Green Chemistry of the Future: Co-Electrosynthesis of Biobased Platform Chemicals and Hydrogen

Abstract

The European Green Deal sends a strong signal for a climate-friendly and CO2-neutral economy. An important aspect to support this is a sustainable and reduced use of resources as well as efficient and green conversion technologies for renewable value-added products. For this reason, electrosynthetic approaches become increasingly important, as electrochemistry fulfils several criteria of green chemistry and offers the possibility to directly use current from renewable energy sources [3]. However, electrolysis and electrosynthesis currently often require the use of platinum group metals (PGM) and need separators, which are mostly based on perfluorinated and polyfluorinated alkyl substances (PFSA). Classical water electrolysis for production of green hydrogen also requires high overvoltage’s, which is due to the oxygen evolution reaction (OER). This is where coupling systems come in, in which the sluggish OER is replaced by a thermodynamically more efficient reaction, such as the electrooxidation of organic substances (EOO). An example of this is the electrooxidation of biobased 5-HMF or various sugars (xylose, glucose) to platform chemicals. When coupled with the hydrogen evolution reaction (HER), the EOO of 5-HMF to 2,5-furandicarboxylicacid (FDCA) requires a theoretical cell voltage of 0.3 V. In contrast, theoretical cell voltages of 1.23 V are required for the OER/HER [5]. With the focus on sustainable and energy-efficient systems, the simultaneous production of platform chemicals and green H2 via paired electrolysis offers high potential. [1-7]Previous studies have mainly focused on electrode materials, morphology and its electrocatalytic activity in divided batch cells. A strongly alkaline environment is considered advantageous for the electro-organic oxidation reaction, while the HER is reported to be kinetically slower in alkaline than in acidic conditions. Overall, the coupled electrolysis of H2 and platform chemicals is described as a promising technology in the development stage. [5-7]In this context, the present research explores paired electrosynthesis of platform chemicals and H2 to advance sustainable and efficient energy sources. A central goal is the prototype development of an undivided flow reactor in TRL4. Particular attention will be paid to mild operating conditions (such as a mild-alkaline environment, low operating pressures and low temperatures), PGM-free catalysts and the elimination of PFSA materials. To achieve this goal, various milestones have been defined. Among them is the development of 3D electrodes with suitable and selective catalysts. These are to be electrochemically tested in a flow-through test cell on a laboratory scale. In order to create a basis for analysis, the electrode reactions were first investigated electrochemically in a typical divided H-cell and reference measurements were carried out on nickel-based materials. In this work, NiOOH sheet and foam electrodes were electrochemically produced and subsequently investigated by cyclic voltammetry (CV) followed by bulk electrolysis. On this basis, suitable analytics (HPLC, UV-VIS) were also determined to quantify and classify the derivatives of the electrosynthesis process. These pre-experiments form the basis for the ongoing development of initial concept ideas for a modular test cell that allows various materials and structures to be electrochemically investigated.Overall, this research contributes to advancing sustainable and efficient energy sources and enabling the production of platform chemicals from renewable raw materials. Acknowledgments The authors thank the European Union’s Horizon Europe research and innovation programme under grant agreement N° 101070856 ELOBIO (Electrolysis of Biomass) for funding.