WO2013030376A1 - Process for the electrochemical reduction of co2 catalysed by an electrochemically active biofilm - Google Patents

Abstract

The present invention relates to a process for the electrochemical reduction of CO₂ catalysed by an electrochemically active biofilm, in the presence of a metal cathode and Geobacter sulfurreducens.

Description

Process for the electrochemical reduction of C0 ₂ catalyzed by a biofilm

 electrochemically active

The present invention relates to a process for the electrochemical reduction of C0 ₂ catalyzed by an electrochemically active biofilm and its use for the valorization of C0 _2, in particular glycerol.

The microorganisms can adhere spontaneously on all types of surfaces and form films called biofilms consisting of said microorganisms, a matrix of exopolymeric substances (polysaccharides, proteins, macromolecules ...) that they excrete, substances produced by microbial metabolism and accumulated compounds from the medium or from the degradation of the support surface. It has been discovered that biofilms grown on conductive surfaces are able to utilize these surfaces to evacuate electrons from their metabolism (DR Bond et al., Science 295 (2002) 483, and LM Tender et al., Nature Biotechnology (2002) 821, HJ Kim et al., Enzyme and Microbial Technology (2002) 145).

Other biofilms have been shown to catalyze the reduction of C0 ₂ on materials such as graphite and carbon (Nevin et al .: mBio 1 (2): e00103-10, doi: 10.1 128 / mBio.00103-10 , as well as Villano et al .: Bioressource Technology 2010, 101, 3085-3090) which, in their initial state devoid of biofilm, are not known to ensure high rates of C0 ₂ reduction. These biofilms can be used to evacuate from the colonized surface electrons of the system to a dissolved compound.

Methods of electrochemical reduction of CO ₂ in the presence of microorganisms are already described in the literature. Indeed, the article by Nevin et al. discloses a method for electrochemically reducing CO ₂ in acetate from a Sporomusa ovata culture colonizing a graphite electrode. In addition, the article by Villano et al. relates to a process for the electrochemical reduction of CO ₂ to methane from a culture of Methanobacterium palustre and in the presence of a carbon electrode. However, these articles describe electrochemical C0 ₂ reductions with relatively low current densities, of the order of 0.7 A / m ² and 0.5 to 1.3 A / m ^2, respectively.

There is therefore a need for more efficient C0 ₂ electrochemical reduction processes for obtaining higher current densities. Unexpectedly, the present inventors have demonstrated that the electrochemical reduction of CO ₂ can thus be improved by means of a metal cathode. A method for the electrochemical reduction of fumarate to succinate by means of a stainless steel cathode and the microorganism Geobacter sulfurreducens is described in Electrochimica Acta 53 (2008), p.2494-2500. However, this article does not describe or suggest a method of electrochemical reduction of C0 ₂ . In addition, Geobacter sulfurreducens is only known as a catalyst for the fumarate succinate reaction and is not considered as a potential catalyst for CO ₂ reduction. According to a first object, the invention relates to a method for the electrochemical reduction of carbon dioxide (CO ₂ ) by means of a metal cathode, in the presence of microorganism (s) forming an electrochemically active biofilm on the surface of said cathode metal, and in the presence of an electrolyte solution comprising succinate and / or a succinate precursor, said precursor being a natural acceptor of electrons of the microorganism forming the biofilm.

According to the invention, the precursor of the succinate may be either an oxidized precursor of the succinate or a derivative of said oxidized precursor. In the context of this presentation, unless otherwise stated, the term "natural electron acceptor" means any substance capable of being reduced and capable of recovering the electrons of the microorganism that have been transferred to the cathode. For example, fumarate can be mentioned.

 In the context of the invention, and unless otherwise stated, the term "oxidized succinate precursor" means a compound which leads to the succinate after having undergone a reduction step. For example, fumarate can be mentioned.

 In the context of the invention, and unless otherwise stated, the "oxidized precursor" of the succinate acts as an oxidant, while the succinate acts as a reducing agent in an oxidation-reduction reaction.

