers to a means by which the heat generated during the operation of the hydrogen fuel cell can be dissipated. A heat exchanger serves as the preferred heat conductor. The heat exchanger enables heat transfer via a fluid, which has proven particularly suitable in the context of the invention, since the water from the hydrogen fuel cell can be used for this purpose.

[0081] By means of the heat conductor, preferably the heat exchanger, the heat generated by the hydrogen fuel cell can advantageously be used to supply heat to other devices. Thus, the preferred energy source can enable not only the use of electrical energy but also the use of thermal energy, thus advantageously providing versatile energy-related application options. For example, the heat can be transferred to a radiator or heater to enable operation, for example, in means of transportation such as automobiles.

[0082] In a further preferred embodiment, the energy source is characterized in that the energy source has a second pump, wherein oxygen can be introduced into the fuel cell by means of the pump.

[0083] The second pump can advantageously optimize the supply of oxygen from the environment to the hydrogen fuel cell. As mentioned above, oxygen serves as the oxidant for the hydrogen fuel cell. The pump can advantageously regulate the amount of oxidant or oxygen, which in turn can be useful for operating the preferred energy source.

[0084] In a further aspect, the invention preferably relates to a system comprising an energy converter and a preferred energy source, wherein the energy converter and the energy source are operatively connected to one another, wherein the energy converter is preferably a motor, particularly preferably an electric motor. An energy converter means a device capable of converting a first form of energy into a second form of energy. A motor refers to a special energy converter that can convert a form of energy, for example, but not limited to, thermal, chemical, hydraulic, pneumatic and / or electrical energy, into kinetic energy. An electric motor serves to convert electrical energy into kinetic energy. The operative connection here means a connection such that the energy provided by the preferred energy source can be transferred to the energy converter. This can be done, for example, via an electrical connection.

[0085] Advantageously, the preferred energy source also offers a drive option for energy converters, such as engines, especially electric motors. In particular, the hydrogen fuel cell generates electrical current from hydrogen by reversing electrolysis. The hydrogen and atmospheric oxygen (oxygen from the environment) react to form water, generating electrical energy that can preferably be used for an electric motor. In particular, means of transport in which the preferred system can be used achieve particularly long ranges, since a long-lasting hydrogen supply to the hydrogen fuel cell is enabled by the preferred energy source. Since the energy generation or energy supply is essentially climate-neutral, this results in a significant improvement for a more climate-friendly, energy- and power-efficient drive for means of transport.

[0086] In a further preferred embodiment, the system is characterized in that the system comprises a heat conductor, preferably a heat exchanger, wherein a hydrogen fuel cell of the energy source is connected to the heat conductor, preferably the heat exchanger.

[0087] The heat conductor, preferably a heat exchanger, advantageously allows the thermal energy generated during operation of the energy source, particularly the hydrogen fuel cell, to be utilized. In addition to the electrical energy, the resulting thermal energy can also be utilized. By installing a heat conductor, preferably a heat exchanger, the thermal energy can be transferred particularly reliably and effectively.

[0088] In a further aspect, the invention preferably relates to a use of a preferred energy source in a Bayer process for producing aluminum.

[0089] The Bayer process is used in aluminum production, whereby aluminum hydroxide must be burned to aluminum oxide in a single process step. Advantageously, the preferred energy source is also suitable for use in the Bayer process. If the foam anode contains aluminum as a material, aluminum hydroxide is produced, which can be fed directly into the Bayer process, thus advantageously saving the energy required for burning. Furthermore, the production of energy-intensive, high-purity materials can be omitted, which is also advantageous in terms of energy efficiency. Just as the preferred energy source can provide the recyclable discharge product aluminum hydroxide for aluminum production and reduce energy consumption, a hydrogen fuel cell eliminates water. This enables a climate-friendly, particularly CO2-free, application for climate-friendly energy generation.

[0090] In a further preferred embodiment, the use of a preferred energy source relates to the operation of a stationary, semi-stationary and / or dynamic device, wherein the stationary device is preferably selected from a group comprising a power plant, a generator, a motor and / or a battery, wherein the semi-stationary application is preferably a construction device, preferably a crane and / or an excavator, wherein the dynamic device is preferably a means of transport, preferably selected from a group comprising a car, truck and / or bus.

[0091] Thus, there are particularly many possible applications for the preferred energy source. In particular, there are many advantages in electromobility, for example in trains, ships, cars, trucks and / or buses. In the context of the invention, such devices are classified as dynamic devices. A dynamic device refers to a device that makes it possible to cover long distances at an increased, in particular accelerated, speed. As with dynamic devices, locomotion is possible using a semi-stationary device, but covering longer distances is not the primary purpose. The aforementioned cranes and / or excavators are classified as semi-stationary devices. With a stationary device, there is preferably no independent locomotion, so it includes the aforementioned power plants, emergency generators, batteries (as reserve batteries), etc.

