WO2023079234A1

WO2023079234A1 - Method for producing hydrogen by electrochemically reforming an alcohol catalyzed by radioactive platinoids

Info

Publication number: WO2023079234A1
Application number: PCT/FR2022/052057
Authority: WO
Inventors: Charles BRUSSIEUX; Christophe COUTANCEAU; Isabelle HABLOT; Delphine LEHUBY
Original assignee: Orano
Priority date: 2021-11-02
Filing date: 2022-10-31
Publication date: 2023-05-11
Also published as: FR3128719B1; FR3128719A1

Abstract

The invention relates to a method for producing hydrogen by electrochemically reforming an alcohol. This method comprises electrolyzing alcohol in an electrolytic cell comprising an anode, an electrolyte and a cathode, and is characterized in that at least part of the outer surface of the anode comprises one or more radioactive platinoids selected from among palladium, ruthenium and rhodium, these one or more radioactive platinoids being derived from an acidic aqueous solution containing fission products from a spent nuclear fuel.

Description

PROCESS FOR THE PRODUCTION OF HYDROGEN BY ELECTROCHEMICAL REFORMING OF ALCOHOL CATALYZED BY RADIOACTIVE PLATINOIDS

DESCRIPTION

TECHNICAL AREA

The present invention relates to the field of hydrogen production.

More specifically, it relates to a process for the production of hydrogen by electrochemical reforming - also called electrolysis - of an alcohol in which one or more radioactive platinoids, resulting from an acidic aqueous solution of fission products of a nuclear fuel used, are used as catalysts for the electrooxidation reaction of these alcohols.

PRIOR ART

Due to its high mass energy density and its ability to be oxidized in the presence of oxygen in the form of pure water without releasing CO2, hydrogen is considered an important energy vector for carrying out the energy transition. .

If hydrogen is likely to be used as a reagent in fuel cells to produce electricity, its first destination currently remains industry. In fact, 75 million tonnes are consumed annually by the chemical industry, of which nearly 45% for oil refining.

To date, the steam reforming of hydrocarbons, mainly methane, is the most widely used hydrogen production process to supply the industry with hydrogen because it is by far the most economical. Steam reforming consists of reacting methane with water at temperature and in the presence of catalysts to produce a mixture of H2, CO2, CO, residual CH4 and water (called syngas). At the steam reactor outlet, the hydrogen is separated and purified. However, for every ton of hydrogen produced by steam reforming, approximately 10 tons of CO2 are emitted and generally released into the atmosphere.

Hydrogen production processes that limit or even eliminate greenhouse gas emissions and, in particular, CO2 emissions are therefore being studied to complete its production by steam reforming, or even gradually replace it.

A process which is the subject of all the attention is the electrolysis of water which consists in decomposing, in an electrolysis cell, water into oxygen and hydrogen gas under the effect of an electric current.

Although this process has the advantage of producing pure hydrogen (i.e. free of CO, CO2, etc., unlike the hydrogen produced by steam reforming), it requires applying to the terminals of the cell electrolysis of voltages significantly higher than the reversible voltage linked to the H2O = H2 + O2 reaction which, under standard conditions (1 bar), is 1.23 V at 25°C, which corresponds to energy consumption electricity of 33 kWh per kg of hydrogen produced. The production of hydrogen by electrolysis of water is therefore expensive.

To significantly reduce this energy consumption and, consequently, the production costs of hydrogen, it has been proposed to produce the latter by electrolysis of oxygenated organic compounds and, in particular, of alcohols derived from oleaginous biomass (such as glycerol produced by the reaction of transesterification with methanol of triglycerides which is implemented for the production of first-generation biofuels) or lignocellulosic biomass (such as the ethanol produced during the fermentation of the sugars present in the waste of second-generation biofuel industries).

Indeed, the reversible voltage linked to the electrochemical decomposition of alcohols is typically less than 0.1 V at 25° C., which allows a significant reduction in the consumption of energy necessary for the production of hydrogen.

In addition, the electrolysis of oxygenated organic compounds can lead to the production of co-products whose added value is greater than that of oxygen, which is the only co-product resulting from the electrolysis of water. For a detailed description of the principles which are at the basis of the production of hydrogen by electrolysis of oxygenated organic compounds as well as of the most significant works having been carried out to date on this subject, the reader is invited to refer to book Production of Clean Hydrogen by Electrochemical Reforming of Oxygenated Organic Compounds by C. Lamy, C. Coutanceau and S. Baranton, published in 2020 by BG Pollet (Elsevier, Amsterdam), hereinafter reference [1].

