Stève Baranton

Biomass-assisted water electrolysis is a technology that attracts more and more attention because it relies on a non-thermal conversion process and biomass is the most abundant contemporary source of carbon, and therefore the best renewable CO₂-neutral substitute to fossil resources. Amongst molecules issued from biomass, glucose represents the most abundant one [1]. Moreover, the free energy of glucose electrooxidation into CO₂ (eq. 1) leads to a electrochemical potential under standard conditions at 25 °C of -0.012 V vs SHE (standard hydrogen electrode), a significantly lower value than that of the standard water oxidation potential (+1.23 V vs SHE) [2]. This allows expecting low cell voltages for hydrogen production and makes the electro-oxidation of glucose at the anode with simultaneous generation of hydrogen at the cathode in electrosynthesis reactors a promising and efficient process for the co-production of hydrogen and bio-sourced value-added chemicals. C₆H₁₂O₆ + 6 H₂O g 6 CO₂ + 24 H⁺ + 24 e^- E° = -0.012 V vs SHE (1) Although thermodynamically favorable, the electrooxidation reaction of glucose is kinetically slow (complex multielectronic reaction). Ultrasounds (US) have already been used to improve the kinetics of electrochemical reactions [2,3]. In the present contribution, we aim at investigating the electrooxidation of 0.1 M of glucose (and possibly derivatives) in 0.1 mol L⁻¹ NaOH on polycrystalline Pt and Ni surfaces under silent and ultrasonic conditions. The effect of US ranging from low to high frequency domains will be investigated. Linear sweep voltammograms and chronoamperograms (CA) will be recorded to compare activity (onset potential and current densities) and stability of the system. High-performance liquid chromatography will be used to analyze reaction products accumulated in the CA experiments and to determine the influence of US on selectivity. References. T. Rafaïdeen, S. Baranton, C. Coutanceau. Electrooxidation of glucose/xylose mixtures on PdAu based nanocatalysts. ChemElectroChem 9 (2022) e202101575. https://doi.org/10.1002/celc.202101575 N. Neha, Md H. Islam, S Baranton, C. Coutanceau, B. Pollet, Assessment of the beneficial combination of electrochemical and ultrasonic activation of compounds originating from biomass. Ultrasonics - Sonochemistry 63 (2020) 104934. F. Foroughi, M. Tintor, Al. Y. Faid, S. Sunde, G. Jerkiewicz, C. Coutanceau, B. G. Pollet. In-situ Sonoactivation of Polycrystalline Ni for the Hydrogen Evolution Reaction (HER) in Alkaline Media. ACS Appl. En. Mat. 6 (2023) 520−4529. https://doi.org/10.1021/acsaem.2c02443 . Acknowledgements. This work is part of the EU-ELOBIO project. The project ELOBIO received funding from the European Union’s Horizon Europe EIC-2021- PATHFINDERCHALLENGES-01-04, under grant agreement Nº 101070856.