In the context of the invention, and unless otherwise indicated, the term "derivative of an oxidized succinate precursor" means a compound which makes it possible to terminate the oxidized succinate precursor by means of a chemical reaction such as dehydration. Mention may in particular be made of malate, which can lead to fumarate (oxidized precursor of succinate) by dehydration, said dehydration being able to be catalyzed by an enzyme present in the cells of the microorganism used in the process.

According to one embodiment, when the succinate precursor is a derivative of the oxidized precursor of the succinate, said derivative is subjected to a preliminary step leading to said oxidized precursor.

 According to one embodiment, the method according to the invention comprises a prior step of dehydrating the derivative of the oxidized succinate precursor, such as malate, to yield the oxidized precursor. In particular, mention may be made of a preliminary step of dehydrating malate to fumarate, said dehydration reaction being catalyzed by an enzyme present in the cells of the microorganism used in the process. In the context of this presentation, and unless otherwise stated, the term "electrochemically active biofilm" (EA biofilm) means any film formed by an electrochemically active microorganism capable of forming on the surface of a metal electrode through microorganism (s), and which catalyzes electrochemical reactions.

The cathode with the electrochemically active biofilm formed on its surface and / or in the electrolytic solution capable of forming a biofilm EA is hereby designated by the term "biocathode" or microbial cathode.

According to one embodiment, the succinate and / or its precursor is (are) dissolved in the electrolytic solution.

According to one embodiment, the process for the electrochemical reduction of carbon dioxide (CO ₂ ) is carried out in the presence of an electrolytic solution comprising succinate.

 According to another embodiment, the process of the invention is carried out in the presence of an electrolytic solution comprising a succinate precursor. In particular, the process of the invention is carried out in the presence of an electrolytic solution comprising an oxidized precursor of the succinate, such as fumarate. In particular, the process of the invention is carried out in the presence of an electrolytic solution comprising an oxidized precursor derivative of succinate, such as malate.

According to another embodiment, the process of the invention is carried out in the presence of an electrolytic solution comprising succinate and one of its precursors. In particular, the succinate precursor is an oxidized precursor of the succinate, such as fumarate. In particular, the succinate precursor is a derivative of the oxidized precursor of succinate, such as malate.

Preferably, the succinate precursor is an oxidized precursor of the succinate, such as fumarate.

According to one embodiment, the concentration of succinate and / or succinate precursor is from 10 to 60 mM, preferably from 20 to 50 mM, and preferably about 50 mM.

According to the invention, the electrochemical reduction of CO ₂ may comprise a preliminary step of reducing a succinate precursor, which is a natural acceptor of electrons of the microorganism forming the biofilm, to form succinate. According to one embodiment, this preliminary step is carried out using an electrolytic solution comprising said succinate precursor, in particular fumarate. According to another embodiment, the preliminary step is carried out using an electrolytic solution comprising a derivative of the natural acceptor of electrons such as malate. In particular, the derivative of the natural acceptor of electrons leads to the natural acceptor of electrons by chemical reaction, in particular dehydration which is catalyzed by an enzyme present in the cells of the microorganism.

When the electrolyte solution containing the microorganism is in contact with CO ₂ , for example under an atmosphere of N ₂ : CO ₂ (80: 20%) at a given potential, the fumarate can be reduced first with respect to CO ₂ because it is well known that fumarate is a natural electron acceptor of this microorganism. However, both reductions can occur simultaneously during the process. Without wishing to be bound by theory, the reduction of fumarate prior to C0 ₂ could be related to the redox potentials of fumarate and C0 _2.

Thus, according to one embodiment, this preliminary step is performed when the process is carried out in the presence of an electrolytic solution comprising a succinate precursor. In particular, this preliminary step makes it possible to reduce the oxidized precursor, such as fumarate, to succinate according to the following reactions:

C4H4O4 (fumarate) + 2H ⁺ + 2e ^" → C ₄ H ₆ O ₄

According to one embodiment, this preliminary step is catalyzed by the microorganisms forming a biofilm on the cathode as described above.

