The following description relates to an electrical device that converts the energy of oxygen into electricity by using polyoxometalates (POMs).

BACKGROUND OF THE INVENTION

A solar cell, or photovoltaic cell, is an electrical device that converts the energy of light into electricity by a photovoltaic effect, which is a physical and chemical phenomenon. A specific form of solar cells are dye-sensitized solar cells. An exemplary dye-sensitized solar cell was first described by the research team of Prof. Gratzel (O'Regan et al. (1991 ), Nature 353, 737). The solar cell of Gratzel includes a semiconductor electrode formed of metal oxide coated with photosensitive dye molecules that absorb visible light to generate an electron- hole pair, a counter electrode including a platinum catalyst, and an electrolyte that fills a space between the semiconductor electrode and the counter electrode and includes a redox ion pair. Since then, extensive research has been made with respect to dye-sensitized solar cells.

The inventors of the present application aimed at providing electrochemical cells that can provide energy with the aid of solar light and in the absence of solar light.

SUMMARY OF THE INVENTION

In addition of the activation of the electrons via solar light, it has been found that the activation of the electrons can also be carried out via oxidation of polyoxometalates by oxygen or by hydrogen peroxide. The activation/separation of the electrons relies on the reduction of oxygen to superoxide and simultaneous oxidation of the POMs, as depicted in Figure 1 , or by release of superoxide due to the reaction of the POMs with hydrogen peroxides, as depicted in Figure 1 a. Furthermore, it is possible to activate POMs by solar light, as depicted in Figures 3-3d.

The present invention therefore relates to the following embodiments (1 ) to (16). (1 ) An electrical device comprising a first electrode, a second electrode spaced apart from said first electrode and an electrolyte provided between the first electrode and the second electrode, wherein said electrolyte comprises at least one polyoxometalate (POM).

(2) The electrical device of item (1 ), which is an electrochemical cell.

(3) The electrical device of item (1 ) or (2), the electrolyte is a liquid electrolyte.

(4) The electrical device of any one of the preceding items, wherein the electrolyte comprises a redox pair.

(5) The electrical device of item (4), wherein the redox pair comprises or consists of at least one oxidized POM and at least one reduced POM.

(6) The electrical device of any one of the preceding items, further comprising titanium dioxide, a doped titanium dioxide, hydrogenated titanium dioxide, a perovskite, a doped perovskite, zinc oxide or doped zinc oxide.

(7) The electrical device of any one of the preceding items, wherein the POM is selected from the group consisting of heteropolyanions, isopolyanions and Mo-blue and Mo- brown reduced POM clusters.

(8) The electrical device of any one of the preceding items, wherein the POM is a heteropolyoxometalate or a heteropolyoxoacid.

(9) The electrical device of any one of the preceding items, wherein the POM can be oxidized by atmospheric oxygen or by hydrogen peroxide.

(10) The electrical device of any one of the preceding items, wherein the first electrode and/or the second electrode comprises a layer of Sn02.

(1 1 )The electrical device of any one of the preceding items, which is a metal-air battery. (12)The electrical device of item (1 1 ), wherein the anode comprises or consists of a metal, and the cathode comprises said at least one POM.

(13)The electrical device of item (12), wherein the metal is lithium.

(14) The electrical device of any one of items (1 1 ) to (13), wherein said metal-air battery is a paint, a coating, a varnish or a lacquer, or a part of said paint, coating, varnish or lacquer.

(15)The electrical device of any one of items (1 ) to (14), which is a dye-sensitized solar cell comprising a dye or a solar cell comprising POMs which can be activated by solar light and/or oxygen.

(16) A method of generating electric current, comprising feeding or contacting the electrical device of any one of items (1 ) to (15) with atmospheric oxygen, and optionally exposing it to light.

