In Situ Growth of Porous Ultrathin Ni(OH)₂ Nanostructures on Nickel Foam: An Efficient and Durable Catalysts for Urea Electrolysis

Abstract

Urea electrolysis is a potential energy-efficient hydrogen (H 2 ) production method that can simultaneously purify urea-rich wastewater. However, the lack of inexpensive and effective electrocatalysts for the urea oxidation reaction (UOR) hampers its widespread use. Herein, hierarchically porous and ultrathin Ni(OH) 2 nanostructures in situ grown onto nickel foam (Ni(OH) 2 @NF) are developed as efficient and durable electrocatalysts for UOR via a simple and cost-effective ultrasonic/heating-assisted activation strategy. The ultrathin Ni(OH) 2 nanostructures comprise highly active surfaces and rapid diffusion pathways for active species; meanwhile, the excellent electrical conductivity of the NF skeletons effectively improves the charge transfer of the catalyst. Consequently, this Ni(OH) 2 @NF electrode exhibits excellent urea catalytic activity (low oxidation potential of ∼1.35 V at 10 mA cm −2 ) and has remarkable operational stability (potential increase by only 0.22% after 40 h of durability testing) that is superior to most UOR catalysts. By employing the freestanding electrode as the anode and commercial Pt/C supported on NF as the cathode, this two-electrode urea electrolysis cell exhibited a current density of 50 mA cm −2 at a low cell voltage (1.45 V, 250 mV below a urea-free counterpart) with a robust durability (>40 h). This work provides a valuable insight for designing scalable and high-performance UOR electrocatalysts, which are promising for utilization in energy-efficient H 2 production.

Ni3S2/Ni Heterostructure Nanobelt Arrays as Bifunctional Catalysts for Urea-Rich Wastewater Degradation

“…Nickel-based catalysts have attracted considerable attention due to their high activity and abundant reserves, − such as Ni­(OH) 2 nanostructures, three-dimensional (3D) NiO nanowalls, and NiO–Ni nanosheets . They perform exceptional UOR activity as anode catalysts toward UOR.…”

A three-dimensional nanostructure of NiFe(OH)X nanoparticles/nickel foam as an efficient electrocatalyst for urea oxidation

“…So far, many different types of nanoparticles have been synthesized, such as NiCo nanoparticles, [14][15][16] NiFe nanoparticles, [17][18][19] CoFe nanoparticles 20 and so on. Compared with the metal materials widely used in OER reaction, UOR mainly centers on nickel based materials, such as nickel-based oxide, [21][22][23] Ni alloys, 24,25 Ni-based hydroxides oxides, [26][27][28] suldes and so on, [29][30][31][32] which is closely related to its principle. The main reason is that there are some active enzymes that decompose urea in the human body, and the active center is the nickel atom, which decomposes urea into carbon dioxide and water.…”

Nanostructured β−NiS Catalyst for Enhanced and Stable Electro−oxidation of Urea

“…Since then, Ni−based catalysts have been extensively studied as the catalysts for UOR. For instance, the electrocatalytic performance of Ni(OH) 2 with various morphologies, such as Ni(OH) 2 nanoparticle [13], Ni(OH) 2 nanotube [14], Ni(OH) 2 nanocube [15], and NiO nanosheet [16] have been investigated. Moreover, recent studies reveal that urea undergoes an electrochemical−chemical (EC) mechanism [17][18][19]:…”