Water electrolysis is a promising technology that can use renewable energies (solar and wind) to produce green hydrogen [1]. In particular, Anion Exchange Membrane Water Electrolysis (AEMWE) offers the combined advantages of the mature Alkaline Water Electrolysis technology and the high efficiency and high dynamic range of the Proton Exchange Membrane Water Electrolysis [2]. This combination of advantages allows the AEMWE technology to be operated with non-PGM electrodes [3], non-perfluorinated membrane with a high dynamic range favoring its use with intermittent renewable energy for the production of green hydrogen. The development of AEMWE requires production of efficient catalytic materials at industrial scale and integration in membrane electrode assemblies (MEAs). In this work, we have developed three families of non-noble catalysts: nickel based materials, iron free catalysts [4, 5] and high entropy materials. They are designed for both anode and cathode of AEM electrolyzers. High performances cathodes are developed with low PGM loading alloy catalysts. These materials (cathode and anode) are produced with highly scalable synthesis methods involving water as solvent and the reactants used are low-cost, widely available chemical compounds. The catalysts obtained are high surface area (up to 100 m²/g) nanostructured materials, ensuring a high catalytic activity for AEMWE electrodes. The development of different catalyst families allows the optimization of electrodes in a wide range of operating conditions (temperature, nature of the membrane and hydroxide concentration in the circulating electrolyte) Catalyst application is critical for preparing efficient MEA’s. The catalyst coating has been performed in two configurations: catalyst coated substrate (CCS) and catalyst coated membrane (CCM). In both configurations, the ink formulation is optimized to improve the catalyst dispersion and the catalyst/polymer coating on the substrate or membrane. The best coating conditions have been determined for both anodes and cathodes to prepare electrodes that improve the catalyst performances. This phase is crucial to avoid negative interactions between the different components of the electrode [6] and create a good interface with the membrane. The resulting MEAs were tested in our electrolyzer with different configurations (5 and 50 cm²) for performance and durability in a temperature range from 60°C to 80°C. Depending on the operating conditions and the catalyst families chosen, the performance exceeded 3 A/cm² with a cell voltage below 2 V (Figure 1). [1] M. Chatenet, B. G. Pollet, D. R. Dekel, F. Dionigi, J. Deseure, P. Millet, R. D. Braatz, M. Z. Bazant, M. Eikerling, I. Staffell, P. Balcombe, Y. Shao-Horn, H. Schäfer, Water electrolysis: from textbook knowledge to the latest scientific strategies and industrial developments, Chem. Soc. Rev., 2022, 51, 4583–4762 [2] H. A. Miller, K. Bouzek, J. Hnat, S. Loos, C. I. Bernäcker, T. Weißgärber, L. Rontzsch, J. Meier-Haack, Green hydrogen from anion exchange membrane water electrolysis: a review of recent developments in critical materials and operating conditions, Sustainable Energy Fuels, 2020, 4, 2114–2133 [3] E. Cossar, F. Murphy, E. A. Baranova, Nickel-based anodes in anion exchange membrane water electrolysis: a review, J. Chem. Technol. Biotechnol., 2022, 97, 1611–1624 [4] A. F. Staerz, M. van Leeuwen, T. Priamushko, T. Saatkamp, B. Endrődi, N. Plankensteiner, M. Jobbagy, S. Pahlavan, M. J. W. Blom, C. Janáky, S. Cherevko, P. M. Vereecken, Effects of Iron Species on Low Temperature CO2 Electrolyzers, Angew. Chem. Int. Ed., 2024, 63, e202306503 [5] G. A. Lindquist, Q. Xu, S. Z. Oener, S. W. Boettcher, Membrane Electrolyzers for Impure-Water Splitting, Joule 2020, 4, 2549–2561 [6] E. Cossar, F. Murphy, J. Walia, A. Weck, E. A. Baranova, Role of Ionomers in Anion Exchange Membrane Water Electrolysis: Is Aemion the Answer for Nickel-Based Anodes?, ACS Appl. Energy Mater. 2022, 5, 9938−9951 Figure 1

Since ages, fossil fuel resources are being used to produce raw materials for daily life purposes. There is a need for vital substitute as with time, demand is increasing due to a significant rise in population and prices are hiking due to less accessibility of the reservoirs. Lignocellulosic biomass (composed of lignin, cellulose, and hemicellulose) estimated production is 146 billion metric tons a year. It can therefore represent the best alternative carbon resource to produce energy and fine chemicals for industry. In this context monosaccharides (glucose and methylglucoside) and disaccharides (cellobiose and trehalose), which are the most important carbon resources and are potentially electrochemically active, need to be studied deeply. Electro-reforming of these saccharides can provide hydrogen together with supplementary valuable industrial compounds. For this purpose, Pt/C and Pt₉Bi₁/C were synthesized and characterized using various techniques like TEM, TGA, AAS, and XRD. Linear scan voltammetry for the oxidation of saccharides (glucose and cellobiose bearing a reductive anomeric function and methylglucoside and trehalose with protected anomeric function) was first studied in a classical three-electrode cell to estimate the activity followed by in-situ FTIR to determine reaction intermediates and species formed as a function of the electrode potential. Pt₉Bi₁/C has been observed to be the most active and selective catalyst so far was used as anode and Pt/C as the cathode to perform electro-reforming of the mentioned saccharides in a two-electrode electrolysis cell to produce high-value added compounds at the anode with simultaneous production of hydrogen at the cathode. Reaction products were analyzed by HPLC, MS and ¹³C NMR to confirm the nature of species formed. The faradaic yield, the selectivity and the reaction rate and the energy consumption (cost) are determined with respect to the experimental conditions used. Besides the impact of temperature and concentrations, the effect of ultrasonic irradiations on electro-oxidation of glucose and methylglucoside on a Pt electrode was also studied. An increase in current density was observed in the presence of ultrasonic irradiations due to the formation of OH radicals and mass transfer kinetics enhancement.

