ABSTRACT
In the past decade, organic electrosynthesis has emerged as an atom- and energy-efficient strategy for harvesting renewable electricity that provides exceptional control over the reaction parameters. A profound and fundamental understanding of electrochemical interfaces becomes imperative to advance the knowledge-based development of electrochemical processes. The major strategy toward an efficient electrochemical system is based on the advancement in material science for electrocatalysis. Studies on the complex interplay among electrode surface, electrolyte, and transformation intermediates have only recently started to emerge. It involves acquiring atomic-scale insights into the electrochemical double layer, for which the identity and concentration of composing ions play a crucial role. In this study, we present how the identity and concentration of alkali cations impact the selectivity of aldehyde functionality electroreduction. As a case-study transformation, we set the electrochemical conversion of 5-hydroxymethylfurfural (HMF), a promising biomass-derived feedstock for the sustainable production of polymer or fuel precursors. Our findings reveal a consistent trend of the selectivity shift towards 2,5-bis(hydroxymethyl)furan (BHMF) as a function of cation size and concentration, rationalized by specific cation adsorption at the glassy carbon (GC), followed by the increase in the electrode surface charge density.
ABSTRACT
The electrochemical conversion of biomass-based compounds to fuels and fuel precursors can aid the defossilization of the transportation sector. Herein, the electrohydrodimerization of 5-hydroxymethylfurfural (HMF) to the fuel precursor 5,5'-bis(hydroxymethyl)hydrofuroin (BHH) was investigated on different carbon electrodes. Compared to boron-doped diamond (BDD) electrodes, on glassy carbon (GC) electrodes a less negative HMF reduction onset potential and a switch in product selectivity from BHH to the electrocatalytic hydrogenation product 2,5-di(hydroxymethyl)furan (DHMF) with increasing overpotential was found. On BDD, the electrohydrodimerization was the dominant process independent of the applied potential. An increase in the initial HMF concentration led to suppression of the competing hydrogen evolution reaction and DHMF formation, resulting in higher BHH faradaic efficiencies. In contrast, BHH selectivity decreased with higher initial HMF concentration, which was attributed to increased electrochemically induced HMF degradation. Finally, it was demonstrated that even a simple graphite foil can function as an active HMF electroreduction catalyst.
ABSTRACT
RATIONALE: The development of an interface to analyze liquid sample streams with direct analysis in real time mass spectrometry (DART-MS) is of great interest for coupling various analytical techniques, using non-volatile salts, with MS. Therefore, we devised an enclosed ionization interface and a sample introduction system for the versatile analysis of liquid samples with DART-MS. METHODS: The sample introduction system consists of a nebulizer, a spray chamber and a transfer line, while the confined ionization interface is created by implementing a cross-shaped housing between ion source outlet and mass spectrometer inlet. Methodical studies of the effects of various setup parameters on signal intensity and peak shape were conducted, while its diverse applicability was demonstrated by coupling with high-performance liquid chromatography (HPLC) for the analysis of alcohols, organic acids and furanic compounds. RESULTS: The confinement of the ionization interface results in a robust setup design with a well-defined ionization region for focusing of the sprayed sample mist. Thereby, an increase in analyte signal intensity by three orders of magnitude and improved signal stability and reproducibility were obtained in comparison with a similar open ionization interface configuration. Additionally, the successful quantification of alcohols could be demonstrated as well as the compatibility of the setup with HPLC gradient elution. CONCLUSIONS: A versatile setup design for the analysis of liquid sample streams with DART-MS was devised for monitoring reactions or hyphenating analytics with MS. The design minimizes interferences from the laboratory surroundings as well as allows for safe handling of hazardous and toxic chemicals, which renders it suitable for a broad range of applications.
