Progress toward a better understanding of the urea oxidation by electromediation of Ni(III)/Ni(II) system in alkaline media

Hopsort, Guillaume; Carmo, Diana Pereira Do; Latapie, Laure; Loubière, Karine; Serrano, Karine Groenen; Tzedakis, Théodore

doi:10.1016/j.electacta.2023.141898

Cited by 19 publications

(39 citation statements)

References 64 publications

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“…It is assumed that all the active sites in the reactive layer (δ < z < δ þ μ) are electronic conductors, in contact with the ions in solution. This hypothesis is supported by the following points: according to previous work, 30 one ER/HCR cycle occurs more than 100 times at low scan rates (i.e., <1 mV s À1 ). The nickel(III) or nickel(II) cannot thus crystallize in an organized lattice, which creates some disorder in this layer.…”

Section: Model Assumptionsmentioning

confidence: 54%

“…Data obtained for a S/V ratio of 8 are extracted from our previous work. 30 In addition to examining the validity of the model for an enhanced value of S/V ratio, an alkaline electrolysis was carried out using an anode surface of 26 cm 2 in 130 mL of electrolyte. A good correlation is observed between the experiments and the model since the maximum deviation of urea concentration is observed at 6%.…”

Section: Urea Electrolysis On Nickel Electrode: Case Results and Comp...mentioning

confidence: 99%

“…As a preliminary step, it was verified that (i) the chemical reaction that occurred when the alkaline urea solution was put into contact with chemically synthesized nickel(III) particles led to the productions of by‐products in the liquid phase identical to those that took place on the bare nickel electrode, and (ii) the total organic carbon (TOC) concentration decreased during the reaction. For this purpose, the analytical procedure established in our previous study 30 was used, involving ionic chromatography and nonpurgeable organic carbon.…”

Section: Methodsmentioning

confidence: 99%

“…Based on previous work, 30 The urea degradation mechanism from electrogenerated nickel(III) site can be classified into the nucleophilic oxidation reaction class 50,51 (as for the methanol oxidation on nickel(III) 52 ), involving two pathways successively: (i) electrogenerated Ni(OH) 2 catalyst dehydrogenation reaction followed by (ii) a spontaneous nucleophilic dehydrogenation reaction. First, the urea is adsorbed on a nickel(III) site, 53 formed by the catalyst dehydrogenation reaction of nickel(II) oxidation.…”

Section: Proposed Mechanism For the Complete Urea Electrooxidationmentioning

confidence: 99%

“…moreover, at the initial time, the massive nickel electrode is only composed of nickel(0). As a result of polarization, the layer thickness grows toward the massive nickel(0) electrode: a previous study using i – E curves highlights that 110 layers of active sites are formed 30 . For forming a new layer, a hydroxide ion should be present and must diffuse/migrate from the bulk, according to Equation ().…”

Section: Global Modeling Of the Urea Electrooxidationmentioning

confidence: 99%

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Indirect urea electrooxidation by nickel(III) in alkaline medium: From kinetic and mechanism to reactor modeling

et al. 2023

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This study consists in the determination of two kinetic laws of urea oxidation (UO) and electrooxidation (UEO) in alkaline media on nickel(III). Two kinds of active sites were examined, the first one derived from a Ni(OH)2 powder and the second from a massive nickel electrode. Partial orders of nickel(III) (two for UO and five UEO) enable to conclude about (i) the urea adsorption on two nickel(III) sites and (ii) that a multistep oxidation of urea occurs involving five nickel(III) site electroregenerations. A multipathway mechanism is also proposed to explain UEO facilitated by the nickel(III)/nickel(II) mediation system, and to predict the by‐products' formation previously identified (). At last, a model combining the UEO kinetic law previously established, with diffusive and convective transport phenomena was developed. A consistent correlation (maximum deviation of 6%) between laboratory electrolysis results with the model' predictions was obtained under different operating conditions, enabling the validation of this model.

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Section: Model Assumptionsmentioning

confidence: 54%

Section: Urea Electrolysis On Nickel Electrode: Case Results and Comp...mentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Proposed Mechanism For the Complete Urea Electrooxidationmentioning

confidence: 99%

Section: Global Modeling Of the Urea Electrooxidationmentioning

confidence: 99%

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Indirect urea electrooxidation by nickel(III) in alkaline medium: From kinetic and mechanism to reactor modeling

et al. 2023

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Understanding the Mechanism of Urea Oxidation from First‐Principles Calculations

Tatarchuk,

Choueiri,

MacKay

et al. 2024

ChemPhysChem

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Developing electrocatalysts for urea oxidation reaction (UOR) works toward sustainably treating urea‐enriched water. Without a clear understanding of how UOR products form, advancing catalyst performance is currently hindered. This work examines the thermodynamics of UOR pathways to produce N2, NO2−, and NO3− on a (0001) β‐Ni(OH)2 surface using density functional theory with the computational hydrogen electrode model. Our calculations show support for two major experimental observations: (1) N2 favours an intramolecular mechanism, and (2) NO2−/NO3− are formed in a 1:1 ratio with OCN−. In addition, we found that selectivity between N2 and NO2−/NO3− on our model surface appears to be controlled by two key factors, the atom that binds the surface intermediates to the surface and how they are deprotonated. These UOR pathways were also examined with a Cu dopant, revealing that an experimentally observed increased N2 selectivity may originate from increasing the limiting potential required to form NO2−. This work builds towards developing a more complete atomic understanding of UOR at the surface of NiOxHy electrocatalysts.

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Energy‐saving hydrogen production by heteroatom modulations coupling urea electrooxidation

Lu,

Zheng,

Wang

et al. 2024

EcoMat

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Developing efficient electrocatalysts with low‐cost for the urea oxidation reaction (UOR) is a significant challenge in energy‐saving H2 production owing to its lower thermodynamic potential. Heteroatom incorporation strategy has been proven to boost electrocatalytic activity by altering electronic structures and revealing more active sites on catalysts. Herein, nickel hydroxide nanosheets with various vanadium incorporation (Vx‐Ni(OH)2) were developed through a facile hydrothermal approach. By optimizing the incorporated vanadium contents, V6‐Ni(OH)2 catalyst exhibited easily accessible active sites and enhanced charge transfer with structural advantages, then assembled as the working electrode for urea‐assisted H2 production. Consequently, V6‐Ni(OH)2 catalyst demonstrated superior UOR activity compared with other incorporated samples with an overpotential of 1.33 V and a Tafel slope of 28.3 mV dec−1. Theoretical calculations revealed that the improved UOR activity was attributed to the potential determining step of V‐Ni(OH)2, which exhibited lower energy in comparison with the pristine Ni(OH)2 and increased electronic states density near the Fermi level. Both experimental and theoretical calculations confirmed vanadium incorporation on Ni(OH)2 could modify the electronic structure of Ni(III) species, improving electrical conductivity, and optimizing the adsorption energy for key reaction intermediates. Furthermore, the crucial contribution of vanadium incorporation with optimized electronic structures to the high UOR activity of Ni(OH)2 is demonstrated.image

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Progress toward a better understanding of the urea oxidation by electromediation of Ni(III)/Ni(II) system in alkaline media

Cited by 19 publications

References 64 publications

Indirect urea electrooxidation by nickel(III) in alkaline medium: From kinetic and mechanism to reactor modeling

Indirect urea electrooxidation by nickel(III) in alkaline medium: From kinetic and mechanism to reactor modeling

Understanding the Mechanism of Urea Oxidation from First‐Principles Calculations

Energy‐saving hydrogen production by heteroatom modulations coupling urea electrooxidation

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