Synergistic Combination of Triazole and BDC-MOF with TM-LDH in a One Pot for Improved Electrocatalytic Urea Oxidation

Abstract

The development of highly efficient and low-cost electrocatalysts for the urea oxidation reaction (UOR) is crucial for advancing urea fuel cell technologies. In this work, MgZnFe-layered double hydroxide (LDH), LDH/BDC-MOF, and LDH/1,2,4-triazole (LDH/TZ) nanocomposites were successfully synthesized via a simple one-pot co-precipitation method. The structural, morphological, textural, and thermal properties of the prepared materials were investigated using XRD, FTIR, SEM, EDX, BET, and TGA analyses. SEM observations revealed that pristine LDH consisted of stacked thin nanosheets with significant layer aggregation, whereas LDH/BDC-MOF exhibited MOF-pillared structures and LDH/TZ formed a highly porous interconnected three-dimensional network that effectively suppressed nanosheet restacking. BET analysis showed a remarkable enlargement in pore size from 6.7 nm for LDH to 34.5 nm for LDH/TZ. The electrocatalytic performance toward UOR was evaluated by cyclic voltammetry, chronoamperometry, and electrochemical impedance spectroscopy in 1.0 M KOH, containing different urea concentrations. Among all investigated electrodes, LDH/TZ exhibited the highest catalytic activity, delivering anodic current densities of 106, 132, 166, 180, and 202 mA cm−2 at urea concentrations of 0.2, 0.4, 0.6, 0.8, and 1.0 M, respectively. Furthermore, LDH/TZ displayed a lower onset potential of 0.41 V compared with 0.49 V for LDH/BDC-MOF and 0.56 V for pristine LDH. The enhanced activity was further supported by a high double-layer capacitance of 9.7 μF cm−2, a large electrochemically active surface area of 0.24 cm2, and a low charge-transfer resistance of 2.9 Ω. Chronoamperometric measurements demonstrated excellent durability with a stable current density of approximately 73 mA cm−2 after 3600 s, while cyclic stability reached 94% after 100 cycles. The superior performance of LDH/TZ is attributed to the synergistic effect of the nitrogen-rich triazole ligand, enlarged pore structure, enhanced active-site exposure, and accelerated charge-transfer kinetics, highlighting its strong potential as an efficient electrocatalyst for direct urea fuel cell applications.