Hydrogen (H₂) is a platform molecule for several industrial processes; the Haber-Bosch process for the production of ammonia (nitrogen fertilizers), energy carrier (H₂/O₂ fuel cells), fuel desulphurization, glass, and electronics among others. Currently, its production is mainly based on the thermal decomposition of fossil fuels, leading de facto to CO or CO₂ emissions and excessive energy consumption. Several subsequent steps are also necessary to purify H₂ from traces of CO (poison for electrocatalysts). Water electrolysis that is an elegant carbon-free pathway to produce H₂ is facing major challenges due to the use of precious and/or rare metals (Pt, Ru, Ir) and high energy consumption. The relation between the consumed electrical energy W(in kWh/kg_H2) and the cell voltage U(in V) is W = 26.59×U. Since most overpotential comes from the positive electrode, one can imagine substituting the oxidation of water (OER) by that of organic compounds such as glycerol (GlyOR) or glucose (GlcOR) to lower the cell voltage and thus improve the efficiency of electrolysis, as it can be seen in Figure 1, panel 1c. Also, the selective oxidation of certain biomass derivatives would lead to chemical products of interest, thus leading to a cogeneration process that can decrease again the overall cost [1]. Furthermore, for a long time, the development of electrocatalysts has been based on colloidal chemistry in solution before immobilization on the electrodes, which leads to durability issues. We have therefore initiated synthesis methods to grow metal particles directly onto 3D electrodes [2]. Herein, we are presenting strategy that enable to design and fabricate electrocatalytic interfaces by growing metallic nanostructures directly onto Gas Diffusion Layer (GDL) electrodes (panels 1a and 1b) that can be used directly in electrolysis reactors coupling inorganic (H₂) and organic electrosynthesis to significantly reduce the overall cost. Indeed, the principle of a reversible electrochemical converter capable of operating in battery mode (energy) and electrolyzer mode (H₂) is kinetically impossible for water (2H₂ + O₂ = 2H₂O): lesser than 1 V can be extracted in fuel cell mode while larger value of at least 1.5 V is required to split water. For biomass-based organics, it is theoretically feasible (see panel 1c), based on a model equivalent to that of enzymes [3]. We present here the study of an advanced dual electrosynthesis system operating at a significantly reduced external energy input. Specifically, we performed selective oxidation of glucose at GDL@AuNPs by the anomeric carbon in C1-position without any function protection to yield gluconate as added-value chemical.

Acknowledgments

The authors gratefully acknowledge financial support from the CNRS Energy unit (Cellule Energie) through the project “PEPS19-ELECTROFUEL”, the French National Agency (ANR) through the LabEx CheMISyst (ANR-10-LABX-05-01), and the European Institute of Membranes of Montpellier through the Exploratory Project COGENFC (PAT-Axis-Energy-2018).

References

1. Holade Y. et al., J. Electrochem. Soc. 165, H425-H436 (2018).
2. Holade Y. et al., J. Mater. Chem. A 4, 17154-17162 (2016).
3. Suraniti E. et al., Nat. Commun. 9, Article number: 3229 (2018)