As indicated in this reference, if the feasibility of the production of hydrogen by electrolysis has been largely demonstrated for several oxygenated organic compounds (formic acid, methanol, ethanol, glycerol, etc.), in particular in an electrolysis cell with an exchange membrane of protons, it turns out that the electrooxidation kinetics of these compounds is relatively slow, which leads to high anode overvoltages and, therefore, to high cell voltages at the current density which is required to obtain a rate high hydrogen production.

Therefore, the development of industrially usable electrolyzers requires the ability to increase this electro-oxidation kinetics, which implies having more active electrocatalysts than those proposed to date, which are typically bi- or trimetallic electrocatalysts with palladium and/or platinum base (see reference [1]).

It is known, from FR-A-1 336 077, hereinafter reference [2], that the reactions implemented in fuel cells and other electrochemical energy generators can be catalyzed by a radioisotope such as carbon- 14, nickel-63, cobalt-60 or a promethium isotope.

It is also known to extract PGMs from aqueous nitric solutions by electrochemical reduction and, in particular, from solutions simulating solutions resulting from the processing of spent nuclear fuel. Studies relating to this type of extraction have notably been published by K. Koizumi et al. in J. Nucl. Sci. Technol., 1993, 30(11), 1195-1197, hereinafter reference [3], by MY Kirshin et al. in Radiochemistry 2005, 47(4), 365-369, hereinafter reference [4] and by M. Jayakumar et al. in Desalination and Water Treatment 2009, 12, 34-39, hereafter reference [5]. However, none of these studies does not envisage that the PGMs thus extracted can be used as electrocatalysts.

However, it so happens that, in the context of their work, the Inventors have observed that radioactive platinoids originating from an aqueous solution of fission products from spent nuclear fuel have, at identical electrolysis potential, an ability to catalyze the electro-oxidation reaction of an alcohol which is much higher than that exhibited by non-radioactive platinoids.

And it is on these experimental findings that the invention is based.

DISCLOSURE OF THE INVENTION

The subject of the invention is therefore a method for producing hydrogen by electrochemical reforming of an alcohol, which comprises electrolysis of the alcohol in an electrolysis cell comprising an anode, an electrolyte and a cathode, and which is characterized in that at least part of the external surface of the anode comprises one or more radioactive platinoids chosen from palladium, ruthenium and rhodium, this or these radioactive platinoids being derived from an acidic aqueous solution containing products of fission of spent nuclear fuel.

In accordance with the invention, the acidic aqueous solution containing fission products from a spent nuclear fuel can be any acidic aqueous solution produced during the processing of a spent nuclear fuel provided that it contains fission products, denoted below PF, including platinoids which are maintained in the form of ions in the presence of oxidizing compounds such as nitric acid or perchloric acid and/or complexing ions such as chlorides or fluorides.

Thus, it may in particular be:

- a solution resulting from the operations of dissolving spent nuclear fuel in a strong acid such as nitric acid, and clarifying (for example, by centrifugation) the dissolution liquor thus obtained;

- a solution resulting from an acid attack of fines from the dissolution of spent nuclear fuel, i.e. solids of small particle size which have not been dissolved during the fuel dissolution operation and which have therefore been separated from the dissolution liquor during the clarification operation of this liquor; or

- a solution depleted in uranium and plutonium but rich in FP, to which we give the name of raffinate and which results from the operations of extraction, separation and purification of uranium and plutonium which are typically implemented in the processing of spent nuclear fuel.

In the context of the invention, it is preferred that the acidic aqueous solution containing FPs be a solution resulting from an acid attack of fines from the dissolution of a spent nuclear fuel. More specifically, it is preferred that it be a solution resulting from an attack by nitric acid or a mixture of acids comprising nitric acid, such as a mixture of nitric and hydrofluoric acids , dissolving fines from a PUREX process (from Plutonium Uranium Refining by Extraction).

The PUREX process, as it is implemented in the French spent nuclear fuel processing plant at La Hague, is described in the monograph Treatment and recycling of spent nuclear fuel - Actinide partitioning - Application to waste management of the Commissariat à atomic energy, published in 2008 by Le Moniteur, hereinafter reference [6].