[0092] In particular, light metal as a material for the foam anode of the metal-air battery as a new energy storage device offers an innovative technology to increase the share of renewable energies in the overall energy balance, since overproduction or supply gaps can be closed by intermediate storage in the light metal.

[0093] Particularly in the growing field of electromobility, but also in stationary devices and applications, CO2 emissions are significantly reduced. Furthermore, dependence on exhaustible fossil fuels is significantly reduced. Existing infrastructure, such as gas stations, can continue to be used and can be modernized during a transition phase from fossil fuels to the provision of the preferred energy source, especially its components.

[0094] In particular, the storage of hydrogen by the foam anode of the preferred energy source or its activation potential advantageously enables incomparably safe transport, storage and / or provision options compared to currently used storage options.

[0095] Furthermore, it is particularly advantageous that the high energy density of BEVs not only enables longer ranges but also enables the selective supply of energy to remote locations, such as deserts and / or crisis areas. The elimination of difficult-to-access and maintenance-intensive supply lines is a particularly significant advantage. The average person skilled in the art recognizes that technical features, definitions, and advantages of preferred embodiments that apply to the preferred energy source also apply to the preferred system and the preferred use, and vice versa.

[0096] The aspects of the invention will be explained in more detail below using examples, without being limited to these examples.

[0097] FIGURES

[0098] Short description of the characters

[0099] Fig. 1 Schematic representation of a preferred embodiment of the energy source according to the invention

[0100] Fig. 2 Measurement results of a feasibility study of the energy source according to the invention

[0101] Detailed description of the characters

[0102] Fig. 1 serves to schematically represent a preferred embodiment of the energy source according to the invention.

[0103] The energy source comprises a metal-air battery 1 and a hydrogen fuel cell 2. The metal-air battery 1 comprises a foam anode 5 and a gas diffusion electrode 7 as the cathode. Furthermore, a fluid connection means is present between the metal-air battery 1 and the hydrogen fuel cell 2. Due to the effect of parasitic corrosion, hydrogen s is produced at the foam anode 5, which can be introduced into the hydrogen fuel cell 2 through the fluid connection means.

[0104] The energy source enables a particularly high energy yield and a high level of efficiency. The hydrogen s, which is inherently performance-reducing for the metal-air battery 1, is introduced into the hydrogen fuel cell 2, whereby a pore structure of the foam anode 5 enables a particularly high level of hydrogen production through parasitic corrosion, which can be used for the hydrogen fuel cell 2. In particular, the pore size can optimize hydrogen production and thus the operation of the energy source, which is a major advantage. Furthermore, the energy source has a low mass due to the pore structure of the foam anode 5, which is of great benefit for its suitability for applications, for example in the context of means of transportation. The energy source is suitable for a wide variety of applications and also has advantageous effects in these.This makes it possible to achieve even greater ranges with BEVs than is currently possible with state-of-the-art technology. Furthermore, the energy source can be provided with simple means and little effort, which also has a positive impact on cost and economic efficiency.

[0105] Furthermore, the energy source is characterized by its climate friendliness, as it can provide energy that is essentially CO2-neutral, as this is not produced as a byproduct in the chemical reaction of the hydrogen fuel cell. Only water 9 remains as a product of the hydrogen fuel cell 2, which results from the reaction of hydrogen and oxygen ß from the environment. A fluid control unit 12 is attached to the fluid connection means, which makes it possible to regulate the transport of the hydrogen 8. The flow rate and / or the amount of hydrogen 8 supplied can be regulated.

[0106] The energy source, in particular the hydrogen fuel cell 2, provides electrical energy and thermal energy. The energy source advantageously enables the efficient use of both energy forms. For this purpose, an electrical circuit 13 and an electrical charge 11 are shown in Fig. 1. The electrical charge 11 is conducted from the foam anode 5 of the metal-air battery 1 to an electrical consumer s, while the electrical circuit 13 leads from the hydrogen fuel cell 2 to the electrical consumer 3. Thermal energy can, in turn, be used for another component or device, for example, a heater 4, via heat conductor 10.

[0107] Fig. 2 shows measurement results recorded as part of a feasibility study of the invention. The electrical voltage [V] and the electrical current [mA] are plotted against time [s]. Curve I shows the voltage of the metal-air battery, curve II is dedicated to the voltage of the hydrogen fuel cell. Curve III represents the current of the hydrogen fuel cell, and curve IV the current of the metal-air battery.

[0108] A metal-air battery with a foam anode containing aluminum (aluminum foam-air battery) was used. The aluminum foam-air battery is connected to a commercially available hydrogen fuel cell via a hose. The resulting hydrogen is transferred from the aluminum foam-air battery to the hydrogen fuel cell via this hose. The hydrogen fuel cell is also supplied with oxygen by a pump.

