Optimizing the reactivity of surface confined cobalt N4-macrocyclics for the electrocatalytic oxidation of l-cysteine by tuning the Co(II)/(I) formal potential of the catalyst

Gulppi, Miguel; Recio, Francisco J.; Tasca, Federico; Ochoa, Gonzalo; Silva, Juan F.; Pavez, Jorge; Zagal, José H.

doi:10.1016/j.electacta.2013.07.230

Cited by 22 publications

(8 citation statements)

References 26 publications

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“…For example, the electrocatalytic activity for ORR of MN4-macrocyclic metalloporphyrins (MP) and metallophthalocyanines (MPc) (M = Fe, Co and Mn) is linked to four main reactivity descriptors: (a) the M(III)/M(II) formal potential of the complex, (b) M–O 2 binding energies, (c) d-electron-occupancy of the metallic center, and (d) donor–acceptor intermolecular hardness. ,, These descriptors are dominated by the ability of the ligands to modulate the electronic structure of the metal center and its ability to bind an extraplanar ligand such as O 2 or any reacting molecule. This is true not only for ORR but for many other electrochemical reactions catalyzed by MN4 complexes as shown in several papers. ,− As expected, electron-withdrawing substituents located on the ligand (P or Pc) remove electron density from the metal center and shift the M(III)/M(II) formal potential to more positive values. This makes the metal center “more noble” or more Pt-like and harder to oxidize.…”

Section: Introductionsupporting

confidence: 63%

Theoretical and Experimental Reactivity Predictors for the Electrocatalytic Activity of Copper Phenanthroline Derivatives for the Reduction of Dioxygen

et al. 2019

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We have systematically studied the catalytic activity of a series of substituted bisphenanthroline Cu complexes adsorbed on glassy carbon electrodes for the oxygen reduction reaction (ORR) in aqueous media. The aim of this work is to test reactivity descriptors for ORR previously proposed for MN4 complexes. As the active site is the Cu(I) center, the foot of the wave for O 2 reduction on electrodes modified with Cu bisphenanthrolines appears at potentials very close to the [Cu(II)phen 2 ] ad ++ + e − ⇆ [Cu(I)phen 2 ] ad + redox process. Generally, the catalytic activity as (log i)E versus the E Cu(II)/(I) °redox potentials follows a linear correlation with a slope close to +0.120 V/decade, where the activity increases as the E Cu(II)/(I) °becomes more positive. This indicates that electron-withdrawing substituents on the ligand favor the reaction by shifting the E Cu(II)/(I) °to more positive values, making the Cu center more noble. This shift in the E Cu(II)/(I) °is essentially an electronic effect. However, another way to stabilize the Cu(I) state is by placing groups on the ligand that hinder the [Cu(II) square-planar ] ad ++ /[Cu(I) tetrahedral ] ad+ change. We have found that this steric effect seems to be more prominent than the electronic effects caused by electron-withdrawing groups and the increase in the catalytic activity for ORR is more pronounced.

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Section: Introductionsupporting

confidence: 63%

Theoretical and Experimental Reactivity Predictors for the Electrocatalytic Activity of Copper Phenanthroline Derivatives for the Reduction of Dioxygen

et al. 2019

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“…In particular, Co phthalocyanine (CoPc) was reported to be an electrocatalysts for the oxygen reduction reaction (ORR) by Jasinski (1964). Later the activity of those complexes was studied for other important reaction like the CO 2 reduction (Morlanes et al, 2016;Zhang et al, 2017), and the oxidation of L-cysteine (Gulppi et al, 2014), hydrazine (Geraldo et al, 2002(Geraldo et al, , 2008Venegasa et al, 2017), thiocyanate (Linares-Flores et al, 2012) and thiols (Bedioui et al, 2007) and also for their bio-mimicking activity (Zagal et al, 2010;Venegas et al, 2017;Herrera et al, 2018;Riquelme et al, 2018a). The search for electrocatalysts for the ORR as active and durable as the rare and costly Pt (which is the industrial standard for this reaction) is still pushing the search for a non-precious metal catalyst.…”

