WATER-SPLITTING WITH BACTERIORHODOPSIN-SENSITIZED

PHOTOELECTRODE

This patent application claims the benefit of European Patent Application EP17382464.0 filed on July 14, 2017.

The present disclosure relates to methods and devices for use in

photoelectric conversion. BACKGROUND ART

An important milestone in the solar cells was the invention of excitonic solar cell called dye sensitized solar cells (DSSC). In DSSC, light active synthetic dye (organic or organometallic) is usually bound to nanostructured wide gap metal oxide semiconductor and used as photo sensitized to harvest the solar energy and generate excitons. Bio-sensitized solar cells (BSSC) are based on the phenomenon of photon triggered electron ejection by light activated proteins. DSSC and BSSC systems differ mainly in the electron donor- synthetic dye in the former and light-activated biomolecules in the later.

Bacteriorhodopsin (bR), a membrane protein found in the archae

Halobacterium salinarum is a natural light activated protein, holds high promise for solar energy conversion. bR has remarkable functional stability against a high concentration of salt (up to 5 M NaCI) and thermal stability even up to ~140 °C, in dry state and with high quantum efficiency. In addition, bR functionally tolerates broad range of pH (5-1 1 ). It is easy and inexpensive to clone and express.

For engineered applications, bacteriorhodopsin is purified as membrane patches, known as purple membrane (PM). Purple membrane is a large cell membrane patch, which is composed of multiple bacteriorhodopsin molecules and their associated lipids. This structure provides it a high degree of chemical stability and resistance to thermal degradation. It is called PM due to its distinct purple color, which is due to its absorption peak near 570 nm. Purple membrane has been shown to maintain functionality at temperatures up to 80° C. in water and 140° C. dried. In the dried state, as well as the wet state, PM retains its light absorption properties and photochemical activity for years.

The use of bacteriorhodopsin for light scavenger devices dates back to earliest 90s. Since then, it has been studied the behavior of the protein and the biological cycle it performs for the proton pump when receiving sunlight and the direct application of the protein on conductive oxides to take advantage of the differential of potential that generates.

In J Nanoscience and Nanotech, 2009, 9, 1679-1687, Thavasi V. et al, it was described the operation of a solar plate based on TiO ₂ nanoparticles with bR immobilized as a electrode (FTO/TiO ₂ /bR) and FTO/AI electrode in KCI electrolyte at pH 8. A short-circuit current of 0.089 mA/cm ² and an open- circuit potential of 0.35 V was achieved under an excitation of 40 mW/cm ² . The study demonstrates the viability of the bacteria to be used as a charge generator through solar radiation. However, its approach does not

contemplate taking advantage of the associated hydrogen generation.

The most promising field of use of bacteriorhodopsin as a base in a solar device is in harnessing its ability to separate and pump protons from water. However, adaptations must be made, such as the addition of a polymer layer (Nafion) that only passes the protons, creating a potential differential between the medium (water) and the other end of the polymer layer. This type of technology is the one that is currently used in fuel cells. In US9023989 it is described a photovoltaic cell based on bacteriorhodopsin, exposing how the protein can be targeted on a substrate and modified by mutations to improve transmembrane proton transfer and covalent attachment between the protein and the substrate. However, despite describing that these photovoltaic cells based on bacteriorodpsin generate hydrogen gas from water and can be harnessed to produce electricity, it does not expose any design how to take advantage of this hydrogen.

In Adv. Colloid and Interface Sci. 2015, 225: 194-202 it is disclosed bio-nano hybrid materials based on bacteriorhodopsin conjugated to different nanomaterials and its application in solar H ₂ generation systems.

SUMMARY The present invention provides a reversible bio sensitized photoelectric conversion and H ₂ to electricity conversion device comprising a first compartment (A) and a second compartment (B); the first compartment (A) comprises a first photoanode electrode (A1 ) and a second electrode (A2) with a water-containing medium (4) therebetween; wherein a polymeric membrane (C) is disposed between the first compartment (A) and the second

compartment (B); the second compartment (B) comprises a third electrode (B1 ), and an hydrogen collecting deposit (B2).

The reversible bio sensitized photoelectric conversion and H ₂ to electricity conversion device of the invention comprises the following elements extending from its front end surface to its opposing back end surface, which corresponds with the direction of incident light (c.f. Fig. 1 ): i) a first compartment (A) which comprises a first photoanode electrode (A1 ), and a second electrode (A2), which may work as an anode or as a cathode, with a water-containing medium (4) therebetween;

ii) a polymeric membrane (C) disposed between the first compartment (A) and the second compartment (B); and

iii) a second compartment (B) which comprises a third electrode (B1 ), which may work as a cathode or as an anode depending of the role of the second electrode (A2) being opposite to it, and an hydrogen collecting deposit (B2); wherein

the first compartment (A), extending from its front end surface to its opposing back end surface (i.e. in the direction of incident light), comprises:

i.1 a first photoanode electrode (A1 ) which comprises: i.1 .1 a layer of a visible or UV and visible radiation transparent conductor material (1 ); i.1 .2 a first conductive metallic material (2); and i.1 .3 optionally, one or more of a proton pumping photoactive biological layers (3) comprising oriented purple membrane containing bacteriorhodopsin protein or any of its genetic variants; stabilized bacteriorhodopsin protein-based sensitizer or any of its genetic variants; or mixtures thereof; the proton pumping photoactive biological layers (3) being deposited on the first conductive metallic material (2); i.2 a water-containing medium (4); i.3. a second electrode (A2) which comprises: i.3.1 optionally, one or more of a proton pumping photoactive biological layers (5) comprising oriented purple membrane containing bacteriorhodopsin protein or any of its genetic variants; stabilized bacteriorhodopsin protein-based sensitizer or any of its genetic variants; or mixtures thereof; and i.3.2 a second conductive metallic material (6); the proton pumping photoactive biological layers (5) being deposited on the second conductive metallic material (6); and i.3.3 a layer of a visible or UV and visible radiation transparent conductor material (7); with the proviso that at least one of the proton pumping photoactive biological layers (3) or (5) are present.

Accordingly, the present invention relates to a reversible bio sensitized photoelectric conversion and H ₂ to electricity conversion device comprising one or more of a proton pumping photoactive biological layers comprising oriented purple membrane which contains bacteriorhodopsin protein or any of its genetic variants; stabilized bacteriorhodopsin protein-based sensitizer or any of its genetic variants; or mixtures thereof; the proton pumping

photoactive biological layers being deposited on the surface of the first conductive metallic material of the first phothoanode electrode and on the second conductive metallic material of the second electrode.

The presence of the proton pumping photoactive biological layers, results in the generation of a proton gradient when sunlight (or any other suitable visible radiation) incides to it. Thus, it can be used to generate an electrical current and hydrogen gas via photoelectric-based water splitting; the hydrogen thus generated may be stored in the hydrogen collecting deposit (B2). When the system operates in the reverse mode, hydrogen is supplied from the hydrogen collecting deposit (B2) in order to generating electricity.