According to the invention, the step of reducing the succinate precursor and reducing CO ₂ can be successive or simultaneous. In particular, the two steps are simultaneous.

In a particular aspect, the method of electrochemical reduction of carbon dioxide according to the invention comprises the formation of glycerol.

According to the invention, the glycerol can be obtained by reaction, at the cathode, of CO ₂ with succinate according to the following reaction:

1/2 C ₄ H ₆ 0 ₄ + C0 ₂ + 7H ⁺ + 7e- -> C ₃ H ₈ 0 ₃ + H ₂ 0 the succinate being contained in the initial electrolytic solution or resulting from the preliminary step of reducing the succinate precursor, such as fumarate.

According to the invention, the glycerol can also be obtained according to the following reactions, consisting of an initial dissolution of C0 ₂ to form hydrogen carbonate, which then reacts with the succinate:

C0 ₂ + H ₂ 0 <==> HC0 ₃ ^" + H ⁺

1/2 C ₄ H ₆ 0 ₄ + HCO ₃ ^" + 8 H ⁺ + 7e- -> C ₃ H ₈ 0 ₃ + 2H ₂ 0 the succinate being contained in the initial electrolytic solution or resulting from the preliminary reduction step succinate precursor such as fumarate.

The valorization of C0 ₂ by the synthesis of platform molecules constitutes a considerable industrial stake as much to reduce the releases of C0 ₂ as to free the chemistry of its dependence on fossil carbon sources. It is becoming increasingly urgent to replace fossil sources with sources of renewable organic compounds that can open up new ways of synthesizing complex compounds and fuels. For fuel production, we now measure the limits of bioethanol-type sectors that come up against competition with agricultural products intended for food. Thus, there is a need in the search for alternative ways of synthesis.

According to a second subject, the present invention relates to a process for upgrading carbon dioxide (CO ₂ ), comprising reducing the CO ₂ to glycerol electrochemically. One of the advantages of the process according to the invention is therefore the valorization of C0 ₂ in glycerol, which constitutes an intermediate of choice (platform molecule) for the synthesis of complex molecules. According to one particular aspect, the recovery method according to the invention comprises the implementation of the electrochemical reduction method of CO ₂ according to the invention described above and hereinafter.

According to a particular aspect of the present invention, the process of electrochemically reducing CO ₂ can be carried out by means of a metal cathode. Typically, the metal of the cathode is selected from iron, titanium, copper, chromium, nickel, zinc and their various alloys, especially steel, and more particularly stainless steel.

 Preferably, the metal cathode is made of stainless steel.

Among the stainless steels, there are 304L, 316L, 254 SMO steels. Preferably, the method according to the invention uses a steel cathode 254 SMO.

Typically, the cathodes may have any possible surface morphology, in particular the cathodes may be microstructured. Advantageously, the surface materials can be pretreated in bulk or at the surface, so as to optimize both their ability to adhere the EA biofilm, their electronic conductivity and their ability to promote the development of highly EA biofilms. It is known that increased roughness promotes the development of effective EA biofilms. Any modification of the surface morphology: grooving, sanding, micro- and nanostructuring, etc., which will have the effect of increasing the area available for microbial adhesion and promoting this adhesion, will also be favorable to the system.

According to another aspect of the invention, the electrochemical reduction of the process can be carried out in the presence of one or more microorganisms (s) forming an electrochemically active biofilm on the surface of the metal cathode.

Typically, the microorganism (s) is (are) selected from Geobacter, Desulfuromonas, Shewanella, Geopsychrobacter, Rhodoferrax, Geothrix. Preferably, the method according to the invention uses Geobacter, in particular Geobacter sulfurreducens and in particular the strain Geobacter sulfurreducens PCA (ATCC51573). Thus, the inventors have advantageously shown that Geobacter Sulfurreducens can catalyze the electrochemical reduction of CO ₂ by biofilm formation on the surface of a metal cathode, in particular a cathode made of stainless steel, and in the presence of succinate and / or a precursor of succinate. According to the invention, glycerol is also produced easily without implementing the steps of separation of usual fermentation must.

