WO2012022363A1

WO2012022363A1 - Method for fabricating electrodes for one-compartment fuel cells based on carbon nanotube buckypaper

Info

Publication number: WO2012022363A1
Application number: PCT/EP2010/005136
Authority: WO
Inventors: Laith Hussein; Michael Krüger; Gerald Urban
Original assignee: Albert-Ludwigs-Universität Freiburg
Priority date: 2010-08-20
Filing date: 2010-08-20
Publication date: 2012-02-23

Abstract

The present invention relates to a method for fabricating electrodes for a fuel cell and to a one-compartment fuel cell. In particular, a method for fabricating an electrode for a bio-fuel cell comprises the steps of fabricating a buckypaper electrode support material; providing a suspension of carbon nanotubes; decorating said carbon nanotubes with a catalytically active component thereto; and coating at least one surface of said buckypaper electrode support material with said decorated suspension. Furthermore, a fuel cell comprises an anode for performing an oxidation of a fuel component, said anode being formed from a buckypaper electrode support material with a coating on at least one surface, said coating being fabricated from decorated carbon nanotubes; and a cathode for performing a reduction of dioxygen molecules, said cathode being formed from a buckypaper electrode support material with a coating on at least one surface, said coating being fabricated from decorated carbon nanotubes.

Description

METHOD FOR FABRICATING ELECTRODES FOR ONE-COMPARTMENT FUEL

CELLS BASED ON CARBON NANOTUBE BUCKYPAPER

The present invention relates to a method for fabricating electrodes for a fuel cell and to a one-compartment fuel cell comprising an anode and a cathode formed from a bucky- paper electrode support material.

Fuel cells have been investigated recently for a wide field of applications to convert chemical energy directly into electrical energy. In particular, for miniaturized applications, direct electron transfer fuel cells which do not use mediators for supporting the electron transfer, have been developed lately. In this case, the electrons are transferred directly from the electrode to the dioxygen molecule or from the fuel molecule to the electrode via a catalytically active component, such as an enzyme or a catalytic metal. In these systems, the coupled overall process is the redox transformation of the fuel component, for instance an enzyme substrate like D-glucose, which can be considered as a catalyzed electrode process.

In contrast to conventional direct fuel cells, the challenge of an implantable direct glucose fuel cell is that it must run under physiological conditions while the fluid contains both reactants (glucose and oxygen) in a single compartment. These mixed-reactant fuel cells are considered as an attractive power source and are in high demand for small medical devices (e.g. cardiac pacemaker) and biosensors, in particular when deriving electricity from a high energy glucose molecule, which can be considered as ubiquitous in physiological environments.

Generally, there are two kinds of biofuel cell designs: one is called biotic design, and the other is called abiotic. The first relies on biocatalysts (e. g. enzymes and microorgan- isms), while the other utilizes abiotic catalysts (e. g. inorganic or precious metal-based catalysts).

The presently limited progress on the abiotic fuel cells is due to a catalyst poisoning effect, which results in a significant decrease in catalytic activity. Most of recent development therefore has been focused on fuel cells utilizing biotic systems. Long-term per- formance, low power density and insufficient electrode design, however, have been hin- dering the progress for many of biotic systems. Recently, there have been impressive achievements made regarding the abiotic design, but these were done in an alkaline medium and in a two-compartment fuel cell. It is based on an abiotic anode that was fabricated from inexpensive chemical dyes while a commercial air-breathing electrode was used as the cathode. The fuel cell was able to obtain more than 2.5 mWcm^"2 at 0.3 V , as described in Scott D and Liaw B Y: 2009 "Harnessing electric power from monosaccharides— a carbohydrate-air alkaline fuel cell mediated by redox dyes" Energy Environ. Sci. 2 965-969.

