Fluorine Engineered Self-Supported Ultrathin 2D Nickel Hydroxide Nanosheets as Highly Robust and Stable Bifunctional Electrocatalysts for Oxygen Evolution and Urea Oxidation Reactions

Developing highly efficient noble-metal-free electrocatalysts with a scalable and environmentally friendly synthesis approach remains a challenge in the field of electrocatalytic water splitting. To overcome this problem, self-supported fluorine-modified 2D ultrathin nickel hydroxide (F-Ni(OH)₂) nanosheets (NSs) for the oxygen evolution reaction (OER) and urea oxidation reaction (UOR) are prepared with a scalable and ascendant one-step synthesis route. The enhanced redox activity, electrical conductivity and a great number of exposed active sites of the heterogeneous catalysts improve charge migration for the electrocatalytic reactions. The density of states of the d orbitals of the Ni atoms significantly increases near the Fermi level, thereby indicating that the Ni atoms near the F-dopants promote electrical conduction in the Ni(OH)₂ monolayer. The F-Ni(OH)₂ electrocatalyst exhibits notable OER and UOR activity with onset potentials of 1.43 and 1.16 V versus RHE, respectively required to reach 10 mA cm⁻², which are comparable to those of commercial noble-metal-based electrocatalysts. With RuCo-OH nanospheres, the settled F-Ni(OH)₂||RuCo-OH cell requires merely 1.55 and 1.37 V to reach 10 mA cm⁻² with superb durability for 24 h in overall water and urea electrolysis, respectively. Overall, high-quality, and efficient noble-metal-free electrocatalysts for overall water and urea electrolysis can be prepared with a simple, scalable, and reproducible preparation method.