Preferentially, said microorganism for forming the biofilm is Geobacter sulfurreducens and said natural electron acceptor is fumarate.

The said microorganism (s) forming a biofilm EA on the surface of the metal cathode may exist spontaneously in the electrolyte. Alternatively or cumulatively, it may be envisaged to seed the electrolyte with suitable microorganisms in all possible forms (inocula, culture broths, lyophilizates, etc.). For this purpose, it is also possible to use, as inoculum, samples of known media which may contain microorganisms easily forming EA biofilms, such as sludges of aqueous effluents (for example purification plants), sediments or marine biofilms. composts and any other medium known to those skilled in the art to give EA biofilms.

The seeding can be done at the beginning of the start-up of the device, it can also possibly be renewed during operation to reactivate the device, for example to mitigate a decrease in its effectiveness or after an operating incident. Thus, the method according to the invention may further comprise the step of seeding the electrolyte with said microorganism. Preferentially, the concentration of the inoculum according to the invention is approximately 10% v / v.

According to the invention, the natural electron acceptor of the microorganism, in particular the fumarate, is preferably present in the culture medium of the microorganism as well as in the electrolytic solution present in the electrochemical reactor.

According to a particular embodiment, the microorganism is added to the electrolyte solution containing the natural electron acceptor, when the culture medium of the microorganism reaches a desired optical density. For example, the microorganism may be added when the optical density in the culture medium is about 0.4 to 620 nm. According to the invention, the concentration of fumarate in the electrolyte may be between 0 and 9 g / l, preferably between 0.6 and 8 g / l, more preferably between 1 and 4.5 g / l.

The process according to the invention can be carried out using any electrochemical cell, generally known to those skilled in the art.

Typically, the electrochemical reduction reaction according to the invention can be carried out in an electrochemical reactor comprising a working electrode, a reference electrode and a counter-electrode. Preferably, the reference electrode is Ag / AgCl, the counter electrode is platinum, and the working electrode (biocathode) is super-austenic stainless steel (254SMO).

In a particular aspect, the electrodes may be previously polarized in the electrolytic medium favorable to the formation of suitable biofilms at an imposed potential that promotes the development of EA biofilms.

 Typically, the bias potential of the biocathode may be less than -0.3V relative to the Ag / AgCl reference electrode. Preferably, the polarization potential of the biocathode can be in the range of values from -1.0V to -0.3V, more particularly from -1.0V to -0.6V relative to the reference electrode Ag / AgCl .

According to the invention, the method may comprise the application of a stress on the microorganisms used in the process, said stress making it possible to release the product glycerol stored inside the cells of said microorganisms. In the context of the invention, and unless otherwise stated, "stress" is understood to mean a change in experimental conditions affecting the development of the microorganisms of the process and not leading to the cell death of the cells of said microorganisms. It may especially be mentioned any stress known to those skilled in the art, such as an increase in potential or a change in the chemical composition of the solution.

According to one embodiment, in continuous mode, the application of the stress is regulated according to the consumption of the succinate and / or precursor of the succinate in solution. In particular, the stress is applied when the concentration of succinate and / or succinate precursor is practically zero. According to one embodiment, the method according to the invention comprises the application of a potential increase with respect to the potential applied during the synthesis phase. This increase in potential advantageously makes it possible to release the glycerol produced and stored inside the cells of the microorganisms used in the process.

According to one embodiment, the method of the invention may comprise the application of a potential increase of from 150mV to 700 mV, preferably from 200mV to 500mV, and preferably from about 200mV. The process according to the invention advantageously leads to high current densities of between 20 and 200 A / m ² , preferably between 25 and 100 A / m ² , more preferably between 25 and 50 A / m ² .