DESCRIPTION OF THE DRAWINGS

Figure 1 depicts the principle of operation of the electrical device of the current application. In one embodiment, the cathode comprises or substantially consists of graphite, which is layered with at least one transparent conductive oxide (TCO) and further by a glass plate; the anode comprises or substantially consists of at least one TCO, which is layered with a glass plate; the electrolyte system comprises a redox couple, which is based on iodine and/or on POM; and the electrolyte further comprises T1O2, or doped Ti0 ₂ particles, a perovskite, a doped perovskite, zinc oxide particles or doped zinc oxide particles, wherein POM is deposited on the particles. The following further explanations are given with respect to Figure 1 : Electrolyte (left side): I2/I or POM; e : I2 + -> I or POM _ox + e -> POM _red ; Anode: TCO; Electrolyte (right side): e.g. I2/I or POM-based ionic liquids itself.

Figure 1a refers to an embodiment of the invention wherein the POM acts as cathode and reacts with hydrogen peroxide. As in Figure 1 the cathode is layered with at least one transparent conductive oxide (TCO) and further by a glass plate; the anode is a metal such as Li, Al, Zn, Na, K, Mg or Fe. The electrolyte system comprises a redox couple, which is based on iodine and/or on POM. The following further explanations are given with respect to Figure 1 a: POM as cathode material and electrolyte in hydrogen peroxide-metal-batteries (Metal = Li; Al, Zn, Na, K Mg, Fe); ^* : cathode can be the porous material coated with POM (without glass + TOO); Electrolyte: e.g. POM-ionic liquid or others; POM: Release O2 and reactivation of POM by H2O2.

Figure 1 b shows the principle of superoxide release by reaction of POM with oxygen or hydrogen peroxide. The following further explanations are given with respect to Figure 1 b: Kat _Red (left side): The catalyst release hyperoxide radicals. These radicals have the ability to initiate various electrochemical processes; Kat _Red (right side): The oxidized form of the catalyst can be reduced again by air and/or hydrogen peroxide and electrons.

Figure 2 depicts the principle of operation of the metal-air battery of the present invention. In this embodiment the cathode comprises one or more POMs. The following further explanations are given with respect to Figure 2: POM as cathode-material in air-metal- batteries (Metal: Li, Al, Zn, Na, K, Mg); Electrolyte: e.g. POM-lonic Liquids or others; Cathode: e.g. carbon, porous pores coated with POM.

Figures 2a and 2b depict a conventional meal air battery and a metal air battery according to the invention. The following further explanations are given with respect to Figure 2a: Metal: e.g. Al, Zn, Mg, Fe, Li; POM catalyst: catalyst producing O2 from air. The following further explanations are given with respect to Figure 2b: Metal: e.g. Al, Zn, Mg, Fe, Li; catalyst: as electrode (and electrolyte); Ionic liquid catalyst: catalyst producing 0 ₂ from air (POM).

Figure 3 depicts the principle of operation of the solar cell of the present invention. One of the electrodes is a glass plate layered with TCO, the other electrode is also a glass plate layered with TCO and graphite. The POMs are deposit on T1O2 nano-particles which are placed between the two glass plates. The POMs convert the energy of light into electricity by the photovoltaic effect.

Figure 3a depicts a solar cell, wherein the activation of the POMs is carried out by solar light. The cathode is a conductive glass layered with T1O2. The anode is a glass layered with TCO and conductive graphite. The POMs are between the glass plates to convert the energy of solar light into electricity. The POMs also act as electrolyte. Figures 3b and 3c depict solar cells wherein the activation of the POMs is carried out by solar light and oxygen. In Figure 3b a conductive glass plate is coated with porous graphite including POMs. A separator is placed over the graphite layer. The other electrode is a conductive glass plate layered with T1O2. Between this glass plate and the separator POMs are placed which convert the energy of solar light into electricity. Additionally, air (oxygen) can be fed laterally to the graphite electrode, wherein the POMs present in the graphite generate superoxide. The device of Figure 3c differs from the device of Figure 3b in that the POMs which convert the energy of solar light into electricity are included in the T1O2 layer. The following further explanations are given with respect to Figure 3b: porous structure: e.g. non-woven filter material; Graphite: Carbon. The following further explanations are given with respect to Figure 3c: porous structure: e.g. non-woven filter material; Porous layer: porous layer coated with graphite and POM; Layer: layer of T1O2 coated with POM; Graphite: Carbon.

