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

Abstract

Urea oxidation reaction (UOR) has received a high level of recent interest since electrochemical oxidation of urea can remediate harmful nitrogen compounds in wastewater and accomplish hydrogen fuel production simultaneously. Thus, urea is considered to be potential hydrogen energy source that is inherently safe for fuel cell applications. However, the catalytic reaction suffers from slow kinetics due to six electron transfer in UOR. In this work, β phase NiS is successfully prepared through facile hydrothermal reaction, in which diethanolamine (DEA) was added as chelating agent leading to 3D nanoflower morphology. The crystal structure, surface morphology, and chemical bonding of the β−NiS were characterized by X–ray diffraction (XRD), scanning electron microscope (SEM), and X−ray photoelectron spectroscopy (XPS), respectively. The UOR performance of NiS was evaluated by means of linear sweep voltammetry (LSV), Tafel analysis, electrochemical impedance spectroscopy (EIS), chronoamperometry, and chronopotentiometry in 1 M KOH electrolyte containing 0.33 M urea. Compared to the Ni(OH)2 counterpart, NiS exhibits lower onset potential, increased current responses, faster kinetics of urea oxidation, lower charge transfer resistance, and higher urea diffusion coefficient, leading to the enhanced catalytic performance toward UOR. Moreover, the developed NiS catalyst exhibits superior stability and tolerance towards urea electro−oxidation in 10,000 s test.

Durable Pulse-Electrodeposited Ni–Fe–S Nanosheets Supported on a Ni–S Three Dimensional Pattern as Robust Bifunctional Electrocatalysts for Hydrogen Evolution and Urea Oxidation Reactions

“…Third, the formation of NiOOH during the UOR process is identified as an active species, further enhancing the overall catalytic performance. Additionally, the inclusion of Fe in the system plays a pivotal function in facilitating the desorption of formed CO 2 from the surface, rendering CO 2 desorption a spontaneous and favorable process. , …”

“…Additionally, the inclusion of Fe in the system plays a pivotal function in facilitating the desorption of formed CO 2 from the surface, rendering CO 2 desorption a spontaneous and favorable process. 12,66 Figure 4e depicts the LSV curves for a two-electrode system featuring optimized Ni−Fe−S@Ni−S electrodes. This configuration includes a tandem arrangement of Ni−Fe−S@Ni−S || Ni−Fe−S@Ni−S electrodes strategically designed to facilitate both urea and water oxidation processes.…”

Transition Metal‐Based Catalysts for Urea Oxidation Reaction (UOR): Catalyst Design Strategies, Applications, and Future Perspectives

“…𝛽-NiMoO 4 exhibits the most efficient urea oxidation performance, with the lowest charge transfer resistance (34.0 𝜔), Tafel slope (40 mV dec −1 ), and opening potential compared with 𝛼-NiMoO 4 and hydrate NiMoO 4 •xH 2 O. Wu et al used simple hydrothermal reaction and diethanolamine (DEA) as a chelating agent to synthesize 𝛽-phase NiS with 3D nanoflower morphology, which shows excellent urea oxidation activity and tolerance. [120] Xie et al prepared graded cerium doped 𝛼-Ni(OH) 2 nanoarrays (Ce:𝛼-Ni(OH) 2 /NF) and 𝛽-Ni(OH) 2 nanoarrays (Ce: 𝛽-Ni(OH) 2 /NF) by hydrothermal method. [79] The excellent catalytic activity is derived from the phase engineering to modulate catalyst activity.…”

Recent Development of Nickel-Based Electrocatalysts for Urea Electrolysis in Alkaline Solution

“…For instance, S-doped Ni(OH) 2 demonstrates metallic property ( Figure 8 e), which effectively promotes electron transport resulting in high UOR performance ( Figure 8 f) [ 58 ]. Due to the better conductivity of S and Se (with respect to O), nickel sulfides [ 59 , 60 , 61 ] and nickel selenides [ 8 , 62 , 63 ] have been widely employed as electrocatalysts for the UOR. In addition, N-doping has been shown to promote the formation of Ni 3+ active sites for electro-oxidation of urea [ 64 ].…”