The abiotic mixed-reactant approach could greatly simplify the fuel cell design for im- plantable devices, but the electrocatalysts still need to be tolerant to the presence of the other reactant (e.g. oxygen or glucose). Furthermore, implantable fuel cells must run under physiological conditions as well. Moreover, the catalytic systems have to be highly selective for the formation of the desired product, especially for the cathodic reaction, to suppress the formation of hydrogen peroxide which normally enhances the corrosion of the electrode material and polymer membrane. With non-tolerant catalysts, glucose would directly transfer its electrons to the available oxygen and no power could be provided to an external circuit.

Buckypaper, which in the following is also abbreviated "BP", is a self-supported mat of entangled assemblies (ropes and bundles) of carbon nanotubes (CNT) forming a well- defined membrane-like black film. It was originally developed to handle carbon nanotubes in a simpler and more efficient manner. BP has several advantages over carbon nanotube films prepared by other methods. BP is highly porous, flexible, self-supporting, electrically conductive and can be formed to almost any arbitrary shape and size. Some of the properties of multiwalled carbon nanotube (MWNT) BP have been investigated for quite some time, but their potential use as fuel cell electrodes and sensor devices started relatively recently.

The present invention relates to an improved method for fabricating a novel enzyme decorated BP-based biocathode and nanoparticles decorated-BP as efficient abiotic cathodes and anodes. These BP-based electrodes have been tested by various electro- chemical methods and found superior in comparison to well-known electrodes based e. g. on carbon black as electrode support material. Such conventional electrodes based on carbon black are for instance described in A. Habrioux, T. Napporn, K. Servat, S. Tingry, K.B. Kokoh, Electrochemical characterization of adsorbed bilirubin oxidase on Vulcan XC 72R for the biocathode preparation in a glucose/0₂ biofuel cell, Electrochim. Acta, In Press (2009).

The object underlying the present invention is to provide an improved method for fabri- eating an electrode for a fuel cell, which can be produced in a more economic and reproducible manner on the one hand, and allows the production of electrodes having improved characteristics when used in fuel cells of the abiotic and biotic type, on the other hand.

This object is solved by the subject matter of the independent claims. Advantageous em- bodiments of the present invention are the subject matter of the dependent claims.

The present invention is based on the idea that a particularly effective way of fabricating an electrode for a fuel cell comprises the steps of fabricating a buckypaper electrode support material, providing a suspension of carbon nanotubes and functionalizing these carbon nanotubes and then decorating them with a catalytically active component. The buckypaper support is coated with at least one catalyst layer with this suspension. By such a fabrication method, highly efficient electrodes which can be handled easily, can be provided. The raw material can be kept on stock on a large scale (several tons).

It could be shown that these electrodes have a high efficiency, stability and catalytic activity. In particular, when measuring the oxygen reduction reaction (ORR), a high limiting current density for this biocathode could be observed. Furthermore, the ability to catalyze electrode reaction via a mediatorless direct electron transfer is possible for this material. In the case of an enzyme, it could be shown that the electron is transferred directly from the buckypaper-based electrode to the dioxygen molecule via the active site of the enzyme. Furthermore, the electrode material according to the present invention provides enhanced glucose-tolerance and catalytic properties in regards to the ORR for a biotic buckypaper-based cathode. Consequently, the decorated buckypaper electrode according to the present invention exhibits superior properties, rendering it a promising support material for biofuel cell electrodes to power small devices and biosensors.

According to the present invention, decoration of the carbon nanotubes in suspension is either done by immobilizing an enzyme to the suspended carbon nanotubes or by attaching catalytic metals, such as platinum nanoparticles or gold/platinum alloyed nanoparti- cles to the carbon nanotubes. This results in either a biotic or an abiotic fuel cell, respectively.

According to the present invention, a tailor-made porous nanostructure network of multi- walled carbon nanotubes is provided that allows for an improved oxygen diffusion and provides electron transport pathways. Furthermore, a high mesoporous surface area of the buckypaper can significantly increase the accessibility for the supported enzymes.

According to the present invention, the immobilized enzyme may be an oxidase or a reductase, for instance bilirubin oxidase or laccase. However, it is clear for a person skilled in the art that all other suitable enzymes, may be immobilized to the suspended carbon nanotubes in the way according to the present invention.