Figure 3d depicts a conventional solar cell (Gratzel-cell) and a solar cell according to the invention. The following further explanations are given with respect to Figure 3d: Ionic liquid catalyst: catalyst producing 0 ₂ from air (POM).

Figures 4 and 4a refers to the electrical devices used in Examples 1 and 1 a of the invention.

DETAILED DESCRIPTION

The present invention pertains to an electrical device comprising at least one polyoxometalate (POM). Preferably, the electrical device is an electrochemical cell.

Polyoxometala tes

The POM is not particularly limited, as long as it can be oxidized by atmospheric oxygen or hydrogen peroxide. The POM may be any POM disclosed in Hutin M., Rosnes M.H., Long D.-L. and Cronin L. Polyoxometalates: Synthesis and Structure - From Building Blocks to Emergent Materials. In: Jan Reedijk and Kenneth Poeppelmeier, editors. Comprehensive Inorganic Chemistry II, Vol 2. Oxford: Elsevier; 2013. p. 241-269. The disclosure of Hutin et al. is incorporated herein by reference. In another embodiment, the POM is a heteropolyoxometalate. For example, (hetero)polyoxometalate may be of the formula (I), (II), (III), (IV) or (V):

[A _n ] ^m+ [XM _q Z _r-q-o Z ^! _o 0 _s ] ^m - (I), wherein

m- is the negative charge of the (hetero)polyoxometalate anion,

m+ is the positive charge of the cation(s) A,

lm-1 = lm+1

n is the number of cation(s) A required to provide the positive charge m+,

Z and Z’ are independently selected from W and Mo,

X is selected from P, Si, Ge, Al and B,

M is selected from Ti, V, Mn, Fe, Co, Ni, Zn and Cr,

r = 11 or 12,

o = 0 or 1 ,

s = 37, 38, 39 or 40,

when r = 1 1 , q = 0, 1 , 2, 3, 4, 5, 6, 7, 8 or 9,

when r = 12, q = 0, 1 , 2, 3, 4, 5, 6, 7, 8, 9 or 10, and

when r = 12, s = 40, X = P and q is 0, 1 , 2 or 3, M is not V;

[A„] ^m+ [XM _q Z, _-q-o Z’o024] ^m - (II), wherein

m- is the negative charge of the (hetero)polyoxometalate anion,

m+ is the positive charge of the cation(s) A,

lm-1 = lm+1

n is the number of cation(s) A required to provide the positive charge m+,

Z and Z’ are independently selected from W and Mo,

X is selected from P, Si, Ge, Al and B,

M is selected from Ti, V, Mn, Fe, Co, Ni, Zn and Cr,

t = 4 or 6,

o = 0 or 1 ,

when t = 6, q = 0, 1 , 2, 3 or 4,

when t = 4, q = 0, 1 or 2, and

when t = 4 and X = P, q is 1 , 2 or 3; [An] ^m+ [XpM _q Z _6-q -p-oZ’oOl9] ^m - (III), wherein

m- is the negative charge of the (hetero)polyoxometalate anion, m+ is the positive charge of the cation(s) A,

lm-1 = lm+1

n is the number of cation(s) A required to provide the positive charge m+, Z and Z’ are independently selected from W and Mo,

X is selected from P, Si, Ge, Al and B,

M is selected from Ti, V, Mn, Fe, Co, Ni, Zn and Cr,

o = 0 or 1 ,

p = 0 or 1 , and

q = 0, 1 , 2 or 3

when p = 0, M is not V;

[A„] ^m+ [X2M _q Zl8- _q -oZ’o062] ^m - (IV), wherein

m- is the negative charge of the (hetero)polyoxometalate anion, m+ is the positive charge of the cation(s) A,

Im-I = Im+I

n is the number of cation(s) A required to provide the positive charge m+, Z and Z’ are independently selected from W and Mo,