[0109] A resistor was connected to each voltage source so that the electrical voltages and currents could be measured. The resistance connected to the hydrogen fuel cell is 51 Ω, while the resistance connected to the aluminum foam-air battery is 100 Ω.

[0110] As can be seen in Fig. 2, the aluminum foam-air battery builds up a voltage immediately after the addition of the electrolyte (0.7 L NaOH 4 mol / l - 4 N standard solution). A corresponding current is measured. Both the voltage and the current are maintained continuously, with a slight downward trend due to aluminum oxidation. After a slight delay, the hydrogen fuel cell also begins to build up a voltage and generate an electric current, thus definitively demonstrating the feasibility of the invention. The delay is due to the time required by the aluminum foam-air battery to produce enough H2 to fill the tube and feed the hydrogen fuel cell.

[0111] After approximately 1 hour, the anode of the aluminum foam-air battery, comprising 0.379 g of Al-99.5 foam (approximately 10 mm x 9 mm x 18 mm) with an average thickness (between the pores) of 0.3 mm, begins to degrade. This can be seen in Fig. 2 from the fluctuations in current and voltage, which is indicated by the circle and the note "Foam anode degrades."

[0112] There, the anode briefly loses contact with the arrester several times due to the ratio of the anode and pore size. After approximately 1 hour and 10 minutes, the aluminum foam anode finally loses contact with the arrester, and the aluminum foam-air battery shuts down.

[0113] Individual pieces of aluminum foam are still floating in the electrolyte and continue to oxidize. This further demonstrates the added value of the energy source according to the invention. Although the aluminum foam-air battery has already stopped working, the aluminum foam in the electrolyte continues to generate H2 due to aluminum oxidation, which supplies the hydrogen fuel cell. This can be seen in Fig. 2 from the measured current and voltage, which remain constant until the end of the test approximately 0.5 h after the aluminum foam-air battery has stopped working.

[0114] Test protocol for the feasibility study according to the results from Fig. 2

[0115] Aluminum foam-air battery

[0116] Anode:

[0117] • Material: AI 99.5 foam (aluminum content of at least 99.5%)

[0118] • average web thickness of 0.3 mm

[0119] • Mass: 0.379 g

[0120] • Dimensions: 10 mm x 9 mm x 18 mm

[0121] Cathode:

[0122] • Activated carbon 1-3 mm, from peat, grey, steam-activated broken carbon 1 kg

[0123] • Insert basket for SONOREX insert vessels, inner diameter 60 mm, mesh size 1 x 1 mm

[0124] • Rotilabo® filter paper circles 0 90 mm, thickness 0.16 mm, type 111 A, filter paper for qualitative analyses. Made of 100% cellulose, ash content 0.06%, 100 pieces, very fast filtering.

[0125] • Graphite leads 0 3.15 mm as conductor

[0126] Electrolyte:

[0127] • 0.7 L sodium hydroxide solution 4 mol / l - 4 N standard solution

[0128] Resistors:

[0129] • On the metal-air battery 100 Q

[0130] • On the hydrogen fuel cell 51 Q

[0131] Hydrogen fuel cell

[0132] • Reversible PEM fuel cell, dimensions: 54 mm x 54 mm x 17 mm, weight 70 g, socket 2 mm, fuel cell function: open circuit voltage: 0.9 V, max. current: 0.36 A, max. power: 0.21 W, LEYBOLD (LB Didactic) Ü2 supply: aquarium pump 100 l / h

[0133] REFERENCE SYMBOL LIST

[0134] 1 metal-air battery

[0135] 2 hydrogen fuel cell

[0136] 3 Electrical consumer

[0137] 4 Heating

[0138] 5 foam anode

[0139] 6 Oxygen

[0140] 7 Gas diffusion electrode

[0141] 8 Hydrogen

[0142] 9 Water

[0143] 10 heat conductors

[0144] 11 Electric charge

[0145] 12 Fluid control unit for hydrogen transport

[0146] 13 Electrical wiring

[0147] BIBLIOGRAPHY

[0148] Girishkumar, Girish, et al. "Lithium- air battery: promise and challenges." The Journal of Physical Chemistry Letters 1.14 (2010): 2193-2203.

[0149] Armand, Michel, and J-M. Tarascon. "Building better batteries." nature 451.7179 (2008): 652-657.

[0150] Zhang, Tianran, Zhanliang Tao, and Jun Chen. "Magnesium-air batteries: from principle to application." Materials Horizons 1.2 (2014): 196-206.

[0151] Elia, Giuseppe Antonio, et al. "An overview and future perspectives of aluminum batteries." Advanced Materials 28.35 (2016): 7564-7579.