Accordingly, in the context of the present disclosure, the term "reversible bio sensitized photoelectric conversion and H ₂ to electricity conversion device" means that it may operate in both modes: a direct mode for the generation of electric current and hydrogen by solar radiation via water splitting, and a reverse mode for the generation of an electric current with supply of hydrogen. In general terms, overall water-splitting reaction comprises that the

photocatalyst absorbs photon energy greater than the band-gap energy of the material and generates photo-excited electron hole pairs. Under irradiation, electrons in the valence band of the semiconductor photocatalyst are excited into the conduction band, leaving holes in the valence band. These photo- generated electrons and holes cause reduction of H ⁺ to H ₂ and oxidation of H ₂ O to O ₂ , respectively.

The following basic reaction scheme can be proposed for the water splitting reaction occurring in the direct mode of operation according to the present invention:

i) In compartment (A) (electrodes (A1 ) and (A2) are working as anodes) 4H ₂ O 4H ⁺ + 4OH ^"

4OH ^" 4e ^" + 2H ₂ O + O ₂ 2H ₂ O ^ 4H ⁺ + O ₂ ii) In compartment (B) (electrode (B1 ) is working as cathode) 4H ⁺ + 4e ^" 2H ₂

Whereas, when the system operates in the reverse mode, the reaction scheme occurring is as follows:

i) In compartment (B) (electrode (B1 ) is working as anode)

H ₂ 2H ⁺ + 2e ^"

ii) In compartment (A) (electrode (A2) is working as cathode)

4e ^" + 4H ⁺ + O ₂ H ₂ O Therefore, the reversible bio sensitized photoelectric conversion and H ₂ to electricity conversion device of the invention is closed and reversible, which may be used in both processes:

i) water splitting for hydrogen generation with the correspondent energy production; and

ii) generation of electric current by hydrogen conversion.

The innovation is a device closed, so it can be commercialized as solar module or solar glass, using personalized size to adapt the module, and generate the electricity in the same place where it is consumed, avoiding the transport. Other known devices with similar functionality as those disclosed in documents mentioned above are open systems, supplying input components to ensure a correct functionality. Furthermore, open systems are applied in huge electricity installations in order to produce hydrogen or electricity.

The device works in the range of visible or visible and UV light, thus it can be used outdoor, both in sunny or in adverse weather conditions (i.e. shadows, storms or cloudy), and indoor.

The present device is reversible. Thus, the device produces electricity and hydrogen simultaneously in direct mode, storing the hydrogen inside the system. Additionally, in reverse mode, it is used when there is no visible light or direct light to convert de hydrogen stored in electricity. The reverted mode is acting as a battery, because hydrogen can be stored and later on converted it into electricity depending on the energy demand. The possibility to use the hydrogen deposit as a battery allows the device supplying energy at night, reducing space, and reducing costs because no battery is needed. The invention also provides a photoelectric conversion element that incorporates the bio sensitized photoelectric conversion device as defined herein. Preferably, the photoelectric conversion element is a solar cell.

BRIEF DESCRIPTION OF THE DRAWINGS

Non-limiting examples of the present disclosure will be described in the following, with reference to the appended drawings, in which:

Fig. 1 represent a cross-sectional view of the bio sensitized photoelectric conversion device according to an embodiment of the present invention. Fig 2 shows a comparison of the energy of the device of the present invention provided in different combinations of direct irradiation versus diffuse irradiation was performed. Efficiency vs. direct/diffuse spectrum of the device of the invention (1 ), a silicon poly-crystalline (2) and the device of the invention without H ₂ (3)

Fig. 3 shows the voltage generated (measured by voltammeter) by the device of the present invention when working in sunlight (direct operation mode) and without it (reverse mode).

Fig. 4 represent the sequence of tanks used in the lyer-by-lyer method.

DETAILED DESCRIPTION OF THE INVENTION

Throughout the figures the same reference numbers will be used for matching parts.

In some embodiments, the first photoanode electrode (A1 ) comprises one or more of a proton pumping photoactive biological layers (3).

In accordance with some embodiments, the second electrode (A2) comprises one or more of a proton pumping photoactive biological layers (5). Alternatively, in accordance with some embodiments, both the first

photoanode electrode (A1 ) and the second electrode (A2) comprise one or more of a proton pumping photoactive biological layers (3) and (5).

The reversible bio sensitized photoelectric conversion and H ₂ to electricity conversion device of the present invention uses one or more of a proton pumping photoactive biological layers comprising oriented purple membrane which contains bacteriorhodopsin protein or any of its genetic variants;

stabilized bacteriorhodopsin protein-based sensitizer or any of its genetic variants; or mixtures thereof; to generate a proton gradient that is harnessed to produce electrical energy and hydrogen.

It is known in the art that under oxygen limited conditions the Halobacterium cell grows planar purple membrane (PM) patches in the form of a hexagonal two-dimensional crystalline lattice of bR trimers. In accordance with an embodiment of the present invention, the proton pumping photoactive biological layer present in the first photoanode electrode, the second electrode, or both, may comprise oriented purple membrane which contains bacteriorhodopsin protein or any of its genetic variants.

Alternatively, in accordance with an embodiment of the present invention, the one or more proton pumping photoactive biological layers present in the first photoanode electrode, the second electrode, or both, may comprise stabilized bacteriorhodopsin protein-based sensitizer or any of its genetic variants.

Stabilized bacteriorhodopsin protein-based sensitizer refers to protein-based sensitizer derived from bacteriorhodopsin protein which has been stabilized. Stabilization can be accomplished by mixing the bacteriorhodopsin-based sensitizer with a surfactant. A preferred class of surfactants is protein stabilizing surfactants, such as peptide surfactants.

The terms "wild type bacteriorhodopsin" and "native bacteriorhodopsin", as used herein, both refer to the form of bacteriorhodopsin as it occurs in nature. Further, as used herein, the terms "mutant bacteriorhodopsin", "mutated bacteriorhodopsin" and "bacteriorhodopsin genetic variant" all refer to a bacteriorhodopsin protein in which the amino acid sequence of a wild type or native bacteriorhodopsin protein has had at least one of its amino acids replaced with a different amino acid.

There are different native Halobacterium salinarum strains accessible both in commercial sources and from different international depositary authorities under the Budapest Treaty. Thus, for example, H. salinarum S9 and L3 strains are commercially accessible.

Additionally, it is known that bacteriorhodopsin is formed by a proteic part, named bacterioopsin and a retinal unit. Bacterioopsin is codified by gen bop. Cloning and sequence analysis of a H. halobium DNA fragment that includes the structural gene for bacteriorhodopsin and sequences flanking the NH ₂ and COOH termini was described in Proc.Natl Acad. Sci. USA 78/1 1 (1981 ) 6744- The skilled person in the art knows different methods of site-directed mutagenesis, such as Dunn, R., et al., The bacteriorhodopsin gene. Proc Natl Acad Sci U S A, 1981 . 78(1 1 ) 6744-6748; Landt, O., H . Grunert, and U. Hahn, A general method for rapid site-directed mutagenesis using the polymerase chain reaction. Gene, 1990. 96(1 ) 125-128; and Juncosa- Ginesta, M., et al., Improved efficiency in site-directed mutagenesis by PCR using a Pyrococcus sp. GB-D polymerase. Biotechniques, 1994. 16(5) 820- 823.