Section: Introductionmentioning

confidence: 99%

Oxygen Reduction Reaction at Penta-Coordinated Co Phthalocyanines

et al. 2020

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From the early 60s, Co complexes, especially Co phthalocyanines (CoPc) have been extensively studied as electrocatalysts for the oxygen reduction reaction (ORR). Generally, they promote the 2-electron reduction of O 2 to give peroxide whereas the 4-electron reduction is preferred for fuel cell applications. Still, Co complexes are of interest because depending on the chemical environment of the Co metal centers either promote the 2-electron transfer process or the 4-electron transfer. In this study, we synthetized 3 different Co catalysts where Co is coordinated to 5 N atoms using CoN4 phthalocyanines with a pyridine axial linker anchored to carbon nanotubes. We tested complexes with electro-withdrawing or electro-donating residues on the N4 phthalocyanine ligand. The catalysts were characterized by EPR and XPS spectroscopy. Ab initio calculations, Koutecky-Levich extrapolation and Tafel plots confirm that the pyridine back ligand increases the CoO 2 binding energy, and therefore promotes the 4-electron reduction of O 2. But the presence of electron withdrawing residues, in the plane of the tetra N atoms coordinating the Co, does not further increase the activity of the compounds because of pull-push electronic effects.

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“…These structures are macrocycles with metal centers like iron [22][23][24][25][26][27][28], cobalt [29][30][31][32], copper [33][34][35], and nickel [33,34,36] bearing 4 pyrrolic nitrogen atoms. Porphyrins and phthalocyanines have been used as electrodes and have been reported for a wide range of reactions such as the ORR [32,[37][38][39][40], reduction of CO 2 [41][42][43][44][45], and the oxidation of H 2 O 2 and hydrazine [46,47] organic [48][49][50][51][52], biological [53,54] and inorganic compounds [55][56][57][58][59][60][61][62], as well as other forms of bio-mimicking [63,64]. They are also interesting since they may be readily bound to the surface of electrode materials such as carbon nanomaterials …”

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Penta-coordinated transition metal macrocycles as electrocatalysts for the oxygen reduction reaction

Govan

Orellana

Zagal

et al. 2020

J Solid State Electrochem

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The oxygen reduction reaction (ORR) is a highly important reaction in electrochemistry. The following short review details recent advances in novel non-precious metal catalysts containing transition metal macrocycles for use in the ORR. Unbound, many of these electrodes were found to generate high levels of side products such as O 2 − and H 2 O 2 via 2-electron processes, and for this reason, it is aimed to create systems which would favor a 4-electron process which would completely convert oxygen to H 2 O. The 4electron reduction of O 2 releases the most energy in a fuel cell. Novel catalytic materials containing metal macrocycles were created mimicking the structure of enzyme metal centers, the metal in the macrocycle bound to a fifth axial ligand. These structures were observed to exhibit improved catalytic activity, and in the case of cobalt, phthalocyanine systems were observed to move away from the inefficient 2-electron process towards the more complete 4-electron process in alkaline media. Both experimental results (XPS, EPR, cyclic voltammetry and polarization curves) and theoretical models were gathered for various pentacoordinate systems and various electronic effects of the axial ligand on metal center were proposed. Penta-coordinate macrocycles are an important tool for further manipulating and tuning the electronic behavior of transition metal centers for catalysis of the ORR.

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Optimizing the reactivity of surface confined cobalt N4-macrocyclics for the electrocatalytic oxidation of l-cysteine by tuning the Co(II)/(I) formal potential of the catalyst

Cited by 22 publications

References 26 publications

Theoretical and Experimental Reactivity Predictors for the Electrocatalytic Activity of Copper Phenanthroline Derivatives for the Reduction of Dioxygen

Theoretical and Experimental Reactivity Predictors for the Electrocatalytic Activity of Copper Phenanthroline Derivatives for the Reduction of Dioxygen

Oxygen Reduction Reaction at Penta-Coordinated Co Phthalocyanines

Penta-coordinated transition metal macrocycles as electrocatalysts for the oxygen reduction reaction

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