Copyright © 2011 American Scientific Publishers All rights reserved Printed in the United States of America Journal of Nanoscience and Nanotechnology Vol 11, 2983–2989, 2011 Hydronium Adsorption on OOH Precovered Pt(111) Surface: Effects of Electrode Potential Do Ngoc Son1 ∗ , Bach Thanh Cong2 , and Hideaki Kasai1 Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan Department of Physics, Hanoi University of Science, 334 Nguyen Trai, Hanoi, Vietnam Using the Density Functional Theory-based total energy calculations, the hydronium adsorption on the OOH precovered Pt(111) surface is studied The electrode potential is modeled by varying the electron affinity of the reduction center [OOH+H3 O(H2 O)]+ Two possible structures of this reduction center on the Pt surface are HOOH + 2H2 O and 2(OH) + 2H2 O Evidently, the dissociation of HOOH into 2(OH) can be accomplished by changing the electrode potential to the higher value by 0.16 V The activation energy for the dissociation is approximately 0.1 eV The optimized structures are also obtained Keywords: Hydrated Hydronium Ion, Platinum Surface, Electrode Potential, Electron Affinity, Activation Energy OH ad + H3 O+ + e− 2H2 O Reductive desorption (RD) Delivered by Ingenta to: Nanyang Technological University (6) IP: 46.148.31.236 On: Wed, 08 Jun 2016 09:59:12 The Pt(111) surface has long been the best electrocatCopyright: American Scientific Publishers alyst for the oxygen reduction (ORR) due to its role Reactions (2)–(6) represent two adsorption pathways: as the rate controlling reaction in electrochemical energy One is through the dissociative adsorption (3) that forms conversion.1–3 Fully understanding the mechanism of the adsorbed oxygen atom (Oad on the surface, followed by oxygen reduction on the Pt surface is highly desirable in a reductive transition (4) from Oad to adsorbed hydroxyl both fundamental and applicable aspects Over the Pt sur(OH)ad In this pathway, the first electron transfers after face in aqueous perchloric and sulfuric acid media, the DA of O2 ; the other pathway is through the molecular oxygen reduction to water can be observed in four-electron adsorption (2), followed by a reductive adsorption (5) in steps in the presence of hydronium ion H3 O+ , which which first electron transfers after the O2 adsorption In or appears by the charge comes from the membrane both cases, the reaction is completed by the reductive defects in water created by excess protons on the cathdesorption of (OH)ad (6) Experimental and density funcode of proton exchange membrane fuel cells The overall tional theory (DFT) investigations found that O2 favorably ORR is + − adsorbs on clean Pt(111) surface, as expressed in (2), in 6H2 O (1) O2 + 4H3 O + 4e two possible configurations The first is a surface-parallel The four-electron steps of intermediate reactions, which configuration centered over a bridge site as a -bound were introduced in our previous work,7 are proposed as paramagnetic O2 − superoxo (bridge) state The second is follows a tilted configuration over a three fold fcc hollow site in a (2) O2 O2 ad Molecular adsorption -bound nonmagnetic O2 2− peroxo (hollow) state.8–16 The superoxo state is more stable than the peroxo state Both (3) O2 2Oad Dissociative adsorption (DA) adsorption states are observed at high coverages, but only OH ad + H2 O Oad + H3 O+ + e− the peroxo state is observed at low coverages.17 The DA (3) was studied by Yotsuhashi et al.,18 wherein O2 dissociReductive transition (RT) (4) ates into two Oad atoms as O2 approaches to the Pt surface O2 ad + 2H3 O+ + 2e− OH ad + 2H2 O at a positive value of potential energy corresponding to the O–O distance about Å and the center of mass of O2 to Pt Reductive adsorption (RA) (5) surface about 1.5 Å The reductive transition (4) has been ∗ done in the work of Son et al.7 Author to whom correspondence should be addressed INTRODUCTION 1533-4880/2011/11/2983/007 doi:10.1166/jnn.2011.3903 2983 RESEARCH ARTICLE J Nanosci Nanotechnol 2011, Vol 11, No Hydronium Adsorption on OOH Precovered Pt(111) Surface: