SUPPORTING INFORMATION

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SUPPORTING INFORMATION

Elucidating Mechanistic Origin of Catalytic Activity of Fe(111) Surface and Nanocluster Towards Electrochemical Nitrogen Reduction Reaction

Arunendu Das,†_{Akhil S. Nair}† _{and Biswarup Pathak*}, †, ‡

†_{Discipline of Chemistry, Indian Institute of Technology Indore, Simrol, Indore 453552, India}

‡_{Discipline of Metallurgy Engineering and Materials Science, Indian Institute of Technology}

Indore, Simrol, Indore 453552, India *Email: [email protected]

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Contents

Figure S1. Convergence plots of (a) Fe(111) surface with respect to vacuum (Å), (b) Fe55 NC

with respect to cell size(Å3_).

Table S1. The convergence results for each of the following Fe(111) Surface and Fe55 NC systems.

Figure S2. Spin-polarised total density of states plot for Fe(111) surface with and without using

Hubbard+U correction (U = 4.5 eV).

Table S2. The thermodynamic corrections ZPE (eV), TS (eV K-1_{) at 298 K for gas phase} molecular species taken from ref.12

Table S3. The thermodynamic corrections ZPE (eV) for adsorbed intermediate species in each

elementary reduction step over the Fe(111) Surface and Fe55 NC systems.

Table S4. ZPE (eV), E (eV), G (eV) for adsorbed species involved in PDS over Fe(111) ∆ ∆

Surface with and without U.

Figure S3. Nitrogenous intermediates N2Hx (x = 1-3) and NHx (x = 1-2) species on Fe(111)

surface and their bond parameters. Blue, cyan and yellow colours represent N, H and Fe atoms, respectively. Bond length values are expressed in units in the figure. Å

Figure S4. Changes in N-N bond length of N-N based intermediate species and Bader charges of

Fe in each of the intermediate species following associative mechanism over Fe(111) surface.

Figure S5. I. Charge density difference of *N2Hx (x = 0-2) species (top and side views in a-c)

with an isosurface value = 0.01eÅ-3_{. Red and green colours represent accumulation and depletion}

of charge of an isosuface. II. Spin density of *N2Hx (x = 0-2) species on Fe(111) surface (a-c)

with an isosurface = 0.001 eÅ-3_{. Cyan, blue and yellow colours represent H, N and Fe atoms,}

respectively.

Table S5. Adsorption characteristics of NRR intermediates on Fe(111) surface and comparison

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Figure S6. p-COHP density of states plot for Fe-N interaction in *NH3 between Fe(111) surface and Fe₅₅NC.

Figure S1. Convergence plots of (a) Fe(111) surface with respect to vacuum (Å), (b) Fe55 NC

with respect to cell size(Å3_).

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Table S1. The convergence calculation results for each of the following Fe(111) Surface and

Fe55 NC systems.

Model System

Vacuum Energy cut-off (eV) k-points Total Energy (eV)

10 500 3 x 2 x 1 -367.03213 15 500 3 x 2 x 1 -366.98425 Fe(111) Surface Vacuum (Å) ₂₀ ₅₀₀ _{3 x 2 x 1} _-366.97247 20 x 20 x 20 350 1 x 1 x 1 -400.48273 22 x 22 x 22 350 1 x 1 x 1 -400.46680 NC _Size 3)

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Figure S2. Spin-polarised total density of states plot of d-orbital for Fe(111) surface with and

without using Hubbard+U correction (U = 4.5 eV).

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Table S2. The thermodynamic corrections ZPE (eV), TS (eV K-1_{) at 298 K for gas phase} molecular species taken from ref.12

Gas phase molecule

ZPE (eV) TS (eV K-1₎

N₂(g) 0.211 0.592

H₂(g) 0.344 0.404

NH₃(g) 0.985 0.596

Table S3. The thermodynamic corrections ZPE (eV) for adsorbed intermediate species in each

elementary reduction step over the Fe(111) Surface and Fe55 NC systems.

