Nanoporous Bimetallic Metal-Hydroxide Organic Frameworks for Urea-Assisted Natural Seawater Electrolysis

Abstract Metal-hydroxide organic frameworks (MHOFs), featuring a synergistic interplay between metal hydroxides and metal−organic frameworks, exhibit tremendous potential as next-generation electrocatalysts for water splitting. However, their underlying catalytic mechanisms remain insufficiently understood. Herein, through a single hydrothermal method, the nanoporous NiCo-MHOF-6 was directly grown on nickel foam (NF). Doping Co into the Ni-MHOF framework changes the electronic configuration of the active metal centers, consequently promoting improved electrocatalytic performance. During the OER, NiCo-MHOF-6 requires a overpotential of only 356 mV to attain 500 mA cm−2, and retains 90.6% of its initial current over 220 h at a constant 1.55 V vs. RHE. In practical seawater electrolysis, the assembled electrolyzer exhibits energy-efficient performance, requiring only 1.57 V to deliver 200 mA cm−2 and sustaining stable operation for 210 h at 240 mA cm−2. Furthermore, when the urea oxidation reaction (UOR) takes the place of the anodic OER, only 1.30 V is needed to drive 10 mA cm−2, and the system runs continuously for 144 h. Operando Raman spectroscopy and X-ray absorption measurements show that in situ transformation into high-valent γ-NiOOH, which is key to its faster reaction kinetics. This work provides a viable pathway toward low-energy H2 generation via urea-assisted seawater electrolysis.