Amorphous FeOOH Quantum Dots on NiMn-LDH Nanosheets for Highly Efficient Urea-Assisted Overall Water Splitting

The development of low-cost, earth-abundant electrocatalysts is essential for advancing hydrogen-based energy technologies, yet conventional water splitting remains constrained by the sluggish oxygen evolution reaction (OER). Substituting OER with the urea oxidation reaction (UOR) offers a more favorable alternative, reducing the reaction potential while simultaneously addressing wastewater remediation. Herein, we develop a heterostructured electrocatalyst of amorphous FeOOH quantum dots (QDs) uniformly anchored on NiMn layered double hydroxide (LDH) nanosheets grown on nickel foam (NF). The ultrathin conductive NiMn-LDH scaffold offers high surface accessibility and tunable redox activity, while the FeOOH QDs introduce abundant active centers that accelerate charge transfer and optimize OH^- and urea adsorption. As a result, FeOOH QDs/NiMn-LDH/NF requires only a low overpotential of 1.42 V to reach 50 mA cm^-2 for OER and 1.33 V for UOR, with small Tafel slopes of 31 and 29 mV dec^-1 and exhibits outstanding long-term durability of 50 h. Moreover, the heterostructured electrocatalyst shows competent activity for the hydrogen evolution reaction (η₁₀ = 125 mV) and delivers an average Faradaic efficiency of ≈95.7% during electrolysis, confirming highly selective charge-to-hydrogen conversion. This enables efficient urea-assisted overall water electrolysis at only 1.44 V. This work underscores the synergistic integration of LDH nanosheets with amorphous QDs as a versatile and scalable strategy to engineer next-generation bifunctional electrocatalysts for energy-efficient hydrogen production coupled with wastewater treatment.