Electrochemical conversion of biomass-derived furanics for production of renewable chemicals and fuels

Replacing fossil-based fuels and chemicals with biobased alternatives can help alleviate our heavy dependence on petroleum sources, reduce the global carbon footprint, and strengthen our energy security. Electrocatalytic conversion of biomass-derived platform molecules is an emerging route for sustainable fuel and chemical production, with the advantages of eliminating harmful reagents, being tunable, and potentially being driven by renewable electricity. However, the widespread application of organic electrocatalysis is hindered by limitations such as low catalytic activity, product selectivity and energy efficiency. The goals of this work were to explore the electrochemical conversion of biobased furanics and develop more efficient electrocatalysts and processes for fuel and chemical production. The electrochemical reduction of furfural was investigated on metal electrodes in acidic aqueous electrolytes. Two mechanisms, namely electrocatalytic hydrogenation and direct electroreduction, were distinguished through a combination of voltammetry, bulk electrolysis, thiol-electrode modifications, and kinetic isotope effect studies. Better understanding of the underlying mechanisms and pathways enabled the manipulation of product selectivity. By rationally tuning applied potential, electrolyte pH, and bulk furfural concentration, the selective and efficient formation of a biofuel additive (i.e. 2-methylfuran) or a precursor for polymer and resin synthesis (i.e. furfuryl alcohol) was achieved. Pairing 5-(hydroxymethyl)furfural (HMF) reduction and oxidation half-reactions in a single electrochemical cell enabled efficient HMF conversion to biobased monomers. Electrocatalytic hydrogenation of HMF to 2,5-bis(hydroxymethyl)furan (BHMF) was achieved under mild conditions using Ag/C as the cathode catalyst. The competition between Ag-catalyzed HMF hydrogenation to BHMF and undesired HMF hydrodimerization and hydrogen evolution reactions was sensitive to cathode potential. Accordingly, precise control of the cathode potential was critical for achieving high BHMF selectivity and efficiency. In contrast, the selectivity of HMF oxidation facilitated by a homogeneous electrocatalyst, 4-acetamido-TEMPO (ACT, TEMPO = 2,2,6,6‐tetramethylpiperidine‐1‐oxyl), together with an inexpensive carbon felt electrode was not dependent on anode potential. Thus, it was feasible to conduct HMF hydrogenation to BHMF and oxidation to 2,5-furandicarboxylic acid (FDCA) in a single cathode-potential-controlled cell, achieving remarkable overall electron efficiency

Electrochemical conversion of biomass-derived furanics for production of renewable chemicals and fuels

Replacing fossil-based fuels and chemicals with biobased alternatives can help alleviate our heavy dependence on petroleum sources, reduce the global carbon footprint, and strengthen our energy security. Electrocatalytic conversion of biomass-derived platform molecules is an emerging route for sustainable fuel and chemical production, with the advantages of eliminating harmful reagents, being tunable, and potentially being driven by renewable electricity. However, the widespread application of organic electrocatalysis is hindered by limitations such as low catalytic activity, product selectivity and energy efficiency. The goals of this work were to explore the electrochemical conversion of biobased furanics and develop more efficient electrocatalysts and processes for fuel and chemical production. The electrochemical reduction of furfural was investigated on metal electrodes in acidic aqueous electrolytes. Two mechanisms, namely electrocatalytic hydrogenation and direct electroreduction, were distinguished through a combination of voltammetry, bulk electrolysis, thiol-electrode modifications, and kinetic isotope effect studies. Better understanding of the underlying mechanisms and pathways enabled the manipulation of product selectivity. By rationally tuning applied potential, electrolyte pH, and bulk furfural concentration, the selective and efficient formation of a biofuel additive (i.e. 2-methylfuran) or a precursor for polymer and resin synthesis (i.e. furfuryl alcohol) was achieved. Pairing 5-(hydroxymethyl)furfural (HMF) reduction and oxidation half-reactions in a single electrochemical cell enabled efficient HMF conversion to biobased monomers. Electrocatalytic hydrogenation of HMF to 2,5-bis(hydroxymethyl)furan (BHMF) was achieved under mild conditions using Ag/C as the cathode catalyst. The competition between Ag-catalyzed HMF hydrogenation to BHMF and undesired HMF hydrodimerization and hydrogen evolution reactions was sensitive to cathode potential. Accordingly, precise control of the cathode potential was critical for achieving high BHMF selectivity and efficiency. In contrast, the selectivity of HMF oxidation facilitated by a homogeneous electrocatalyst, 4-acetamido-TEMPO (ACT, TEMPO = 2,2,6,6‐tetramethylpiperidine‐1‐oxyl), together with an inexpensive carbon felt electrode was not dependent on anode potential. Thus, it was feasible to conduct HMF hydrogenation to BHMF and oxidation to 2,5-furandicarboxylic acid (FDCA) in a single cathode-potential-controlled cell, achieving remarkable overall electron efficiency.</p