Effects of Electrode Potential Son et al RESEARCH ARTICLE It is important to notice that there are two electrons in the reductive adsorption reaction (5), which can be further divided into the following two steps In the first electron reduction step, potentials, reaction energies, and activation energies for redox reactions under the electrode potential Therefore, we need a charge self-consistent theory for these problems An ab initio charge self-consistent theory has been developed by Anderson’s research group.22 The electrode + − O2 ad + H3 O + e Oad OH + H2 O (7) potential was modeled by varying the electron affinities of the reactant complex The transition state structures O2 ad gets molecularly adsorbed before the proton is and activation energies were reported for the four onetransferred from the hydronium ion to O2 ad , and simultaelectron steps of oxygen reduction In order to investigate neously reduces one electron to form an adsorbed end-on intermediate Oad OH on the Pt surface with Oad on top site the effects of electrode potential, an alternative approach The reaction (7) was also investigated in Ref [7] would be either to charge the Pt layer, or put the system The second electron reduction can proceed through the under the influence of an external field By charging the following serial reduction and/or direct reduction in which Pt layer, the work function of metal is varied A strong the reductive adsorption is continued by succeeding to (7) electric field across the double layer results in the surin the presence of another hydronium ion face charge First-principles computational approach to a Serial reduction: The relatively stable intermediate charged surface and interface, and the solution–electrode Oad OH can be decomposed into adsorbed oxygen and interface, under a bias voltage (an electrode potential) hydroxyl6 with a small barrier yielding coadsorbed oxygen in the framework of slab models were also introduced and hydroxyl (Oad + (OH)ad , in the work of Otani et al.23 24 The method is called the Effective Screening Medium-Based First Principles Oad OH Oad + OH ad (8) Molecular Dynamics The dependence of activation enerbefore interacting with another hydronium and reduces gies on the electrode potential can also be revealed by second electron to form 2(OH)ad as the following reactions using phenomenological models for relating electrode currents to activation Gibbs energies These models is based + − Oad + OH ad + H3 O + e Oad + H2 Oad + H2 O (9) on the view point of expanding the activation Gibbs enerOad + H2 OadDelivered OH by (10) giesTechnological about the reversible potential One of these modad Ingenta to: Nanyang University IP: 46.148.31.236 On: Wed,els 08isJun 2016 09:59:12 the linear approximation, which gives rise to the The decomposition is primarily driven American by the Scientific Publishers Copyright: Butler-Volmer equations and provides insight into the lin19 chemisorption of hydroxyl ear regions of Tafel plots of the log of the current density Direct reduction: The Oad OH intermediate in (7) can as a function of the electrode overpotential.25 The other is directly interact with another hydronium ion and reduce the harmonic model, which has linear and quadratic terms the second electron with the following reaction,6 and a parameter attributed to the solvent reorganization Oad OH + H3 O+ + e− HOad OH + H2 O (11) energy accompanying the electron transfer Marcus and others have developed this model based on the electronto form an end-on adsorbed hydrogen peroxide HOad OH transfer equations for characterizing outer-sphere electronThis peroxide readily dissociates homolytically to form transfer reactions where electron tunneling is associated 2(OH)ad as shown in reaction (12), with a sudden charge in the redox state.26–28 In this work, we study reactions (11) and (12) on HOad OH OH ad (12) the same footing utilizing the Density Functional Theory In this paper, the research shall be focused on the based on exchange correlation functional, which has been intermediate reactions (11) and (12) taking into account recognized as good method in describing chemical systhe electrode potential of the Pt surface using the Dentems When the electron is loaded into the slab, the charge sity Functional Theory Understanding the dependence of mainly goes to the Pt surface causing the change in the mechanism, structures, and activation energies on the elecFermi level The charge will then transfer from the Pt surtrode potential is one of main research topics in the surface to the reduction center and enhances its electron affinface chemical reaction sciences The formation of (OH)ad ity by varying the applied electrode potential The electron by the electrooxidation of H2 O and its potential depenaffinity then modifies the optimized geometry of the reducdence on Pt electrodes has been studied with a view toward tion center understanding its mechanism using the non-charge selfThis paper is organized as follows: In Section 2, we give consistent Atom Superposition and Electron Delocalizadetails of the computational method used in this study In tion Molecular Orbital models.20 21 This model is high Section 3, we sequentially present the simulation results accuracy for predicting the changes in bond polarizafor the reductive transition and the reductive adsorption, tions and hybridizations as a function of electrode potential However, it was not applicable to predict accurate and lastly in Section 3, we draw the conclusions 2984 J Nanosci Nanotechnol 11, 2983–2989, 2011 Son et al Hydronium Adsorption on OOH Precovered Pt(111) Surface: Effects of Electrode Potential COMPUTATIONAL METHOD (a) (b) Fig (a) Model for the calculation of potential energy surface The distances from the hydrogen H2 to the Pt surface and to the hydronium ion O3 are denoted by Pt–H and O–H, respectively (b) The potential energy surface as a function of Pt–H and O–H At the minimum energies Min1 = −0 17 eV at (Pt–H = 3.7 Å, O–H = 1.7 Å), and Min2 = − 57 eV at (Pt–H = 2.9 Å, O–H = Å), the HOOH and the separated 2(OH) are formed, respectively The dissociation of HOOH into 2(OH) follows the least energy pathway, the arrowed curve J Nanosci Nanotechnol 11, 2983–2989, 2011 2985 RESEARCH ARTICLE hydronium ion shall be hydrated by the water molecule before reacting with OOH In this paper, we focus the We perform the DFT-based total energy calculations utilizresearch on the reaction (11), in which the hydronium ing the Vienna ab initio simulation package VASP.29–31 For ion H3 O+ is hydrated by one water molecule, OOH + the exchange correlation energy, we use the Perdew-BurkeH3 O+ (H2 O) + e− , on the Pt(111) surface We also investiErnzerhof (PBE) derivatives of the generalized gradient gate the effects of electrode potential on the dissociation of approximation,32 which is good for the non-uniform charge HOOH into 2(OH) following the reaction (12) on the same density systems The electron-ion interaction is described footing The optimized structures, the minimum energies, using the projector-augmented-wave (PAW) method33 34 the activation energies for the HOOH formation and for with plane waves up to the cutoff energy of 400 eV Calcuthe dissociation of HOOH into 2(OH), can be obtained by lations for the reactions (11) and (12) on the same footing studying the potential energy for the hydrated hydronium are performed with a three-layer slab of Pt(111) (4 × 4), ion toward the Pt surface A slab model in Figure 1(a) is and a vacuum space of 14.65 Å in the supercell Each Pt used for the calculation of the potential energy surface To layer consists of 16 atoms with nearest neighbor distance avoid confusion, just few important indexes of Pt atoms of 2.78 Å All Pt atom positions in slab are fixed in the (labeled 1, 2, and 3) are shown in this figure The optisimulation This causes an error of 0.01 eV in the total mized structure of the OOH intermediate adsorbed with an energy calculations as compared with the first-Pt layer end on the Pt surface, which was obtained in Ref [7], has relaxed case We have chosen sufficiently large supercell the bond distances of