According to one particular embodiment, the electrochemical reduction reaction according to the invention can be carried out within an electrochemical reactor whose anode and cathode compartments can be separated by a separator element allowing the migration of ions between said anode and cathode compartments. . According to the invention, said separator element can then be an electrochemical bridge known to those skilled in the art, such as a proton exchange membrane (PEM), a cationic membrane, a ceramic, an ultrafiltration membrane (UF), anion exchange membrane (AEM), a bipolar membrane, or a single polymer separator (gaseous) or any other separation allowing the ionic conduction known to those skilled in the art; For example, the commercial membranes Nafion® 1 17 or 1 135 or CM1-7000S can be cited.

In the context of this disclosure, unless otherwise stated, the term "anode compartment" means the compartment of the electrochemical cell comprising the anode.

As part of this presentation, unless otherwise stated, the term "cathode compartment" means the compartment of the electrochemical cell comprising the cathode. The following examples illustrate the invention without limiting it.

FIGURES

FIG. 1 schematically represents the electrochemical reactor according to the invention comprising a working electrode (1), a reference electrode (2) and a counter-electrode (3), immersed in 2L of electrolyte solution (4) and 0 , 5 L of gas supernatant (N ₂ , C0 ₂ or a mixture of both) (5).

 Figure 2 shows the amperometric tracking of the working electrode. The current I (mA) is given as a function of the time expressed in days.

Figure 3 shows the cyclic voltammetry (CV) obtained after the injection of the bacteria into the electrochemical reactor with bubbling N ₂ : C0 ₂ (80: 20%) just after the inoculum (curve 1), after formation of the electroactive biofilm under bubbling of N ₂ : C0 ₂ (80: 20%) at a time t of about 7 days (curve 2) and during the bubbling of N ₂ (100%) (curve 3). This figure represents current densities J (Am ^"2 ) as a function of potential E (V) vs. Ag / AgCl.

EXAMPLES 1. Materials and methods

1.1. Strain, environments and growing conditions

 The strain Geobacter sulfurreducens PCA (ATCC51573) was purchased from DSMZ (Deutsche Sammlung von Mikroorganismen und Zellkulturen). The culture medium and the growth conditions of the strain used are identical to those described by Dumas et al. (Electrochimica Acta 53, 2008, 2494-2500). The culture of Geobacter sulfurreducens was maintained by liquid means.

The electrolytic solution in which the biocathodes were prepared is identical to the culture medium, but it does not contain acetate and the final fumarate concentration is 4 gL ^-1 (25 mM) .The electrochemical reactor containing the electrolytic solution was thermostated at 30 ° C and bubbled with N ₂ : C0 ₂ (80: 20%) for 12 h The bacteria (7.5 ± 0.5%, v / v) were injected into the electrochemical reactor when their optical density in the medium The culture of N ₂ : C0 ₂ was maintained at a lower rate after inoculation to ensure anaerobiosis.

1.2. Electrochemical reactor and electrodes

The electrochemical reactor contained 2L (± 10%) of electrolytic solution and a supernatant space of 0.5L (see reactor diagram in Figure 1). It is conventionally composed of a working electrode (1), a reference electrode (2) and a counter-electrode (3). The 7.5 cm ² surface working electrode is made of super-austenitic stainless steel UNS S31254 (254SMO) with a composition of: 0.01% C, 19.9% Cr, 6% Mo, 17.8% Ni, 0.5% Mn and 0.02 % N. The reference electrode is an Ag / AgCl electrode (which consists of a 2 mm silver wire coated with silver chloride) whose potential in the medium is 0.3 V vs ESH (Standard Electrode to Hydrogen) and the counter electrode a platinum grid made with a platinum wire 0.38 mm in diameter.

