Electrochemical oxidation and reduction of 5-hydroxymethylfurfural in alkaline water electrolyzers

The progressive climate change caused by humans and the insufficient counteractions taken in recent years are reasons for an urgent energy transition. However, this will not succeed solely through expanding renewable energy sources such as wind turbines, solar parks, and water turbines. Electrolyzers, which can store electricity from renewable energy in molecules such as hydrogen, but also have the potential to use renewable energy to replace petrochemical-based large-scale processes for synthesizing various chemicals, will play a central role. In particular, sustainable biomass molecules such as 5-Hydroxymethylfurfural (HMF) can drastically reduce the overall cell potential. Thus, the energy consumption of electrolyzers, while providing valuable products, expands the potential of electrolyzers for the future. For this reason, in addition to scale-up problems in electrochemical cells, this work deals with the electrochemical conversion of HMF in anion exchange membrane water electrolyzers. Specifically, the oxidation of HMF is catalyzed by nickel-based layered double hydroxides. Here, the NiFe(-Cl-)-LDH@NF catalyst showed 100% HMF conversion and 100% selectivity towards the desired product 2,5-Furandicarboxylic acid (FDCA), with high stability. Furthermore, it was shown that, in addition to the hydrogenation of HMF, hydrogenolysis is also possible under strongly alkaline conditions. The copper oxide-based mixed metal oxide catalysts are partially reduced to high-active metal oxide-derived catalysts under the investigated reaction conditions. In particular, CuO/Fe2O3/CF showed high selectivity towards the 5-Methylfurfurylalcohol (MFA) hydrogenolysis product. Moreover, it was possible to establish a correlation between the HMF reduction product selectivities and the hydrogen evolution reaction rate. Finally, not only the HMF oxidation reaction (HMFOR) and reduction reaction (HMFRR) could be combined in one electrolysis cell, but also the HMFOR and CO2 reduction reaction could be combined. In establishing HMFOR in a CO2 electrolyzer, it was possible to develop the HMF system further, using a bipolar membrane, into a continuous system operating at high current densities. Thus, this work provides fundamental insights into the materials science and electrocatalysis of HMFOR and HMFRR, as well as the implementation of these processes as anode and cathode of membrane electrolyzer devices, combined with conventional counter reactions, such as the OER and HER, as well as in combination with a less conventional counter reaction such as the CO2RR. Together the results of this dissertation build a bridge between laboratory and industrial approaches for the electrochemical conversion of HMF and, therefore, of biomass in principle.

Author dc:creator

• Hauke, Philipp Marcel

Advisor dc:contributor.advisor

• Strasser, Peter

Licence dc:rights.uri

• http://rightsstatements.org/vocab/InC/1.0/

Language dc:language.iso

en

Identifier URI

https://doi.org/10.14279/depositonce-18699

OAI identifier oai:identifier

oai:depositonce.tu-berlin.de:11303/19901