Converting the Negative Ni-Mn Synergy into Positive in Lower-Coordination Layered Double Hydroxide/Metal-Organic Framework Heterojunction for Efficient Water and Urea Electrooxidation

Abstract

Developing efficient and robust earth-abundant bifunctional electrocatalysts for the anodic oxygen evolution reaction (OER) and urea oxidation reaction (UOR) is crucial for promoting sustainable H₂ generation via water or urea electrolysis. In this study, a bifunctional lower-coordination NiMn-bimetallic layered double hydroxide/metal-organic framework (LC-NiMn-LMF) nanoheterojunction electrocatalyst is reported. The X-ray photoelectron spectroscopy (XPS) and X-ray absorption fine structure (XAFS) analysis confirm the presence of abundant low-coordination atoms (LCAs) in LC-NiMn-LMF. The optimized LC-NiMn-LMF achieves a low overpotential of 232 mV for OER and a low potential of 1.33 V for UOR at 10 mA cm⁻². Moreover, it demonstrates a low voltage of 1.885 V at 500 mA cm⁻² and excellent durability for 100 h (500 mA cm⁻²) in an anion exchange membrane water electrolyzer. Mechanistic studies reveal that the improved catalytic performance arises from the synergistic interaction between adjacent LCAs, specifically Ni in LDH and Mn in MOF. This interaction effectively suppresses the overoxidation of Mn ions into inactive Mn(IV) valence state and stabilizes reaction intermediates, enhancing the intrinsic activity. This work offers a promising strategy for designing multifunctional electrocatalysts for advanced water and urea electrolysis technologies.