The accompanying drawings are incorporated into and form a part of the specification to illustrate several embodiments of the present invention. These drawings together with the description serve to explain the principles of the invention. The drawings are merely for the purpose of illustrating the preferred and alternative examples of how the invention can be made and used, and are not to be construed as limiting the invention to only the illustrated and described embodiments. Furthermore, several aspects of the described embodiments may form individually or in different combinations solutions according to the present invention. Further features and advantages will become apparent from the following more particular description of the various embodiments of the invention, as il- lustrated in the accompanying drawings, in which like references refer to like elements and wherein:

Fig. 1 shows the buckypaper electrode support material fabrication process based on a vacuum filtration technique;

Fig. 2 shows a schematic representation of the preparation of buckypaper biocathodes, wherein the enzyme is immobilized on A) carbon black or B) functionalized carbon nanotubes;

Fig. 3 shows potentiodynamic measurements for the ORR activity of buckypaper-based biocathodes; Fig. 4 shows a schematic perspective view of a direct glucose fuel cell based on an abiotic buckypaper electrode;

Fig. 5 shows a detail of Fig. 4;

Fig. 6 shows the potentiodynamic measurements for the ORR activity of the abiotic elec- trade, according to the present invention, as shown in Fig. 4;

Fig. 7 shows a potentiodynamic polarization curve for a buckypaper-based abiotic glucose fuel cell according to the present invention.

With reference to the Figures, in the following the fabrication and test of buckypaper electrodes according to the present invention will be described in detail. The BP fabrication is performed as illustrated in Fig. 1. In short, 100 mg of as-received MWCNTs were dispersed in 200 mL of an aqueous solution containing 1 wt. % Triton X- 100 (Sigma Aldrich) under mechanical stirring for 30 min followed by sonicating with an ultrasonic bath (Bandelin Sonorex, RK 102 H) for 3 h. The resulting suspension was cen- trifuged for 15 min at 2700 rpm to remove bigger agglomerates of MWCNTs. The super- natant, containing a stable CNT-suspension, was then filtered through a nylon membrane filter with pore size of 0.45 μιη (Whatman, UK) and compressed under vacuum by an oil-free diaphragm pump (KNF Neuberger, Germany). The resulting homogeneous black film was washed repeatedly with an excess of deionised water, followed by isopro- pyl alcohol and acetone. The prepared CNT-film was kept at room temperature for 30 min and then dried in a vacuum oven at 50 °C overnight. BP films exceeding a thickness of 80 Mm could be easily peeled-off , resulting in a freestanding buckypaper support material. Diameters of 40 to 50 mm are achieved.

Firstly, the preparation of bilirubin oxidase (BOD) buckypaper-based biocathodes will be explained as an example of an enzymatic cathode. For a person skilled in the art, how- ever, it is clear that the principles according to the present invention can also be applied to other enzymatic catalysts, such as cytochrome c, peroxidase, ferredoxin, plastocyanin, azurin, azotoflavin, glucose oxidase, and a variety of blue multicopper-containing oxidases. The BP supported BOD catalysts were prepared according the scheme illustrated in Fig. 2. BP pieces (1.0 cm x 2.0 cm) were cut out of a 15 pm thick BP film. Bilirubin oxidase (BOD, Amano-3, [EC 1.3.3.5], activity 2.44 unit mg) from M. verrucaria, (Amano Pharmaceutical Co., Japan) and the mediator, 2, 2'-azinobis(3-ethylbenzothiazoline-6-sulfonate) diammonium salt (ABTS^2-) from Sigma Aldrich were used. Typically, 1 mg of this enzyme was dispersed in 0.2 M phosphate buffer solution (pH 7.4) and then directly mixed with a solution of defined amount ABTS in phosphate buffer solution as well. The functionalized CNTs (f-CNTs) and the Vulcan XC-72R (for comparison) were dispersed in phosphate buffer solution by assisting of ultrasonication followed by mixing with the solution of BOD and ABTS in order to immobilize the enzyme onto the surface of the support, respectively. Afterward, both suspensions were directly dropped (adsorbed) onto the BP to form BOD/CNT-BP and BOD/C-BP catalysts. Finally, both BOD electrodes were cured and dried under nitrogen at room temperature.