The increasing demand of energy and high value-added compounds, and the extinction of fossil resource reservoirs result in replacing fossil resources with biomass. Cellulose and hemicellulose represent 40 to 60 wt% of agriculture green wastes and can be considered as raw materials. After transformation of these biopolymers into saccharides, the latter can serve as platform molecules to produce chemicals with high value added and/or industrial interest. In that context carbohydrates need to be studied more deeply for obtaining every possible outcome. Focusing on environmental problems, electro-reforming can provide hydrogen together with a supplementary valuable industrial compound, but this last process must show very high selectivity and low cost to compete with classical biotechnological methods for sugar conversion. monosaccharides, disaccharides and oligosaccharides are complex molecules bearing several oxygenated functions (primary alcohol, secondary alcohol, anomeric group) that are potentially electrochemically reactive. Therefore, it is needed to develop catalysts displaying very high activity at low potentials and very high selectivity towards a given compound. For this purpose, the synthesis and characterization of Pt-based binary catalysts will be presented and their electrocatalytic behavior towards the oxidation of saccharides (glucose and cellobiose bearing a reductive anomeric function, and methylglucoside and trehalose with a protected anomeric function) will be first studied by linear scan voltammetry in a classical three-electrode cell to evaluate their activity and by in situ infrared spectroscopy to determine reaction intermediates and products as a function of the electrode potential. Best candidates will be used as anode catalysts to perform the electroreforming of saccharides in a two-electrode electrolysis cell with simultaneous production of hydrogen at the cathode. Reaction products will be analyzed by HPLC, MS, and ¹H and ¹³C NMR to determine the selectivity and the efficiency of the system. From the electrochemical and analytical results, the high efficiency of the Pt₉Bi₁/C catalysts will be emphasized, the electro-reactivity of the different functions determined, and reaction mechanisms discussed.

PtCuBi selective electrooxidation of glycerol to value-added chemicals.

The continuous rise of global warming and depletion of fossil fuel resources has led to the development of new ways of valorization of non petro-sourced chemicals. In this objective, it is important to develop electrochemical valorization processes of CO₂, a greenhouse gas, for the synthesis of valuable molecules. When the CO₂ electroreduction is performed in aqueous media, the competitive HER will decrease the energetic efficiency and the rapid deactivation of reaction intermediates will lead to side products such as CO, formic acid, oxalic acid and small chain hydrocarbons [1]. To circumvent these issues and create value added chemicals, reductive electro-carboxylation reactions can be performed in polar aprotic solvents (DMF, DMSO, acetonitrile or NMP) in the presence of tetraalkylammonim bromide or chloride as electrolytes [2]. In this work, we focused on non-aqueous bio-sourced solvent, the γ-valerolactone (GVL), to perform a carboxylation reaction of bio-sourced molecules like furfural by electroreduction of CO₂. The reductive electro-carboxylation of furfural was studied at a Pt/C electrode was studied in a bio-sourced GVL with tributylmethylammonium chloride (TBMACl) as electrolyte. The solvent behavior in the CO₂ reduction potential range was studied by in situ FTIRS measurements which indicated that GVL reacted at the electrode in the absence of furfural and/or of CO₂, while the presence of furfural and/or of CO₂ made the solvent much less reactive. The electrochemical study showed that the CO₂ electroreduction started at from the high cathodic potential of −0.8 V vs SCE (saturated calomel electrode) and the coupling of electrochemistry with in situ FTIRS demonstrated that it reacted with furfural. The reductive electro-carboxylation was then performed in an electrolysis cell. The cell voltage was maintained at 2.0 V (corresponding to a cathode potential of -1.9 V vs. SCE) for 24 h. In absence of furfural, gas chromatography coupled with mass spectroscopy (GC–MS) analyses revealed the formation of oxalic acid (coupling reaction of CO₂) as main reaction product. In the presence of furfural in the reaction medium, a new carboxylated specie, 2-furyl(hydroxy)acetic acid, was identified as the main reaction product. ¹H NMR and LC-MS analyses further confirmed the formation of this compound, demonstrating the potentialities of bio-sourced solvents for reduction electro-carboxylation of a bio-sourced molecule by reduction of CO₂[3]. [1] Y. Hori, Electrochemical CO₂ reduction on metal electrodes, in: C. Vayenas, R. White, M. Gamboa-Aldeco (Eds.), Modern Aspects of Electrochemistry, 42, Springer, NewYork 2008, pp. 89–189 [2] R. Matthesses, J. Fransaer, K. Binnemans, D.E. De Vos, Electrocarboxylation: towards sustainable and efficient synthesis of valuable carboxylic acids, Beilstein J. Org.Chem. 10 (2004) 2484–2500. [3] Florent Boissou, S. Baranton, M. Tarighi, K. De Oliveira Vigier, C. Coutanceau, The potency of γ-valerolactone as bio-sourced polar aprotic organic medium for the electrocarboxlation of furfural by CO₂. J. Electroanal. Chem. 848 (2019) 113257

