Introducing Sulfur in VNi-Layered Double Hydroxide Enables Efficient Electrocatalytic Oxidation of Benzylamine with High Current Densities

The replacement of the thermodynamically unfavorable anodic oxygen evolution reaction (OER) with a more favorable organic oxidation reaction, such as the anodic oxidation of benzylamine, has garnered significant interest in hybrid water electrolyzer cells. This approach promises the production of value-added chemicals alongside hydrogen fuel generation, improving overall energy efficiency. However, achieving high current density for benzylamine oxidation without interference from OER remains a challenge, limiting the practical efficiency of the electrolyzer cell. In this study, we investigated a room temperature method for sulfur introduction in VNi-layered double hydroxide (LDH) catalyst and its application for electrocatalytic benzylamine oxidation. The S-introduction in VNi-LDH was found to modulate the electronic states of nickel and vanadium, increasing the number of active sites, electrochemical surface area, and charge transfer properties. The resulting S-VNi-LDH catalyst achieved a high current density of 400 mA cm^-2 at only 1.39 V vs RHE potential for benzylamine oxidation, avoiding interference from oxygen evolution. The catalyst demonstrated 100% selectivity (Faradaic Efficiency = 98.6%) for the conversion of benzylamine into benzonitrile within 2.5 h of the reaction. In a two-electrode electrolysis system, S-VNi-LDH achieved a current density of 400 mA cm^-2 at a cell voltage of 1.50 V when OER was substituted with benzylamine oxidation. The S-VNi-LDH showed energy consumption of 4.67 kWh/m³ H₂ for OER and 1.31 kWh/m³ H₂ during benzylamine oxidation, indicating a high energy efficiency with exceptional stability over five cycles, maintaining 98.6 ± 0.4% FE and consistent voltage. The S-VNi-LDH also oxidized various amines, including substituted benzylamines and secondary amines, achieving high conversion (95-97%) and faradaic efficiency (85.8-98%). This study presents an eco-friendly, room-temperature method for S-doping in VNi-LDH, which out performed the reported catalysts in the literature.