The qualitative composition of the acidic aqueous solutions produced during the treatment of spent nuclear fuel and, in particular, that of the solutions resulting from an acid attack of fines from the dissolution of spent nuclear fuel varies according to the type of nuclear fuel, the type of nuclear reactor in which the fuel was irradiated, the irradiation conditions to which the fuel was subjected and, in particular, the burnup rate, as well as the time during which the spent fuel was cooled after leaving the reactor nuclear.

Nevertheless, such aqueous solutions include a number of FPs in significant amounts including palladium (Pd), ruthenium (Ru) and rhodium (Rh) for cooling times of less than about 30 years and palladium (Pd) and rhodium (Rh) for longer cooling times.

As previously indicated, the anode of the electrolysis cell must have at least a part of its external surface which comprises palladium, ruthenium and/or radioactive rhodium from an acidic aqueous solution of fission products from spent nuclear fuel.

Which means that the anode can be:

- either a solid anode, that is to say an anode which is made of one of these radioactive platinoids or of an alloy of these, for example, a Pd/Ru, Pd/Rh or Pd alloy /Ru/Rh,

- or an anode which comprises a support, or substrate, electrically conductive of which all or part of the outer surface comprises a deposit of one or more of said radioactive platinoids.

It is this second type of anode which is preferred in the context of the invention.

Such an anode can in particular be obtained:

- by electrodeposition, or electrochemical deposition, of the platinoid(s) on the electrically conductive support, or else

- by electroless chemical deposition of the platinoid(s) on the electrically conductive support, that is to say by chemical reduction of the platinoid(s) in solution by means of a reducing agent such as hydrazine (as described, for example, by J. F. Rivadulla et al in J. Phys. Chem. B 1997, 101, 8997-9004, hereinafter reference [7]), a hypophosphite (as described, for example, by M. I. C. F. Costa et al. in ISRN Organic Chemistry 2011 , article ID 759817, 1-7, hereinafter reference [8]) or a borohydride (as described, for example, by S. Lankiang et al. in Electrochemica Acta 2015, 182, 131-142, hereinafter reference [ 9]).

In the context of the invention, it is preferred that the deposition of the radioactive PGM(s) on the electrically conductive support is carried out by electrodeposition because this deposition technique is easier to implement than an electroless chemical deposition in the case of radioactive materials and avoids, moreover, having to use chemical reagents such as reducing agents and complexing agents.

Whatever the deposition technique used, the electrically conductive support can be made of any material provided that it has high electronic conductivity, electrochemical stability and, in particular, resistance to oxidation, as well as chemical stability, in especially in acidic and basic environments. Thus, it may in particular be:

- a carbon support and, in particular, glassy carbon,

- a stainless steel support,

- a support in a metal such as platinum, titanium or tantalum, or in a metal alloy,

- a support in an oxide such as titanium dioxide (Ti O2), a nitride such as titanium nitride (Ti N), or a carbonitride such as titanium carbonitride (TiCN),

- a support made of an electrically conductive polymer such as polyaniline, polypyrrole or polythiophene, as described, for example, by A. Lima et al. in Journal of Applied Electrochemistry 2001, 31, 379-386, reference [10] below, and by C. Coutanceau et al. in Electrochimica Acta 1995, 40(17), 2739-2748, hereinafter reference [U].

Among these, preference is given to a carbon support (because carbon is completely neutral with respect to oxidation-reduction reactions) and, more particularly, to a vitreous carbon support.

As previously mentioned, the acidic aqueous solutions produced during the processing of spent nuclear fuel include palladium, ruthenium and rhodium.

As a result, a deposit made by electrodeposition or chemical reduction from such a solution (without prior separation of the platinoids) typically comprises a mixture of palladium, ruthenium and rhodium.

However, it is preferred that this deposit mainly comprises palladium, that is to say that the palladium represents more than 50% by mass, preferably at least 70% by mass and, even better, at least 80% by mass of the mass of the deposit.