Pt1–O1 = 2.75 Å, Pt2–O2 = 2.02 Å, to avoid interactions between hydronium ions and oxyO1–O2 = 1.44 Å, and O1–H1 = 1.01 Å The distance Pt– gen atoms of different unit cells The surface Brillouin H2 of hydrogen H2 to the Pt surface is denoted by Pt–H, zone integration is done using the special point sample and O–H denotes for the distance from H2 to the hydrotechnique of Monkhorst and Pack with × × samnium oxygen O3 The potential energy surface, in general, pling meshes.35 The cutoff energy and the vacuum space can be obtained when the H3 O+ (H2 O) complex is moved and the sampling meshes are tested to ensure the contoward the Pt surface along the slab normal to the oxygen vergence of calculations In addition, water molecules are O2 of the OOH intermediate However, in details, for each included in the periodic supercell since the water molecule fixed value of Pt–H, O–H is varied by moving the hydrohas a large dipole moment, which gives rise to the nonnium oxygen O3 along the extended line of O2–H2 In this Delivered by Ingenta Nanyang Technological University negligible effect on the energetic of hydronium ion to: on the Pt atoms and H2 and O3 are fixed while all IP: 46.148.31.236 On: Wed,calculation, 08 Jun 2016 09:59:12 Pt surface The dipole correction is taken into account in the others are allowed Copyright: American Scientific Publishers to relax Fixing Pt atoms causes an the simulation.36 37 error in the total energy calculation of 0.01 eV The total energy of the Pt(111)-OOH + H3 O+ (H2 O) + e− complex as a function of O–H and Pt–H is obtained and presented in RESULTS AND DISCUSSION Figure 1(b) This figure is partitioned into three different areas for three different states of the complex denoted by In our previous paper,7 the optimized structure for the Phase 1, 2, and by the black curves OOH + H2 O formation was found, in which OOH is an In Phase 1, the OOH+H3 O+ (H2 O)+e− complex, which end-on adsorbed on the Pt(111) surface If the next hydro+ has a large Pt–H above 3.3 Å and a small O–H less than nium ion H3 O approaches the OOH + H2 O complex, the Hydronium Adsorption on OOH Precovered Pt(111) Surface: Effects of Electrode Potential Å, is in the initial state corresponding to the isolated H3 O+ (H2 O) over the Pt–OOH For the large distances of Pt–H (greater than 3.1 Å) and O–H (greater than Å), the OOH + H3 O+ (H2 O) + e− complex passes through its structure in Phase The hydrated hydronium ion H3 O+ (H2 O) is closed enough to the OOH intermediate, and there is the transfer of proton H2 from H3 O+ (H2 O) to OOH to form HOOH weekly adsorbed on the Pt surface The minimum energy, Min1 = − 17 eV at (Pt–H = 3.7 Å, O–H = 1.7 Å), corresponds to the HOOH formation This value of minimum energy is originated from a transition state on the interface (the black line) of Phase and Phase at (Pt–H = 3.3 Å, O–H = 2.6 Å) The optimized structure of HOOH + 2H2 O and the corresponding total charge density are shown in Figures 2(a) and (b), respectively At Min1, O1 is side-adsorbed on Pt1 while O2 is on the top of Pt2 O1H1 is almost parallel to the Pt surface, while O2H2 is in the direction of the surface normal, and angles (H1O1O2) = 101 and (H2O2O1) = 100 The bond distances of the HOOH formation are listed in Table I This table shows that O1–H1 is 0.07 Å shorter, while O1–O2 is 0.02 Å longer, than those of (a) Son et al OOH in the initial state, respectively The calculated distance of O1–O2 is in good agreement with the results obtained in Refs [38–39] The total charge density of the HOOH formation is shown in Figure 2(b), where HOOH is interpreted as a set of the identical center roundish curves closest to the Pt surface The outer most contour curve describes the bonding of HOOH with 2H2 O and also the adsorbed state of the HOOH + 2H2 O complex on the Pt surface As shown in Figure 1(b), there is a gradual transition from Phase to Phase on varying O–H for large enough Pt–H Independently, the OOH + H3 O+ (H2 O) + e− complex can also transit directly from Phase to Phase for its initial state with a short enough distance