Keywords: electrocatalytic oxidation, glucose, methylglucoside, cellobiose, trehalose, electrolysis, platinum, bismuth, selectivity Different catalysts (Pt/C, Pt₉Bi₁/C, Pt₉Sn₁/C, Pt₇Ni₃/C, Pt₇Sn₃/C and Pd₃Au₇/C) have been synthesized by a “water in oil” micro-emulsion method with nominal metal loading of 40 wt% and further characterised by physicochemical methods: thermogravimetric analysis, transmission electron microscopy, X-Ray diffraction, etc., to assess the metal loading, composition and size of nanoparticles. Linear scan voltammograms (Fig.1) have been performed to study the electrocatalytic behaviour of the catalysts towards electro-oxidation of glucose, methylglucoside, cellobiose and trehalose in 0.1 M NaOH as background electrolyte at 0.05 V s^-1 scan rate. Pt₉Bi₁/C, most active one, leads to the lowest onset potentials of ca. 0.050 V, 0.100 V, 0.050 V and 0.200 V vs RHE for glucose, methylglucoside, cellobiose and trehalose oxidation respectively. To further gain an insight about the mechanism and species formed, in situ Fourier transform infrared spectroscopy has been used which demonstrated that in the case of glucose and methylglucoside oxidation, different reaction products were formed, i.e. gluconate and methyglucuronate, respectively¹. In the case of cellobiose, a reducing disaccharide, transformation of C1 anomeric function to carboxylic acid occurred, while in the case of trehalose, a non-reducing disaccharide, mono and dicarboxylic acids were formed from C6 oxidation. Chronoamperometry measurements were carried out for 6 hours in a 25 cm² electrolysis cell with Pt₉Bi₁/C as anode catalyst for the electro-oxidation of 0.1 M glucose, methylglucoside, cellobiose and trehalose and Pt/C as cathode catalyst with simultaneous production of hydrogen at different potentials. The reaction products formed every hour for 6 hours were neutralized, identified and quantified by HPLC, MS and ¹H and ¹³C NMR. At low cell voltages, high selectivity and significant conversion yields to monocarboxylic acids of these saccharides were obtained. Acknowledgements: the authors gratefully acknowledge the INCREASE Federation (FR CNRS 3707), the technogreen chair, the European communities (FEDER) through the ECONAT project, the “Région Nouvelle Aquitaine” and the PEPS CNRS Energie for financial supports. N. Neha, S. R. B. Kouamé, T. Rafaïdeen, S. Baranton, C. Coutanceau. Remarkably Efficient Carbon-Supported Nanostructured Platinum-Bismuth Catalysts for the Selective Electrooxidation of Glucose and Methyl-glucoside, Electrocatalysis (2020) DOI : 10.1007/s12678-020-00586-y. Figure 1

The effects of cell voltage and of concentration of sugars (glucose and xylose) on the performances of their electro-reforming have been evaluated at a Pd₃Au₇/C anode in 0.10 mol L⁻¹ NaOH solution. The catalyst synthesized by a wet chemistry route is first comprehensively characterized by physicochemical and electrochemical techniques. The supported catalyst consists in alloyed Pd₃Au₇ nanoparticles of circa 6 nm mean diameter deposited on a Vulcan XC72 carbon support, with a metal loading close to 40 wt%. Six-hour chronoamperometry measurements are performed at 293 K in a 25 cm² electrolysis cell for the electro-conversion of 0.10 mol L⁻¹ and 0.50 mol L⁻¹ glucose and xylose at cell voltages of +0.4 V, +0.6 V and +0.8 V. Reaction products are analyzed every hour by high performance liquid chromatography. The main products are gluconate and xylonate for glucose and xylose electro-reforming, respectively, but the faradaic yield, the selectivity and the formation rate of gluconate/xylonate decrease with the increase of aldose concentration, whereas lower faradaic yields and higher formation rates of gluconate/xylonate are observed at +0.8 V than at +0.4 V (higher chemical yields).