Morphology-controlled nickel-organic framework nanosheet arrays for efficient urea electrolysis in alkaline media

Urea electrolysis is considered as a promising energy-saving hydrogen production technique to substitute the water electrolysis, but it is restricted by the lack of efficient and cost-effective catalysts. Herein, nickel foam supported three-dimensional (3D) nickel-organic framework nanosheet arrays (Ni-BDC-t/NF, where t is the reaction time) comprising Ni2+ and an organic ligand of 4,4-biphenyl dicarboxylic acid (BDC) are synthesized as catalyst for urea electrolysis in alkaline media. Benefiting from the highly exposed Ni active sites and fast electron transfer rate endowed by 3D nanosheet array architecture, the structurally optimized Ni-BDC-10/NF exhibits preeminent electrocatalytic activity and durability toward urea oxidation reaction (UOR). To deliver a high current density of 100 mA cm-2, the required UOR potential of Ni-BDC-10/NF is only 1.50 V vs. RHE. Significantly, by further coupling with the cathodic hydrogen evolution reaction, the urea electrolysis system based on Ni-BDC-10/NF self-supporting anode exhibits a dramatic voltage decrease by 340 mV at a current density of 50 mA cm-2 as compared with that of water electrolysis under the same conditions. This study provides some new ideas for developing high-efficiency nickel-based organic framework catalysts and their application in urea-related energy storage devices.