As mentioned above, and shown in Fig .1 , the reversible bio sensitized photoelectric conversion and H ₂ to electricity conversion device comprises a first compartment (A) and a second compartment (B); the first compartment (A) comprises a first photoanode electrode (A1 ) and a second electrode (A2) with a water-containing medium (4) therebetween; wherein a polymeric membrane (C) is disposed between the first compartment (A) and the second compartment (B); the second compartment (B) comprises a third electrode (B1 ), and an hydrogen collecting deposit (B2). The first compartment (A) extends from a front end surface to an opposing back end surface (which corresponds with the direction of incident light, c.f. Fig. 1 ), wherein the front end surface of compartment (A), when the bio sensitized photoelectric conversion device of the invention is in use, it is irradiated with an incident light.

In some embodiments, the incident light may be natural sunlight or any type of radiation source having a wavelength in the central range of the solar spectrum. Generally, incident light comprising a wavelength in the 280-1 100 nm region may be used. Preferably in the 350-850 nm region, being particularly preferred in the 500-650 nm region.

In accordance with some embodiments of the present invention, the layer of a UV and visible radiation transparent conductor material of the first

photoanode electrode (1 ) and of the second electrode (7) are independently selected from graphene; carbon nanotubes (CNT); ultra thin metal films;

Fluorine doped Tin Oxide (FTO) coated glass; Transparent Conductive Oxides (TCO) and transparent conducting polymers such as Poly(3,4- ethylenedioxythiophene) (PEDOT), Poly(3,4-ethylenedioxythiophene)

PEDOT: poly(styrene sulfonate) PSS and Poly(4,4-dioctyl

cyclopentadithiophene). In some examples of these embodiments, the layer of a UV and visible radiation transparent conductor material (1 ) and of the second electrode (7) are independently selected from graphene; Transparent Conductive Oxides (TCO) and transparent conducting polymers such as Poly(3,4- ethylenedioxythiophene) (PEDOT), Poly(3,4-ethylenedioxythiophene)

PEDOT: poly(styrene sulfonate) PSS and Poly(4,4-dioctyl

cyclopentadithiophene). Particularly, in some examples, the layer of a UV and visible radiation transparent conductor material (1 ) and of the second electrode (7) is graphene. In some embodiments, the first conductive metallic material of the first photoanode electrode (2) and the second conductive metallic material of the second electrode (6) are independently selected from platinum, gold, silver, graphite, aluminum, TiO ₂ , carbon nanotubes, graphene, reduced graphene oxide (rGO), TiO ₂ doped by Au nanoparticles, Au nanoparticles doped by palladium nanoparticles, TiO ₂ doped Ag nanoparticles, a semiconductor metal oxide, TiO ₂ /Pt nanoparticles, TiO ₂ /rGO, Pt/Co/TiO ₂ , and mixtures thereof.

In some examples of these embodiments, the first conductive metallic material of the first photoanode electrode (2) is selected from Au

nanoparticles, Ag nanoparticles, Pt nanoparticles, TiO ₂ doped by Au nanoparticles, Au nanoparticles doped by palladium nanoparticles, TiO ₂ doped by Ag nanoparticles, and mixtures thereof. In particular examples, the first conductive metallic material of the first photoanode electrode (2) is Au nanoparticles.

In some examples of these embodiments, the second conductive metallic material (6) is selected from TiO ₂ , Pt nanoparticles, TiO ₂ doped by Pt nanoparticles; TiO ₂ /rGO, Pt/Co/TiO ₂ , and mixtures thereof. In particular examples, the second conductive metallic material (6) is TiO ₂ .

In some embodiments of the present invention, the first compartment (A) may comprise the following elements extending from its front end surface to its opposing back end surface (which corresponds with the direction of the incident light), which it is in contact with the polymeric membrane:

1 ) a first photoanode electrode (A1 ) which comprises:

i) optionally, a protective and light-transmissive material (10);

ii) a layer of a UV and visible radiation transparent conductor material

(1 ); examples of suitable transparent conducting materials are graphene; carbon nanotubes (CNT); ultra thin metal films; Fluorine doped Tin Oxide (FTO) coated glass; Transparent Conductive Oxides (TCO) and transparent conducting polymers such as Poly(3,4-ethylenedioxythiophene) (PEDOT), Poly(3,4-ethylenedioxythiophene) PEDOT: poly(styrene sulfonate) PSS and Poly(4,4-dioctyl cyclopentadithiophene);

iii) a first conductive metallic material (2), examples of suitable first conductive metallic materials are platinum, gold, silver, graphite, aluminum, TiO ₂ , carbon nanotubes, graphene, reduced graphene oxide (rGO), TiO ₂ doped by Au nanopartides, Au nanopartides doped by palladium

nanopartides, TiO ₂ doped Ag nanopartides and mixtures thereof;

and

iv) optionally, one or more of a proton pumping photoactive biological layers (3) comprising oriented purple membrane which contains

bacteriorhodopsin protein or any of its genetic variants; stabilized

bacteriorhodopsin protein-based sensitizer or any of its genetic variants; or mixtures thereof; the proton pumping photoactive biological layer being deposited on the first conductive metallic material;

2) a water-containing medium (4);

3) a second electrode (A2) which comprises:

v) optionally, one or more of a proton pumping photoactive biological layers (5) comprising oriented purple membrane which contains

bacteriorhodopsin protein or any of its genetic variants; stabilized

bacteriorhodopsin protein-based sensitizer or any of its genetic variants; or mixtures thereof;

vi) a second conductive metallic material (6), examples of suitable second conductive metallic materials are platinum, gold, silver, graphite, aluminum, TiO ₂ , carbon nanotubes, graphene, reduced graphene oxide (rGO), TiO ₂ doped by Au nanopartides, Au nanopartides doped by palladium nanopartides, and TiO ₂ doped by Ag nanopartides, a semiconductor metal oxide, TiO ₂ /Pt nanopartides, TiO ₂ /rGO, Pt/Co/TiO ₂ , and mixtures thereof; the proton pumping photoactive biological layer being deposited on the second conductive metallic material;

and

vii) a layer of a UV and visible radiation transparent conductor material (7); examples of transparent conducting materials are graphene; carbon nanotubes (CNT); ultra thin metal films; Fluorine doped Tin Oxide (FTO) coated glass; Transparent Conductive Oxides (TCO) and transparent conducting polymers such as Poly(3,4-ethylenedioxythiophene) (PEDOT), Poly(3,4-ethylenedioxythiophene) PEDOT: poly(styrene sulfonate) PSS and Poly(4,4-dioctyl cyclopentadithiophene);

with the proviso that at least one of the proton pumping photoactive biological layers (3) or (5) are present; preferably both of the proton pumping

photoactive biological layers (3) and (5) are present.