All electrochemical measurements were performed with a computer controlled Bio-Logic 6-channel VMP2-potentiostat/galvanostat. No stirring or agitation of the solution was applied to the cell during BP-electrode testing. Experiments with cells under mechanical stirring were also performed, and the performance of the cells was greatly improved. All experiments were conducted at room temperature and ambient pressure. Pt wire was used for electrode contact to minimize corrosion interference. To take a further insight into the substrate effect of f-CNT, two bilirubin oxidase biocath- odes (geometric area 2.0 cm²) were tested using f-CNT and Vulcan XC-72 as the bio- catalyst support, namely, BOD/f-CNT-BP and BOD/C-BP, respectively. The Vulcan XC- 72 electrodes correspond to the known electrodes described in the article A. Habrioux, T. Napporn, K. Servat, S. Tingry, K.B. Kokoh, Electrochemical characterization of adsorbed bilirubin oxidase on Vulcan XC 72R for the biocathode preparation in a glucose /O₂ bio- fuel cell, Electrochim. Acta, In Press (2009).

Fig. 3 shows the electrocatalytic activity of BOD/C-BP and BOD/f-CNT-BP towards ORR wherein curve (a) relates to a BOD-ABTS immobilized enzyme on carbon black, and wherein curve (b) relates to a BOD-ABTS immobilized enzyme on functionalized carbon nanotube according to the present invention; the measurement was performed in air- saturated 0.2M phosphate buffer solution, pH 7.4, in presence of 10 mM glucose in quiescent condition, with a sweep rate of 3 mV per second. Here, we observe a plateau-like current density at 0.6 V vs. RHE: -0.272 mA cm^"2 for BOD/C-BP and -0.70 mA cm^'2 for BOD/f-CNT-BP. The former is a little higher than the reported limiting current density of -0.2 mA cm^"2 was only observed but by using a rotating disc electrode with a rotation rate of 100 rpm and higher, whereas the latter is more than 2.5 times than the former, suggesting that the f-CNT biocatalyst support enhances the reaction rate on BOD/f-CNT-BP.

To the best knowledge of the inventors, it is the first time to observe such an effective ORR promotion of the f-CNT supported BOD towards ORR in the presence of glucose in comparison to a BOD/C-BP cathode. This high performance may result from higher elec- tronic conductivity, lower impurities and higher mesopore (2-50 nm) area (279.34 m²g ¹ for f-CNT and 142.5 m²g ¹ for Vulcan XC-72R carbon black). Even if carbon black possess a similar value for the specific surface area (S_BET ca. 260 m²g^"1), not all the pores could be effective and accessible for enzyme molecules due to the higher amounts of micropores (less than 2 nm in diameters). Fig. 4 and 5 show an advantageous embodiment of an abiotic direct glucose fuel cell (DGFC) according to the present invention.

The main problem which has to be solved in single compartment or implantable DGFC is the development of tolerant and selective cathodes and anodes by using the proper elec- trocatalysts. In other words, a selective and tolerant (resistant) anode catalyst for glucose oxidation reaction (GOR) in presence of oxygen and other biomolecules and also a tolerant cathode for oxygen reduction reaction (ORR) in presence of glucose have to be provided, and a 4-electron transfer mechanism to form water has to be established to avoid the formation of hydrogen peroxide which results in a corrosion effect of polymer membrane and carbon support . As may be derived from Fig. 4, the direct glucose fuel cell 100 comprises two electrodes fabricated from a buckypaper electrode support material according to the present invention. Firstly, an anode 102 is provided which is decorated with gold/platinum alloyed nanoparticles as catalysts for the electro-oxidation of D-glucose. Secondly, another buckypaper-based electrode which is decorated with platinum nanoparticles forms the cathode 104 for electro-reducing dioxygen. Two membrane filters 106, 108 are arranged at both sides of the anode 102. Membrane 108 separates the active surfaces of the an- ode 102 and the cathode 104 from each other, allowing protons to pass from the anode to the cathode.

