Density Functional Theory Study of Iron Phthalocyanine Porous

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Density Functional Theory Study of Iron Phthalocyanine Porous Layer Deposited on Graphene Substrate: A Pt-Free Electrocatalyst for Hydrogen Fuel Cells Sean Mussell, and Pabitra Choudhury J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.5b10327 • Publication Date (Web): 29 Feb 2016 Downloaded from http://pubs.acs.org on March 1, 2016

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The Journal of Physical Chemistry

Density Functional Theory Study of Iron Phthalocyanine Porous Layer Deposited on Graphene Substrate: A Pt-Free Electrocatalyst for Hydrogen Fuel Cells

Sean Mussell and Pabitra Choudhury* Department of Chemical Engineering, New Mexico Institute of Mining and Technology, Socorro, NM 87801

Abstract This paper details the use of ab initio Density Functional Theory (DFT) to analyze a potential Ptfree

catalyst,

non-bonded

iron

phthalocyanine

mono-layer

on

graphene

substrate

(FePc/graphene), for an approximation of catalytic pathway and properties in oxidation reduction reaction of H2 and O2 to produce water. DFT calculations show that associative mechanism, where O2 molecules chemisorbed on Fe site and prefer hydrogenation to O−OH intermediate species with ambient H+ and electron transfer followed by subsequent water formation reaction (WFR), is found to dominate for the FePc/graphene surface. Throughout the entire oxygen reduction reaction (ORR) process, the initial reduction of O2 to O−OH reaction appears to be the rate limiting step with a reaction barrier of 0.68 eV. The complete free energy profile suggests that oxygen molecules are inherently favorable for reduction into water on FePc functionalized graphene surface.

Keywords: first-principles calculations, electrocatalytic reactions, metal phthalocyanine, cathode catalyst, fuel cells

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1. Introduction Fuel cells can offer higher energy density than batteries when long term use is required and can offer higher efficiencies than generators. Fuel cells offer a high potential for commercial and industrial use, however, there are several shortcomings of current technology, which needs to be overcome to make them economically enticing at low temperature.1 One of the main cost prohibitive features of fuel cells is the use of a large amount of platinum catalysts on both electrodes. Furthermore, one of the most important barriers for complete fuel cell reactions is related to the slow rate of cathode reaction where O2 is reduced, known as oxygen reduction reaction (ORR). However, Pt-based catalysts, which have been traditionally used on the cathode electrode, suffer from slower kinetics in comparison to the anode reaction2-3, declining activity, crossover, and poisoning effects.4-5 Therefore, various nanostructured and non-precious catalysts have been investigated6, including nitrogen-doped carbon nanotubes or graphene,7-10 metal-Nx-C structures11-13 and metal-N4 coordinated macrocycles.14-16

Many metal-N4-macrocyclic

compounds, such as phthalocyanines and porphyrins, have also been widely investigated for ORR both theoretically and experimentally,17-39 among which Fe-N4-macrocycle seems to have the best performance for ORR.40-41 However, the poor electron conductivity of FePc may lead to poor performance of the ORR process. The electro chemical performance and stability of FePc can be improved if FePc is supported on reduced graphene.26 In this paper, to better understand the electrocatalytic reaction steps on the FePc non-bonding functionalized pristine graphene substrate, we have performed first-principles spin-polarized density functional theory (DFT) calculations.

We have calculated elementary electro-chemical catalytic reaction steps and

investigated possible reaction mechanisms at mild reaction conditions for the ORR. We have also explored various reaction pathways for all different possible reaction steps for full catalytic


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reaction cycles on the FePc non-bonding functionalized pristine graphene substrate. These calculations include the ORR and water formation reaction (WFR) processes in practical fuel cell operation conditions. We have also identified the rate-limiting steps in ORR and WFR in both gas phase and aqueous environments. We have hypothesized that FePc/graphene system would act like a heterogeneous system as FePc can form an ordered monolayer porous surface on the graphene substrate in the nm scale. Even though FePc looks like a single molecule but when deposited on the 2D substrate such as graphene, the whole FePc/graphene could act like a porous catalyst surface like metal oxides. Moreover, graphene surface also has very high electron mobility which will allow the electron to transport from one place to the active sites for the ORR reaction very quickly.

2. Computational Methods Density functional theory (DFT) calculations were carried out using the Vienna Ab-initio Simulation Package (VASP)42-44.

The projector augmented wave method was applied to

describe the interactions between valence electrons and frozen cores45. An energy cutoff of 400 eV was used. All calculations used spin-polarized DFT. The Perdew−Burke−Ernzerhof (PBE)46 form of the generalized gradient approximation (GGA) was used to describe the exchange and correlation interactions. An efficient semiempirical scheme proposed by Grimme47 to account for long range dispersion (van der Waals interactions) corrections was used in all of the calculations. The Gaussian smearing method with a width of 0.1 eV around the Fermi level was applied to facilitate convergence. The electronic energies were converged to 10−6 eV. Ionic relaxations were performed until the residual forces on ions were less than 0.02 eV/Å.