In the context of the present disclosure, the term "transparent conducting layer" or "layer of a transparent conductor material" and variants, are interchangeable and they refer to a layer of optically transparent and electrically conductive material, wherein optically transparent means that the material allows passing both UV and visible radiation. In some embodiments, the bio-sensitized photoelectric conversion device is encapsulated in a protective and light-transmissive material or covered by a light-transmissive layer (10). A preferred protective layer is quartz glass, or any structural polymeric material transparent over the entire light spectrum. In accordance with a preferred embodiment of the present invention, the first photoanode electrode (A1 ) comprises a first conductive metallic material (2) selected from platinum, gold, silver, graphite, aluminum, TiO ₂ , carbon nanotubes, graphene, reduced graphene oxide (rGO), TiO ₂ doped by Au nanoparticles, Au nanoparticles doped by palladium nanoparticles, and TiO ₂ doped Ag nanoparticles and mixtures thereof.

In accordance with an embodiment of the present invention Au may be substituted by Ag, thus resulting in an improvement of the rB absorption range near to UV light (blue), but the catalytic efficiency decrease vs Au.

In accordance with an embodiment of the present invention, Au may be substituted by Pt which provides more catalyst effectiveness, and when the system is producing electricity from hydrogen, the two electrodes of the upper part (first electrode (A1 ) and second electrode (A2)) can be connected in parallel, thus increasing the H ₂ - electricity conversion efficiency. In accordance with another embodiment of the present invention, Au may be substituted by TiO ₂ doped by Au nanoparticles, which changes its absorption range towards the visible (560 nm) by increasing the catalytic activity of the split of the water and allowing the catalysis of the reaction 4OH→ 4e ^" + 2H ₂ O + O ₂ which is produced at the electrode. It also allows UV light to be absorbed by the TiO ₂ of the second anode electrode. In accordance with another embodiment of the present invention, Au may be substituted by Au nanoparticles doped by palladium nanoparticles, which increases the catalytic yield of Au, improving the reaction

4OH ^" 4e ^" + 2H ₂ O + O ₂

In accordance with an additional embodiment of the present invention, Au may be substituted by TiO ₂ doped Ag nanoparticles.

In accordance with another preferred embodiment of the present invention, the second electrode (A2) comprises a second conductive metallic material

(6) selected from a semiconductor metal oxide, platinum nanoparticles, TiO ₂ , TiO ₂ /Pt nanoparticles, TiO ₂ /rGO, Pt/Co/TiO ₂ , and mixtures thereof.

In accordance with an embodiment of the present invention, TiO ₂ may be replaced by Pt nanoparticles. Pt nanoparticles provides more catalyst effectiveness, but increase the cost and loss the efficiency in the UV range.

In accordance with another embodiment, TiO ₂ may be substituted by TiO ₂ /Pt nanoparticles. This configuration improves catalysis, efficiency to split water but increases the cost.

In accordance with an embodiment of the present invention, TiO ₂ may be substituted by TiO ₂ /rGO. With this configuration, the photocurrent may be increased up to 9 times.

In accordance with another embodiment of the present invention, TiO ₂ may be substituted by Pt/Co/TiO ₂ . This triple alloy may be used to improve the catalytic activity of Pt and TiO ₂ and the electronic flow through the graphene by electromagnetic activity.

In accordance with an embodiment of the present invention, nanoparticles of the conductive material or carbon nanotubes decorated with said

nanoparticles may be applied. Using nanotubes improves the conductivity of electrons but reduces catalytic performance.

The polymeric membrane (C) is selected between those known polymeric membranes which allow the passage of protons. A suitable example of polymeric membrane for use in the device of the present invention is, but not limited to Nafion.

In some embodiments, the second compartment (B) may comprise the following elements extending from its front end surface which it is in contact with the polymeric membrane to its opposing back end surface: i) optionally, a layer of a UV and visible radiation transparent conductor material (8); examples of transparent conductor materials are graphene; carbon nanotubes (CNT); ultra thin metal films; Fluorine doped Tin Oxide (FTO) coated glass; Transparent Conductive Oxides (TCO) and transparent conducting polymers such as Poly(3,4-ethylenedioxythiophene) (PEDOT), Poly(3,4-ethylenedioxythiophene) PEDOT: poly(styrene sulfonate) PSS and Poly(4,4-dioctyl cyclopentadithiophene); ii) a third conductive metallic material (9) selected from platinum, gold, silver, graphite, aluminum, TiO ₂ , carbon nanotubes, graphene, reduced graphene oxide (rGO), TiO ₂ doped by Au nanoparticles, Au nanoparticles doped by palladium nanoparticles, TiO ₂ doped by Pt nanoparticles, TiO ₂ /rGO,

Pt/Co/TiO ₂ , and TiO ₂ doped by Ag nanoparticles and mixtures thereof;

the third conductive metallic material working as a cathodic electrode;

and optionally iii) an hydrogen collecting deposit (B2).

In accordance with an embodiment of the present invention, the third conductive metallic material (9) is selected from a semiconductor metal oxide, platinum nanoparticles, TiO ₂ , TiO ₂ doped by Pt nanoparticles, TiO ₂ /rGO, Pt/Co/TiO ₂ , and mixtures thereof.

Deposition of the third conductive metallic material (9) of compartment (B) onto the polymeric membrane (C) may be performed by any of the known methods described in the art.

In some embodiments, a layer of a UV and visible radiation transparent conductor material (8) may be previously deposited, preferably by chemical vapor deposition, onto the polymeric membrane (C) surface to improve the conductivity of the membrane and then, the third conductive metallic material (9) is deposited onto the transparent conductor material layer (8) by e.g electrodeposition.

The one or more of a proton pumping photoactive biological layers

comprising oriented purple membrane (3, 5) which contains

bacteriorhodopsin protein or any of its genetic variants; stabilized

bacteriorhodopsin protein-based sensitizer or any of its genetic variants; or mixtures thereof; may be deposited on the surface of the first and second conductive metallic materials by a number of methods known in the art. In some embodiments, the proton pumping photoactive biological layers may be generated either by using electrophoretic deposition or by electrostatic layer- by-layer deposition.

In accordance with a particular embodiment of the present invention, proton pumping photoactive biological layers are deposited by electrostatic layer-by- layer deposition.

The layer by layer deposition method to deposit the protein on a substrate comprises to submerge the substrate in a sequence of tanks containing suitable materials for a defined period of time (see Fig. 4):

Start with tank A to tank F (note that between process C and D there is a drying time, which may be from 5-10 minutes, preferably 7 minutes; and the same case between processes F and A). The process is cyclic, so that at the end of the deposit F starts again with the A. One cycle results in depositing one layer of protein on the substrate.

The materials of each of the deposits are as follows:

- Tank A: Poly (diallyl dimethylammonium) chloride, PDDA, Mw:

10,000-20,000, which was dissolved in 20 mmol L-1 in milli-Q Water (pH 6.8).

- Tanks B and C: Water milli-Q at 6.8 pH

- Tank D: The PM (Purple membrane = Br) was used at a

concentration of 0.5 mg / ml of bR and the pH was adjusted to 8.6 using 0.1 M NaOH before each experiment

- Tanks E and F: water milli-Q at 8.6 pH using 0.1 M NaOH before each experiment.