The operating conditions under which the electrodeposition or the chemical reduction of the platinoid(s) will be carried out will therefore be chosen accordingly, which falls within the normal skills of a person skilled in the art given the abundant literature relating to the techniques of deposition of platinoids and, in particular, palladium on supports. As for the mass content of the palladium in the deposit, it can easily be checked by dissolving this deposit by immersing the support comprising it in a highly concentrated solution of a strong acid, for example nitric acid, or of a mixture of acids. strong and by subjecting the solution resulting from this dissolution to a quantitative and qualitative analysis, for example by inductively coupled plasma atomic emission spectrometry (ICP-AES).

As known per se and, in particular, from reference [4] for palladium, in a radioactive medium, the electrolytic reduction of platinoid ions competes with the autocatalytic reduction of nitrate ions (NO3) into nitrite ions (NO2) and this competition is all the more intense to the detriment of the PGM reduction reaction when the nitric acid and nitrous acid contents are so high as to make impossible, beyond a certain stage, the deposition of PGMs by electrodeposition on certain types supports such as carbon supports.

In this case, it may be necessary, depending on the nature of the electrically conductive support and with the aim of reducing the rate of reduction of the nitrate ions, to carry out a deposit on part or on the whole of the external surface of this support. on which the electrodeposition of the radioactive platinoid(s) is to be made, of a non-radioactive metallic element chosen from among palladium, tantalum, niobium, stainless steel, chromium, titanium, zirconium or any other material stable electroconductor in the electrodeposition medium and on which the reduction of nitrate ions is slow, before proceeding with the deposition of the radioactive platinoid(s).

An anode is thus obtained, the external surface of the electroconductive support of which comprises a deposit of said non-radioactive metallic element under the deposit of the radioactive platinoid(s).

In accordance with the invention, the electrolysis cell is advantageously an electrolysis cell with two compartments separated, preferably by a cation exchange membrane and, even better, an electrolysis cell with a proton exchange membrane, or PEMEC of Proton Exchange Membrane Electrolysis Cell.

As known per se, a PEMEC cell typically comprises: - a central component, called Assembly-Membrane-Electrodes (AME), itself comprising:

* a gas-tight polymer membrane which is typically a perfluorinated sulfonic membrane and which acts as a proton-conducting electrolyte, electronic separator and gas separator,

* an anode which, in the case where the PEMEC cell is used to electrolyze an alcohol, is the site of the oxidation of this alcohol,

* a cathode which is the seat of the reduction of the protons having migrated through the membrane into molecular hydrogen,

- two diffusion layers which are arranged on either side of the MEA and whose role is to allow electrical contact as well as the supply of reagents (alcohol + water) and the evacuation of products; And

- two current collector plates which are themselves arranged on either side of the diffusion layers and which can be monopolar (if the electrolysis cell is an individual cell) or bipolar (if the electrolysis cell is associated with other cells in an electrolysis module).

In the case where the oxidation reaction of the alcohol at the anode is complete, the following half-reaction is considered:

However, the breaking of the carbon-carbon bond in alcohols being difficult at the low temperatures at which electrolyses take place (< 100 °C), ketones in the case of secondary alcohols, and aldehydes and carboxylic acids in the case of primary alcohols, can be produced according to the following half-reactions: for a primary alcohol: R-CH ₂ OH R-CHO + 2H ⁺ + 2e ^_ (2), or

R-CH ₂ OH + H ₂ O R-COOH + 4H ⁺ + 4e" (3), or

R-CH ₂ OH + 2H ₂ O R'-OH + CO ₂ + 6H ⁺ + 6e" (4), etc., for a secondary alcohol: RI-CHOH-R ₂ RI-CO-R ₂ + 2H ⁺ + 2nd ^_ (5).

For the reduction of protons at the cathode, the following half-reaction is considered: n(H ⁺ + e ) (n/2)H ₂ (6), the sums of the half-reactions (2), (3), (4) or (5) with (6) leading to the reactions below: for a primary alcohol:

(7), or

R-CH2OH + 2H ₂ O R'-OH + CO ₂ + 3H ₂ (9), etc., for a secondary alcohol: R1-CHOH-R2 R1-CO-R2 + H2 (10).

It goes without saying, however, that other types of electrolytic cells can be envisaged such as, for example, an anion exchange membrane electrolysis cell, or AEMEC from Anion Exchange Membrane Electrolysis Cell, an alkaline electrolysis cell , or AEC from Alkaline Electrolysis Cell, a cell with a porous compartment separation membrane or a cell without compartment separation.

