Insights into the Electrochemical Reduction of 5‐Hydroxymethylfurfural at High Current Densities

Abstract

The electrocatalytic reduction of 5-hydroxymethylfurfural (HMF) is highly selective to 2,5-bishydroxymethylfuran (BHMF) at pH = 9.2, diluted HMF solutions, and low current densities. In this work, the electrochemical reduction of 0.05 m HMF solutions was investigated in the 5-50 mA cm À 2 current density range over an AgCu foam electrocatalyst. The selectivity towards the formation of BHMF or the dimerization depended on the current density, likely due to differences in the electrode potential, and on the reaction time. Operating at current densities of 40-50 mA cm À 2 allowed to find a trade-off between HMF and H 2 O activation, achieving 85 % BHMF selectivity and fostering the productivity (0.567 mmol cm À 2 h À 1 ), though coproducing H 2 . The electrochemical characterization by Tafel slopes and electrochemical impedance spectroscopy indicated that the HMF reduction was kinetically favored in comparison to the hydrogen evolution reaction and that the process was limited by charge transfer.

Electrocatalytic Refinery of Biomass-Based 5-Hydroxymethylfurfural to Fine Chemicals

“…Sanghez de Luna et al reportedly applied high current density on highly active Cu foam-based Ag/Cu GD 55 in a concentrated HMF solution (50 mM). 77 It was found that conduction at a current density 40 to 50 mA cm −2 allowed a "trade-off" between HMF hydrogenation and the HER and exhibited 85% DHMF selectivity and significant production of 0.567 mmol cm −2 . In this reaction to obtain high DHMF production, the applied potential for current density needs to be in the HER window, in which HMF reduction is favored over H 2 production on Ag/Cu GD, and there is sufficient H* on the electrode to prevent HMF dimerization and to ensure HMF hydrogenation is more competitive.…”

“…Current density changes the mechanism and product selectivity because of product distribution caused via the concentration overpotential. Sanghez de Luna et al reportedly applied high current density on highly active Cu foam-based Ag/Cu GD in a concentrated HMF solution (50 mM) . It was found that conduction at a current density 40 to 50 mA cm –2 allowed a “trade-off” between HMF hydrogenation and the HER and exhibited 85% DHMF selectivity and significant production of 0.567 mmol cm –2 .…”

Electroreductive upgradation of biomass into high-value chemicals and energy-intensive biofuels

“…For the construction of double sites, the combination of a precious metal (Ag or Ru) with Cu is found to be a suitable candidate for the hydrogenation of HMF. [83][84][85] In the macro aspect, the introduction of Cu directly leads to the dispersion of noble metal sites and the improvement of the electrocatalytic activity. In the micro aspect, the electron transfer from the catalyst to HMF increases, resulting in the decrease in energy barrier and Gibbs free energy of the HMF hydrogenation reaction relative to the direct utilization of Ag, as certified by density functional theory (DFT) calculations.…”

Recent progress of Cu-based electrocatalysts for upgrading biomass-derived furanic compounds

“…Very recently, this 3D nanostructured Ag/Cu ED was further utilized in operation at high current densities (40-50 mA cm −2 ), which enabled a trade-off between the activation of HMF and H 2 O with remarkable selectivity (85%) and productivity (0.567 mmol cm −2 h −1 ). 85 The smaller size of AgCu nanoalloys (Ag 1 Cu 1 /PA, Ag 3 Cu 1 / PA, and Ag 1 Cu 3 /PA) loading on pyrolyzed sodium alginate (PA) enabled the faster kinetic of ECH. 86 With an average size of 7.4 nm, Ag 1 Cu 1 /PA performed the optimal selectivity of 94% for BHMF, with a favorable ECH over HER in a 0.05 M borate buffer solution over a wide potential ranging from −0.26 to −1.12 V vs. RHE.…”

“…Very recently, this 3D nanostructured Ag/Cu ED was further utilized in operation at high current densities (40–50 mA cm −2 ), which enabled a trade-off between the activation of HMF and H 2 O with remarkable selectivity (85%) and productivity (0.567 mmol cm −2 h −1 ). 85…”