of Pt–H (less than 3.3 Å) Phase is interpreted as the deep well interfacing with Phase for small O–H and with Phase for large O–H As stated before that the calculation of the potential energy surface is obtained by varying each fixed value of Pt–H and O–H is altered to find the minimum energies Thus, for small distances of Pt–H lower than that at Min1 (Pt–H = 3.7 Å, O–H = 1.7 Å) of the HOOH formation, H2 is interpreted as being forced to move toward the Pt (b) RESEARCH ARTICLE Delivered by Ingenta to: Nanyang Technological University IP: 46.148.31.236 On: Wed, 08 Jun 2016 09:59:12 Copyright: American Scientific Publishers (c) (d) Fig (a) The optimized structure of the HOOH + 2H2 O formation on the Pt surface (b) The contour plot of the total charge density of the HOOH + 2H2 O complex (c) The optimized structure of the 2(OH) + 2H2 O formation on the Pt surface (d) The contour plot of the total charge density of the 2(OH) + 2H2 O complex 2986 J Nanosci Nanotechnol 11, 2983–2989, 2011 Son et al Hydronium Adsorption on OOH Precovered Pt(111) Surface: Effects of Electrode Potential Table I List of parameters of the HOOH + 2H2 O and the 2(OH) + 2H2 O Intermediates Pt–O1 (Å) Pt–O2 (Å) OOH (Phase 1) HOOH (Phase 2) O1–H1 (Å) O2–H2 (Å) 06 94 75 99 01 96 05 02 01 2(OH) (Phase 3) a O1–O2 (Å) 44 46 50a ∼ 50b 64 ∼ 30a Minimum energy (eV) Fermi energy of Pt Slab (eV) −0.17 (Min1) −0 55 −1.57 (Min2) −0 71 b Ref [38] Ref [39] J Nanosci Nanotechnol 11, 2983–2989, 2011 2987 RESEARCH ARTICLE surface This enforcement is possible by varying the elecThe transition must overcome a barrier at the interface of these two phases This transition is understood as the distrode potential.39 When H2 is forced to lower positions, sociation of HOOH into 2(OH) The activation energy for the reduction center [OOH + H3 O(H2 O)]+ passes through this dissociation is directly related to the classical barrier its structure in Phase The minimum energy, Min2 = height, i.e., the energy difference between the maximum − 57 eV at (Pt–H = 2.9 Å, O–H = Å), corresponds energy of the saddle point at (Pt–H = 3.0 Å, O–H = 1.2 Å) to the two separated OH formation on the Pt surface, and the energy Min1 Thus, the transition from Phase 2(OH) + 2H2 O The optimized structure of 2(OH) + 2H2 O to Phase corresponding to the dissociation of HOOH and the corresponding total charge density are presented into 2(OH) must overcome an activation energy of about in Figures 2(c) and (d), respectively The energy difference 0.1 eV of Min1 and Min2 is 1.4 eV Figure 2(c) shows that O1 As aforementioned, the potential energy surface was and O2 adsorb on the top of Pt1 and Pt2, respectively, and obtained by varying Pt–H and O–H For each fixed Pt–H, the hydrogen H1 intervenes between O1 and O2 separatO–H is gradually changed by fixing O3 at different posiing these two oxygen atoms The bond distances in the tions to obtain the optimized structures of the reaction 2(OH) + 2H2 O formation are also pointed in Table I One center This method is equivalent to applying the elecfound that Pt–O1 and Pt–O2 are decreased and shorten trode potential onto the Pt slab If the electrode potential by 0.98 Å and 0.7 Å, correspondingly, compared to those Nanyang Technological University is altered, the Fermi level of the slab is varied, leading to of HOOH + 2H2 O It meansDelivered that O1 by andIngenta O2 are to: much 08 Junthe 2016 09:59:12 amount of electron transfer from the Pt slab stronger bound on the Pt surface IP: The46.148.31.236 bond distance ofOn: O2-Wed,modify Copyright: American Scientific Publishers to the reduction center [OOH + H3 O(H2 O)]+ adsorbed on H2 is the same for both cases while O1–H1 and O1–O2 the surface, and hence, modifying the electron affinity of increases by 0.03 Å and 1.18 Å, respectively, compared to the reduction center Due to the thermal fluctuations, if the those of HOOH + 2H2 O Additionally, the obtained value electron affinity matches the electron chemical potential of of O1–O2 is comparable to that in the work of Ref [39] the Pt slab, the reduction center will pass