In the case where the electrolysis cell is a PEMEC, then the polymer membrane may in particular be one of the perfluorinated sulfonic membranes which are marketed under the trade references Nafion™ and Aquivion™, while the cathode may in particular be based on platinum nanoparticles placed on a carbon support.

As known per se, the electrolysis of alcohol can be carried out in an acid medium or in an alkaline medium (cf. reference [1]).

However, it is preferred, within the scope of the invention, for it to be carried out in an alkaline medium, for example an aqueous solution comprising 1 mol/L of sodium hydroxide in ultrapure water, because the oxidation kinetics of alcohols is faster in an alkaline medium than in an acid medium.

In accordance with the invention, the alcohol subjected to electrolysis is preferably a straight-chain saturated aliphatic alcohol, which may be a monoalcohol such as methanol, ethanol, propanol or n-butanol, or or a polyalcohol, or polyol, such as ethylene glycol, propylene glycol, glycerol, sorbitol, mannitol and xylitol.

Preferably, the alcohol is a bio-sourced alcohol, that is to say from oleaginous biomass or lignocellulosic biomass, such as ethanol, glycerol, sorbitol, mannitol and xylitol. Most preferably, the alcohol is ethanol or bio-based glycerol.

In addition to the advantages mentioned above, which are those offered by an alcohol electrochemical reforming process compared to that of water (lower energy consumption, recovery of alcohols from biomass, production of co-products (aldehydes, carboxylic acids, etc.) with greater added value than oxygen which is the only co-product of the electrochemical reforming of water, etc.), the invention has the following advantages:

- due to the coupling of the catalytic and radioactive activities of platinoids on the electro-oxidation reaction of alcohols, that of very significantly increasing the anodic oxidation currents, at a given electrolysis potential, compared to those obtained by catalytic activation alone, which can result in an increase in the rate of production of hydrogen at the cathode of the electrolyser for the same electrical energy consumed, or else, a reduction in the electrical energy consumed for a same rate of hydrogen evolution at the cathode; And

- that of allowing, in the case where the acidic aqueous solution of fission products is a solution resulting from an acid attack of fines from the dissolution of a spent nuclear fuel or a raffinate from a process for treating a spent fuel , recovery of a source of PGMs which today constitutes high-level waste and, thereby, to reduce the mass of waste destined for disposal in deep layers.

Other characteristics and advantages of the invention will become apparent from the additional description which follows, which relates to tests which made it possible to validate the invention and which refers to the appended figures.

It goes without saying, however, that this additional description is only given by way of illustration of the object of the invention and should in no way be interpreted as a limitation of this object. BRIEF DESCRIPTION OF FIGURES

Figure 1 and Figure 2 show the results of tests aimed at evaluating, by linear voltammetry in a 1 mol/L sodium hydroxide solution containing 0.1 mol/L of ethanol, the electrolytic activity in the electro-oxidation reaction of ethanol to ethanal deposition of radioactive PGMs obtained from an aqueous solution of acid attack of fines from dissolution of spent nuclear fuel (curves

1) and comparing it to that of deposits made using an inactive solution simulating the solution of radioactive PGMs (curves 2 and 3 in figure 1; curves 2 and 4 in figure

2); in these figures, the abscissa axis corresponds to the polarization, denoted E and expressed in V versus Hg/HgO, while the ordinate axis corresponds to the current density, denoted J and expressed in mA/cm ² .

FIG. 3 represents the results of tests aimed at evaluating, by cyclic voltammetry, in a 1 mol/L sodium hydroxide solution, the active surface of deposits of radioactive PGMs obtained from an aqueous etching solution acid of fines from the dissolution of a spent nuclear fuel (curves 1) and to compare it with that of other types of deposits made using an inactive solution simulating the solution of radioactive platinoids under the same conditions (curves 2); in this figure, the abscissa axis corresponds to the polarization, denoted E and expressed in V versus Hg/HgO, while the ordinate axis corresponds to the current density, denoted J and expressed in mA/cm ²

DETAILED DISCUSSION OF PARTICULAR EMBODIMENTS

The tests which are reported below were carried out with a view to evaluating the catalytic activity in the reaction of electro-oxidation of ethanol to ethanal of deposits of radioactive platinoids obtained from an aqueous solution of attack acid of dissolving fines of a spent nuclear fuel - this solution being called real solution in what follows - and to compare it with that:

- on the one hand, deposits of non-radioactive PGMs obtained from an aqueous solution simulating the acid attack solution of fines from the dissolution of a spent nuclear fuel, referred to as simulated solution in the following, and - on the other hand, deposits of radioactive PGMs obtained from the real solution then covered by a deposit of non-radioactive PGMs obtained from the simulated solution.

