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.