through its strucThe significant change in the O1–O2 distance occurs by tures that are of HOOH + 2H2 O or 2(OH) + 2H2 O The the intervention of the hydrogen H2 between O1 and O2 electron chemical potential of the Pt electrode is the negThis intervention stems from H2 was forced toward the ative of the work function 39 Thus, the electron affinity, Pt surface, which can be done by changing the electrode EA, is potential making the variation in the electron affinity of EA = − = − Evacuum − EFermi (13) the reduction center [OOH + H3 O(H2 O)]+ , which shall be discussed later in this manuscript Additionally, it can be Here, the vacuum level and the Fermi level of Pt slab seen that O1–H1 is 0.04 Å shorter than that of OOH are denoted by Evacuum and EFermi , respectively In order to in the initial state This change in O1–H1 stabilizes the obtain the vacuum level, the potential energy as a function partially occupied ∗ orbitals of oxygen O1 The total of z along the surface normal is calculated The obtained charge density of the 2(OH) + 2H2 O formation is shown curve presented in Figure is the local potential of the Pt in Figure 2(d), where 2(OH) is presented by two sets of slab, in which the average vacuum level is approximately the identical center roundish curves, while in the case of Evacuum = 69 eV HOOH + 2H2 O is only one set, closest to the Pt slab surDifferent structures of the reduction center were face The presentation of the total charge densities could obtained, which are of HOOH + 2H2 O and 2(OH) + 2H2 O help us to distinguish the difference between the HOOH The corresponding Fermi levels for these structures, as formation and the 2(OH) formation The outer most conshown in Table I, are −0.55 eV and −0.71 eV, respectour curve describes the bonding of 2(OH) with 2H2 O, tively Using Eq (13), the electron affinities of these two also the adsorbed state of the 2(OH) + 2H2 O complex on structures can be obtained, correspondingly, EA1 = −5 24 the Pt surface eV and EA2 = −5 eV The work functions are also Figure 1(b) also shows that there is a possibility for the deduced that are = 24 eV and = eV, respecreduction center transit from Phase to Phase along the tively The difference of the two electron affinities is 0.16 eV least reaction pathway as described by the arrowed curve RESEARCH ARTICLE Hydronium Adsorption on OOH Precovered Pt(111) Surface: Effects of Electrode Potential Son et al hydrogen atoms loose its charge The charge gain of oxygen atoms attains from hydrogen atoms and from the Pt slab The total charge gain of the reduction center from the Pt slab is approximately +0 93e and +1.72e for Phase and Phase 3, respectively These amounts of charge mainly go to oxygen atoms O1 and O2, as shown in Table II When the charge of O1 and O2 increases, the repulsive force between these oxygen atoms also increases, pushing them far from with each other, and hence, giving the space between O1–O2 for H2 to occupy The distance O1–O2 is increased, as shown in Table I, to form two separated OH adsorbed on the Pt surface When the Pt electrode is applied with the more positive potential of 0.16 V compared to the case of the HOOH formation in Phase 2, the Fermi level of the electrode is decreased from −0.55 eV to Fig Local potential of the Pt(111) slab The curve is flat for z ranging −0.71 eV, increasing the electron transfer from the elecfrom to over The average of the flat part of the local potential trode into the reduction center This change in the electron corresponds to the average vacuum level of the Pt slab The average vacuum level is 4.69 eV transfer varies the electron affinity of the reduction center, arranging the optimal structures in Phase and Phase as the electron affinity of the reduction center matches the On the scale of the standard hydrogen electrochemical electron chemical potential of the Pt slab As have seen potential, the electrode potential U is given as in the above analysis, the O1–O2 is stretched, while O1– H1 is shrunken, compared to OOH in the initial state The eU = − eV (14) stretching of the