Also reported is a test aimed at assessing the catalytic activity, also in the reaction of electro-oxidation of ethanol to ethanal, of deposits of non-radioactive PGMs obtained from the simulated solution to which an element radioactive, in this case technetium-99.

Are therefore described in the following:

- the preparation of the real solution,

- the preparation of the simulated solution,

- the production of deposits from these solutions,

- linear voltammetry tests aimed at evaluating the electrocatalytic activity of the different types of deposits, and

- cyclic voltammetry tests aimed at evaluating the active surface of the different types of deposits.

I - Preparation of the real solution:

Dissolution fines from the processing of nuclear fuels at La Hague are subjected to an acid attack treatment for 24 hours which is carried out by means of an aqueous solution comprising 7 mol/L of nitric acid and 11 mol/L of L of hydrofluoric acid, in an autoclave heated to 170°C.

After opening the autoclave, nitric acid at 0.5 mol/L is added to the aqueous solution resulting from the acid attack. The minimum nitric acid and hydrofluoric acid contents of this solution are then 5.7 mol/L and 8.8 mol/L respectively.

The aqueous solution thus obtained contains, in addition to uranium, non-platinoid fission products (Fe, Ni, Cr, Mo, Te, Zr, etc.) and fission products from the family of platinoids, namely palladium 0.34 g/L), ruthenium 1.8 g/L) and rhodium (0.27 g/L).

II - Preparation of the simulated solution: The simulated solution is prepared by dissolution in the microwave at 180° C. and for 1 hour of a mixture of reagents comprising iron, nickel and chromium (in the form of 304 L stainless steel flakes), molybdenum (in the form of MoOs), rhenium (in the form of F^O?) to simulate technetium, zirconium (in the form of ZrÜ2), palladium (in the form of Pd(NOs)2, H2O) , ruthenium (in the form of RU(NO)(NO3)S), and rhodium (in the form of Rh(H2O)(OH)3- _y (NO3) _y ) in a medium composed of nitric acid 5 .7 M and 8.8 M hydrofluoric acid.

Only the uranium present in the aqueous solution prepared in point I above is not simulated.

The amounts of reagents dissolved in the HNO3/HF medium are chosen so that the mass composition of the simulated solution is identical to that of the aqueous solution prepared in point I above.

Ill - Production of PGM deposits:

Il 1.1 - Deposits of non-radioactive PGMs from the simulated solution:

Electrodeposition of the simulated solution is performed on a series of vitreous carbon (CV) electrodes.

The CV electrodes are electrodes marketed by the company BioLogic under the reference A-002417. They are in the form of glassy carbon rods 5 mm in diameter (ie 0.196 cm ² ) which are embedded in a polyetheretherketone (PEEK) envelope.

Deposits are made using:

- an electrolytic cell comprising:

* a tank 6.3 cm in diameter, to receive 50 mL of electrolytic solution (i.e. 1.8 cm in height of electrolytic solution),

* the CV electrode as the working electrode,

* a gold wire crimped in a CV plate, the whole being embedded in a PEEK envelope as a counter-electrode,

* a CV electrode identical to the working electrode as pseudo reference electrode; a BioLogic VSP-300 potentiostat, and by applying a potential of 0.21 V versus ENH (normal hydrogen electrode), i.e. -0.88 V versus CV, for 5 minutes.

Analysis by ICP-AES of the deposit thus produced on one of the electrodes (after dissolution of this deposit by immersion of the electrode in nitric acid at 14.3 mol/L for 24 hours) shows that the deposits are rich in palladium (> 80% by mass) but also include ruthenium (>7% by mass) and rhodium (>3% by mass).

Il 1.2 - Deposits of radioactive PGMs from the real solution:

As part of their work, the Inventors found that, in accordance with the teaching of reference [4], it was not possible for them to obtain by electrodeposition a deposit of platinoids from the real solution on electrodes in CV because in the presence of radioactivity, the reduction of the NOs" ions into NC ions actually takes over the reduction of the platinoid ions during the polarization of the CV and thus prevents the deposition of these platinoids.

