A nickel(<scp>ii</scp>) complex under water-oxidation reaction: what is the true catalyst?

Feizi, Hadi; Bagheri, Robabeh; Jagličić, Zvonko; Singh, Jitendra Pal; Chae, Keun Hwa; Song, Zhenlun; Najafpour, Mohammad Mahdi

doi:10.1039/c8dt03990a

Cited by 32 publications

(30 citation statements)

References 53 publications

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“…The group of Najafpour showed the deposition of nickel oxide from a salen precursor under basic conditions [70] . After a thorough investigation, the formation of nickel oxide particles from a phthalocyanine complex was also observed [71] . Garrido‐Barros et al .…”

Section: Methodsmentioning

confidence: 99%

Potential‐ and Buffer‐Dependent Catalyst Decomposition during Nickel‐Based Water Oxidation Catalysis

Hessels

Detz

et al. 2020

ChemSusChem

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The production of hydrogen by water electrolysis benefits from the development of water oxidation catalysts. This development process can be aided by the postulation of design rules for catalytic systems. The analysis of the reactivity of molecular complexes can be complicated by their decomposition under catalytic conditions into nanoparticles that may also be active. Such a misinterpretation can lead to incorrect design rules. In this study, the nickel‐based water oxidation catalyst [NiII(meso‐L)](ClO4)2, which was previously thought to operate as a molecular catalyst, is found to decompose to form a NiOx layer in a pH 7.0 phosphate buffer under prolonged catalytic conditions, as indicated by controlled potential electrolysis, electrochemical quartz crystal microbalance, and X‐ray photoelectron spectroscopy measurements. Interestingly, the formed NiOx layer desorbs from the surface of the electrode under less anodic potentials. Therefore, no nickel species can be detected on the electrode after electrolysis. Catalyst decomposition is strongly dependent on the pH and buffer, as there is no indication of NiOx layer formation at pH 6.5 in phosphate buffer nor in a pH 7.0 acetate buffer. Under these conditions, the activity stems from a molecular species, but currents are much lower. This study demonstrates the importance of in situ characterization methods for catalyst decomposition and metal oxide layer formation, and previously proposed design elements for nickel‐based catalysts need to be revised.

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Section: Methodsmentioning

confidence: 99%

Potential‐ and Buffer‐Dependent Catalyst Decomposition during Nickel‐Based Water Oxidation Catalysis

Hessels

Detz

et al. 2020

ChemSusChem

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“…A Tafel slope of 90 mV/decade was obtained (Figure 6c), indicating that the composite is a moderate catalyst in comparison to most reported heterogeneous catalysts based on nickel oxide (40--105 mV/decade). [41][42][43][44][45][46][47] A catalytic current of 0.38 mA was observed after the electrolysis for 48 hr ( Figure S11), revealing that the composite catalyst had a moderate durability.…”

Section: Electrocatalysis For Wormentioning

confidence: 99%

“…[18,19] While many molecular catalysts derived from the complexes of Mn, [20,21] Fe, [22][23][24] Co, [25][26][27] and Cu [28][29][30][31] have been intensively investigated, studies on nickel-based complexes active for WOR are still limited. [32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47] A nickel(II) macrocyclic complex, [Ni(meso-L)](ClO 4 ) 2 (L = 5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacy-clotetradecane) was reported as the first nickel homogeneous electrocatalyst for water oxidation, showing a Faradaic efficiency of 97.5% and turnover number (TON) of 15. [32] Thereafter several homogeneous catalysts based on mononuclear nickel complexes were developed.…”

Section: Introductionmentioning

confidence: 99%

“…[33][34][35][36][37][38][39][40] Meanwhile, some nickel complexes acted as precatalysts forming nickel oxide species active for WOR. [41][42][43][44][45][46][47] Complex [Ni(meso-L)](ClO 4 ) 2 and two nickel polypyridine complexes have two labile coordination sites for water molecules. It was proposed that they catalyzed WOR by the intramolecular coupling of two metal-oxygen moieties (I2M) pathway.…”