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The FePc functionalized graphene surface is periodic in the x and y directions, and the z dimension was chosen to be large enough so that the interactions with periodic images were negligible. A slab model was used for the graphene sheet with an optimized C−C bond length (1.42 Å) and a 25 Å vacuum layer separating the sheets. The periodic x and y dimensions of supercell were 17.07 × 14.78 Å2. A 3 × 3 × 1 Monkhorst-Pack k-point mesh was chosen to The nudged elastic band (NEB)48-51 method with climbing

reduce the computational cost.

images was used for energy barrier calculations of the reaction. Quasi-Newton-Broyden method was employed for geometry relaxation until the maximal forces on each relaxed atom were less than 0.03 eV/Å. The reaction energy is defined as the difference in the total DFT energies of the products and the reactants, with a negative value being energetically favorable. We have used quantitatively reasonable model for large supercells for our calculations based on experimental information52-56 and our previous publications.57-59 To evaluate the free energy reaction profile, we first obtained the total electronic energies of surface bound species involving in each elementary reaction step using sole DFT calculations. Then the second derivatives of the Hessian matrix were obtained by a finite difference method implemented in VASP. Once the Hessian matrix was determined, it was mass-weighted and then diagonalized to obtain the eigenvalues and eigenvectors, which yielded the vibrational frequencies and normal modes.

Zero-point-energy (ZPE) corrected energies and partition

functions were obtained from these calculations. The partition functions were constructed based on the frequencies (harmonic approximation), including contributions from the electronic, translational, rotational, and vibrational degrees of freedom.60

Finite temperature

thermodynamic model calculations were carried out to obtain the free energies (G = E + EZPE − TS) of surface bound species and using the TAMKin program61-62 as implemented in our


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previous publication.63 Note that the eigenfrequencies corresponding to the global translational and rotational modes of the system were automatically labeled as zero frequencies. The free energy of hydrogen molecules, were calculated by combining both computational and experimental results as described in our previous publication.64 The free energy of H2O was calculated in the gas phase at 300 K with a pressure of 0.035 bar since at this pressure gas phase H2O was in equilibrium with liquid water at 300 K.65-66 The free energy of O2 was obtained from the reaction O2 + 2H2 = 2H2O for which a free energy change is 4.92 eV. Finally, for the reactions involving proton-electron pair transfer steps, the reaction free energy can be computed by referencing to the computational hydrogen electrode (CHE) model, described by Nørskov et al. in 2004.65 The free energy change for a general electrochemical reaction (A* + H+ + e- ⟺ AH*, where, * denotes the surface bound species) at a given potential, V and pH = 0 can be represented by the following equation:66

∆ = ∗ − ∗ − [ − ]

(1)

To incorporate the effects of water solvation environment on the reaction free energy of each elementary reaction step, we used a continuum solvation model with a smooth dielectric function (eqn. 2) by solving the Poisson-Boltzmann equation numerically in the periodic slab. = 1 + − 1

(2)

where, is the relative permittivity of the bulk solvent and is the cavity shape function, given by

=

!/ # & $√

(3)

The parameter nc determines at what value of the electron density the dielectric cavity forms, and σ is the parameter that determines the width of the diffuse cavity. This solvation model was also



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tested and implemented to study the solvation effect on various systems recently.67-71 Note that we also performed separate frequency calculations while using continuum solvation model to calculate free energy of each surface bound species.67

3. Results and Discussion The surface of iron phthalocyanine functionalized graphene was analyzed with DFT for a thermodynamic prediction of the electrochemical reactions between oxygen molecules and protons at the cathode electrode on the FePc functionalized graphene surface to determine its potential as a Pt-free cathode catalysts for the ORR of a fuel cell. Before starting the ORR reaction steps, a structural optimization was first performed for FePc functionalized graphene. The binding energy of FePc on the graphene surface was found to be -2.70 eV. This high binding energy of FePc on the graphene makes the FePc monolayer surface become stable at practical fuel cell operating conditions, consistent with recent experimental evidence.26 The Bader charge analysis of the optimized FePc/graphene surface indicates that a 0.124e- amount of charge transfer takes place from graphene to the monolayer FePc film, which could act like p-type semiconductor towards adsorption of oxidative analytes, consistent with previous findings.72 To begin the ORR reaction, an oxygen molecule was first added to the system at a distance where it would physically adsorb to the surface and allowed to reach a minimum energy state. It was found that O2 gas can have two different physisorption states. They are known as end-on, ' − ( bond length of 2.21 Å, and side-on, ' − ( bond length of 2.22 Å, configurations with adsorption energies of -0.18 eV and -0.32 eV, respectively. This is consistent with previous findings.28 The O2 molecule can then be chemically bonded


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with the central Fe atom on the FePc surface with an adsorption energy of -0.81 eV. The adsorption energy of the O2 gas molecule is defined as: )*+ = ),-./0123 − ),-./0 − )23

(4)

where, ),-./0123 , ),-./0 and )23 are the total energies of the FePc/graphene with the adsorbed O2 molecule, the isolated FePc/graphene and the isolated O2 gas molecule, respectively. Note that negative values of Ead are favorable and positive values are unbound relative to the separated species. The most stable chemisorbed O2 molecule on FePc/graphene configuration is shown in Fig. 1.

Figure 1. Optimized structural configurations for chemisorbed oxygen molecule on FePc functionalized graphene surface. The cyan, blue, mauve, red and white spheres represent C, N, Fe, O and H, respectively.