The working electrode (1) has been drilled and tapped in order to fix a titanium rod which provides the electrical connection. Prior to the experiment, the working electrode (1) was washed according to the protocol described in Dumas et al. (Electrochimica Acta 53, 2008, 2494-2500). The polarization potential was set at -0.6 V vs Ag / AgCl thanks to a potentiostat (Bio-Logic, France). The current was recorded over time throughout the experiment (chronoamperometric monitoring). The chronoamperometry was sometimes interrupted to achieve cyclic voltammetry (CV) at 10 mV / s or 1 mV / s in the potential range of -0.6 V to 0 V vs. Ag / AgCl.

1.3. Quantification of glycerol

The glycerol formed was quantified by a glycerol-specific enzymatic kit (Megazyme glycerol kit K-GCROL, Libios, France) whose detection limit is 10 mg / l.

2. Results Figure 2 shows the amperometric tracking of the working electrode. The current I (mA) is given as a function of the time expressed in days. Seven phases, identified by numbers 1 to 7 and corresponding to polarization (potential Vp) and bubbling conditions, were distinguished in this experiment. In the first phase, the polarization potential was set at -0.6 V vs Ag / AgCl and the anaerobiosis was performed by bubbling N ₂ : CO ₂ (80: 20%). As shown in Figure 2, after 2 days of latency corresponding to the formation of the electroactive biofilm of Geobacter sulfurreducens on the working electrode, the current first increased almost linearly over a time interval At-i (At- i "2.5 days) then stabilized around an average value l _max of the order of -15.5 mA for a time At ₂ (At ₂ " 7 days). The disturbances noted CV in Figure 2 correspond to interruptions of chronoamperometry for the tracing of voltammetry.

The amount of fumarate consumed by reduction following the following reaction:

Fumarate + 2H ⁺ + 2e ^" → Succinate could be calculated by Faraday's law as a function of the recorded intensity One mole of reduced fumarate gives two moles of electrons, ie an amount of electricity equal to 2F (F = Faraday constant = 96,500 Cb) The integration of the intensity of the current as a function of time gave the quantity of electricity, and thus the amount of fumarate consumed.The integration of the intensity over ten and a half days has given 4970 Cb, that is to say the amount of electricity corresponding to the total consumption of the 50 mmol of fumarate initially present in the reactor.The fumarate was therefore completely consumed after 10.5 days identified by the stage A in Figure 2. Once the fumarate was exhausted, the reduction current would have to fall back to zero, and the results in Figure 2 show that the reduction current persisted after 10.5 days, so the bacteria Geobacter sulfurreducens found in the medium another electron acceptor which can only be C0 ₂ from bubbling, only reducible compound provided in the middle in sufficient quantity to maintain the intensity of the current.

In the second phase of the experiment, the anaerobiosis was carried out by bubbling with pure CO ₂ and the polarization potential was fixed at -0.4 V vs Ag / AgCl. Intensity dropped from the range 15-17 mA to the 5-6 mA range, in accordance with the expected variation for electrochemical reaction. This behavior shows that the value of the potential controls the rate of reduction of C0 ₂ . In addition, the bubbling of pure C0 ₂ did not have a significant effect on the reduction current. This behavior could be explained by the fact that the maximum rate of consumption of C0 ₂ by the bacteria has already been reached (Michaelian type behavior).

During the third phase, the system was returned to the initial conditions (Vp = -0.6 V vs Ag / AgCl and bubbling of N ₂ : CO ₂ (80: 20%)). The intensity was initially slightly higher (in absolute value) then returned to the value recorded in phase 1 in the range 15-17 mA (Figure 2, I 4 ^th day approximately). The N ₂ : CO ₂ (80:20%) bubbling was then replaced by pure N ₂ bubbling, thus free of CO ₂ with a potential of -0.6 V vs Ag: AgCl (fourth phase of experience). The current of Reduction has decreased to zero current, demonstrating that the reduced electron acceptor is C0 ₂ .