On the other hand, it was possible for them to obtain deposits of platinoids from the real solution by using electrodes on which non-radioactive platinoids were previously deposited as described in point II 1.1 above.

The deposits of radioactive PGMs are therefore made with the same equipment as that used in point II 1.1 above - with the exception of the working electrode since this already includes a deposit of non-radioactive PGMs - and by applying the same potential as that applied in point II 1.1 above but for 5 minutes.

111.3 - Deposits of non-radioactive PGMs on deposits of radioactive PGMs:

These deposits are made in the same way as that described in point III.1 above except that the electrodes used are electrodes on which radioactive platinoids have been previously deposited as described in point III.2 above.

II 1.4 - Deposits of non-radioactive PGMs from the simulated solution enriched in "Te: These deposits are made on CV electrodes in the same way as that described in point III.l above but using as electrolytic solution, 50 mL of a solution obtained by adding 15 mL of a standard of technetium-99 at 1 g/L to 35 mL of the simulated solution (ie a dilution of the simulated solution by a factor of 0.7).

The 50 mL of solution thus obtained have an activity in "Te of 9.4.10 ⁶ Bq (considering a specific activity of "Te of 6.283.10 ⁸ Bq/g).

IV - Evaluation of the electrocatalytic properties of deposits by linear voltammetry:

The electrocatalytic properties of the different types of deposits in the electro-oxidation reaction of ethanol (CH3CH2OH) to ethanal (CH3CHO) are assessed by linear voltammetry in alkaline medium (1 M NaOH) using an electrolytic cell which includes:

- a tank which is a copy of the one used in point lll.l above,

- an electrode as obtained in points III.l to III.4 above as the working electrode,

- a CV electrode identical to that used in point III.l as a counter-electrode, and

- an Hg/HgO electrode specially designed to be used in a medium comprising 1 mol/L of NaOH and marketed by the company BioLogic under the reference A-013395 as a reference electrode; its potential is 0.14 V versus ENH and -0.1 V versus ECS (saturated calomel electrode).

The potentiostat is also a BioLogic VSP-300 potentiostat.

The electrolyte solution is a 50 mL solution comprising 1 mol/L NaOH and 0.278 mL 95% ethanol.

Figures 1 and 2 illustrate the results obtained for the different types of deposits by applying a bias in the range from -0.55 V versus Hg/HgO and 0.2 V versus Hg/HgO at a scan rate of 20 mV/ s.

In Figure 1:

- the curves denoted 1 correspond to the polarization curves obtained for the electrodes comprising a deposit of radioactive platinoids, - the curves denoted 2 correspond to the polarization curves obtained for the electrodes comprising a deposit of non-radioactive PGMs obtained from the simulated solution without adding "Te", while

- the curves denoted 3 correspond to the polarization curves obtained for the electrodes comprising a deposit of radioactive PGMs covered with a deposit of non-radioactive PGMs.

In Figure 2, the curves denoted 4 correspond to the polarization curves obtained for the electrodes comprising a deposit of non-radioactive PGMs obtained from the simulated solution with addition of "Te" and are compared with curves 1 and 2 of Figure 1.

As shown in FIG. 1, the current densities obtained for the electrodes comprising a deposit of radioactive PGMs (curves 1) are three times higher than those obtained with the electrodes comprising a deposit of non-radioactive PGMs (curves 2). Which means :

- on the one hand, that the electrocatalytic activity of the platinoid deposits made from the real solution is three times higher than that of the platinoid deposits made from the simulated solution and,

- on the other hand, that the presence, under the deposits of radioactive PGMs, of a deposit of non-radioactive PGMs is not likely to affect the electrocatalytic properties of the deposits of radioactive PGMs because these properties are induced by the first layer atom of catalyst which is located in contact with the electrolytic solution.

This last point is confirmed by the fact that, as also shown in figure 1, the fact of covering a deposit of radioactive PGMs by a deposit of non-radioactive PGMs (curves 3) leads to current densities and, therefore, to a electrocatalytic activity, which are of the same level as those obtained for non-radioactive PGM deposits (curves 2).

Figure 2 shows that the addition of a radioactive element such as technetium-99 at a level of 0.3 g/L in the simulated solution does not have a significant impact on the activity electrocatalytic non-radioactive PGM deposits obtained from this solution.