Section: Introductionmentioning

confidence: 99%

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Nickel (II) tetrapyridyl complexes as electrocatalysts and precatalysts for water oxidation

Ren

Xie

et al. 2020

Applied Organom Chemis

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Two nickel complexes, [Ni(tpen)](ClO4)2.0.5CH3COCH3 (1) and [Ni(tpbn)](ClO4)2 (2), of tetrapyridyl ligands N,N,N′,N′‐tetrakis(2‐pyridyl‐methyl)‐1,2‐ethanediamine (tpen) and N,N,N′,N′‐tetrakis(2‐pyridyl‐methyl)‐1,4‐butanediamine (tpbn) were prepared and their catalysis for water oxidation reaction (WOR) studied. In 0.1 M phosphate buffer solution (PBS) of pH 8.0, complex 1 is a homogeneous molecular catalyst with an overpotential of ~440 mV and a Faradaic efficiency of 89%. At pH ≥ 9.0, complex 1 degraded gradually during the catalytic process and formed NiOx composite (nickel oxide with general formula NixOyHz) active for WOR. In contrast, complex 2 deteriorated under measured conditions (pH 8.0–12.0) and formed NiOx composite active for WOR. The NiOx composite derived from 1 in 0.1 M PBS at pH 11.0 showed an activity with an overpotential of ~500 mV, a Tafel slope of ~90 mV/decade and a Faradaic efficiency of 97%. Mechanisms were proposed for water oxidation catalyzed by 1 and 2. This work revealed that the catalytic activity of the nickel complexes was related to the flexibility of the tetrapyridyl ligands and the adaptability of the coordination sphere of the nickel(II) center.

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“…In the last several decades, numerous efforts have been made in developing transition metal complex‐based water oxidation catalysts (WOCs), [7–12] such as ruthenium, [13–23] iridium, [24–27] vanadium, [28] manganese, [29–35] iron, [36–42] cobalt, [43–51] nickel, [52–58] and copper complexes [59–67] . Since the report of the first molecular copper WOC in 2012 by Mayer and co‐workers, [60] the copper‐based molecular catalysts have received growing attention due to the advantages of their low cost and rich redox properties.…”

Section: Introductionmentioning

confidence: 99%

Molecular Mechanism of the Mononuclear Copper Complex‐Catalyzed Water Oxidation from Cluster‐Continuum Model Calculations

Yan

Fang

et al. 2022

ChemSusChem

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Cluster-continuum model calculations were conducted to decipher the mechanism of water oxidation catalyzed by a mononuclear copper complex. Among various OÀ O bond formation mechanisms investigated in this study, the most favorable pathway involved the nucleophilic attack of OH À onto the * + LÀ Cu II À OH À intermediate. During such process, the initial binding of OH À to the proximity of * + LÀ Cu II À OH À would result in the spontaneous oxidation of OH À , leading to OH * radical and Cu II À OH À species. The further OÀ O coupling between OH * radical and Cu II À OH À was associated with a barrier of 14.8 kcal mol À 1 , leading to the formation of H 2 O 2 intermediate. Notably, the formation of "Cu III À O *À " species, a widely proposed active species for OÀ O bond formation, was found to be thermodynamically unfavorable and could be bypassed during the catalytic reactions. On the basis the present calculations, a catalytic cycle of the mononuclear copper complex-catalyzed water oxidation was proposed.

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A nickel(ii) complex under water-oxidation reaction: what is the true catalyst?

Abstract: A Ni(ii) complex as a water-oxidizing catalyst under electrochemical conditions was studied and the role of Ni oxide as a true catalyst was investigated.

Cited by 32 publications

References 53 publications

Potential‐ and Buffer‐Dependent Catalyst Decomposition during Nickel‐Based Water Oxidation Catalysis

Potential‐ and Buffer‐Dependent Catalyst Decomposition during Nickel‐Based Water Oxidation Catalysis

Nickel (II) tetrapyridyl complexes as electrocatalysts and precatalysts for water oxidation

Molecular Mechanism of the Mononuclear Copper Complex‐Catalyzed Water Oxidation from Cluster‐Continuum Model Calculations

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