In some embodiments of the present invention, construction of the first photoanode electrode (A1 ) of the first compartment (A) comprises the following steps:

i) depositing a layer of a UV and visible radiation transparent conductor material (1 ) on the surface of a protective and light-transmissive material (10); preferably deposition is made by chemical vapor deposition; ii) electrodeposition of the first conductive metallic material (2) onto the transparent conductor material layer (1 ); and

iii) depositing the one or more proton pumping photoactive biological layers (3) onto the first conductive metallic material (2).

In some examples of the present invention, the protective and light- transmissive material (10) is selected from quartz-glass and any structural polymeric material transparent over the entire light spectrum;

In some embodiments of the present invention, construction of the second electrode (A2) of the first compartment (A) comprises the following steps: i) depositing a layer of a UV and visible radiation transparent conductor material (7) on the polymeric membrane (C) surface;

ii) depositing the second conductive metallic material (6); preferably deposition is made by chemical vapor deposition; onto the UV and visible radiation transparent conductor material (7); and

iii) optionally, depositing the one or more proton pumping photoactive biological layers (5) on the second conductive metallic material (6). In some examples of the present invention, the water-containing medium (4) may be formed of a substantially UV and visible radiation transparent substance capable of conducting hole charge carriers. In some examples, the water-containing medium may be one of a solid, liquid, or gel electrolytic material that is optically transmissive, with a low conductivity, and able to provide protons. In accordance with an embodiment of the present invention, milli-pure / milli-Q water may be used as the water-containing medium (4).

In some other examples, the water-conductive medium (4) is a electrolytic aqueous solution containing, preferably 0.01 to 5 M, more preferably from 0.1 to 2 M of a supporting salt. Examples of the supporting salts are those of the formula M _m X _n in which: M may be selected from magnesium, calcium, lithium, potassium and sodium; X may be selected from anions of weak or strong acids selected from carbonates, bicarbonates, sulfates, hydroxides and halides. In some of these cases, the supporting salt may be selected from NaHCO ₃ , NaCO ₂ CH ₃ , KHCO ₃ , K ₂ CO ₃ , Na ₂ SO ₄ , K ₂ SO ₄ , KCI and KCIO ₄ . The pH value of the electrolytic aqueous solution is preferably around the neutral value, that is, preferably 5 to 10, more preferably 6 to 9.

In another examples, the water-conductive medium (4) is a solid electrolyte. Examples of solid electrolytes preferably used in the present invention include yttria-stabilized zirconia, beta-alumina solid electrolyte, lanthanum trifluoride, silver iodide, copper(l) iodide, rubidium silver iodide (RbAgl ₂ ), Ag ₂ Hgl ₄ . and polymer electrolytes prepared by introducing a salt as an ion carrier into a polymer medium such as gelatin, agar, polyvinyl alcohol and commonly employed cation exchange resins and anion exchange resins.

In particular examples, the water-conductive medium (4) comprise a chloride salt, preferably KCI in a concentration in the range of 50 mM to 0.1 M KCI. The amount of water-conductive medium (4) may be determined by the amount of oxygen that is generated. The chemical balance must be

maintained 4OH ^" 4e ^" + 2H ₂ O + O ₂

If the concentration of O ₂ increases, the equilibrium tends to the left.

The reversible bio sensitized photoelectric conversion and H ₂ to electricity conversion device herein described takes advantage of most of the range of UV-visible light. This way it can achieve greater performance in adverse weather conditions. The system is closed, thus it avoid the water supply and avoid a conventional PEMFC to take advantage of H ₂ . The the reversible bio sensitized photoelectric conversion and H ₂ to electricity conversion device herein described is capable of producing energy at the same time as hydrogen and is reversible, being able to store this hydrogen and become again electric energy in the same system without need of an additional system.

Furthermore, the the reversible bio sensitized photoelectric conversion and H ₂ to electricity conversion device of the present invention shows a higher efficiency (higher than 17%) than known systems based on rhodopsin.

The direct operation mode of the system is based on the imbalance that the protein causes in the water. The protein, when receiving sunlight from the part of the solar spectrum, displaces the free protons. In the environment, a pH gradient is generated up to 4 units and causes the water balance to shift to the right:

2H ₂ O H ₃ O ⁺ + OH ^"

This imbalance in the presence of catalysts such as Au, Ag or Pt at the anode and Pt, TiO ₂ and rGO at the cathode promote reactions that facilitate the displacement of electrons.

In basic environment catalyzed with gold, it occurs: 4OH→ 4e ^" + 2H ₂ O + O ₂

In acid environment at the cathode is produced: 4H ⁺ + 4e ^" 2H ₂ (gas)

In accordance with some embodiments, the system may operate in the reverse mode. That occurs when the protein stops receiving energy from the photons, it stops pumping protons. The H ₂ formed, catalyzed by the presence of Pt in the cathode tends to oxidize

2H ₂ 4H ⁺ + 4e ^"

And the oxygen present in the water tends to be reduced in the presence of Pt /TiO ₂ generating an inverse current

4e ^" + 4H ⁺ + O ₂ 2H ₂ O

Fig. 1 represent a side section of the bio sensitized photoelectric conversion device of the present invention.

The reactions occurring in direct operation mode are:

In part A:

4H ₂ O 4H ⁺ + 4OH ^"

4OH ^" 4e ^" + 2H ₂ O + O ₂

In part B: H ₂ 2e ^" + 2H ⁺ E = 3.6 Vdc

Whereas the reactions occurring in reverse mode are: In part B:

H ₂ 2H ⁺ + 2e ^" In part A:

2e ^" + 2H ⁺ + ½ O ₂ H ₂ O E = 0.9 Vdc

Thus, in accordance with some embodiments of the present invention, the system is activated when it receives photons from the solar irradiation, both visible and UV part of the light spectrum. Upon receiving photons, bR generates a proton gradient across the polymeric membrane. The proton transport mechanism of bR is facilitated by absorption of light in the 500-650 nm wavelength region. Upon absorption of light, the protein undergoes a number of conformational changes resulting in proton translocation. These protons pass to part (B) of the system, thanks to the polymeric membrane (C), causing the electrons in part (A) to pass also to part (B) through the

electrodes and generating H ₂ .

The bR transforms the received photons into a proton pump with the following cadence: 1 photon - 1 proton each 8-12 ms (photocycle depends on different mutant variant).

When the system operates in the reverse mode, the hydrogen formed during the direct mode and storaged in the hydrogen collecting deposit (B2), is again separated into protons and electrons. Thanks to the electronics of the system, electrons return from part (B) to part (A) through the electrodes, causing the protons through the membrane also to return to part (A).

The electronic of the system is connected as follows:

In direct mode:

i) A1 is connected to B1 and

ii) A2 is connected to B1

In reverse mode:

i) B1 is connected to A2

The connexions are fixed, and depending of the mode, direct or reverse, the switch allows the pass of the electricity of A1 to B1 and simultaneously A2 to B1 in direct mode or allows the pass of the electricity from B1 to A2 in reverse mode. The switch also is open when there is overpotential or overpression for security of the system.