From the input side 1 10 of the fuel cell 100, glucose and oxygen may enter. As this is generally known, the catalyzed electrochemical reaction comprises the reduction of di- oxygen at the cathode 104, producing water and an intermediate product (e.g. hydrogen peroxide), and on the other hand, the oxidation of D-glucose at the anode, forming gluconic acid, intermediate products and carbon dioxide. This chemical reaction leads to a flow of electrons (i.e. current) from the anode 102 to the cathode 104.

Theoretically, the oxidation of one glucose molecule yields as much as 24 electrons. However, on the surface of a platinum anode, glucose is primarily oxidized to gluconic acid, yielding two electrons, only. The succeeding oxidation steps are much slower and do not significantly contribute to the overall electron yield.

The stacked membranes 106, 108 and buckypaper electrodes 102, 104 are fixed mechanically between a polycarbonate end plate 1 12 and a polycarbonate frame 1 14, the latter having an opening 1 16 for introducing glucose and oxygen, and for removing un- desired reaction products. Silicon rubber gaskets 1 18 seal the fuel cell 100 tightly. The electric contacts for electrically contacting the buckypaper electrode support material are not shown in the drawing for the sake of clarity.

The unique properties of buckypaper (BP) such as a high electric conductivity of 25 S cm^"1 (indicated from the four-point probe method) and a big specific mesopore area of 400 m² g^"1 (indicated from N₂-physisorption measurements), have been utilized to obtain high metal loading of nanoparticles. This results in an enhancement of the electroactive surface area (EASA), while still enabling a low electrode thickness. In an abiotic approach, we applied water in oil microemulsion method in order to obtain 40 wt. % metal nanoparticles (NPs) loading with very well-defined surface composition. For the cathode side we used Pt-NPs decorated-BP, while in case of the anode we used Au₇oPt3o al- loyed-NPs decorated-BP.

Fig. 6 shows the electrochemical testing of BP-based cathode. The ORR electrocatalytic activities of abiotic BP-based electrodes were tested to verify their glucose-tolerance in oxygen-saturated phosphate buffer solution (0.2 M, pH 7.4) containing 10 mM glucose with a scan rate 5 mV s^"\ 1000 rpm (mechanical stirring) and at 25°C. The ORR behavior using potentiodynamic measurements for Pt/PB-based electrode and AuPt/BP- based electrodes and their electrochemical responses can be directly compared as follows: A fast kinetic reaction on the Pt/PB-based electrode can be observed when compared to a plateau-like diffusion process for AuPt/BP-based electrode. The ORR is more favorable on the Pt/BP-based electrode than on the AuPt/BP-based electrode at 0.3 V vs. RHE. The magnitude of the ORR diffusion-limiting current obtained with the Pt/PB-based electrode at 0.1 V vs. RHE is higher by a factor of about 10 times than for AuPt/BP-based electrode. Lower overpotentials occur for the Pt/BP-based electrode which might be attributed to a lower poisoning effect of phosphate ions and glucose on Pt nanoparticles than on AuPt alloyed nanoparticles.

Here, potentiodynamic measurements clearly demonstrate that the Pt/BP-based electrode has a better performance for the ORR and a higher stability during repetitive potential scans (data not shown) compared to the AuPt/BP-based electrode

