DFT Analysis of Elementary N Electro-Reduction Kinetics on ...
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Advisor:Dr.Michael
Janik
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DFTAnalysisofElementaryN2Electro-ReductionKineticsonTransitionMetalSurfaces
SharadMaheshwari
October31st,2018
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Keyassumptionsmade:• Usesonlyelementarythermodynamics;nobarriers
• AssumesBEPforallelementaryintermediatesofassociativemechanism
Montoya,J.H.,etal.(2015).Chemsuschem8(13):2180-2186.
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Associative mechanism – an opportunity?
Bligaard,T.etal.J.Catal.224(1):206-217.
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Tafel-like
Heyrovsky-like
“Reference” TransitionInitial
Tafel and Heyrovsky-like schemes on Fe (100) and Fe (110)
Initial
Reference
Transition
G.Rostamikia,etal.,JournalofPowerSources2011,196,9228-9237.
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Distal pathway under Heyrovsky-like steps on Fe (110) has lowest barriers
• Preferredpathwaychangesasthesurfaceorschemechanges
• Heyrovsky-likestepsingeneralhaslowerbarriers
Fe(1
10)
Fe(1
00)
Tafel-Distal Tafel-Alternating Heyrovsky-AlternatingHeyrovsky-Distal1.0
0.0
-1.0
-2.0
Relativ
efreeene
rgy(eV)at0
V-
RHE
S.Maheshwarietal.,JournalofChemicalPhysics,(2018)(Accepted)
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BEP relationships fail to hold across N-H formation steps on Fe
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Kinetic over-potential larger than thermodynamic over-potential
KO–Over-potentialtomakebarrierforeachstep≤0.4eVat0V-RHE
TO–Over-potentialtomakeΔGofeachstep≤0eV
Over-po
tentialU
(V)
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Kinetic Volcano and HER limits NRR on transition metals
• BEPrelationshipacrosstransitionmetalsdonotholdverywell
• HERishighlyselectiveacrossalltransitionmetals
HERNH→ NH2
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Activ
ationEne
rgy(eV)
Proton transfer agent can alter the activation barrier
• Usingexplicitwatermolecules,essentiallycapturedthesolvationeffectswith3H2O
• Amineandcarboxylicacidhaverelativelysmallerbarrier
H XR
N N HMetal Metal
HXR
N NHEactivation
RXH–Co-catalystlikeH2O,MeOH,HCOOH,CH3NH2etc.
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Acknowledgement
Collaborators:Dr.LaurenGreenlee(UniversityofArkansas)Dr.JulieRenner(CaseWesternReserve)Dr.GholamrezaRostamikia(NorthCarolinaState)
Dr.MichaelJanikAllthemembersoftheJanikLab
ThankYou!