Electrocatalytic Oxygen Activation by Carbanion Intermediates of Nitrogen-Doped Graphitic Carbon

Li, Qiqi; Noffke, Benjamin W.; Wang, Yilun; Menezes, Bruna Rafaela da Silva; Peters, Dennis G.; Raghavachari, Krishnan; Li, Liang-shi

doi:10.1021/ja413179n

Cited by 68 publications

(73 citation statements)

References 39 publications

(55 reference statements)

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“…Therefore, the monodentate activation of molecular oxygen on optimal nitrogen-doped graphitic materials would be enabled by hydrogenation and driven by the available charge. The identified activation mechanism should take place in the same potential region where the hydrogenation process takes place, as has been already observed experimentally [32]. By focusing on the monodentate activation, fundamental effects would have been brought to light, explaining the experimental observations originating this research, and enabling the discussion of different configurations.…”

Section: Discussionsupporting

confidence: 57%

“…It has been suggested that the hydrogenation of pyridinic-nitrogen dopants in graphitic materials can be involved in the activation of the ORR in alkaline solutions [32]. Since this process depends not only on the pH but also on the electrode potential, the hydrogenation of pyridinic nitrogen-dopants can take place actually under alkaline conditions.…”

Section: Resultsmentioning

confidence: 99%

“…We will provide computational evidence that the hydrogenation of pyridinic nitrogen-dopants could play a key role in the activation of molecular oxygen on nitrogen-doped graphitic materials. The hydrogenation [32] of pyridinic nitrogen-dopants in graphitic materials has been associated to high ORR activity in alkaline media. However, to our knowledge, no relevant role has been previously explicitly attributed to hydrogenated pyridinic nitrogen-dopants in explaining the activation of the ORR on the investigated materials.…”

Section: Introductionmentioning

confidence: 99%

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Understanding the chemisorption-based activation mechanism of the oxygen reduction reaction on nitrogen-doped graphitic materials

Ferre-Vilaplana

Herrero

2016

Electrochimica Acta

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Section: Discussionsupporting

confidence: 57%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Understanding the chemisorption-based activation mechanism of the oxygen reduction reaction on nitrogen-doped graphitic materials

Ferre-Vilaplana

Herrero

2016

Electrochimica Acta

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“…The virtual invariance of the double layer indicates that the Aza-CMP material does not have any functional groups in the material capable of having a redox process, aside from those related to the peaks at 0.16 V, which assures the quality of the material. This latter peaks can be associated to the hydrogenation of the nitrogen atoms, as has been proposed for nitrogendoped graphene 32 When the Aza-CMP material is modified with Co(II), the double layer increases, which clearly indicates that the cobalt has been clearly incorporated into the Aza-CMP materials (Figure 2). However, the peaks at 0.16 V disappear.…”

Section: Resultsmentioning

confidence: 56%

An Aza-Fused π-Conjugated Microporous Framework Catalyzes the Production of Hydrogen Peroxide

et al. 2016

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ABSTRACT:The electrochemical production of hydrogen peroxide can be implemented in small-scale plants under "on demand" approach. For that, selective catalysts for the oxygen reduction reaction (ORR) towards the desired species are required. Here, we report about the synthesis, characterization, ORR electrochemical behavior and reaction mechanism of an aza-fused π-conjugated microporous polymer, which presents high selectivity towards hydrogen peroxide. It was synthesized by polycondensation of 1,2,4,5-benzenetetramine tetrahydrochloride and triquinoyl octahydrate. A cobaltmodified version of the material was also prepared by a simple post-synthesis treatment with a Co(II) salt. The characterization of the material is consistent with the formation of a conductive robust porous covalent laminar poly-aza structure. The ORR properties of these catalysts were investigated using rotating disk and rotating disk-ring arrangements. The results indicate that hydrogen peroxide is almost exclusively produced at very low overpotential values on these materials. Density functional theory calculations provide key elements to understand the reaction mechanism. It is found that, at the relevant potential for the reaction, half of the nitrogen atoms of the material would be hydrogenated. This hydrogenation process would destabilize some carbon atoms in the lattice and provides segregated charge. On the destabilized carbon atoms, molecular oxygen would be chemisorbed with the aid of charge transferred from the hydrogenated nitrogen atoms and solvation effects. Due to the low destabilization of the carbon sites, the resulting molecular oxygen chemisorbed state, which has the characteristics of a superoxide species, would be only slightly stable and would promote the formation of hydrogen peroxide.