X is selected from P, Si, Ge, Al and B,

M is selected from Ti, V, Mn, Fe, Co, Ni, Zn and Cr,

o = 0 or 1 ,

q = 0, 1 , 2, 3, 4, 5, 6, 7, 8, 9, 10, 1 1 , 12, 13, 14, 15 or 16, and

when X = P, q is 1 , 2 or 3;

[A„] ^m+ [X5M _q Z30-q-oZ’oOl10] ^m - (V), wherein

m- is the negative charge of the (hetero)polyoxometalate anion, m+ is the positive charge of the cation(s) A,

Im-I = Im+I n is the number of cation(s) A required to provide the positive charge m+, Z and Z’ are independently selected from W and Mo,

X is selected from P, Si, Ge, Al and B,

M is selected from Ti, V, Mn, Fe, Co, Ni, Zn and Cr,

o = 0 or 1 ,

q = 0, 1 , 2, 3, 4, 5, 6, 7, 8, 9, 10, 1 1 , 12, 13 ,14, 15, 16, 17, 18, 19, 20, 21 , 22, 23, 24, 25,

26 or 27; wherein A is selected from one or more cations and comprises at least one cation selected from the group consisting of H ⁺ , quaternary ammonium cations, quaternary phosphonium cations and tertiary sulfonium cations.

Electrolyte

A liquid electrolyte, a gel-type electrolyte or a solid electrolyte may be used as the electrolyte. The electrolyte for an electrical device of the present invention may be a liquid electrolyte including an organic solvent. The organic solvent may be a non-volatile or low-volatile organic solvent, and may have a boiling point of, in one embodiment, about 120° C or higher, and in another embodiment, about 150° C or higher.

The organic solvent may be, for example, propandiol-1 , 2-carbonate (PDC), ethylene carbonate (EC), diethylene glycol, propylene carbonate (PC), hexamethylphosphoramide (HMPA), ethyl acetate, nitrobenzene, formamide, g-butyrolactone (GBL), benzyl alcohol, N- methyl-2-pyrrolidone (NMP), acetophenone, ethylene glycol, trifluorophosphate, benzonitrile (BN), valeronitrile (VN), acetonitrile (AN), 3-methoxy propionitrile (MPN), dimethylsulfoxide (DMSO), dimethyl sulfate, aniline, N-methylformamide (NMF), phenol, 1 ,2-dichlorobenzene, tri-n-butyl phosphate, o-dichlorobenzene, cellenium oxychloride, ethylene sulfate, benzenethiol, dimethyl acetamide, N,N-dimethylethaneamide (DMEA), 3- methoxypropionnitrile (MPN), diglyme, cyclohexanol, bromobenzene, cyclohexanone, anisole, diethylformamide (DEF), dimethylformamide (DMF), 1 -hexanethiol, hydrogen peroxide, bromoform, ethyl chloroacetate, 1 -dodecanthiol, di-n-butylether, dibutyl ether, acetic anhydride, m-xylene, p-xylene, chlorobenzene, morpholine, diisopropyl etheramine, diethyl carbonate (DEC), 1 -pentandiol, n-butyl acetatel -hexadecanthiol, or the like, and may not be limited thereto. For example, the organic solvent may be any one of various materials that are used as a solvent for an electrolyte for a solar cell in the art. Such organic solvents may be used alone or in combination of two or more of these.

The electrolyte typically comprises a redox pair. The redox pair of the electrolyte composition may be iodide/triiodide (17b ), bromine/bromide (Br2/Br), or thiocyanogen/thiocyanate (SCN)2/SCN .The electrolyte for an electrical device of the invention may include, as a redox pair, Land b , and the iodine ion (b) may be provided from an iodide salt. The iodide salt may not include an alkali metal, and the iodide salt may be an ionic liquid, such as an imidazolium salt, a pyridinium salt, a quaternary ammonium salt, a pyrrolidinium salt, a thiazolinium salt, a pyridazinium salt, an isothiazolidinium salt, or an isooxyzolidinium salt. The ionic liquid may be in a molten state in a wide temperature range, including room temperature, and may have high electrochemical stability, high ion conductivity, low melting point, and thermal stability.