The chemisorbed O2 configuration on FePc/graphene surface shows that the O2 molecule prefers to be adsorbed on the FePc surface pointing one O atom to the Fe atom with a ' − ( bond distance of ~1.77 Å and the second O atom pointing outward with an angle (∠' − ( − () of~120.8o. The ( − ( bond length is elongated to ~1.28 Å from the normal ( − ( bond length



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of 1.21 Å (for a gaseous state O2 molecule). These configurations are similar to the previous results.28 From the Bader charge analysis, it also shows that the O2 molecule gains a total 0.402e- extra charge during chemisorption. Out of these, only a 0.153e- charge accumulated on outer O atom while the remaining 0.249e- charge accumulated on the inner O atom bonded to the Fe atom. The charge distribution of the O2 molecule is contrary to that of the charge distribution of O2 molecule when adsorbed on FePc surface only.28 This could be due to the presence of graphene substrate which loses a 0.231e- amount of charge from its surface during O2 adsorption. The last, 0.171e- charge, comes from FePc and acting as a p-type semiconductor. To gain further insight into the electronic effects, we also computed both the charge density difference (CDD) isosurface and the plane-averaged charge density difference (CDD). These are shown in Fig. 2(a) and Fig. 2(b) for the chemisorbed O2 on FePc functionalized graphene surface. We calculated CDD as: ∆6 = 6,-./023 − 6,-./0 − 623

(5)

where, 6,-./023 , 6,-./0 , 623 are the charge density of the combined system, isolated FePc/graphene and O2 molecule with geometry fixed at optimized ones in FePc/graphene-O2. We note that a substantial amount of charge accumulates on the O2 molecule, shown by the lime color isosurface in Fig.2(a). Similarly, the plane-averaged CDD was calculated perpendicular to the graphene plane.

Positive values indicate accumulation while negative values indicate

depletion of the electron charge density. There is clear evidence from the Fig. 2(b) that there was electron depletion from both graphene and FePc layers, whereas, a substantial amount of charge accumulates on O2 layers,

consistent with isosurface calculations.

Both

thermodynamically favorable adsorption energy and ( − ( bond stretching due to excess charge


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transfer to the O2 molecule, are two positive indications of a favorable first step towards the catalytic ORR.

Figure 2. (a) Charge density difference plots between FePc/graphene and O2 of the chemisorbed states of oxygen reaction on the FePc/graphene surface. The cyan, blue, mauve, red and white spheres represent C, N, Fe, O and H, respectively. The lime surface indicates the accumulated charge. The isosurface plotted is 0.015 e-/Å3. (b) The plane-averaged CDD along the surface normal direction of chemisorbed O2 on FePc/graphene surface (black solid line). The black, purple, and red dot lines mark the positions of graphene, FePc and O2 plane.

From here, two possible electrocatalytic reaction mechanisms, both of which involved ORR and water formation reaction (WFR), were tested. The first reaction mechanism had the O2 bond being cleaved and subsequent electrocatalytic reaction steps (i.e. water formation reaction (WFR)), occurring on each oxygen site separately.

This mechanism is known as dissociative

mechanism. A second reaction mechanism was the subsequent water formation reaction during ORR for reduced O2/O−OH with ambient H+ and additional electrons can be completed followed by WFR on the FePc/graphene surface. This mechanism is known as associative or peroxy mechanism, specially, where O2 does not dissociate before it is hydrogenated.65 In both reaction mechanisms, the final products are two H2O molecules.

Reaction scheme shows possible



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reaction paths we explored for these two ORR mechanisms on FePc functionalized surface. The complete ORR elementary reaction steps with free energy change at 300 K at pH = 0 for both mechanisms are also presented in Tables S1- S7 in supplementary document.

Reaction scheme. Proposed reaction paths for complete oxygen reduction reaction (ORR) followed by water formation on FePc/graphene surface, starting from chemisorbed oxygen state to production of two water molecules. Green arrows represent associative mechanism and blue arrows represent dissociative mechanism.

With the dissociative mechanism, the first elementary step is where the chemisorbed O2 molecule is dissociated into two separate O atoms on the surface, where one O atom bonded to Fe metal of FePc and the second O atom bonded to edge N site of FePc), as shown in inset of Figure 3. This dissociation reaction was found to be slightly endothermic with a reaction energy of 0.04 eV in gas phase. The reaction became exothermic with a reaction energy of -0.25 eV in the presence of aqueous environment. We have then created 6 linearly interpolated images between the initial state (IS) or chemisorbed state and final state (FS).

The NEB barrier

calculations are then performed using the climbing image nudged elastic band method with 6


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images, and vibrational frequencies were evaluated to confirm minima and transition states. The activation energy barrier for this ( − ( bond cleavage was calculated to be 2.55 eV without solvation effects and 2.70 eV with the water solvation effect included, as shown in Fig. 3. The transition state was calculated from climbing image NEB calculations and had only one imaginary vibrational frequency. The imaginary frequencies were found to be of 148.68 cm-1 without solvation corrections and 113.71 cm-1 with water solvation corrections. It is evidenced from the activation energy barrier calculations that the presence of aqueous environment can create an extra resistance for the O2 dissociation step due to the higher stability of the chemisorbed O2 as shown in Table S1-S6.

Both the activation barriers suggest that the

dissociation of O2 on FePc/graphene surface is the rate limiting step for this dissociative ORR mechanism. The high energy barrier for the ( − ( bond scission step clearly indicates that the complete ORR steps on FePc/graphene surface via this mechanism is almost impossible at normal fuel cells operating conditions. In spite of the high energy barrier for the ( − ( bond scission step, free energies of subsequent oxygen hydration steps were also calculated to verify the rate determining step of complete dissociative mechanism, as presented in Tables S1-S6. The only noticeable point from the first mechanism is that subsequent ORR/oxygen hydration step occurring at each oxygen site produces each water molecule separately. We also calculated the free energy landscapes of elementary reaction steps of all possible different dissociative pathways, as shown in Figs. S1-S6, in the supplementary document. Out of these pathways, only the most favorable free energy landscapes of the dissociative mechanism excluding and including water solvation effects at two different electrode potentials (0 V and 1.23 V) are shown here in Fig. 4a and Fig. 4b. The results clearly indicate that O2 dissociation step is the main rate limiting step for this dissociative mechanism.



