Mechanism and kinetics of the electrocatalytic reaction responsible for the high cost of hydrogen fuel cells

Cheng, Tao; Goddard, William A.; An, Qi; Xiao, Hai; Merinov, Boris V.; Morozov, Sergey I.

doi:10.1039/c6cp08055c

Cited by 53 publications

(51 citation statements)

References 52 publications

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“…The QM was at the level of PBE including D3 London dispersion (van der Waals attraction) corrections that was previously applied successfully to the oxygen reduction reaction (O 2 + protons H 2 O) on Pt and the CO 2 and CO reduction reactions on Cu surfaces. [17][18][19][20][21][23][24][25] Correcting the DFT for phonons to get free energies at experimental reaction conditions, and carrying out extensive kinetic Monte Carlo calculations to obtain the steady state populations at the conditions of the single crystal experiments (673°K , 15 atm H , atm N , and 1.5 torr NH 3 ) leads to a predicted TOF=17.7 sec-1 per 2x2 Fe(111) surface site, in excellent agreement with the single crystal experimental rate of TOF= 9.7 sec-1 per site. This suggests that the accuracy of PBE-D3 for the critical barriers may be of the order of 0.04 eV.…”

Section: Discussionmentioning

confidence: 99%

“…16 The reason is that this level of QM has been validated recently for several systems. Thus reference 17 carried out systematic studies for the oxygen reduction reaction (ORR, O 2 + protons H 2 O) on Pt(111) using the same PBE-D3 level as in this paper. Including 5 layers of explicit solvent in QM metadynamics on all reaction steps, comparisons could be made to experimental activation barriers for two values of the external potential.…”

Section: Methodsmentioning

confidence: 99%

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Reaction Mechanism and Kinetics for Ammonia Synthesis on the Fe(111) Surface

et al. 2018

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The Haber-Bosch industrial process for synthesis of ammonia (NH) from hydrogen and nitrogen produces the millions of tons of ammonia gas annually needed to produce nitrates for fertilizers required to feed the earth's growing populations. This process has been optimized extensively, but it still uses enormous amounts of energy (2% of the world's supply), making it essential to dramatically improve its efficiency. To provide guidelines to accelerate this improvement, we used quantum mechanics to predict reaction mechanisms and kinetics for NH synthesis on Fe(111)-the best Fe single crystal surface for NH synthesis. We predicted the free energies of all reaction barriers for all steps in the mechanism and built these results into a kinetic Monte Carlo model for predicting steady state catalytic rates to compare with single-crystal experiments at 673 K and 20 atm. We find excellent agreement with a predicted turnover frequency (TOF) of 17.7 s per 2 × 2 site (5.3 × 10 mol/cm/sec) compared to TOF = 10 s per site from experiment.

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Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Reaction Mechanism and Kinetics for Ammonia Synthesis on the Fe(111) Surface

et al. 2018

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“…Another indication of possible polymer character for water is that recent QM metadynamics calculations of electrocatalytic reactions with five layers of explicit solvent discovered that Grotthuss chains of up to six waters dominate the transition-state structures for the proton transfer events involved in the oxygen evolution reaction on Pt (15) and for the CO reduction reaction on Cu (16). This somewhat surprising result may arise from the polymer chains in the water solvent.…”

Section: Discussionmentioning

confidence: 99%

Liquid water is a dynamic polydisperse branched polymer

Naserifar

Goddard

2019

Proc. Natl. Acad. Sci. U.S.A.

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We developed the RexPoN force field for water based entirely on quantum mechanics. It predicts the properties of water extremely accurately, withTmelt= 273.3 K (273.15 K) and properties at 298 K: ΔHvap= 10.36 kcal/mol (10.52), density = 0.9965 g/cm3(0.9965), entropy = 68.4 J/mol/K (69.9), and dielectric constant = 76.1 (78.4), where experimental values are in parentheses. Upon heating from 0.0 K (ice) to 273.0 K (still ice), the average number of strong hydrogen bonds (SHBs, rOO≤ 2.93 Å) decreases from 4.0 to 3.3, but upon melting at 273.5 K, the number of SHBs drops suddenly to 2.3, decreasing slowly to 2.1 at 298 K and 1.6 at 400 K. The lifetime of the SHBs is 90.3 fs at 298 K, increasing monotonically for lower temperature. These SHBs connect to form multibranched polymer chains (151 H2O per chain at 298 K), where branch points have 3 SHBs and termination points have 1 SHB. This dynamic fluctuating branched polymer view of water provides a dramatically modified paradigm for understanding the properties of water. It may explain the 20-nm angular correlation lengths at 298 K and the critical point at 227 K in supercooled water. Indeed, the 15% jump in the SHB lifetime at 227 K suggests that the supercooled critical point may correspond to a phase transition temperature of the dynamic polymer structure. This paradigm for water could have a significant impact on the properties for protein, DNA, and other materials in aqueous media.

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“…The U theo was found to correlate well with detailed kinetic analysis, given that the protonation barriers during ORR calculated by using explicit water molecules were surmountable (0.1–0.5 eV) at ambient temperature …”

Section: Methodsmentioning

confidence: 68%

Importance of Ligand Effects Breaking the Scaling Relation for Core–Shell Oxygen Reduction Catalysts

Back

Jung

2017

ChemCatChem

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Tremendous recent efforts have been made toward developing highly active oxygen reduction reaction (ORR) catalysts with a minimized usage of noble metal Pt by using Pt alloys and core–Pt shell structures. A main computational framework for such a goal has been the search for a new material with the *OH binding slightly weaker than Pt based on the conventional volcano relation of ORR activity versus *OH binding energy. In this work, by using carbides and nitrides as core materials, we demonstrate that the conventional scaling relation between *OH and *O can be completely broken owing to a significant ligand–Pt orbital interactions in the core–Pt shell structure, and in such cases, the usual catalyst design strategy of tuning the *OH binding energy of Pt to a weaker leg of the volcano can mislead the prediction. In these cases, one needs to consider all reaction intermediates to appropriately predict the activity of ORR catalysts. We additionally show that, although the transition metal nitrides and carbides studied here as core materials all induce an undesired tensile strain to the Pt overlayers with a stronger *OH binding, a proper tuning of the ligand (core) effects in the Pt1 and Pt2 overlayers core–shell configurations can lead to an activity comparable to or slightly better than Pt.

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Mechanism and kinetics of the electrocatalytic reaction responsible for the high cost of hydrogen fuel cells

Cited by 53 publications

References 52 publications

Reaction Mechanism and Kinetics for Ammonia Synthesis on the Fe(111) Surface

Reaction Mechanism and Kinetics for Ammonia Synthesis on the Fe(111) Surface

Liquid water is a dynamic polydisperse branched polymer

Importance of Ligand Effects Breaking the Scaling Relation for Core–Shell Oxygen Reduction Catalysts

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