According to an embodiment of the present invention, the iodide salt is an imidazolium salt. The imidazolium salt may be, for example, at least one salt selected from the group consisting of 1 -methyl-3-propylimidazolium iodide, 1 ,3-dimethylimidazolium iodide, 1-ethyl- 3-methylimidazolium iodide, 1 -butyl-3-methylimidazolium iodide, 1-methyl-3- pentylimidazolium iodide, 1 -hexyl-3-methylimidazolium iodide, 1 -heptyl-3- methylimidazolium iodide, 1 -methyl-3-octylimidazolium iodide, 1 ,3-diethylimidazolium iodide, 1 -ethyl-3-propylimidazolium iodide, 1-ethyl-3-butylimidazolium iodide, 1 ,3- dipropylimidazolium iodide, and 1 -butyl-3-propylimidazolium iodide.

A concentration of the iodide salt may be in a range of about 0.1 to about 2 M. In one embodiment, when the concentration of the iodide salt is within this concentration range, the delivery of electrons through a redox reaction, that is, the delivery of electrons to a ground state of POM is easily performed. For example, the concentration of the iodide salt may be in a range of about 0.5 to about 1.5 M.

Also, the electrolyte may further include, in addition to the iodide salt, iodine (b) to form a redox pair. When an amount of iodine is too small, regeneration due to the delivery of electrons to POM molecules by virtue of a redox reaction may not be efficiently performed, and when an amount of iodine is too great, the amount of the iodide salt is relatively too small, and thus ions may not efficiently conduct and efficiency of the device may decrease. The concentration of iodine may be, for example, in a range of about 0.01 to about 0.5 M. In another embodiment the electrolyte contains an organic redox system. For example, the electrolyte may contain quinone/hydroquinone or violuric acid.

In a particular embodiment, the electrolyte contains a redox system which comprises or consists of one or more POMs. Any POM which can act as ionic liquid is suitable as electrolyte. For example, POMs comprising alkyl-amino chains or being capable of forming alkyl-ammonium cations, or POMs comprising alkyl-phosphonium cations or being capable of forming alkyl-phosphonium cations, are suitable as redox system and/or electrolyte in accordance with this invention. In this embodiment, no additional redox system as described hereinabove (e.g. based on iodine) is required. The redox system can be described as POMoxidized/POM _reduced . In a specific embodiment, P0M _Oxidized /P0M _{red ced} is the sole redox system in the electrolyte of the device.

According to an embodiment of the present invention, the electrolyte for a device of the invention may further include guanidine thiocyanate. Guanidine thiocyanate is composed of a guanidine cation and a thiocyanate anion, and when added into an electrolyte, the guanidine thiocyanate may exist in a dissociated state, that is, as a cation and an anion. According to an embodiment of the present invention, the guanidine thiocyanate is added at a concentration of 0.2 M or lower to the electrolyte.

The electrolyte may further comprise a metal oxide, e.g. indium tin oxide (ITO), aluminum doped zinc oxide (AZO), antimony doped tin dioxide (ATO), fluorine doped tin dioxide (FTO), tin-doped indium oxide or conductive impurity doped titanium oxide (T1O2). In another embodiment, the electrolyte does not contain titanium oxide (T1O2). In yet another embodiment the electrolyte does not contain a metal oxide.

Electrodes

The first electrode typically is the cathode. It may include a conductive layer. The conductive layer may include a conductive metal oxide selected from the group consisting of indium tin oxide (ITO), fluorine tin oxide (FTO), ZnO-(Ga203 or AI2O3), a tin-based oxide, an antimony tin oxide (ATO), zinc oxide, and a mixture thereof. For example, Sn0 ₂ , which has conductivity, transparency, and heat resistance, may be used; indium tin oxide (ITO), which is relatively inexpensive, may be used alone; and a composite layer of indium tin oxide (ITO) and other metal oxides, which are used to reduce a resistance after heat treatment, may be used.