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Figure 3. Free energy profile for ( − ( bond scission step on FePc/graphene surface for the first possible electrocatalytic reaction step of dissociative mechanism without (solid line) and with (dashed line) solvation corrections. The numbers indicate the energies relative to the reference system of chemisorbed O2 on FePc/graphene surface. The transition state is shown as the maxima on the energy landscape. The x-axis corresponds to the reaction coordinate along the dissociation reaction pathway.

Figure 4. Electrocatalytic reaction free energy landscapes of ORR followed by complete WFR steps for the dissociative mechanism at two different potentials (a) without water solvation


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correction and (b) with water solvation model. The numbers indicate the energies relative to the reference system of two H2O molecules produced on the FePc/graphene surface.

Next, the energy landscapes for the associative electrocatalytic mechanism were generated stepwise addition of one H+ and an additional electron. The energy landscapes are calculated step by step starting from chemisorbed O2 on FePc/graphene surface, as shown in Fig. 5. This was to simulate the ambient H+ and additional electrons (proton-electron pair) around the chemisorbed O2 (O−O) on FePc/graphene. It is known that O2 can combine with H+ to form O−OH+ in an acidic environment and the whole system becomes neutral.8 Hence, O−OH+ could be simplified to O−OH. Subsequent adsorbed H+ could be taken as H by considering the appropriate ionization potential. The free energy changes of all the elementary reaction steps of the associative mechanism at 300 K at pH = 0 are given in Table S7. For the first H addition to the reaction to O−O, H was initially kept ~3.5 Å from the top O atom of O−O bound to FePc/graphene.

The H atom is absorbed by the reduced O−O, forming a kind of

H−O−O−FePc/graphene complex during the simple relaxation. This indicates that in case of association mechanism, there is no activation barrier like dissociation mechanism where O−O bond is being cleaved in the first step and then subsequent ORR steps occurring followed by water formation reaction. The reaction free energy is found to be -0.47 eV without solvation effects and -0.55 eV with solvation corrections at a 0 V electrode potential. However, at maximum fuel cell electrode potential, the free energy changes are found to be 0.76 eV and 0.68 eV for gas phase reactions and reaction in aqueous environment, respectively. For the reaction between the second H and H−O−O−FePc/graphene, H was initially placed with a distance of 3.5 Å from the O of H−O and formed a H2O molecule. The bond angle was characterized as



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∠H−O−H of 102.5°, which is close to the ∠H−O−H found in a free H2O molecule. It was also observed that even though the H atom was placed near the O atom bonded with FePc, the system would form the same configuration as earlier. This means that we would not expect to see any H2O2 intermediate species via two-electron reduction for this associative mechanism. This could be due to high energy level of the highest-occupied 3d orbital of FePc.30 This observation is consistent with the previously described mechanism.73 Hence, we have not considered the twoelectron reduction mechanism to produce H2O2 in our further calculations. The reaction free energy for this water molecule formation was found to be highly exothermic.

A reaction free

energy of -2.08 eV was found for the gas phase calculations. The reaction was adjusted to -2.06 eV with a water solvation environment and a 0 V electrode potential as shown in Table S7. This water molecule is bound to second O atom, which is bonded to Fe atom with a distance of 1.65 Å, via H-bonding with a distance of 1.91 Å. Subsequently, we introduced a third H+ and an additional electron to the system. The H atom is bonded to remaining O atom attached to the FePc/graphene surface. (H2O)H−O−FePc/graphene complex is formed during this step. The reaction free energy for this step is found to be -0.74 eV without solvation effects and -0.79 eV with solvation corrections with a 0 V electrode potential. A fourth H+ was introduced next with an additional electron. The relaxed structure with the fourth H reacts shows a reaction with bonded OH on the FePc/graphene. From this step a second H2O molecule is produced. The reaction free energy is found to be -1.02 eV in gas phase and -0.82 eV with solvation corrections at a 0 V electrode potential. It is worthwhile to point out that water molecule produced from the WFR elementary step is in equilibrium with the gas phase water molecule as O−H bond distances and ∠H−O−H bond angle are similar to free water molecule, an assumption made in all of our previous calculations presented earlier in Tables S1-S7.


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The gas phase free energy landscapes were calculated at two different electrode potentials; V = 0 V & 1.23 V, and at pH = 0 for the electrocatalytic reaction via associative mechanism, as shown in Fig. 5a. The free energy landscapes in aqueous environment for complete ORR followed by WFR steps were also calculated at two different electrode potentials; V = 0 V & 1.23 V, and at pH = 0 by using the continuum solvation model described earlier as showing in Fig. 5b. Free energy profile (Fig. 5b) shows that the rate-determining step appears at the first reduction step, O2 (chemisorbed) → HO−O* reaction at maximum fuel cell operating potential (1.23 volt), with a reaction barrier of 0.68 eV at practical aqueous environment. This rate limiting step is consistent with the previous model of metal-coordinated nitrogen-doped carbons.73 However, this rate limiting step is different than that of ORR reaction on Pt(111) surface65, 74 and FeN4-Graphene surface,75 where OH hydrogenation step determined the overall ORR activity. We have also found that the water solvation effects on the free energy of intermediate species are small, while the water solvation can help to stabilize adsorbed O2, OOH and OH intermediates as shown in the Table S7.