The polarization and power density plot of complete biofuel cell tests are shown in Fig. 7. This high power density about 250 μ\Λ cm^"2 can set a new benchmark for future efforts in developing one-compartment abiotic biofuel cell working at neutral electrolyte (pH = 7.4). In particular, Fig. 7 shows potentiodynamic polarization curves for a BP-based abiotic glucose fuel cell in 10 mM glucose of O₂-saturated PBS (0.2M, pH 7.4), with a scan rate 5mV s^"1 at 25 °C. In summary, typical BP-films according to the present invention are 41 mm in diameter with thicknesses ranging between 1 pm and 200 μιτι. The BP has a highly porous surface structure with a BET specific surface area of 290 m² g^'1 and has high wide pore size distribution (+/- 20 nm) with an average pore sizes of 34 nm. The BP film is highly electrically conductive with conductivities in the order of 2000-4000 S m^'1. The surface struc- ture has been investigated using the HRSEM and typical images show the mesoporous structure of the BP-film. TEM images of nanoparticles decorated f-MWNTs generated using a water in oil (W/O) microemulsion method are described by Habrioux et al. 2007 "Activity of Platinum-Gold Alloys for Glucose Electrooxidation in Biofuel Cells", J. Phys. Chem. B 111 10329-10333, For providing an abiotic anode electrocatalyst, bimetallic (AuPt) alloyed nanoparticles supported on MWNTs with a 40 wt. % metallic loading were prepared by a W/O microe- mulsion technique. These nanoparticles exhibit a high catalytic activity for the glucose electro-oxidation reaction. Since no severe thermal treatment was necessary, particle agglomeration was avoided. A key factor of this preparation technique is that the nuclea- tion of both metals, Pt and Au occurs concomitantly. The electrochemical responses of 40 wt. % nanocatalysts, Pt or Au₇oPt3o alloy, supported on WNTs, respectively, were measured. The cyclic voltammetric measurements were performed in 0.1 M NaOH to electrochemically define the surface composition from reduction current region of formed metal oxides. Electrochemical measurements were taken using a mercury/mercuric oxide reference electrode and a standard glassy carbon working electrode. The scans were repeated several times to ensure reproducibility. The results reveal:

The oxide reduction peaks for Au at +200 mV and Pt at -300 mV vs. Hg/HgO are characteristic for Au-Pt bimetallic alloyed nanoparticles and reflect well-defined surface alloyed composition.

The relatively small H-adsorption/H-desorption waves of platinum in AuPt/f-MWNTs con- firm additionally the well-defined chemical mixing of Au and Pt (bimetallic alloy).

A high electrochemical double layer capacitance was found for both MWNT-based elec- trocatalysts.

To probe the effectiveness of BP as an electrode support material, two BOD BP-based biocathodes (geometric area 2.25 cm²) were prepared. Both of them were 15 pm thick and were prepared using BOD as a biocatalyst immobilized on MWNTs in phosphate buffer solution (0.2 M, pH=7.4). The first was prepared without a mediator (ABTS) and the second was prepared in the presence of ABTS, which are noted as BP-based biocathodes normally after adsorption (immobilized) BOD and ABTS onto BP. The following can be deduced: A fast kinetic reaction occurs for both BP-based electrodes with a well-defined diffusion- limiting plateau. The peak at 465 mV vs. Hg/HgO is assigned to the reduction of ABTS.

The BP-based biocathode in the presence of ABTS exhibits a slightly positive ORR onset potential shift (about 50 mV) in comparison to the ORR onset in the absence of ABTS. The ORR activity is similar on both BP-based biocathodes. There was a slight potential shift (20 mV) at 175 mA cm^"2 vs. Hg/HgO. The reduction of dioxygen follows a 4-electron mechanism for both electrodes (confirmed by Tafel plot).

In summary, the superior performance of the electrodes according to the present inven- tion can be attributed to the structural properties, electrical properties, low impurities of BPs and their high mesopore (2-50 nm) area approx. 340 m²g ^"1. Therefore, a high current density and high enzyme utilization can be achieved. Moreover, the activity enhancement of BP-based biocathode, especially in the absence of mediator (i.e. direct electron transfer) could be explained on the basis of specificity and accessibility for ad- sorbed BOD on BP to oxygen molecules resulting in increasing the ORR kinetics without any role of the mediator (ABTS).