ZPE (eV) ZPE (eV)

Adsorbate (preferred site)

Surface NC

Adsorbed species involved in each

elementary step Surface NC

*N₂_{(LB) 0.12} 0.13 - - - - - - -*NNH (LB) 0.36 0.35 *N₂ *NNH 0.24 0.22 *NHNH (LB) 0.63 0.63 *NNH  *NHNH 0.27 0.28 *NNH₂_(LB) 0.65 0.64 *NNH  *NNH2 0.29 0.29 *NHNH₂_(LB) 0.98 1.01 *NNH₂ *NHNH2 0.33 0.37 *NH₂NH₂_(T) 1.34 0.97 *NHNH₂ *NH2NH2 0.36 -0.04 *N (LB) 0.04 0.04 *NNH₂ *N -0.61 -0.61 *NH (LB) 0.31 0.22 *N  *NH 0.27 0.18 *NH2 (SB) 0.64 0.63 *NH  *NH2 0.33 0.41 *NH3 (T) 0.84 0.83 *NH₂ *NH3 0.20 0.20

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Table S4. ZPE (eV), E (eV), G (eV) for adsorbed species involved in PDS over Fe(111) ∆ ∆

Surface with and without U. Potential Determining

Step in Associative Pathway

ZPE (eV) ∆E (eV) ∆G (eV)

Adsorbate (Surface) U= 0.0 U= 4.5 U= 0.0 U= 4.5 U= 0.0 U= 4.5 *NHNH2 0.988 0.982 0.510 0.516 *NHNH2 + (H+ + e- )  *NH2NH2 *NH₂NH₂ 1.342 1.342 -3.259 -3.259

Figure S3. Nitrogenous intermediates N2Hx (x = 1-3) and NHx (x = 1-2) species on Fe(111)

surface and their bond parameters. Blue, cyan and yellow colours represent N, H and Fe atoms, respectively. Bond length values are expressed in units in the figure. Å

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Figure S4. Changes in N-N bond length of N-N based intermediate species and Bader charges of

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Figure S5. I. Charge density difference of *N2Hx (x = 0-2) species (top and side views in a-c)

with an isosurface value = 0.01eÅ-3_{. Red and green colours represent accumulation and depletion}

of charge of an isosuface. II. Spin density of *N2Hx (x = 0-2) species on Fe(111) surface (a-c)

with an isosurface = 0.001 eÅ-3_{. Cyan, blue and yellow colours represent H, N and Fe atoms,}

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Table S5. Preferred adsorption sites (in parenthesis), adsorption energies (Ead), N-N distance (d N-N), shortest Fe-N distance (dFe-N)for all possible NRR intermediates while adsorbed on periodic

Fe(111) surface. Respective values from previous reports give in parenthesis in italics.19, 25 Adsorbate (preferred site) Ead (eV) dN-N ( )Å dFe-N ( )Å *N*N₍

_

₎(LB) -0.91 (-0.84)25 _1.20 _1.85 *NNH (LB) -3.96 1.30 1.83 *NHNH (LB) -2.86 1.39 1.89 *NNH₂_(LB) -3.57 1.48 1.89 *NHNH₂_(LB) -2.79 1.47 1.98 *NH₂NH₂_(T) -1.33 1.46 2.17 *N (LB) -6.12 (-5.69)19_, (-1.56)25 - 1.78 (1.78)19 *NH (LB) -4.63 (-4.18)19_, (-4.59)25 - 1.88 (1.91)19 *NH2 (SB) -3.38 (-2.81)19, (-3.31)25 - 2.03 (1.98)19 *NH3 (T) -1.06 (-0.70)19, (-0.93)25 - 2.06 (2.12)19

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Figure S6. Comparative study of the p-COHP density of states plot for Fe-N interaction in *NH3

between Fe(111) surface and Fe₅₅NC, respectively. Red and green colours represent up and down spin channel.