Figure 5. Electrocatalytic reaction free energy landscapes of ORR followed by complete WFR steps for the associative mechanism at two different electrode potentials (i.e. 0 V and 1.23 V) (a)



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without a water solvation environment and (b) with a water solvation environment. The numbers indicate the energies relative to the reference system of two water molecules produced on the FePc/graphene surface.

4. Conclusion Our DFT calculations show that the electrocatalytic cycle for ORR and water formation reaction (WFR) on the FePc functionalized graphene surface can occur via two possible mechanisms. The first reaction mechanism was the O2 bond being cleaved with a very high energy barrier of ~2.70 eV and then subsequent ORR steps occurring on each oxygen site separately. Hence, this dissociative mechanism is unfavorable at normal fuel cell operating conditions. To the contrary, the associative mechanism, seems to be the favorable pathway, where the rate-determining step appears at the first reduction step, O2 (chemisorbed) → HO−O* reaction, with a reaction barrier of 0.68 eV at maximum fuel cell operating potential (1.23 volt). We note that mono layer metal phthalocyanines (MPcs) can be grown on graphene surface via ALD process.57-58 Thus, it should be possible to experimentally test our predictions in acidic20 and anhydrous environment. We predict that FePc/graphene materials have strong potential as a possible Pt-free alternative catalyst for fuel cells. However farther studies are required to test susceptibility of these materials to common catalyst poisons, such as CO, and the possibility of metal dissolution or segregation induced by ORR in acid or alkali environment, which are beyond the scope of our current study.

Supporting Information


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Free energy of reaction pathway 1, Free energy of reaction pathway 2, Free energy of reaction pathway 3, Free energy of reaction pathway 4, Free energy of reaction pathway 5 and Free energy of reaction pathway 6 of dissociative mechanism; and reaction free energy of associative mechanism; Zero point energies and entropy corrections of all the intermediate species for dissociative and associative mechanisms; Electrocatalytic reaction free energy landscapes of pathway 1, Electrocatalytic reaction free energy landscapes of pathway 2, Electrocatalytic reaction free energy landscapes of pathway 3, Electrocatalytic reaction free energy landscapes of pathway 4, Electrocatalytic reaction free energy landscapes of pathway 5 and Electrocatalytic reaction free energy landscapes of pathway 6 of dissociative mechanism.

Author Information Corresponding Author: * e-mail: [email protected]. Notes: The authors declare no competing financial interest.

Acknowledgement DFT calculations work was supported from NSF TeraGrid (XSEDE) resources under allocation numbers [TG-DMR130127] and [TG-DMR140131]. Use of the Center for Nanoscale Materials was supported by the US Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.

References



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1. Penner, S. S., et al., Commercialization of Fuel Cells. Prog. Energy Combust. Sci. 1995, 21, 145-151. 2. Markovic, N. M. P. N. R.; Ross, P. N., New Electrocatalysts for Fuel Cells from Model Surfaces to Commercial Catalysts. CATTECH 2000, 4, 110-126. 3. Hoogers, G. T., D.

, Catalysis in Proton Exchange Membrane Fuel Cell Technology.

CATTECH 1999, 3, 106. 4. Winter, M.; Brodd, R. J., What Are Batteries, Fuel Cells, and Supercapacitors? Chem. Rev. 2004, 104, 4245-4270. 5. Rabis, A.; Rodriguez, P.; Schmidt, T. J., Electrocatalysis for Polymer Electrolyte Fuel Cells: Recent Achievements and Future Challenges. ACS Catal. 2012, 2, 864-890. 6. Wu, G.; Zelenay, P., Nanostructured Nonprecious Metal Catalysts for Oxygen Reduction Reaction. Acc. Chem. Res. 2013, 46, 1878-1889. 7. Gong, K.; Du, F.; Xia, Z.; Durstock, M.; Dai, L., Nitrogen-Doped Carbon Nanotube Arrays with High Electrocatalytic Activity for Oxygen Reduction. Science 2009, 323, 760-764. 8. Zhang, L.; Xia, Z., Mechanisms of Oxygen Reduction Reaction on Nitrogen-Doped Graphene for Fuel Cells. J. Phys. Chem. C 2011, 115, 11170-11176. 9. Qu, L.; Liu, Y.; Baek, J.-B.; Dai, L., Nitrogen-Doped Graphene as Efficient Metal-Free Electrocatalyst for Oxygen Reduction in Fuel Cells. ACS Nano 2010, 4, 1321-1326. 10. Gao, F.; Zhao, G.-L.; Yang, S., Catalytic Reactions on the Open-Edge Sites of NitrogenDoped Carbon Nanotubes as Cathode Catalyst for Hydrogen Fuel Cells. ACS Catal. 2014, 4, 1267-1273. 11. Chen, Z.; Higgins, D.; Yu, A.; Zhang, L.; Zhang, J., A Review on Non-Precious Metal Electrocatalysts for Pem Fuel Cells. Energy Environ. Sci. 2011, 4, 3167-3192.


