Spectroscopic insights into the nature of active sites in iron–nitrogen–carbon electrocatalysts for oxygen reduction in acid

Jia, Qingying; Ramaswamy, Nagappan; Tylus, Urszula; Strickland, Kara; Li, Jingkun; Serov, Alexey; Artyushkova, Kateryna; Atanassov, Plamen; Anibal, Jacob; Gümeci, Cenk; Barton, Scott Calabrese; Sougrati, Moulay Tahar; Jaouen, Frédéric; Halevi, Barr; Mukerjee, Sanjeev

doi:10.1016/j.nanoen.2016.03.025

Cited by 289 publications

(233 citation statements)

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“…Having previously shown that Ni 3 (HITP) 2 reduces O 2 electrocatalytically in strongly basic medium (0.1 M KOH), we explored its utility over the wider aqueous pH range and found that the material is competent for ORR catalysis under all alkaline conditions (pH 8 and above), but not in acidic medium. Indeed, cyclic voltammograms (CVs) of Ni 3 (HITP) 2 above pH 8 showed catalytic waves with no loss in current density over 20 cycles, whereas catalytic current decreased with every cycle in acidic media (Figure 2).…”

Section: ■ Results and Discussionmentioning

confidence: 99%

“…Indeed, cyclic voltammograms (CVs) of Ni 3 (HITP) 2 above pH 8 showed catalytic waves with no loss in current density over 20 cycles, whereas catalytic current decreased with every cycle in acidic media (Figure 2). …”

Section: ■ Results and Discussionmentioning

confidence: 99%

“…To derive a kinetic rate law for ORR with Ni 3 (HITP) 2 To determine the number of electrons involved in the rate law, we collected potentiostatic data under O 2 atmosphere on a rotating disk electrode at varying rotation speeds ( Figure S2), which allowed us to determine activation-controlled Tafel slopes. The Tafel slopes are nearly identical at pH 13 and pH 8, −128 mV·dec −1 and −124 mV·dec −1 (Figure 3), respectively, and are close to −118 mV·dec −1 , the value expected for an irreversible 1e…”

Section: ■ Results and Discussionmentioning

confidence: 99%

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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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Section: ■ Results and Discussionmentioning

confidence: 99%

Section: ■ Results and Discussionmentioning

confidence: 99%

Section: ■ Results and Discussionmentioning

confidence: 99%

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

et al. 2017

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“…These can be distinguished from hydrophilic pores of low contact angle that are water-filled. 39 Dashed lines indicate deconvolution of distributions into three (NPC-2000) 33 and two (MOF SR) log-normal distributions with mean radius, r 0 , and volume fractions indicated in the table.…”

Section: Standard 5cmmentioning

confidence: 99%

Resolving Challenges of Mass Transport in Non Pt-Group Metal Catalysts for Oxygen Reduction in Proton Exchange Membrane Fuel Cells

Pavlicek

Barton

Leonard

et al. 2018

J. Electrochem. Soc.

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Mass transport properties of a pair of non-Platinum Group Metal (non-PGM) catalysts in proton exchange membrane fuel cells (PEMFCs) were evaluated through methods developed by Reshetenko et al., demonstrating that the use of different carrier gases can allow for the determination of the mass transport coefficient for oxygen in the gas phase and the electrolyte phase. The gas-phase and non-gas-phase resistances can be elucidated from the slope and intercept, respectively, of the total mass transport coefficient plotted as a function of molecular weight. It was determined through these experiments that the primary sources of mass transfer limitations of the non-PGMs when compared to the PGMs were the catalyst layer (non-gas-phase), rather than the flow fields (gas-phase, primarily Knudsen Diffusion effects), and the gas diffusion layer. This work was combined with a pseudo-2D, isothermal, steady state numerical model to estimate the gas-phase mass transfer coefficient and the fraction of hydrophobic, gas-phase pores in the catalyst layer. Sensitivity studies were also carried out, allowing for more information regarding the influence of several inherent factors on the mass transport limitations, and allow for additional validation of the model beyond simply the quality of the fit.

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“…Thanks to their versatility, they have found a range of exciting applications in spintronics [225][226][227][228][229][230], optoelectronics [231,232], solar cells [233][234][235][236][237][238], and as building blocks of magnetic materials [239][240][241][242][243]. In addition, porphyrin-like centers can be embedded in graphene and carbon nanotubes to be used for oxygen reduction catalysis [244][245][246][247][248][249]. A recent proposal suggests it might be possible to realize topologically protected excitonic states in porphyrin thin films [250].…”

Section: Introductionmentioning

confidence: 99%

A non-perturbative treatment of quantum impurity problems in real lattices

Allerdt¹

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Spectroscopic insights into the nature of active sites in iron–nitrogen–carbon electrocatalysts for oxygen reduction in acid

Cited by 289 publications

References 84 publications

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

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

Resolving Challenges of Mass Transport in Non Pt-Group Metal Catalysts for Oxygen Reduction in Proton Exchange Membrane Fuel Cells

A non-perturbative treatment of quantum impurity problems in real lattices

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Spectroscopic insights into the nature of active sites in iron–nitrogen–carbon electrocatalysts for oxygen reduction in acid

Cited by 289 publications

References 84 publications

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

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

Resolving Challenges of Mass Transport in Non Pt-Group Metal Catalysts for Oxygen Reduction in Proton Exchange Membrane Fuel Cells

A non-perturbative treatment of quantum impurity problems in real lattices

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

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