Paired electrocatalytic hydrogenation and oxidation of 5-(hydroxymethyl)furfural for efficient production of biomass-derived monomers

Electrochemical conversion of biomass-derived compounds is a promising route for sustainable chemical production. Herein, we report unprecedentedly high efficiency for conversion of 5-(hydroxymethyl)furfural (HMF) to biobased monomers by pairing HMF reduction and oxidation half-reactions in one electrochemical cell. Electrocatalytic hydrogenation of HMF to 2,5-bis(hydroxymethyl)furan (BHMF) was achieved under mild conditions using carbon-supported Ag nanoparticles (Ag/C) as the cathode catalyst. The competition between Ag-catalyzed HMF hydrogenation to BHMF and undesired HMF hydrodimerization and hydrogen evolution reactions was sensitive to cathode potential. Also, the carbon support material in Ag/C was active for HMF reduction at strongly cathodic potentials, leading to additional hydrodimerization and low BHMF selectivity. Accordingly, precise control of the cathode potential was implemented to achieve high BHMF selectivity and efficiency. In contrast, the selectivity of HMF oxidation facilitated by a homogeneous electrocatalyst, 4-acetamido-TEMPO (ACT, TEMPO = 2,2,6,6-tetramethylpiperidine-1-oxyl), together with an inexpensive carbon felt electrode, was insensitive to anode potential. Thus, it was feasible to conduct HMF hydrogenation to BHMF and oxidation to 2,5-furandicarboxylic acid (FDCA) in a single divided cell operated under cathode potential control. Electrocatalytic HMF conversion in the paired cell achieved high yields of BHMF and FDCA (85% and 98%, respectively) and a combined electron efficiency of 187%, corresponding to a nearly two-fold enhancement compared to the unpaired cells.This article is published as Chadderdon, Xiaotong H., David J. Chadderdon, Toni Pfennig, Brent H. Shanks, and Wenzhen Li. "Paired electrocatalytic hydrogenation and oxidation of 5-(hydroxymethyl) furfural for efficient production of biomass-derived monomers." Green Chemistry 21, no. 22 (2019): 6210-6219. DOI: 10.1039/C9GC02264C. Posted with permission.</p

Paired electrocatalytic hydrogenation and oxidation of 5-(hydroxymethyl)furfural for efficient production of biomass-derived monomers

Electrochemical conversion of biomass-derived compounds is a promising route for sustainable chemical production. Herein, we report unprecedentedly high efficiency for conversion of 5-(hydroxymethyl)furfural (HMF) to biobased monomers by pairing HMF reduction and oxidation half-reactions in one electrochemical cell. Electrocatalytic hydrogenation of HMF to 2,5-bis(hydroxymethyl)furan (BHMF) was achieved under mild conditions using carbon-supported Ag nanoparticles (Ag/C) as the cathode catalyst. The competition between Ag-catalyzed HMF hydrogenation to BHMF and undesired HMF hydrodimerization and hydrogen evolution reactions was sensitive to cathode potential. Also, the carbon support material in Ag/C was active for HMF reduction at strongly cathodic potentials, leading to additional hydrodimerization and low BHMF selectivity. Accordingly, precise control of the cathode potential was implemented to achieve high BHMF selectivity and efficiency. In contrast, the selectivity of HMF oxidation facilitated by a homogeneous electrocatalyst, 4-acetamido-TEMPO (ACT, TEMPO = 2,2,6,6-tetramethylpiperidine-1-oxyl), together with an inexpensive carbon felt electrode, was insensitive to anode potential. Thus, it was feasible to conduct HMF hydrogenation to BHMF and oxidation to 2,5-furandicarboxylic acid (FDCA) in a single divided cell operated under cathode potential control. Electrocatalytic HMF conversion in the paired cell achieved high yields of BHMF and FDCA (85% and 98%, respectively) and a combined electron efficiency of 187%, corresponding to a nearly two-fold enhancement compared to the unpaired cells