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“…Similar pH-dependent redox activity was reported in a nitrogen-doped graphitic carbon ORR catalyst. 9 With the discussed experimental and computational data in hand, the following mechanism for the 2e − reduction of O 2 on Ni 3 (HITP) 2 emerges (Scheme 1):…”

Section: Acs Catalysismentioning

confidence: 99%

Mechanistic Evidence for Ligand-Centered Electrocatalytic Oxygen Reduction with the Conductive MOF Ni₃(hexaiminotriphenylene)₂

et al. 2017

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Establishing catalytic structure−function relationships introduces the ability to optimize the catalyst structure for enhanced activity, selectivity, and durability against reaction conditions and prolonged catalysis. Here we present experimental and computational data elucidating the mechanism for the O 2 reduction reaction with a conductive nickel-based metal−organic framework (MOF). Elucidation of the O 2 reduction electrokinetics, understanding the role of the extended MOF structure in providing catalytic activity, observation of how the redox activity and pK a of the organic ligand influences catalysis, and identification of the catalyst active site yield a detailed O 2 reduction mechanism where the ligand, rather than the metal, plays a central role. More generally, familiarization with how the structural and electronic properties of the MOF influence reactivity may provide deeper insight into the mechanisms by which less structurally defined nonplatinum group metal electrocatalysts reduce O 2 . KEYWORDS: O 2 reduction, electrocatalysis, metal−organic framework, porous catalysts, 2D materials ■ INTRODUCTIONUnderstanding catalytic kinetics and thermodynamics to construct a reasonable reaction mechanism is central for both elucidating the behavior of a given catalyst and gaining predictive power over structure−function relationships. This predictive power aids in efficiently optimizing catalyst performance by systematically tuning the structural and electronic properties of the catalyst. One class of materials that could benefit from mechanism-guided optimization is nonplatinum group metal (non-PGM) electrocatalysts for the O 2 reduction reaction (ORR) to water (4e − reduction) and/or hydrogen peroxide (2e − reduction). Such catalysts typically include abundant transition metals and/or heteroatoms such as N, O, and S doped into a carbonaceous matrix.1−6 Although quite active and stable during ORR, previously reported non-PGM catalysts often consist of amorphous carbon mechanically blended with transition metal macrocycles or other metal and main group heteroatomic sources. These relatively poorly defined materials do not lend themselves to facile mechanistic studies; the inhomogeneous dispersion and irregular orientation of the dopants throughout the carbon matrix engenders structural ambiguity that makes identification, experimental probing, and computational modeling of active sites difficult.Conversely, highly ordered metal−organic frameworks (MOFs) containing well-defined, spatially isolated active sites present an attractive platform for experimental and computational correlation between the chemical and electronic structure of a given catalyst and the electrocatalytic activity and mechanism, a feat that is traditionally restricted to homogeneous molecular systems. We previously showed that the electrically conductive MOF Ni 3 (HITP) 2 (HITP = 2,3,6,7,10, (Figure 1) functions as

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Electrocatalytic Oxygen Activation by Carbanion Intermediates of Nitrogen-Doped Graphitic Carbon

Cited by 68 publications

References 39 publications

Understanding the chemisorption-based activation mechanism of the oxygen reduction reaction on nitrogen-doped graphitic materials

Understanding the chemisorption-based activation mechanism of the oxygen reduction reaction on nitrogen-doped graphitic materials

An Aza-Fused π-Conjugated Microporous Framework Catalyzes the Production of Hydrogen Peroxide

Mechanistic Evidence for Ligand-Centered Electrocatalytic Oxygen Reduction with the Conductive MOF Ni₃(hexaiminotriphenylene)₂

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Electrocatalytic Oxygen Activation by Carbanion Intermediates of Nitrogen-Doped Graphitic Carbon

Cited by 68 publications

References 39 publications

Understanding the chemisorption-based activation mechanism of the oxygen reduction reaction on nitrogen-doped graphitic materials

Understanding the chemisorption-based activation mechanism of the oxygen reduction reaction on nitrogen-doped graphitic materials

An Aza-Fused π-Conjugated Microporous Framework Catalyzes the Production of Hydrogen Peroxide

Mechanistic Evidence for Ligand-Centered Electrocatalytic Oxygen Reduction with the Conductive MOF Ni3(hexaiminotriphenylene)2

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Mechanistic Evidence for Ligand-Centered Electrocatalytic Oxygen Reduction with the Conductive MOF Ni₃(hexaiminotriphenylene)₂