Cationic Defect Engineering for Promoting Oxidation of 5-Hydroxymethylfurfural While Passivating OER

Electrochemical organic oxidation has shown great industrial potential due to its green, low-carbon, and energy-efficient advantages. However, the competing oxygen evolution reaction (OER) severely impacts the faradaic efficiency and conversion rate of organic oxidation reactions. In this work, we report a method that can promote the oxidation of 5-hydroxymethylfurfural (HMFOR) while suppressing the OER, which is achieved by etching NiMnFe-LDH with <i>N</i>,<i>N</i>-dimethylacetamide (DMF), resulting in the formation of numerous cationic defects. Specifically, at a current density of 50 mA cm^-2, the applied potential for HMFOR decreased by 50 mV, while the OER potential increased by 30 mV. In situ electrochemical impedance spectroscopy found faster reaction kinetics for d-NiMnFe-layered double hydroxide (LDH) compared to that of NiMnFe-LDH in HMFOR, whereas an opposite trend was observed in the OER, confirming that the DMF treatment has opposite effects on the transportation of organic molecules and OH^-. To further investigate the reaction pathways and evolution of intermediates during HMFOR, in situ infrared spectroscopy and theoretical calculations were conducted, which demonstrate that cationic defects not only significantly enhance the adsorption of intermediates but also lower the reaction energy barrier, thus accelerating the reaction rate of HMFOR. This work provides a potential strategy for developing industrial-grade electrocatalysts for high current densities.