The conductive layer may be formed of a single film or a multi-layer film of the conductive metal oxide.

In another embodiment, the first electrode does not contain titanium oxide (T1O2). In yet another embodiment the first electrode does not contain a metal oxide. In a preferred embodiment, the POMs act as cathode material (see Figure 1a and 2a and 2b).

The second electrode typically is the anode. It may be formed of a conductive material, and an insulating material may also be used to form the second electrode as long as a conductive layer is formed to face the first electrode. In this regard, an electrochemically stable material may be used to form the second electrode, and in particular, platinum, gold, or carbon may be used. Also, to improve catalytic effects to oxidation and reduction, a portion of the second electrode facing the first electrode may have a microstructure with an increased surface area, and for example, platinum is used in the form of platinum black, and carbon is used in a porous state. The platinum black may be formed by anodizing platinum or treating platinum with a chloroplatinic acid, and a porous carbon may be formed by sintering carbon fine particles or calcining an organic polymer. Also the second electrode may have a conductive layer as the first electrode.

In another embodiment, the device of the present invention is a metal-air battery, preferably a lithium-air battery. According to this embodiment the POMs act as cathode material. That is, the cathode comprises one or more POMs. The cathode may have any shape and can be made of any suitable material. In a preferred embodiment, the cathode consists of a carbon cathode which is coated with POM. In some of the embodiments, the cathode is flexible (see Figure 2b). Preferably, the cathode substantially consists of a non-woven fabric having pores and at least one POM or porous carbon and at least one POM, wherein the pores of the non-woven fabric or carbon are coated and/or filled with the POM. The non- woven fabric may be a non-woven polymer fabric such as a non-woven polyethylene fabric. Optionally, the POMs may additionally act as electrolyte in this device, as described above. In this embodiment the anode comprises or essentially consists of a metal. Preferably, the metal is selected from lithium, aluminium, zinc, sodium, iron, potassium and magnesium. Most preferably, the anode comprises or essentially consists of lithium. This embodiment is depicted in Figure 2. In a specific embodiment the metal-air battery is a paint, a coating, a varnish or a lacquer, or a part of said paint, coating, varnish or lacquer.

In another embodiment, the cathode is a non-woven polymer fabric coated with the POM and the anode is preferably aluminum, which may be a flexible film or sheet (see Figure 2b and Figures 4 and 4a).

According to the invention, a separator may be placed between the cathode and the anode to separate the cathode from the anode by maintaining the electrolyte permeability (see Figures 3b, 3c and 4a). The separator according to the invention may be made of any suitable material known in the art such as for example porous organic polymer films, inorganic nonwoven fabrics which are not coated with the POM, glass or ceramic material which may be coated for example with ITO, or polypropylene/polyethylene/polypropylene composites.

Methods to manufacture electrochemical cells are generally known in the art.

Mechanism

It is believed that the atmospheric oxygen (O2) oxidizes the POM, whereby the oxygen is converted to superoxide:

POM + O2 ®POM _ox + O2

Another possibility is that hydrogen peroxide reacts with POMs to release superoxide (see Figure 1 a and 1 b).

The superoxide anion then transfers the electron to the anode, whereby it is oxidized to oxygen. Optionally, this may occur via T1O2 nanoparticles or doped T1O2 nanoparticles or perovskite nanoparticles or zinc oxide nano-particles. The electrons finally reach the counter electrode through the circuit.

The oxidized POM (POM _ox ) accepts electrons from the I ion redox mediator leading to regeneration of the basic state of the POM, and two I ions are oxidized to elementary Iodine which reacts with L to the oxidized state, I3 . In another embodiment, the POM itself acts as electrolyte. The oxidized POM accepts electrons directly from the cathode and is thereby converted into a reduced state. The reduced POM is then oxidized by atmospheric oxygen (O2) or hydrogen peroxide, thus yielding oxidized POM and superoxide (see supra). The POM may be the sole electrolyte redox system (see Figure 2b).