Page 19 of 27

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


12. Wu, G.; More, K. L.; Johnston, C. M.; Zelenay, P., High-Performance Electrocatalysts for Oxygen Reduction Derived from Polyaniline, Iron, and Cobalt. Science 2011, 332, 443-447. 13. Liang, W.; Chen, J.; Liu, Y.; Chen, S., Density-Functional-Theory Calculation Analysis of Active Sites for Four-Electron Reduction of O2 on Fe/N-Doped Graphene. ACS Catal. 2014, 4, 4170-4177. 14. Gojković, S. L.; Gupta, S.; Savinell, R. F., Heat-Treated Iron(Iii) Tetramethoxyphenyl Porphyrin Chloride Supported on High-Area Carbon as an Electrocatalyst for Oxygen Reduction: Part Ii. Kinetics of Oxygen Reduction. J. Electroanal. Chem. 1999, 462, 63-72. 15. Harnisch, F.; Wirth, S.; Schröder, U., Effects of Substrate and Metabolite Crossover on the Cathodic Oxygen Reduction Reaction in Microbial Fuel Cells: Platinum Vs. Iron(Ii) Phthalocyanine Based Electrodes. Electrochem. Commun. 2009, 11, 2253-2256. 16. Tkatchenko, A.; Scheffler, M., Accurate Molecular Van Der Waals Interactions from Ground-State Electron Density and Free-Atom Reference Data. Phys. Rev. Lett. 2009, 102, 073005. 17. Zhang, L.; Zhang, J.; Wilkinson, D. P.; Wang, H., Progress in Preparation of Non-Noble Electrocatalysts for Pem Fuel Cell Reactions. J. Power Sources 2006, 156, 171-182. 18. Samanta, S.; Sengupta, K.; Mittra, K.; Bandyopadhyay, S.; Dey, A., Selective Four Electron Reduction of O2 by an Iron Porphyrin Electrocatalyst under Fast and Slow Electron Fluxes. Chem. Commun. 2012, 48, 7631-7633. 19. Li, W.; Yu, A.; Higgins, D. C.; Llanos, B. G.; Chen, Z., Biologically Inspired Highly Durable Iron Phthalocyanine Catalysts for Oxygen Reduction Reaction in Polymer Electrolyte Membrane Fuel Cells. J. Amer. Chem. Soc. 2010, 132, 17056-17058.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 20 of 27

20. Baranton, S.; Coutanceau, C.; Léger, J. M.; Roux, C.; Capron, P., Alternative Cathodes Based on Iron Phthalocyanine Catalysts for Mini- or Micro-Dmfc Working at Room Temperature. Electrochim. Acta 2005, 51, 517-525. 21. Jasinski, R. J., Fuel Cell Electrodes Having a Metal Phthalocyanine Catalyst. Google Patents: 1968. 22. Shi, Z.; Zhang, J., Density Functional Theory Study of Transitional Metal Macrocyclic Complexes' Dioxygen-Binding Abilities and Their Catalytic Activities toward Oxygen Reduction Reaction. J. Phys. Chem. C 2007, 111, 7084-7090. 23. Ma, J.; Wang, J.; Liu, Y., Iron Phthalocyanine as a Cathode Catalyst for a Direct Borohydride Fuel Cell. J. Power Sources 2007, 172, 220-224. 24. Åhlund, J.; Schnadt, J.; Nilson, K.; Göthelid, E.; Schiessling, J.; Besenbacher, F.; Mårtensson, N.; Puglia, C., The Adsorption of Iron Phthalocyanine on Graphite: A Scanning Tunnelling Microscopy Study. Surf. Sci. 2007, 601, 3661-3667. 25. Jahan, M.; Bao, Q.; Loh, K. P., Electrocatalytically Active Graphene–Porphyrin Mof Composite for Oxygen Reduction Reaction. J. Amer. Chem. Soc. 2012, 134, 6707-6713. 26. Jiang, Y.; Lu, Y.; Lv, X.; Han, D.; Zhang, Q.; Niu, L.; Chen, W., Enhanced Catalytic Performance of Pt-Free Iron Phthalocyanine by Graphene Support for Efficient Oxygen Reduction Reaction. ACS Catal. 2013, 3, 1263-1271. 27. Liu, Q.; Zhang, J., Graphene Supported Co-G-C3n4 as a Novel Metal–Macrocyclic Electrocatalyst for the Oxygen Reduction Reaction in Fuel Cells. Langmuir 2013, 29, 38213828.


Page 21 of 27

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


28. Wang, G.; Ramesh, N.; Hsu, A.; Chu, D.; Chen, R., Density Functional Theory Study of the Adsorption of Oxygen Molecule on Iron Phthalocyanine and Cobalt Phthalocyanine. Mol. Simul. 2008, 34, 1051-1056. 29. Cui, L.; Lv, G.; Dou, Z.; He, X., Fabrication of Iron Phthalocyanine/Graphene Micro/Nanocomposite by Solvothermally Assisted Π–Π Assembling Method and Its Application for Oxygen Reduction Reaction. Electrochim. Acta 2013, 106, 272-278. 30. Sun, S.; Jiang, N.; Xia, D., Density Functional Theory Study of the Oxygen Reduction Reaction on Metalloporphyrins and Metallophthalocyanines. J. Phys. Chem. C 2011, 115, 9511-9517. 31. Xiao, K., et al., Surface-Induced Orientation Control of Cupc Molecules for the Epitaxial Growth of Highly Ordered Organic Crystals on Graphene. J. Amer. Chem. Soc. 2013, 135, 3680-3687. 32. Savadogo, O.; Lee, K.; Oishi, K.; Mitsushima, S.; Kamiya, N.; Ota, K. I., New Palladium Alloys Catalyst for the Oxygen Reduction Reaction in an Acid Medium. Electrochem. Commun. 2004, 6, 105-109. 33. Oishi, K.; Savadogo, O., Correlation between the Physico-Chemical Properties and the Oxygen Reduction Reaction Electro Catalytic Activity in Acid Medium of Pd–Co Alloys Synthesized by Ultrasonic Spray Method. Electrochim. Acta 2013, 98, 225-238. 34. Trinh, Q. T.; Yang, J.; Lee, J. Y.; Saeys, M., Computational and Experimental Study of the Volcano Behavior of the Oxygen Reduction Activity of Pdm@Pdpt/C (M = Pt, Ni, Co, Fe, and Cr) Core–Shell Electrocatalysts. J. Catal. 2012, 291, 26-35. 35. Shao, M.; Liu, P.; Zhang, J.; Adzic, R., Origin of Enhanced Activity in Palladium Alloy Electrocatalysts for Oxygen Reduction Reaction†. J. Phys. Chem. B 2007, 111, 6772-6775.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 22 of 27

