Advisor:Dr.Michael

Janik

1

DFTAnalysisofElementaryN2Electro-ReductionKineticsonTransitionMetalSurfaces

SharadMaheshwari

October31st,2018

Keyassumptionsmade:•  Usesonlyelementarythermodynamics;nobarriers

•  AssumesBEPforallelementaryintermediatesofassociativemechanism

Montoya,J.H.,etal.(2015).Chemsuschem8(13):2180-2186.

2

Associative mechanism – an opportunity?

Bligaard,T.etal.J.Catal.224(1):206-217.

3

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.

4

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)

5

BEP relationships fail to hold across N-H formation steps on Fe

6

Kinetic over-potential larger than thermodynamic over-potential

KO–Over-potentialtomakebarrierforeachstep≤0.4eVat0V-RHE

TO–Over-potentialtomakeΔGofeachstep≤0eV

Over-po

tentialU

(V)

7

Kinetic Volcano and HER limits NRR on transition metals

•  BEPrelationshipacrosstransitionmetalsdonotholdverywell

•  HERishighlyselectiveacrossalltransitionmetals

HERNH→ NH2

8

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.

9

Acknowledgement

Collaborators:Dr.LaurenGreenlee(UniversityofArkansas)Dr.JulieRenner(CaseWesternReserve)Dr.GholamrezaRostamikia(NorthCarolinaState)

Dr.MichaelJanikAllthemembersoftheJanikLab

 ThankYou!