The electrochemical oxidation of the biorefinery product 5-(hydroxymethyl)furfural (HMF) to 2,5-furandicarboxylic acid (FDCA), an important platform chemical for the polymer industry, is receiving increasing interest. FDCA-based polymers such as polyethylene 2,5-furandicarboxylate (PEF) are sustainable candidates for replacing polyethylene terephthalate (PET). Herein, we report the highly efficient electrocatalytic oxidation of HMF to FDCA, using Ni foam modified with high-surface-area nickel boride (Ni B) as the electrode. Constant potential electrolysis in combination with HPLC revealed a high faradaic efficiency of close to 100 % towards the production of FDCA with a yield of 98.5 %. Operando electrochemistry coupled to ATR-IR spectroscopy indicated that HMF is oxidized preferentially via 5-hydroxymethyl-2-furancarboxylic acid rather than via 2,5-diformylfuran, which is in agreement with HPLC results. This study not only reports a low-cost active electrocatalyst material for the electrochemical oxidation of HMF to FDCA, but additionally provides insight into the reaction pathway.

No abstract

Die elektrochemischeO xidation des Bioraffinerieproduktes 5-(Hydroxymethyl)furfural (HMF) zu der fürd ie Polymerindustrie interessanten Plattformchemikalie 2,5-Furandicarbonsäure (FDCA) gewinnt immer mehr Aufmerksamkeit. FDCA-basierter Polymere,w ie z. B. Polyethylenfuranoat (PEF), besitzen das Potential, großtechnisch verwendete und auf Erdçl basierende Polymere wie z. B. Polyethylenterephthalat (PET) nachhaltig zu ersetzen. Wir berichten über die hocheffiziente elektrokatalytische Oxidation von HMF zu FDCA an mit Nickelborid beschichtetem Nickelschaum. Die Elektrolyse von HMF bei konstantem Potential gekoppelt mit Hochleistungsflüssigkeitschromatographie (HPLC) zeigt einen hohen FaradayschenW irkungsgrad von nahezu 100 %b ezüglichF DCA als Oxidationsprodukt mit einer Ausbeute von 98.5 %. Operando-ATR-IR gekoppelt mit Elektrochemie belegt, dass HMF bevorzugt über das Intermediat 5-Hydroxymethyl-2-furancarbonsäure (HMFCA) anstatt 2,5-Diformylfuran (DFF) oxidiert wird.D iese Ergebnisse stimmen mit denen der HPLC-Analyse überein. Die vorgestellte Studie berichtet nichtn ur über Nickelborid als einen kostengünstigen Elektrokatalysator fürd ie Oxidation von HMF zu FDCA, sondern gibt auch neue Einblicke in den Reaktionspfad.

A spectroelectrochemical cell is presented that allows investigations of electrochemical reactions by means of attenuated total reflection infrared (ATR-IR) spectroscopy. The electrode holder for the working (WE), counter and reference electrode as mounted in the IR spectrometer cause the formation of a thin electrolyte layer between the internal reflection element (IRE) and the surface of the WE. The thickness of this thin electrolyte layer (d) was estimated by performing a scanning electrochemical microscopy-(SECM) like approach of a Pt microelectrode (ME), which was leveled with the WE toward the IRE surface. The precise lowering of the ME/WE plane toward the IRE was enabled by a micrometer screw. The approach curve was recorded in negative feedback mode of SECM and revealed the contact point of the ME and WE on the IRE, which was used as reference point to perform the electro-oxidation of ethanol over a drop-casted Pd/NCNT catalyst on the WE at different thin-layer thicknesses by cyclic voltammetry. The reaction products were detected in the liquid electrolyte by IR spectroscopy, and the effect of variations in d on the current densities and IR spectra were analyzed and discussed. The obtained data identify d as an important variable in thin-layer experiments with electrochemical reactions and FTIR readout.

transformations might be both thermally or light induced, however, the colloidal deposition synthesis of the Au/TiO 2 catalysts is clearly ruled out as cause for the formation of the reduced phase.