O1–O2 bond stabilizes the partially occupied ∗ orbitals of O1 and O2, while the shrinking of the As determined by (14), 2(OH) is formed at the electrode O1–H1 bond stabilizes the partially occupied ∗ orbitals potential of 0.8 V for = eV This value of the elecof O1 and O2, increasing the electron affinity of the reductrode potential is within theDelivered 1.23 V reversible by Ingentapotential to: Nanyang Technological University as obtained in the upper part on the standard hydrogen scale,IP: and46.148.31.236 closed to the workOn: Wed,tion 08 center Jun 2016 09:59:12 The effects of the electric double layer and the elecCopyright: American Publishers ing voltage of the cathode of the proton exchange mem- Scientific trode potential are incorporated by introducing excess elecbrane fuel cells around 0.8 V on Platinum electrodes.40 trons to a metal-solution interface slab model,22 where The electrode potential of 0.8 V is 0.2 V greater than of a compensating uniform background charge was artifithe OH formation from water decomposition on platinum cially inserted to the vacuum layer to measure the applied electrodes electrode potential In this work, a comparison of two The difference of electrode potentials of the two strucadsorbed states in Phase and Phase are mainly contures in Phase and Phase 2, U , is cerned with The hydrated hydronium ion is formed as − adsorbed on the OOH precovered Pt(111) surface so that U = U − U1 = = 16 V (15) e an electron of hydrogen atom H2 is transferred to the PtOOH This model is neutral, and hence, the uniform backFrom the above analysis, it is found that the dissociation ground charge is not required.41 of HOOH into 2(OH) can be done by applying a more positive potential of 0.16 V onto the Pt electrode In order to understand how much charge variation of the CONCLUSION reduction center corresponding to the 0.16 eV difference in the electron affinity, the Bader charge shall be analyzed In this work, we have studied the formation of HOOH and in the following section 2(OH) on the Pt surface and the transition of the former In Table II, the Bader charge of atoms in the reduction into the latter on the same footing and clarified the effects of the electrode potential using the density functional thecenter was calculated The Bader charge of H2 is zero in ory On varying the position of proton, the potential energy both cases, and H2 remains its role as a proton of the surface was obtained by changing the bond distance of the reduction center Oxygen atoms gain charge while other Table II Bader charge of the HOOH + 2H2 O (Phase 2) and the 2(OH) + 2H2 O (Phase3); (−) charge loss, (+) charge gain Structure Phase Phase 2988 O1 (e) O2 (e) O3 (e) O4 (e) H1 (e) +0 9893 +1 3347 +0 9902 +1 4124 +1 9848 +1 9975 +1 9605 +1 9701 −0 9997 −0 9999 H2 (e) 0 H3 (e) H4 (e) H5 (e) H6 (e) −0 9988 −0 9988 −0 9994 −0 9995 −0 9989 −0 9986 −0 9994 −0 9984 Total gain (e) +0 9286 +1 7195 J Nanosci Nanotechnol 11, 2983–2989, 2011 Son et al Hydronium Adsorption on OOH Precovered Pt(111) Surface: Effects of Electrode Potential 11 Y Xu, A V Ruban, and M Mavrikakis, J Am Chem Soc 126, 4717 (2004) 12 M.-L Bocquet, J Cerda’, and P Sautet, Phys Rev B: Condens Matter Mater Phys 59, 15437 (1999) 13 H Steininger, S Lehwald, and H Ihbach, Surf Sci 117, 342 (1982) 14 N R Avery, Chem Phys Lett 96, 371 (1983) 15 B C Stipe, M A Rezaei, W Ho, S Gao, M Persson, and B I Lundqvist, Phys Rev Lett 78, 4410 (1997) 16 A Panchenko, M T M Koper, T E Shubina, S J Mitchell, and E Roduner, J Electrochem Soc 151, A2016 (2004) 17 B C Stipe, M A Rezaei, and W Ho, J Chem Phys 107, 6443 (1997) 18 S Yotsuhashi, Y Yamada, W A Dino, H Nakanishi, and H Kasai, Phys Rev B 72, 033415 (2005) Acknowledgments: This work is partly supported by 19 E B Yeager, Electrochim Acta 29, 1527 (1984) the Ministry of Education, Culture, Sports, Science and 20 A B Anderson, J Chem Phys 62, 1187 (1975) Technology of Japan (MEXT) through the Grants-in-Aid 21 A B Anderson, Int J Quantum Chem 49, 581 (1994) for Scientific Research (A19206007) and (A20246011) 22 A B Anderson, Electrochim