Thus, in accordance with some embodiments of the present invention, the system operates in the reverse mode, i.e. when no radiation is directed onto the first photoanode electrode (A1 ) of the first compartment (A). In the reverse mode, the H ₂ , which has been formed when radiation strikes and has been stored in the hydrogen collecting deposit (B2), is reduced by the third conductive metallic material (9) present in the third electrode, causing the protons passing through the membrane and return from part B to part A, and together with the oxygen present in the media (in part A) tends to form water in the presence of the second conductive metallic material (7) generating an inverse current. This ensures that the system is completely closed and reversible.

In some examples, when the device is in use, both the bR and the second conductive metallic material (6) of the second electrode (e.g. TiO ₂ ) are working as photoreceptors. The bR absorbs in the light range of the visible spectrum, while the second conductive metallic material (6) absorbs in the UV range.

In the direct mode of operation, the second conductive metallic material (6) performs the photocatalyst function in aqueous environment when it receives photons above the 3.2 eV (388 mm) band causing:

TiO ₂ + hv -» h ⁺ + e ^"

H ₂ O + h ⁺ ^ OH ^" + H ⁺ The polymeric membrane (C) is used as a proton membrane to separate the protons from the medium as hydrogen is formed.

In accordance with an embodiment of the present invention, the polymeric membrane (C) is characterized by transferring protons through itself. In accordance with an embodiment of the present invention, the polymeric membrane (C) may comprise, deposited onto at least one of its surfaces, a layer of a UV and visible radiation transparent conductor material to improve the conductivity of the membrane; in accordance with a preferred

embodiment, the polymeric membrane comprises deposited a layer of a UV and visible radiation transparent conductor material onto both of its surfaces. More preferred, the polymeric membrane comprises graphene layer deposited onto both of its surfaces.

Thus, in accordance with an embodiment of the present invention, the polymeric membrane (C) comprises a graphene layer (7) deposited onto one of its surfaces and onto the graphene layer (7) it is deposited the second conductive metallic material (6) of the second anode electrode; whereas onto the other side of the polymeric membrane, also a graphene layer (8) is deposited thereon and onto that graphene layer (8) it is deposited the third conductive metallic material (9). In accordance with an embodiment of the present invention, only one graphene layer is deposited onto the polymeric membrane, onto the side oriented to the second electrode (A2) or alternatively onto the side oriented to the third electrode (B1 ). In accordance with another embodiment of the present invention, both the second conductive metallic material (6) of the second electrode and the third conductive metallic material (9) of the cathode electrode are directly deposited onto the polymeric membrane. In accordance with an embodiment of the present invention, the photoanode electrode (A1 ) of the first compartment comprises a first conductive metallic material (2) content from 0.02 mg/cm ² to 5 mg/cm ² , from 0.2 mg/cm ² to 5 mg/cm ² ; from 0.14 mg/cm ² to 1 mg/cm ² , from 0.4 mg/cm ² to 1 mg/cm ² , from 0.4 mg/cm ² to 0.8 mg/cm ² , or from 0.6 mg/cm ² to 0.8 mg/cm ² .

In accordance with an embodiment of the present invention, the second electrode (A2) of the first compartment comprises a second conductive metallic material (6) content from 0.01 mg/cm ² to 5 mg/cm ² ; in some particular embodiments the content is comprised from 0.05 mg/cm ² to 4 mg/cm ² . In accordance with some embodiments, the content is comprised from 0.1 mg/cm ² to 3 mg/cm ² ; in additional embodiments, the content is comprised from 0.5 mg/cm ² to 2 mg/cm ² . In some other embodiments, the content is comprised from 1 mg/cm ² to 4 mg/cm ² , more preferably from 2 mg/cm ² to 3 mg/cm ² .

In accordance with an embodiment of the present invention, the third electrode (B1 ) of the second compartment (B) comprises a third conductive metallic material (9) content from 0.02 mg/cm ² to 5 mg/cm ² , from 0.2 mg/cm ² to 5 mg/cm ² ; from 0.1 mg/cm ² to 1 mg/cm ² , or from 0.3 mg/cm ² to 1 mg/cm ² .

A polymeric membrane with the following catalyst amounts may be used:

0.3 mg/cm ² PtC (40%)

3 mg/cm ² TiO ₂ nano, 21 nm max size (TEM) trace materials >99.5 %

In accordance with a preferred embodiment, the UV and visible radiation transparent conductor material is graphene; suitable graphene layer deposited onto the polymeric membrane and onto the first conductive metallic material of the photoanode electrode present in the first compartment (A) may have a resistivity from 10 ^"4 Ω cm to 10 ^"6 Ω cm, preferably 10 ^"5 Ω cm. The transmittance of the graphene layer may be preferably from 90% to 99%, preferably 98%.

In accordance with a particular embodiment of the present invention, the protective and light-transmissive material (10) is quartz glass and the layer of a UV and visible radiation transparent conductor material (1 ) is CVD graphene with a resistivity of 10 ^"5 Qcm and 97% transmittance.

In some examples, for the construction of the first electrode (A1 ),

electrodeposition of Au nanopartides on the substrate may be performed, being the substrate a quartz-CVD graphene part as described above. In accordance with some examples, the electrodeposition of Au nanopartides on the substrate may result in a uniform layer of between 0.3 to 1 .0 mg/cm ² , preferably between 0.4 to 0.8 mg/cm ² , being particularly preferred 0.6 mg/cm ² of nanoAu particles (size between 2.5 - 7 nm). In accordance with an embodiment of the present invention, between 100-400 layers of bR are deposited onto the first conductive metallic material (1 ), preferably 120-300 layers, more preferably between 130-200 layers, being particularly preferably 150 layers.

In accordance with an embodiment of the present invention, between 100-400 layers, preferably 120-300 layers, more preferably between 150-250 layers, being particularly preferably 200 layers of bR are deposited onto the second conductive metallic material (6).

Bacteriorhodopsin exists in highly concentrated clusters termed purple membrane. Within these clusters the concentration of bR is roughly 75%. This protein clusters, embedded in their native lipid matrix can be isolated very effectively through lysis of the bacterial cells followed by differential centrifugation to remove all other cellular debris. Then resulting in highly pure and stable purple membrane fragments. The skilled person knows the methods and conditions to perform such a processes, e.g. those described in US2009142852, which it is herein incorporated by reference.

In accordance with some preferred embodiments, the proton pumping photoactive biological layer comprises oriented purple membrane. In accordance with other embodiments, the proton pumping photoactive biological layer comprises bacteriorhodopsin genetic variants (mutants) in order to achieve the correct orientation and good adhesion of the bR layers. The skilled person in the art may know different bR mutants that enhance packing, orientation, thermodynamic, adhesion and combinations thereof. Accordingly, bR mutants having particular characteristics useful for the generation of solar energy are known in the art. Thus, there are known in the art mutants having the ability to pump chloride anions for brine splitting;

having enhanced ability to covalently attach to metal surfaces and metal- coated particles; or mutants having enhanced the formation of orientated layers in such a way as to increase packing.