36. Son, D. N.; Takahashi, K., Selectivity of Palladium–Cobalt Surface Alloy toward Oxygen Reduction Reaction. J. Phys. Chem. C 2012, 116, 6200-6207. 37. Son, D. N.; Le, O. K.; Chihaia, V.; Takahashi, K., Effects of Co Content in Pd-Skin/Pdco Alloys for Oxygen Reduction Reaction: Density Functional Theory Predictions. J. Phys. Chem. C 2015, 119, 24364-24372. 38. Lamas, E. J.; Balbuena, P. B., Oxygen Reduction on Pd0.75co0.25 (111) and Pt0.75co0.25 (111) Surfaces: An Ab Initio Comparative Study. J. Chem. Theory Comput. 2006, 2, 13881394. 39. Suo, Y.; Zhuang, L.; Lu, J., First-Principles Considerations in the Design of Pd-Alloy Catalysts for Oxygen Reduction. Angew. Chem. Int. Ed. 2007, 46, 2862-2864. 40. Morozan, A.; Campidelli, S.; Filoramo, A.; Jousselme, B.; Palacin, S., Catalytic Activity of Cobalt and Iron Phthalocyanines or Porphyrins Supported on Different Carbon Nanotubes Towards Oxygen Reduction Reaction. Carbon 2011, 49, 4839-4847. 41. Li, Z. P.; Liu, B. H., The Use of Macrocyclic Compounds as Electrocatalysts in Fuel Cells. J Appl. Electrochem. 2010, 40, 475-483. 42. Kresse, G.; Furthmüller, J., Efficiency of Ab-Initio Total Energy Calculations for Metals and Semiconductors Using a Plane-Wave Basis Set. Comput. Mater. Sci. 1996, 6, 15-50. 43. Kresse, G.; Furthmüller, J., Efficient Iterative Schemes for \Textit{Ab Initio} Total-Energy Calculations Using a Plane-Wave Basis Set. Phys. Rev. B 1996, 54, 11169-11186. 44. Kresse, G.; Hafner, J., Ab Initio Molecular Dynamics for Liquid Metals. Phys. Rev. B 1993, 47, 558-561. 45. Kresse, G.; Joubert, D., From Ultrasoft Pseudopotentials to the Projector Augmented-Wave Method. Phys. Rev. B 1999, 59, 1758-1775.


Page 23 of 27

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


46. Perdew, J. P.; Burke, K.; Ernzerhof, M., Generalized Gradient Approximation Made Simple. Phys. Rev. Lett. 1996, 77, 3865-3868. 47. Grimme, S., Semiempirical Gga-Type Density Functional Constructed with a Long-Range Dispersion Correction. J. Comput. Chem. 2006, 27, 1787-1799. 48. Sheppard, D.; Terrell, R.; Henkelman, G., Optimization Methods for Finding Minimum Energy Paths. J. Chem. Phys. 2008, 128, 134106. 49. Henkelman, G.; Jónsson, H., Improved Tangent Estimate in the Nudged Elastic Band Method for Finding Minimum Energy Paths and Saddle Points. J. Chem. Phys. 2000, 113, 9978-9985. 50. Henkelman, G.; Uberuaga, B. P.; Jónsson, H., A Climbing Image Nudged Elastic Band Method for Finding Saddle Points and Minimum Energy Paths. J. Chem. Phys. 2000, 113, 9901-9904. 51. Jónsson, H. M., G.; Jacobsen, K. W., In Classical and Quantum Dynamics in Condensed Phase Simulations. In World Scientific: Singapore, Berne, B. J. C., G.; Coker, D. F., Ed. 1998; p 385. 52. Tanaka, Y.; Mishra, P.; Tateishi, R.; Cuong, N. T.; Orita, H.; Otani, M.; Nakayama, T.; Uchihashi, T.; Sakamoto, K., Highly Ordered Cobalt–Phthalocyanine Chains on Fractional Atomic Steps: One-Dimensionality and Electron Hybridization. ACS Nano 2013, 7, 13171323. 53. Ishida, N.; Fujita, D., Adsorption of Co-Phthalocyanine on the Rutile Tio2(110) Surface: A Scanning Tunneling Microscopy/Spectroscopy Study. J. Phys. Chem. C 2012, 116, 2030020305.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 24 of 27