V - Evaluation of the active surface of deposits by cyclic voltammetry:

The active surface, or real surface, of the different types of deposits is assessed by cyclic voltammetry in an alkaline medium (1 M NaOH) using a similar electrochemical cell and the same potentiostat as those used in point IV above.

Indeed, the active surface of a catalyst deposit is proportional to the integral surface of the polarization curves (surface which is homogeneous with a charge per unit surface) over the range of potentials going from 0 to -0.4 V versus Hg/HgO in the cathode domain.

Figure 3 illustrates the results obtained.

In this figure:

- the curves denoted 1 correspond to the voltammograms obtained for the electrodes comprising a deposit of radioactive platinoids,

- the curves denoted 2 correspond to the voltammograms obtained for the electrodes comprising a deposit of non-radioactive PGMs obtained from the simulated solution without addition of "Te", while

- the curves denoted 3 correspond to the voltammograms obtained for the electrodes comprising a deposit of non-radioactive PGMs obtained from the simulated solution with addition of "Te.

As shown in Figure 3, the deposits of non-radioactive PGMs obtained from the simulated solution have an active surface which is substantially the same whether or not this solution contains "Te.

On the other hand, this active surface is clearly higher than that of the deposits of radioactive PGMs obtained from the real solution.

These results tend to demonstrate that the electrocatalytic activity of radioactive PGM deposits obtained from an aqueous solution of acid attack of dissolving fines from spent nuclear fuel is not related to the extent of the surface of the these deposits but to properties specific to these radioactive platinoids. REFERENCES CITED

[1] Production of Clean Hydrogen by Electrochemical Reforming of Oxygenated Organic Compounds by C. Lamy, C. Coutanceau and S. Baranton, 2020, B. G. Pollet (Ed.), Elsevier, Amsterdam

[2] FR-A-1 336 077

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Claims

1. Process for the production of hydrogen by electrochemical reforming of an alcohol, comprising electrolysis of the alcohol in an electrolysis cell comprising an anode, an electrolyte and a cathode, characterized in that at least part of the external surface of the anode comprises one or more radioactive platinoids chosen from palladium, ruthenium and rhodium, this or these radioactive platinoids being derived from an acidic aqueous solution containing fission products of a spent nuclear fuel.

2. Process according to claim 1, in which the acidic aqueous solution containing fission products results from an acid attack of fines from the dissolution of a spent nuclear fuel.

3. Process according to claim 2, in which the aqueous solution containing fission products results from an attack of dissolution fines from a PUREX process by nitric acid or a mixture of acids comprising nitric acid. .

4. Method according to any one of claims 1 to 3, wherein the anode comprises an electrically conductive support of which all or part of the external surface comprises a deposit of the radioactive platinoid(s).

5. Process according to claim 4, in which the deposit results from an electrodeposition or from a chemical reduction of the radioactive PGM(s) in solution, preferably from an electrodeposition.

6. Method according to claim 4 or claim 5, in which the electrically conductive support is made of carbon, stainless steel, a metal or a metal alloy, a ceramic of the oxide, nitride or carbonitride type, a polymer, or a composite, preferably carbon and more preferably glassy carbon.

7. Method according to claim 5 or claim 6, in which the deposit comprises a mixture of palladium, ruthenium and rhodium.

8. Process according to claim 7, in which the palladium represents more than 50% by mass, preferably at least 70% by mass and, even better, at least 80% by mass of the mass of the deposit.

9. A method according to any one of claims 5 to 8, wherein the outer surface of the electrically conductive support comprises a deposit of a non-radioactive metallic element chosen palladium, tantalum, niobium, stainless steel, chromium, titanium and zirconium, under the deposit of the radioactive platinoid(s).

10. Process according to any one of claims 1 to 9, in which the electrolysis cell is an electrolysis cell with separate compartments, preferably by a cation exchange membrane.

11. Process according to claim 10, in which the electrolysis cell is a proton exchange membrane electrolysis cell.

12. Method according to any one of claims 1 to 11, in which the electrolysis of the alcohol is carried out in an alkaline medium.

13. Method according to any one of claims 1 to 12, in which the alcohol is a biobased alcohol.

14. Process according to claim 13, in which the biobased alcohol is ethanol or glycerol.