In yet another embodiment, the device of the present invention is a metal-air battery, preferably a lithium-air battery (see Figure 2, Figure 2a and 2b). In this embodiment the POMs act as cathode material and optionally as electrolyte (see Figure 2b). The POMs reduce oxygen to yield superoxide. Thereby it is possible to selectively generate UO2, without blocking the cathode with U2O2 which is a problem of known lithium-air batteries. This results in a longer lifetime of the battery and a higher efficiency.

In other embodiment the electrical device is a hydrogen peroxide-metal battery wherein the POMs acts as cathode and reacts with hydrogen peroxide to activate electrons (see Figures 1 a and 1 b).

In yet another embodiment, the device of the present invention is a solar cell which is capable of converting the energy of light into electricity by the photovoltaic effect. The device according to this embodiment comprises a dye which is the dye sensitizer or POMs which are able to absorb light and convert the energy of the light into electricity by the photovoltaic effect. Devices which are in accordance with the invention are described in detail in Figures 3-3d. Preferably, the POMs are ionic-liquid POMs, which may be deposited on titanium dioxide nano-particles or doped titanium dioxide nano-particles or perovskite nano-particles or zinc oxide nanoparticles (see Figure 3). Doped titanium dioxide includes further compounds such as nitrogen or other metals than titanium which are able to shift the absorption of the light from ultraviolet to visible light. In another embodiment, titanium dioxide, doped titanium dioxide, hydrogenated titanium dioxide, perovskite, doped perovskite, zinc oxide or doped zinc oxide including POM(s) which can be activated by solar light are coated on a glass plate as a layer (see Figure 3c). Additionally, it is preferred that the POMs which convert the energy of solar light into electricity are placed between the two electrodes (see Figure 3a). The dye can be any dye that is known to be suitable in dye- sensitized solar cells, e.g. dyes described in Michael R. Travino (2012)“Dye-sensitized Solar Cells and Solar Cell Performance”, ISBN 9781612096339; or in Kalyanasundaram (2010) “Dye-sensitized Solar Cells”. ISBN 9782940222360.

In case the POMs are used to convert the energy of the light into electricity there is no need to use a dye and another electrolyte than POMs in the solar cell. Preferably, the POMs act as a cathode and sole electrolyte redox system.

The device of this embodiment can generate electricity by absorption of light, and additionally due to the reaction of POMs with oxygen or hydrogen peroxide, as described above. Such devices which are described in particular in Figures 3b and 3c. The advantage of these devices is that they generate electricity also in the absence of light.

Examples

Example 1 :

The electrical device contained as cathode a 10 x10 cm non-woven polyethylene fabric having a BET-surface of 1 .5 m ² which was coated with 250 mg of an ionic-liquid POM. The ionic-liquid POM was activated with oxygen or hydrogen peroxide. The anode of the electrical device was an aluminum sheet (see Figure 4).

The determined electrical voltage of the electrical device was 0.55 V when the ionic-liquid POM was activated with oxygen, and 800 mV to 1 .2 V when the ionic-liquid POM was activated with hydrogen peroxide. The generated current was 3 to 7 mA by activating the POMs with hydrogen peroxide.

During a time period of 24 hours it was observed that the electrical voltage decreased. However, after adding distillated water or air or hydrogen peroxide to the nonwoven fabric the electrical voltage could be again increased significantly. As long as the non-woven fabric was moist, the measured electrical voltage could be maintained. Example 1a:

This example corresponds to Example 1 with the exception that between the non-woven fabric (cathode) and the aluminum sheet anode an ITO-coated glass was used as current collector (see Figure 4a).

Example 2:

The construction of the device used in this example corresponded to the construction as depicted in Figure 3 and 3a. Ionic-liquid POMs were mixed with titanium dioxide (anatas) nano-particles having an average particle size of 20 nm such that a white paste was obtained. The produced white paste was able to convert light into electricity. The measured voltage was approx. 0.4 V and the generated current was between 0.7 and 1.3 mA.