In accordance with an embodiment of the present invention, the proton pumping photoactive biological layer comprises a bacteriorhodopsin genetic variant wherein one or more aminoacids of the amino acid sequence in the bacteriorhodopsin protein are replaced with one or more aminoacids that are different from that of the wild type H. salinarum bacteriorhodopsin protein. In some embodiments, the proton pumping photoactive biological layer comprises a bacteriorhodopsin genetic variant wherein one or more aminoacids of the amino acid sequence in the bacteriorhodopsin protein to the loops that are in the intracellular part are replaced with one or more cysteine aminoacids.

Thus, mutants most attuned to Au are anyone who changes an amino acid by a cysteine to the loops that are in the intracellular part. In some embodiments of the present invention, the following known mutants may be used V101 C, M163C, A160C, T247C and E166C, obtaining similar results at the

photocycle level (cycle between pumping and proton pumping) and in orientation.

In some embodiments, the proton pumping photoactive biological layer comprises a bacteriorhodopsin genetic variant wherein one or more glutamic acid of the amino acid sequence in the bacteriorhodopsin protein to the loops that are in the extracellular part are replaced with one or more glutamine aminoacid. Mutants most attuned to TiO ₂ are anyone who changes a glutamic acid to a glutamine from the loops of the extracellular part. In some embodiments, the following known mutants may be used in order to adhere the proteins and ensure orientation and anchorage: E74Q, E194Q, and doublemutant

E194Q/E204Q.

In the above lists of bR mutants, the first letter in each member represents the one letter code for the amino acid that is at that position in the native bR of H. salinarum; the number represents the position of the amino acid starting from the N-terminus (excluding the leader peptide); and the second letter represents the one letter code for the amino acid that is different from the amino acid in the native bR.

The one or more of a proton pumping photoactive biological layers

comprising oriented purple membrane which contains bacteriorhodopsin protein or any of its genetic variants; stabilized bacteriorhodopsin protein- based sensitizer or any of its genetic variants; or mixtures thereof; may be placed onto surfaces using known methods in the art, examples of those methods include, but not limited are electrospray deposition, use of polyhistidine-tags, affinity chromatography, use of antibodies against bR and electrostatic layer-by-layer methods. In accordance with an embodiment of the present invention, the system is used in the direct operation mode for generating electricity by exposing the system to sunlight, which causes the bR to pump protons, causing a large potential difference that is used to generate and electrical current. Thus, in accordance with this embodiment of the present invention, the system is used in a method for generating energy by water splitting, producing oxygen gas at the anode and hydrogen gas at the cathode; the hydrogen gas may be collected, and used as an energy source when the system operates in the reverse mode. Production of energy and hydrogen may be done sequentially or simultaneously.

To store the hydrogen, an inert gas, preferably argon may be used to compensate for the pressure of the upper system and the pressure of the lower system. The inert gas, when is mixed with H ₂ , reduces the risk of explosion. In addition, its weight than the H ₂ weight, thus it keeps the H ₂ at the top closest to the Pt.

For the realization of the connectors, 3 copper frames may be used. The thickness may range from 0.05 to 0.3 mm, preferably 0.1 mm thickness. The system may be sealed with special silicone to prevent H ₂ O from coming in contact with copper; and prevent O ₂ , H ₂ and Ar from escaping.

The connector of the first conductive metallic material (1 ) layer and that of the second conductive metallic material (6) may be connected through a diode and a switch. And also, the connector of the second conductive metallic material (6) and that of the third conductive metallic material (9) may be connected through a diode and a switch.

In accordance with another embodiment of the present invention, it provides a system with operates in alternating current.

Using the system in alternating allows avoiding adding additional deposits of gases and avoiding inverters.

When the system operates in alternating current, in an H ₂ O environment under atmospheric pressure, rB, when activated by photons (in the visible light stream), shifts the water balance to

H ₂ O H ⁺ + OH ^"

by the pumping effect of the protons and creates a pH gradient of between 1 - 4. This causes the environment to become basic, because of the large amount of OH ^" present.

The first conductive metallic material (1 ) catalyzes the reaction

4OH ^" 4e ^" + 2H ₂ O + O ₂

and yields electrons that pass through the layer of a UV and visible radiation transparent conductor material (1 ) and are transported to the other side of the polymeric membrane (C), where there are the protons that demand electrons.

The second conductive metallic material (6) also catalyzes the reaction

4OH ^" 4e ^" + 2H ₂ O + O ₂

and the bR (if present) pumps the protons to the other side of the polymeric membrane (C) by the demand of electrons of the protons.

As a result, the system generates O ₂ and consumes H ₂ O to the extent that the presence of H ₂ O decreases, and the partial pressure of the oxygen increases so that the equilibrium shifts towards the other direction

H ₂ O + O ₂ + 4e ^" 4OH ^"

This causes an attraction to the electrons displaced towards the other side of the polymeric membrane, causing them to return and creating in this way an inverse current until the reaction returns to move in reverse, creating of this form, an alternating current.

When the system operates in alternating current, it facilitates the

management of the equilibrium of the reaction

4OH ⁺ O ₂ + 2H ₂ O + 4e ^"

always maintaining an imbalance in the system, it reduces the energy collection since when the system is in operation (reverse), solar energy is not usable. The AC system, reduces costs of electronic complements as investors. Conventional solar modules generate CC electricity that must be converted to AC electricity so that it can be used in houses or other buildings. The present invention allows avoiding the cost associated to this conversion.

In accordance with an embodiment of the present invention, it provides a system which is transparent. Making the system transparent involves two main advantages:

1 . light that is not absorbed by the module may be absorbed by a conventional silicon module and may therefore overlap and increase efficiency per m ² ;

2. the system may capture sunlight from both directions, thus taking advantage of indirect light, or if installed in a window, take advantage of the light inside and outside.

For this purpose, 2D CVD graphene (97% light-transmissive) may be preferably used, on both sides of the polymeric membrane, i.e. as the layer of a UV and visible radiation transparent conductor material layers (7) and (8), which may serve as a substitute for graphite.

In addition to being light-transmissive, graphene CVD generates another improvement in the system, and is that it does not let gases like H ₂ or O ₂ are transferred through the layer of graphene. In this way, life is extended to the polymeric membrane, being one of the most important critical points in the life cycle of the system. In accordance with an embodiment of the present invention, the deposition of the second conductive metallic material (6), preferably TiO ₂ or PtC

nanoparticles, may be performed by electrospray, generating a uniform layer. Nanoparticles may preferably have a thickness lower than 50 nm, more preferably lower than 30 nm, being particularly preferred when the thickness is lower than 20 nm.

Although only a number of examples have been disclosed herein, other alternatives, modifications, uses and/or equivalents thereof are possible. Furthermore, all possible combinations of the described examples are also covered. Thus, the scope of the present disclosure should not be limited by particular examples, but should be determined only by a fair reading of the claims that follow. Reference signs related to drawings and placed in parentheses in a claim, are solely for attempting to increase the intelligibility of the claim, and shall not be construed as limiting the scope of the claim.

