Abstract:

Electrochemical reduction of biomass-derived 5-hydroxymethylfurfural (HMF) to produce 2,5-dihydroxymethylfuran (DHMF) is a promising approach for biomass upgrading. The achievement of high activity and Faradaic efficiency (FE) in a wide potential window is critical for mature applications considering the significantly varied voltages supplied by different renewable energies. However, it is still challenging due to multiple reaction pathways and the competitive hydrogen evolution reaction. Herein, we synthesized a cooperative catalyst by supporting Ag nanoparticles (AgNPs) on SnO2 nanosheet arrays, which realizes the electrochemical HMF reduction to DHMF with a high FE (>95%) in a wide potential window (from −0.62 to −1.12 V vs reversible hydrogen electrode). Electrochemical and in situ measurements reveal that the AgNPs promote water splitting to generate reactive hydrogen (H*) species, which effectively react with HMF via a Langmuir–Hinshelwood mechanism. Moreover, the AgNPs accelerate the formation of oxygen vacancies on SnO2 under reaction conditions, which act as electrophilic sites to realize the selective adsorption and hydrogenation of the carbonyl bond (C═O) in HMF to yield DHMF. Finally, we designed a coupling system to simultaneously realize the electrochemical reduction and oxidation of HMF to produce DHMF and 2,5-furandicarboxylic acid, showing lower potential at the same current density than that of traditional cathodic HMF reduction coupling anodic oxygen evolution reaction, in an economical manner.

Scheme 1. (a) Schematic Illustration of Electrochemical HMF Reduction to DHMF Driven by Clean Energy; (b,c) Plausible Reaction Mechanisms of Electrochemical HMF Reduction in (b) Previous Work and (c) in This Work

Herein, we designed a cooperative catalyst of Ag nanoparticles (AgNPs) supported on SnO2 nanosheets, which realized efficient electrochemical HMF reduction to DHMF with a high FE (>95%) in a wide potential window from −0.62 to −1.12 V vs reversible hydrogen electrode (RHE), overwhelming most of the reported electrocatalytic works for HMF reduction. Mechanistic experiments reveal that the AgNPs promote the Volmer step of water splitting for H* generation at low potentials, enabling HMF reduction via an L–H mechanism (Scheme 1c). Moreover, the AgNPs accelerate the generation of oxygen vacancies on SnO2 under reaction conditions, which act as electrophilic sites to realize the selective adsorption and activation of C═O in HMF to yield DHMF. Considering that the cathodic HMF reduction process is conventionally coupled with a kinetically sluggish anodic oxygen evolution reaction (OER) that causes large overall electricity consumption, we further designed a coupling system by replacing the anodic OER with HMF electrooxidation to produce 2,5-furandicarboxylic acid (FDCA), achieving a voltage saving of 370 mV at 500 mA cm–2 compared with that in the traditional HMF reduction coupling of the OER process together with 43% energy saving at a constant current of 200 mA, demonstrating an economical method.