Mechanisms of Furfural Reduction on Metal Electrodes: Distinguishing Pathways for Selective Hydrogenation of Bioderived Oxygenates

Electrochemical reduction of biomass-derived platform molecules is an emerging route for the sustainable production of fuels and chemicals. However, understanding gaps between reaction conditions, underlying mechanisms, and product selectivity have limited the rational design of active, stable, and selective catalyst systems. In this work, the mechanisms of electrochemical reduction of furfural, an important biobased platform molecule and model for aldehyde reduction, are explored through a combination of voltammetry, preparative electrolysis, thiol-electrode modifications, and kinetic isotope studies. It is demonstrated that two distinct mechanisms are operable on metallic Cu electrodes in acidic electrolytes: (i) electrocatalytic hydrogenation (ECH) and (ii) direct electroreduction. The contributions of each mechanism to the observed product distribution are clarified by evaluating the requirement for direct chemical interactions with the electrode surface and the role of adsorbed hydrogen. Further analysis reveals that hydrogenation and hydrogenolysis products are generated by parallel ECH pathways. Understanding the underlying mechanisms enables the manipulation of furfural reduction by rationally tuning the electrode potential, electrolyte pH, and furfural concentration to promote selective formation of important biobased polymer precursors and fuels

Mechanisms of Furfural Reduction on Metal Electrodes: Distinguishing Pathways for Selective Hydrogenation of Bioderived Oxygenates

Electrochemical reduction of biomass-derived platform molecules is an emerging route for the sustainable production of fuels and chemicals. However, understanding gaps between reaction conditions, underlying mechanisms, and product selectivity have limited the rational design of active, stable, and selective catalyst systems. In this work, the mechanisms of electrochemical reduction of furfural, an important biobased platform molecule and model for aldehyde reduction, are explored through a combination of voltammetry, preparative electrolysis, thiol-electrode modifications, and kinetic isotope studies. It is demonstrated that two distinct mechanisms are operable on metallic Cu electrodes in acidic electrolytes: (i) electrocatalytic hydrogenation (ECH) and (ii) direct electroreduction. The contributions of each mechanism to the observed product distribution are clarified by evaluating the requirement for direct chemical interactions with the electrode surface and the role of adsorbed hydrogen. Further analysis reveals that hydrogenation and hydrogenolysis products are generated by parallel ECH pathways. Understanding the underlying mechanisms enables the manipulation of furfural reduction by rationally tuning the electrode potential, electrolyte pH, and furfural concentration to promote selective formation of important biobased polymer precursors and fuels.</p

Numerical analysis of anion-exchange membrane direct glycerol fuel cells under steady state and dynamic operations

Copyright © 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. This work develops a one-dimensional model of an alkaline anion-exchange membrane direct glycerol fuel cell (AEM-DGFC) for cogeneration of tartronate and electricity. The model is validated against steady state and dynamic experiments, and shows good agreement. Steady state modeling includes anode and cathode losses and predicts the single cell polarization and power density curves. Coupled mass transport, charge transport, and electrochemical kinetics predict the effects of varying reactant concentration and diffusion layer porosity on single cell performance. The results show that anode overpotential is the major source of loss at middle to high current density regions, due to limited glycerol diffusion at the catalyst layer. Furthermore, the dynamic response of AEMDGFC to step changes in current density is simulated by considering time-dependent species transport and double-layer capacitance charging. Analysis of dynamic simulation reveals that the liquid-phase reactant diffusion is a key factor influencing the transient AEM-DGFC behavior and is very sensitive to diffusion layer design. This new numerical analysis of a glycerol-fed fuel cell demonstrates that a simple, single oxidation product model can successfully predict the steady state and dynamic losses

Carbon nanotubes as catalysts for direct carbohydrazide fuel cells

© 2015 Elsevier Ltd. All rights reserved. As an alternative to potentially carcinogenic hydrazine for fuel cell application, carbohydrazide, which contains lone electron pairs on nitrogen atoms and readily activated N-H bonds, can be catalytically oxidized over metal-free carbon catalysts due to the high equilibrium electromotive force (1.65 V) of its oxidation reaction. Carbon nanotubes are found to electrochemically catalyze the carbohydrazide oxidation reaction more efficiently than carbon black and multi-layer graphene in alkaline media. With carbon nanotubes as the anode catalyst, anode metal-catalyst-free and completely metal-catalyst-free direct carbohydrazide anion exchange membrane fuel cells are shown here to generate a peak power density of 77.5 mW cm-2 and 26.5 mW cm-2, respectively