Throughout the description and claims the word "comprise" and variations of the word, are not intended to exclude other technical features, additives, components, or steps. Furthermore, the word "comprise" encompasses the case of "consisting of. Additional objects, advantages and features of the invention will become apparent to those skilled in the art upon examination of the description or may be learned by practice of the invention. The following examples and drawings are provided by way of illustration, and they are not intended to be limiting of the present invention. Reference signs related to drawings and placed in parentheses in a claim, are solely for attempting to increase the intelligibility of the claim, and shall not be construed as limiting the scope of the claim. Furthermore, the present invention covers all possible combinations of particular and preferred embodiments described herein.

EXAMPLES

Example 1 .

Construction module 5cmx5cm Construction PART A:

1 . Prepare the substrate Quartz glass/ Graphene / nanoAu / Br

A quartz glass + CVD graphene 7cm x 7cm purchase with 97% transmittance, was used as the upper part of the system.

For the construction of the first electrode, an electrodeposition of Au nanoparticles was performed on the substrate (Quartz - graphene) in

5cmx5cm of the total surface, obtaining an uniform layer of 0.6mg / cm ² of nanoAu particles (size between 2.5-7 nm). The resistivity was checked with tester achieving 10 ^"5 Qcm.

150 layers of bR T247C were added to the Au / graphene / Quarzo substrate by the layer by layer method using the robot and the Quarzo part It was covered with a film to prevent the protein from being adhered. bR T247C mutant was previously described in J. Phys. Chem. C 2014, 1 18, 16710-16717.

2. Prepare the substrate bR/ TiO ₂ / Graphene/ Nafion ®/ Graphene / Pt

Nafion® membrane was used as a proton membrane to separate the protons from the medium as hydrogen is formed. A membrane 7cm x 7cm was purchased and contains a monolyer Graphene in both parts with 97% transmittance.

The following catalyst amounts was added with electrospray process on the 5cm x 5cm of the total surface : 0,3 mg/cm ² PtC (40%), and in the other hand 3mg/cm ² TiO ₂ nano, 21 nm max size (TEM) trace materials > 99,5% The resistivity was checked with tester achieving 10 ^"5 Qcm in the both parts.

200 layers of bR E194Q/E204Q were added to the TiO ₂ part substrate by the layer by layer method using the robot and the Pt part It was covered with a film to prevent the protein from being adhered. bR E194Q/E204Q doublemutant was previously described in Biophysical Journal Volume 2004, 86:1673-1681 .

3. Assembly both substrates and placement the Cu connectors.

3 Cu frames 7cm x 7cm x 0,1 cm and 1 cm of width were used as connectors and were attached on the 3 graphene parts of the three electrodes with the aid of adhesive tape.

Special silicone was used to seal the two substrates. It was first applied to the Quarz / Graphene / Au / Protein substrate. 30 ml of water mili-q was used to maintain the proteins and to provide protons to the medium, this was placed on the substrate Quarz / Graphene / Au / Protein. Finally by vacuum and the special silicone was sealed next to the other substrate Protein / TiO ₂ / Graphene / Nafion ® / Graphene / Pt. Construction PART B and assembly to PART A:

This part stores the H ₂ generated by the system, was comprised of a polycarbonate plate 7 cm x 7 cm 1 cm thick. In this case a rubber frame of 7cm x 7cm x 0,5cm and 2 cm of amplitude was used as a joint and was sealed with special silicone to the polycarbonate. To seal the part A with the part B uses special silicone and was realized in an atmosphere of argon to avoid that the gas that was stored initially was oxygen. Finally cables were connected and soldered to the Cu frames in order to be able to perform Voltage and intensity measurements using Voltammeter.

Fig 2 shows a comparison of the energy that the module of the present disclosure provided in different combinations of direct irradiation versus diffuse irradiation was performed.

For this purpose, a spectrophotometer was used, which provided a power of 10W over the 100 cm ² of the prototype. To the lamp was added a filter that allowed providing the power following the light spectrum of the direct light and the one of the diffuse light.

The results were compared vs. a polycrystalline silicon module to see its behavior vs. that of the module of the disclosure. The graphic shows that as the light spectrum becomes more diffuse for the same power, the module of the present disclosure achieves up to 2.5 times more efficiency.

This phenomenon occurs because the lithic spectrum, when it is more diffuse, acquires the composition shown in the following graph. Moving the whole area of the lithic spectrum towards the part closest to the UV that is the range of light where the module has greater absorption.

These diffuse light conditions occur on cloudy days, rain or high pollution areas. This reason means that conventional modules cannot be installed in areas with adverse weather conditions as their cost cannot be amortized. Fig. 3 shows the voltage generated (measured by voltammeter) by the system when working in sunlight and without it. It is observed how the system is generating hydrogen, and how it is being consumed at the moment the electronics is in reverse mode. It is observed that the potential decreases as the hydrogen is being consumed.

Second 0-5: Turn off light (direct electronic)

Second 5-10: Turn on light (direct electronic)

Second 10-15: Swich off /Turn light off (reverse electronic)

Second 15-20: Swich on /Turn light off (reverse electronic)

Second 20-25: Swich off / Turn light off (direct electronic)

Second 25-35: Turn on light (direct electronic)

Second 35-40: Swich off /Turn light off (reverse electronic)

Second 40-50: Swich on /Turn light off (reverse electronic)

The graph shows the potentials generated in (+) when the protein is pumping protons. In this case, the system tends to split the water and generates O ₂ (gas) and H ₂ (gas). When the system operates in a different direction, the presence of pure O ₂ (gas) (without N ₂ ) increases the efficiency of the reaction

4H ⁺ + 4e ^" + O ₂ 2H ₂ O

Up to 3 times more than in a conventional cell, so an excess of O ₂ above 5% is not necessary.

When the system works in this direction (return 4H ⁺ + 4e ^" + O ₂ -> 2H ₂ O) the reaction releases heat, set the working temperature at 60 °C. This facilitates that the system can be installed in colder areas where the heat can be harnessed for heating and keep the system above 0 °C.

The system is capable of storing hydrogen. Of the total energy produced, approximately 50% is converted to Hydrogen. Hydrogen is converted into electric current (55% aprox) at times when there is no sunlight, and provides heat (45% aprox).

The system generates more than twice as much efficiency in diffused light conditions as conventional photovoltaic modules. The pH gradient performed by the protein of up to 4 pH units maintains the upper part that touches the gold at pH = 9, facilitating that the presence of OH ^" is higher and in the part of TiO ₂ at pH = 5, potentiating in these conditions (acid environment) a greater proton production of TiO ₂ . In addition, the protein quickly pumped the free protons making it difficult for the electrons to re-generate less H-H bonds and thus favoring the increase in voltage.

Protons, being rapidly displaced by bR, prevent the formation of superoxidant ions such as O ₂ ^" and OH ^" produced by TiO ₂ .

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