Engineering the Electronic Structure of NiFe Layered Double Hydroxide Nanosheet Array by Implanting Cationic Vacancies for Efficient Electrochemical Conversion of 5-Hydroxymethylfurfural to 2,5-Furandicarboxylic Acid

The utilization of biomass resources is essential for constructing a carbon neutral society. Electrochemical conversion of biomass-derived platform molecule 5-hydroxymethylfurfural (HMF) to 5-furandicarboxylic acid (FDCA) is a highly promising alternative pathway for the production of valuable biobased oxygenated chemicals, which primarily takes advantage of the on-going development of efficient, robust, and inexpensive catalysts. In the present work, a carbon paper-supported nickel-iron layered double hydroxide (LDH) nanosheet array implanted with abundant cationic vacancies (d-NiFe LDH/CP) is employed as a self-standing electrode for oxidation of HMF to FDCA. A 97.35% conversion of HMF and a 96.8% yield of FDCA could be achieved at 1.48 V, with a faradaic efficiency as high as 84.47% in 1 M KOH electrolyte. More importantly, it also exhibits excellent stability for 10 cycles. The successful introduction of M2+ vacancies was proved by electron paramagnetic resonance spectroscopy. X-ray photoelectron spectroscopy results confirmed that the implanted cationic vacancies would effectively raise the electron density of d-NiFe LDH and tailor the electronic structures of metal sites. This results in a significantly increased active site number and lowered charge transfer resistance that facilitate the electrocatalytic performance improvement. Postreaction characterization indicates that the in situ generated metal (oxy)hydroxides are the active species, and the HMF would be oxidized through both chemical and electrochemical pathways. These interesting findings shed light on the innovation of defect-rich catalysts and their promising application in electrochemical biomass derivative upgrading.