Phosphorized CoNi 2 S 4 Yolk-Shell Spheres for Highly Efficient Hydrogen Production via Water and Urea Electrolysis.

Exploring earth-abundant electrocatalysts with excellent activity, robust stability, and multiple functions is crucial for electrolytic hydrogen generation. Porous phosphorized CoNi ₂ S ₄ yolk-shell spheres (P-CoNi ₂ S ₄ YSSs) were rationally designed and synthesized by a combined hydrothermal sulfidation and gas-phase phosphorization strategy. Benefiting from the strengthened Ni ³⁺ /Ni ²⁺ couple, enhanced electronic conductivity, and hollow structure, the P-CoNi ₂ S ₄ YSSs exhibit excellent activity and durability towards hydrogen/oxygen evolution and urea oxidation reactions in alkaline solution, affording low potentials of -0.135 V, 1.512 V, and 1.306 V (versus reversible hydrogen electrode) at 10 mA cm ^-2 , respectively. Remarkably, when used as the anode and cathode simultaneously, the P-CoNi ₂ S ₄ catalyst merely requires a cell voltage of 1.544 V in water splitting and 1.402 V in urea electrolysis to attain 10 mA cm ^-2 with excellent durability for 100 h, outperforming most of the reported nickel-based sulfides and even noble-metal-based electrocatalysts. This work promotes the application of sulfides in electrochemical hydrogen production and provides a feasible approach for urea-rich wastewater treatment.
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