Boosting Urea-Assisted Natural Seawater Electrolysis in 3D Leaf-Like Metal–Organic Framework Nanosheet Arrays Using Metal Node Engineering

Metal node engineering, which can optimize the electronic structure and modulate the composition of poor electrically conductive metal–organic frameworks, is of great interest for electrochemical natural seawater splitting. However, the mechanism underlying the influence of mixed-metal nodes on electrocatalytic activities is still ambiguous. Herein, a strategic design is comprehensively demonstrated in which mixed Ni and Co metal redox-active centers are uniformly distributed within NH2–Fe-MIL-101 to obtain a synergistic effect for the overall enhancement of electrocatalytic activities. Three-dimensional mixed metallic MOF nanosheet arrays, consisting of three different metal nodes, were in situ grown on Ni foam as a highly active and stable bifunctional catalyst for urea-assisted natural seawater splitting. A well-defined NH2–NiCoFe-MIL-101 reaches 1.5 A cm–2 at 360 mV for the oxygen evolution reaction (OER) and 0.6 A cm–2 at 295 mV for the hydrogen evolution reaction (HER) in freshwater, substantially higher than its bimetallic and monometallic counterparts. Moreover, the bifunctional NH2–NiCoFe-MIL-101 electrode exhibits eminent catalytic activity and stability in natural seawater-based electrolytes. Impressively, the two-electrode urea-assisted alkaline natural seawater electrolysis cell based on NH2–NiCoFe-MIL-101 needs only 1.56 mV to yield 100 mA cm–2, much lower than 1.78 V for alkaline natural seawater electrolysis cells and exhibits superior long-term stability at a current density of 80 mA cm–2 for 80 h.