In conclusion, the high catalytic efficiency of BP-based biocathode is believed to be due to the following effects:

(1 ) the tailor-made carbon nanostructure generated from and consistent with MWNTs provided sufficient O₂ diffusion and electron transport path and relatively large surface area and accessibility for supporting enzymes; and

(2) since BP has a high electrical conductivity the enzyme might be adsorbed on the most efficient contact zones for the electronic and electrolytic pathways of the Buckypaper materials (i.e. contacting the electrolyte membrane directly) and hence facilitate direct electron transfer.

As a result, almost the entire surface of the Buckypaper was accessible electrochemi- cally and can be used for an active site. Furthermore, its nanostructure, e.g. alignment, porosity, pore size and thickness can be tailored to achieve the required conditions for the optimized catalyst layer for the fuel cell applications. Finally, it can be concluded that decorated MWNT-BPs exhibit an improved stability as well as better mass transport properties.

Our results demonstrate the high potential of MWNT-BPs as electrode support materials compared to the currently commonly used carbon black support material and are promising electrodes in fuel cells. The shape and size of the electrodes can be adjusted to spe- cific needs and integrated into devices. Further investigations of device performance with respect to bio-compatibility of BP based electrodes for various fuel cell and sensor applications are currently in progress.

Claims

1. Method for fabricating an electrode for a fuel cell, comprising the steps of: fabricating a buckypaper electrode support material; providing a suspension of carbon nanotubes; decorating said carbon nanotubes with a catalytically active component; coating at least one surface of said buckypaper electrode support material with said suspension of decorated carbon nanotubes.

2. Method according to claim 1 , wherein said catalytically active component comprises a catalytic enzyme.

3. Method according claim 2, said enzyme comprising an oxidase or a reductase.

4. Method according to claim 1 , wherein said catalytically active component comprises catalytic metal nanoparticles.

5. Method according to claim 4, wherein said catalytic metal nanoparticles comprise platinum nanoparticles and/or gold/platinum alloyed nanoparticles.

6. Method according to one of the claims 1 to 5, wherein the step of fabricating a buckypaper electrode support material comprises filtering a stable carbon nanotube suspension and compressing the nanotube solid residue under vacuum.

7. Method according to one of the claims 1 to 5, wherein the step of fabricating a buckypaper electrode support material comprises electrodeposition or electro- phoretic deposition.

8. Method according to one of the claims 1 to 7, wherein the step of coating at least one surface of said buckypaper electrode support material with said decorated suspension comprises applying the suspension onto the buckypaper electrode support material and drying the electrode under nitrogen atmosphere at room temperature.

9. Fuel cell (100) comprising: an anode (102) for performing an electro-oxidation of a fuel component, said anode (102) being formed from a buckypaper electrode support with a coating on at least one surface, said coating being fabricated from decorated carbon nanotubes; a cathode (104) for performing a reduction of dioxygen molecules, said cathode (104) being formed from a buckypaper electrode support with a coating on at least one surface, said coating being fabricated from decorated carbon nanotubes.

10. Fuel cell according to claim 9, wherein said decorated coating on said anode (102) comprises between 30 and 50 wt. % gold/platinum alloyed nanoparticles on functionalized carbon nanotubes, f-CNTs, catalyst support.

1 1. Fuel cell according to claim 10, said gold/platinum nanoparticles comprising a molar ratio of between 80 % to 60 % Au and between 20 % to 40 % Pt.

12. Fuel cell according to one of the claims 9 to 1 1 , wherein said decorated coating on said cathode (104) comprises between 30 and 50 wt. % Pt metal nanoparticles on f-CNTs.

13. Fuel cell according to one of the claims 9 to 12, wherein between said cathode (104) and said anode (102), a membrane (108) is formed to separate the anode from the cathode, wherein said coated surfaces of the anode and the cathode are bordering said membrane.

14. Enzymatic fuel cell according to claim 9, wherein said cathode (104) is coated with carbon nanotubes decorated with a catalytic enzyme.

15. Fuel cell according to claim 14, said catalytic enzyme comprising an oxidase or reductase.

16. Fuel cell according to one of the claims 9 to 15, wherein said fuel component comprises glucose.