FIG. 3 shows the cyclic voltammetry (CV) obtained after the injection of the bacteria into the electrochemical reactor (curve 1), after formation of the electroactive biofilm under bubbling of N ₂ : CO ₂ (curve 2) and during the bubbling of N ₂ (curve 3). No reduction current is visible for curve 1 because the electroactive biofilm has not yet been formed. A high reduction current density was observed when the biofilm was formed and bubbled with N ₂ : CO ₂ (curve 2), in agreement with the chronoamperometric results (FIG. 2). On the contrary, the reduction current has disappeared on curve 3 because there is no longer any electron acceptor available in the medium that can be reduced: the fumarate has been totally consumed and the bubbling of N ₂ : C0 ₂ a was replaced by bubbling of pure N2. When the bubbling of N ₂ : CO ₂ was restored (phase 5 of the experiment, Figure 3), the reduction current reappeared at a value very close to that observed during phase 1.

Thus, these data confirm the reduction of carbon dioxide through electrochemically active biofilm on the stainless steel cathode. Once the stream stabilized in phase 5, the bubbling of N ₂ : CO ₂ was again replaced by pure C0 ₂ (phase 6 of the experiment, Figure 2). In stage B, a sample was taken which was analyzed with the glycerol kit. The reduction current produced remained similar to that obtained in phase 5. In a last step (phase 7, FIG. 2), the flow of N ₂ : CO ₂ (80: 20%) was restored. The current then decreased (in absolute value) by about 3 mA / day under the very likely effect of the accelerated aging of the biofilm subjected to extreme operating conditions, in particular during the phases in total absence of C0 ₂ .

Previous results demonstrate that carbon dioxide C0 ₂ was consumed by Geobacter sulfurreducens as an electron acceptor. Analyzes by liquid chromatography coupled with a refractometric detection have demonstrated that the product resulting from the reduction of CO ₂ is glycerol. Analysis of a sample taken from the reactor shortly before the end of the experiment (FIG. 2), carried out with the glycerol-specific enzymatic kit, confirmed the presence of glycerol and made it possible to quantify the concentration of glycerol produced in the electrochemical reactor at the time of sampling is 0.6 g L ^"1 . The maximum values of the current densities obtained are of the order of 25 A / m ² , which is an order of magnitude above any value reported so far for a CO ₂ reduction process.

Claims

Process for the electrochemical reduction of carbon dioxide (CO ₂ ) by means of a metal cathode, in the presence of microorganism (s) forming an electrochemically active biofilm on the surface of said metal cathode, and in the presence of an electrolytic solution comprising succinate and / or succinate precursor, said precursor being a natural acceptor of electrons of the microorganism forming the biofilm. The process according to claim 1, wherein the succinate precursor is selected from an oxidized precursor of the succinate or a derivative of said oxidized precursor. Process according to claim 2, such that the oxidized precursor of the succinate is fumarate The process of claim 2, such that the oxidized precursor derivative of the succinate is malate. A process as claimed in any one of the preceding claims, such that the electrolytic solution comprises succinate. The method of claim 1, such that the electrochemical reduction of CO ₂ comprises a preliminary step of reducing the succinate precursor, which is a natural electron acceptor of the biofilm-forming microorganism, to form succinate. A process according to claim 6, such that the succinate precursor is fumarate. A process as claimed in any one of the preceding claims, wherein said microorganism is Geobacter sulfurreducens and said succinate precursor is fumarate. 9. Process according to one of claims 1 to 8, comprising the formation of glycerol. 10. Process according to any one of the preceding, such that the metal cathode is made of stainless steel. 1 1. A process according to any one of the preceding claims, such that the microorganism is Geobacter sulfurreducens. The method of any one of the preceding claims, which comprises applying stress to the microorganisms. 13. Process for the recovery of carbon dioxide (CO ₂ ), comprising the reduction of CO ₂ to glycerol electrochemically. 14. The method of claim 13, such that the electrochemical reduction is performed by means of a metal cathode. 15. A method according to any one of claims 13 or 14, such that the electrochemical reduction is carried out in the presence of one or more microorganism (s) forming an electrochemically active biofilm on the surface of said metal cathode. 16. The recovery method according to any one of claims 13, 14 or 15, comprising the implementation of the method according to any one of claims 1 to 1 1.