ABSTRACT
5-Hydroxymethylfurfural (HMF), which can be derived from lignocellulosic biomass, is an important platform molecule that can be used to produce valuable biofuels and polymeric materials. Electrochemical reduction of HMF is of great interest as it uses water as the hydrogen source and achieves desired reduction reactions at room temperature and ambient pressure. Hydrogenation and hydrogenolysis are two important reactions for reductive HMF conversion. Therefore, elucidating key characteristics of electrocatalysts that govern the selectivity for hydrogenation and hydrogenolysis is critical in rationally developing efficient and selective electrocatalysts. In this study, combined experimental and computational investigations are used to demonstrate how the adsorption energy of HMF on metal surfaces and the resulting changes in the intramolecular bond lengths of adsorbed HMF directly impact the reduction pathways of HMF. These results make it possible to rationally understand a general trend in the behaviors observed when using various metal electrodes for HMF reduction.
ABSTRACT
2,5-Furandicarboxylic acid (FDCA) has become an increasingly desirable platform chemical to replace terephthalic acid in the production of a variety of polymeric materials, including polyethylene terephthalate. FDCA can be produced by the oxidation of 5-hydroxymethylfurfural (HMF), which can be derived from cellulosic biomass. Oxidation of HMF to FDCA is typically performed under basic conditions. Separation of FDCA is most easily accomplished by lowering the pH until FDCA is insoluble and filtering it from solution. In a large-scale process, this would lead to a high operating cost to purchase the required acid and base and to dispose of the resulting salt waste. In this study, electrochemical oxidation of HMF was carried out in acidic media by using a manganese oxide (MnOx ) anode to remove the need to vary the pH to separate FDCA. The MnOx anode afforded a FDCA yield of 53.8 % in a pHâ 1 H2 SO4 solution, in which FDCA precipitation occurred spontaneously from the same reaction solution without altering the pH or other aspects of the solution composition. Electrochemical oxidation in acidic media offers a new pathway to convert HMF into maleic acid, which is another desirable biomass-derived platform molecule. The performance of the MnOx anode was investigated in comparison with that of a Pt anode to identify unique electrocatalytic properties of the MnOx anode for HMF oxidation.
ABSTRACT
This review focuses on introducing and explaining electrodepostion mechanisms and electrodeposition-based synthesis strategies used for the production of catalysts and semiconductor electrodes for use in water-splitting photoelectrochemical cells (PECs). It is composed of three main sections: electrochemical synthesis of hydrogen evolution catalysts, oxygen evolution catalysts, and semiconductor electrodes. The semiconductor section is divided into two parts: photoanodes and photocathodes. Photoanodes include n-type semiconductor electrodes that can perform water oxidation to O2 using photogenerated holes, while photocathodes include p-type semiconductor electrodes that can reduce water to H2 using photoexcited electrons. For each material type, deposition mechanisms were reviewed first followed by a brief discussion on its properties relevant to electrochemical and photoelectrochemical water splitting. Electrodeposition or electrochemical synthesis is an ideal method to produce individual components and integrated systems for PECs due to its various intrinsic advantages. This review will serve as a good resource or guideline for researchers who are currently utilizing electrochemical synthesis as well as for those who are interested in beginning to employ electrochemical synthesis for the construction of more efficient PECs.