[0152] Rahman, Md Arafat, Xiaojian Wang, and Cuie Wen. "High energy density metal-air batteries: a review." Journal of the Electrochemical Society 160.10 (2013): A1759.

[0153] Egan, D. R., et al. "Developments in electrode materials and electrolytes for aluminium-air batteries." Journal of Power Sources 236 (2013): 293-310.

[0154] Cho, Young-Joo, et al. "Aluminum anode for aluminum-air battery-Part I: Influence of aluminum purity." Journal of Power Sources 277 (2015): 370-378.

[0155] Zhang, Tianran, Zhanliang Tao, and Jun Chen. "Magnesium-air batteries: from principle to application." Materials Horizons 1.2 (2014): 196-206.

[0156] Fan, Liang, Huimin Lu, and Jing Leng. "Performance of fine structured aluminum anodes in neutral and alkaline electrolytes for Al-air batteries." Electrochimica Acta 165 (2015): 22-28.

[0157] Ma, Yibin, et al. "Performance of Mg— 14Li— 1 Al— 0.1 Ce as anode for Mg-air battery." Journal of Power Sources 196.4 (2011): 2346-2350.

[0158] Dr. Oliver Ehret, Center of Automotive Management (CAM), Dossier Wasserstoff-und- Brennstoffzellen, NOW GmbH Nationale Organisation Wasserstoff- und Brennstoffzellentechnologie, 2018.

[0159] Wang, Lei, et al. "A hybrid aluminum / hydrogen / air cell system." International journal of hydrogen energy 38.34 (2013): 14801-14809.

[0160] Yu, Sha, et al. "High power density Al-air batteries with commercial three-dimensional aluminum foam anode." Ionics 26 (2020): 5045-5054.

Claims

PATENT CLAIMS 1. Energy source comprising a metal-air battery (1) and a hydrogen fuel cell (2), characterized in that the metal-air battery (1) has a foam anode (5) and a fluid connection means is present between the metal-air battery (1) and the hydrogen fuel cell (2), so that hydrogen (8) produced at the foam anode (5) by parasitic corrosion can be introduced into the hydrogen fuel cell (2).

2. Energy source according to the preceding claim, characterized in that the foam anode (5) comprises a material selected from a group comprising iron or a light metal, wherein the light metal is preferably selected from a group comprising zinc, magnesium, aluminum, compounds and / or alloys of said light metals.

3. Energy source according to one or more of the preceding claims, characterized in that the foam anode (5) has an average web thickness between 0.1 - 5 mm, preferably between 0.1 - 1 mm, particularly preferably between 0.1 - 0.5 mm, most particularly preferably 0.3 mm.

4. Energy source according to one or more of the preceding claims, characterized in that the foam anode (5) has a degree of purity between 80 - 100%, preferably between 97 - 99%, particularly preferably between 99 - 99.9%, most particularly preferably 99.5%.

5. Energy source according to one or more of the preceding claims, characterized in that the fluid connection means is selected from a group comprising a hose and / or a pipe.

6. Energy source according to one or more of the preceding claims, characterized in that the metal-air battery (1) and the hydrogen fuel cell (2) are present as separate components, wherein the separate components are preferably mounted spatially separated from one another.

7. Energy source according to one or more of the preceding claims, characterized in that the energy source has a fluid control unit (12), wherein the fluid control unit (12) is present on the fluid connection means, between the fluid connection means and the air-metal battery (1) and / or between the fluid connection means and the hydrogen fuel cell (2), wherein the fluid control unit (12) is preferably selected from a group comprising a gas-permeable and liquid-tight membrane, a valve and / or a first pump.

8. Energy source according to one or more of the preceding claims, characterized in that the hydrogen fuel cell (2) is connected to a heat conductor (10), preferably a heat exchanger.

9. Energy source according to one or more of the preceding claims, characterized in that the energy source has a second pump, wherein oxygen can be introduced into the fuel cell by means of the pump.

10. System comprising an energy converter and an energy source according to one or more of claims 1-9, wherein the energy converter and the energy source are operatively connected to one another, wherein preferably the energy converter is a motor, particularly preferably an electric motor.

11. System according to claim 10, characterized in that the system comprises a heat conductor (10), preferably a heat exchanger, wherein a hydrogen fuel cell (2) of the energy source is connected to the heat conductor (10), preferably the heat exchanger.

12. Use of the energy source according to one or more of the preceding claims 1-9 in a Bayer process for producing aluminum.

13. Use of the energy source according to one or more of the previous 1 - 9 for operating a stationary, semi-stationary and / or dynamic device, wherein the static device is preferably selected from a group comprising a power plant, a generator, a motor and / or a battery, wherein the semi-stationary application is preferably a construction device, preferably a crane and / or an excavator, wherein the dynamic device is preferably a means of transport, preferably selected from a group comprising a car, truck and / or bus.

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