Acta 48, 3743 (2003) 23 M Otani and O Sugino, Phys Rev B 73, 115407 (2006) and through the Special Coordination Funds for the Global 24 M Otani, I Hamada, O Sugino, Y Morikawa, Y Okamoto, and Center of Excellence (COE) program (H08) “Center of T Ikeshoji, J Phys Soc Jpn 77, 024802 (2008) Excellence for Atomically Controlled Fabrication Tech25 R J D Miller, G L McLendon, A J Nozik, W Schmickler, nology.” One of the authors (Do Ngoc Son) acknowland F Willig, Surface Electron-Transfer Processes, VCH, New York edges the funding from the Marubun Research Promotion (1995) 26 R A Marcus and N Sutin, Biochim Biophys Acta 81, 265 (1985) Foundation 27 R A Marcus, J Chem Phys 24, 966 (1956) 28 R J D Miller, G L McLendon, A J Nozik, W Schmickler, and F Willig, Surface Electron-Transfer Processes, VCH, New York References and Notes (1995) 29 G Kresse and J Hafner, Phys Rev B 48, 13115 (1993) J O’M Bockris and S U M Khan, Surface Electrochemistry, 30 G Kresse and J Hafner, Phys Rev B 49, 14251 (1994) Plenum, New York (1993) Delivered by Ingenta to: Nanyang Technological University 31 G Kresse and J Furthmuller, Phys Rev B 54, 11169 (1996) M R Tarasevich, A Sadkowski, and E B Yeager, Oxygen elecIP: 46.148.31.236 On: Wed,32.08J Jun 2016 09:59:12 P Perdew, J A Chevary, S H Vosko, K A Jackson, M R trochemistry, Comprehensive Treatise of Electrochemistry, edited Copyright: American Scientific Publishers Pederson, D J Singh, and C Fiolhais, Phys Rev B 46, 6671 (1992); by B E Conway, J O’M Bockris, E B Yeager, S U M J P Perdew, K Burke, and M Ernzerhof, Phys Rev Lett 77, 3865 Khan, and R W White, Plenum, New York (1983), Vol 7, (1996) Chap 33 P E BlÖchl, Phys Rev B 50, 17953 (1994) A J Appleby, J Electroanal Chem 357, 117 (1993) D N Son and H Kasai, Eur Phys J E 29, 351 (2009) 34 G Kresse and J Joubert, Phys Rev B 59, 1758 (1999) M Eikerling, A A Kornyshev, A M Kuznetsov, J Ulstrup, and 35 H J Monkhorst and J D Pack, Phys Rev B 13, 5188 (1976) S Walbran, J Phys Chem B 105, 3646 (2001) 36 J Neugebauer and M Scheffler, Phys Rev B 46, 16067 (1992) M Tuckerman, K Laasonen, M Sprik, and M Parrinello, J Chem 37 L Bengtsson, Phys Rev B 59, 12301 (1999) Phys 103, 150 (1995) 38 Y Wang and P B Balbuena, J Phys Chem B 109, 14894 (2005) D N Son, H Nakanishi, M Y David, and H Kasai, J Phys Soc 39 A B Anderson and T V Albu, J Electrochem Soc 147, 4229 Jpn 78, 114601 (2009) (2000) A Eichler and J Hafner, Phys Rev Lett 79, 4481 (1997) 40 A B Anderson, Electrochim Acta 47, 3759 (2002) A Eichler, F Mittendorfer, and J Hafner, Phys Rev B: Condens 41 E Skúlason, G S Karlberg, J Rossmeisl, T Bligaard, J Greeley, Matter Mater Phys 62, 4744 (2000) H Jónsson, and J K Nørskov, Phys Chem Chem Phys 9, 3241 10 Z Sljivancanin and B Hammer, Surf Sci 515, 235 (2002) (2007) proton and the hydronium oxygen to find the optimized structures of the reduction center [OOH+H3 O(H2 O)]+ By this way, the electron affinity of the reduction center was varied, and hence, the electrode potential takes its effects The change in the electron affinities of HOOH+2H2 O and 2(OH) + 2H2 O is 0.16 eV corresponding to the 0.16 V variation of the electrode potential This research evidently shows that the dissociation of HOOH into 2(OH) can be done by changing the electrode potential The activation energy for the decomposition of HOOH into 2(OH) is about 0.1 eV J Nanosci Nanotechnol 11, 2983–2989, 2011 2989 RESEARCH ARTICLE Received: 31 January 2010 Accepted: 15 March 2010 ... accurate and lastly in Section 3, we draw the conclusions 2984 J Nanosci Nanotechnol 11, 2983–2989, 2011 Son et al Hydronium Adsorption on OOH Precovered Pt(111) Surface: Effects of Electrode Potential. .. nium ion H3 O approaches the OOH + H2 O complex, the Hydronium Adsorption on OOH Precovered Pt(111) Surface: Effects of Electrode Potential Å, is in the initial state corresponding to the isolated... 2983–2989, 2011 Son et al Hydronium Adsorption on OOH Precovered Pt(111) Surface: Effects of Electrode Potential Table I List of parameters of the HOOH + 2H2 O and the 2(OH) + 2H2 O Intermediates Pt–O1