54. Wießner, M.; Kübert, J.; Feyer, V.; Puschnig, P.; Schöll, A.; Reinert, F., Lateral Band Formation and Hybridization in Molecular Monolayers: Ntcda on Ag(110) and Cu(100). Phys. Rev. B 2013, 88, 075437. 55. Liu, X.; Wei, Y.; Reutt-Robey, J. E.; Robey, S. W., Dipole–Dipole Interactions in Tiopc Adlayers on Ag. J. Phys. Chem. C 2014, 118, 3523-3532. 56. Huang, H.; LiangWong, S.; Chen, W.; ShenWee, A. T., Lt-Stm Studies on SubstrateDependent Self-Assembly of Small Organic Molecules. J. Phys. D: Appl. Phys. 2011, 44, 464005. 57. Park, J. H.; Choudhury, P.; Kummel, A. C., No Adsorption on Copper Phthalocyanine Functionalized Graphite. J. Phys. Chem. C 2014, 118, 10076-10082. 58. Park, J. H. K., I.; Choudhury, P.; Sardashti, K.; Prakash, H. C.; Banerjee, S.; Fullerton, S.and Kummel, A. C., Self Assembled Ordered Phthalocyanine Monolayers on 2dsemiconductors for Subnanometer Dielectrics Ald Nucleation. In TECHCON, Austin, TX, United States, 2014. 59. Park, J. H., et al., In-Situ Observation of Initial Stage in Dielectric Growth, and Deposition of Ultrahigh Nucleation Density Dielectric on Two-Dimensional Surfaces. Nano Lett. 2015. 60. McQuarrie, D. A.; Simons, J. D., Physical Chemistry: A Molecular Approach; University Science Books: Sausalito, Ca,, 1997. 61. Ghysels, A.; Verstraelen, T.; Hemelsoet, K.; Waroquier, M.; Van Speybroeck, V., Tamkin: A Versatile Package for Vibrational Analysis and Chemical Kinetics. J. Chem. Inf. Model. 2010, 50, 1736-1750.


Page 25 of 27

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


62. Ghysels, A.; Van Speybroeck, V.; Verstraelen, T.; Van Neck, D.; Waroquier, M., Calculating Reaction Rates with Partial Hessians: Validation of the Mobile Block Hessian Approach. J. Chem. Theory Comput. 2008, 4, 614-625. 63. Choudhury, P.; Johnson, J. K., Methyl Chloride Reactions on Lithiated Carbon Nanotubes: Lithium as Both Reactant and Catalyst. J. Phys. Chem. C 2011, 115, 11694-11700. 64. Choudhury, P.; Bhethanabotla, V. R.; Stefanakos, E., Manganese Borohydride as a Hydrogen-Storage Candidate: First-Principles Crystal Structure and Thermodynamic Properties. J. Phys. Chem. C 2009, 113, 13416-13424. 65. Nørskov, J. K.; Rossmeisl, J.; Logadottir, A.; Lindqvist, L.; Kitchin, J. R.; Bligaard, T.; Jónsson, H., Origin of the Overpotential for Oxygen Reduction at a Fuel-Cell Cathode. J. Phys. Chem. B 2004, 108, 17886-17892. 66. Nie, X.; Luo, W.; Janik, M. J.; Asthagiri, A., Reaction Mechanisms of Co2 Electrochemical Reduction on Cu(1 1 1) Determined with Density Functional Theory. J. Catal. 2014, 312, 108-122. 67. Mathew, K.; Sundararaman, R.; Letchworth-Weaver, K.; Arias, T. A.; Hennig, R. G., Implicit Solvation Model for Density-Functional Study of Nanocrystal Surfaces and Reaction Pathways. J. Chem. Phys. 2014, 140, 084106. 68. Fattebert, J.-L.; Gygi, F., Density Functional Theory for Efficient Ab Initio Molecular Dynamics Simulations in Solution. J. Comput. Chem. 2002, 23, 662-666. 69. Jinnouchi, R.; Anderson, A. B., Electronic Structure Calculations of Liquid-Solid Interfaces: Combination of Density Functional Theory and Modified Poisson-Boltzmann Theory. Phys. Rev. B 2008, 77, 245417.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

70. Wang, H.-F.; Liu, Z.-P., Formic Acid Oxidation at Pt/H2o Interface from Periodic Dft Calculations Integrated with a Continuum Solvation Model. J. Phys. Chem. C 2009, 113, 17502-17508. 71. Li, Y.-F.; Liu, Z.-P.; Liu, L.; Gao, W., Mechanism and Activity of Photocatalytic Oxygen Evolution on Titania Anatase in Aqueous Surroundings. J. Amer. Chem. Soc. 2010, 132, 13008-13015. 72. Tran, N. L.; Kummel, A. C., A Density Functional Theory Study on the Binding of No onto Fepc Films. J. Chem. Phys. 2007, 127, 214701. 73. Zhang, J.; Wang, Z.; Zhu, Z., The Inherent Kinetic Electrochemical Reduction of Oxygen into H2o on Fen4-Carbon: A Density Functional Theory Study. J. Power Sources 2014, 255, 65-69. 74. Zhang, J.; Vukmirovic, M. B.; Xu, Y.; Mavrikakis, M.; Adzic, R. R., Controlling the Catalytic Activity of Platinum-Monolayer Electrocatalysts for Oxygen Reduction with Different Substrates. Angew. Chem. Int. Ed. 2005, 44, 2132-2135. 75. Zhang, J.; Wang, Z.; Zhu, Z.; Wang, Q., A Density Functional Theory Study on Mechanism of Electrochemical Oxygen Reduction on Fen4-Graphene. J. Electrochem. Soc. 2015, 162, F796-F801.


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Density Functional Theory Study of Iron Phthalocyanine Porous

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