O2 Binding Energy Research Articles

Effect of the electrostatic field due to the surface monolayer metal atoms on the dissociation of homonuclear diatomic gases in gas-metal surface reactions

The present paper examines the role of an electrostatic field generated by the outermost monolayer of metal ions prior to gas adsorption in aiding the dissociation of homonuclear diatomic gas molecules. The interaction of five homonuclear diatomic gases, Cl2, F2, H2, N2 and O2, with several pure metals are examined using Coulomb's law to calculate the attractive and repulsive forces between the electrons or ions in the gas molecule and the free surface metallic electrons or ions assuming a Bohr model. These calculations demonstrate that the total energy of the electrostatic fields from the metals can exceed the molecular binding energies of Cl2, F2, and O2 at some distance from the metallic surface thereby suggesting that these gases interact primarily with the metallic surface in their atomic states after molecular bond dissociation prior to reaction. In contrast, H2 and N2 gases do not dissociate prior to reaching the metal surface due to the fact that the effective charge of the gas ions is less than the total electron charge at the outermost electronic shell. The present results correlate linearly with the electrochemical series standard reduction potential as well as with the Pauling electronegativity for several metals.

Insights into CO Oxidation in Cu/CeO2 Catalysts: O2 Activation at the Dual‐Interfacial Sites

AbstractCu clusters supported on CeO2 have been reported as a promising and active catalyst for CO oxidation. However, the identification of interfacial interactions and active sites is still a great challenge. In this work, we demonstrated that interfacial chemistry can be understood and predicted by using a simple descriptor of adsorbate‐surface interactions that uncovers structure‐activity relationships. The catalytic activity of CeO2 supported Cu clusters for CO oxidation was studied by density functional theory. The Cu−Ce dual site mechanism enables the Cu/CeO2 catalyst to have a much lower reaction energy barrier than the Mars‐van Krevelen (M‐vK) mechanism and the Cu‐only mechanism. The reaction energy barriers of Cu/CeO2‐x with an oxygen vacancy on the CeO2 surface were 0.10, 0.37 and 0.77 eV, respectively. The excellent performance of Cu/CeO2 catalysts is related to the interfacial interaction between Cu and CeO2 and their synergistic redox behaviors, and oxygen vacancies facilitate the generation and stabilization of active Cu+ species through the interaction with Cu clusters. And we have identified the binding energy of O2* can describe the CO oxidation activity of Cu/CeO2. Our study provides insight into the nature of active sites for Cu/CeO2 catalysts and guidance for high‐performance.

Hydrogen Bonding Effect on the Oxygen Binding and Activation in Cobalt(III)-Peroxo Complexes.

Cobalt(III)peroxo complexes serve as model metal complexes mediating oxygen activation. We report a systematic study of the effect of hydrogen bonding on the O2 binding energy and the O-O bond activation within the cobalt(III)peroxo complexes. To this end, we prepared a series of tris(pyridin-2-ylmethyl)amine-based cobalt(III)peroxo complexes having either none, one, two, or three amino groups in the secondary coordination sphere. The hydrogen bonding between the amino group(s) and the peroxo ligand was investigated within the isolated complexes in the gas phase using helium tagging infrared photodissociation spectroscopy, energy-resolved collision-induced dissociation experiments, and density functional theory. The results show that the hydrogen bonding stabilizes the cobalt(III)peroxo core, but the effect is only 10-20 kJ mol-1. Introducing the first amino group to the secondary coordination sphere has the largest stabilization effect; more amino groups do not change the results significantly. The amino group can transfer a hydrogen atom to the peroxo ligands, which results in the O-O bond cleavage. This process is thermodynamically favored over the O2 elimination but entropically disfavored.

Identifying Key Descriptors for the Single-Atom Catalyzed CO Oxidation

Identifying Key Descriptors for the Single-Atom Catalyzed CO Oxidation

Probing the Site-Specific Reactivity and Catalytic Activity of Ag n (n = 15-20) Silver Clusters.

Density functional theory calculations within the framework of generalized gradient approximation (GGA), meta-GGA, and local functionals were carried out to investigate the reactivity and catalytic activity of Agn (n = 15–20) clusters. Our results reveal that all the Agn clusters in this size range, except Ag20, adsorb O2 preferably in the bridged mode with enhanced binding energy as compared to the atop mode. The O2 binding energies range from 0.77 to 0.29 in the bridged mode and from 0.36 to 0.15 eV in the atop mode of O2 adsorption. The strong binding in the case of the bridged mode of O2 adsorption is also reflected in the increase in O–O bond distance. Natural bond orbital charge analysis and vibrational frequency calculations reveal that enhanced charge transfer occurs to the O2 molecule and there is significant red shift in the stretching frequency of O–O bond in the case of the bridged mode of O2 adsorption on the clusters, thereby confirming the above results. Moreover, the simulated CO oxidation reaction pathways show that the oxidation of the CO molecule is highly facile on Ag16 and Ag18 clusters involving small kinetic barriers and higher heats toward CO2 formation.

Enhancing the electrocatalytic activity of Fe phthalocyanines for the oxygen reduction reaction by the presence of axial ligands: Pyridine-functionalized single-walled carbon nanotubes

We have examined the electrocatalytic activity of iron phthalocyanine (FePc) and perchlorinated iron phthalocyanine 16(Cl)FePc for the oxygen reduction reaction (ORR) in alkaline medium with the two molecules either adsorbed on the external surface of single-wall carbon nanotubes (SWCNT) or covalently anchored via an axial pyridine ligand on pyridine-functionalized single-wall carbon nanotubes (py-SWCNT). Regardless of the particular phthalocyanine type, the ORR activity is higher when the substrate is py-SWCNT rather than SWCNT. The Tafel slopes for ORR are very similar for the two Fe macrocyclic complexes attached to SWCNTs in the two different configurations, suggesting a common rate-determining step for the ORR for all four catalysts. It is also observed that, for both the SWCNT and py-SWCNT supports, the ORR activity is higher for 16(Cl)FePc than for FePc. This is attributed to the electron-withdrawing effect of the peripheral and non-peripheral chlorine atoms in the macrocyclic ligand. While FeN4 macrocycles are known to be located on the strong binding side of a volcano correlation including several MN4 species, the chlorine substituents decrease the binding energy of O2 on the central Fe cation, thereby moving up the macrocycle catalyst towards the apex of the volcano correlation. Both the carbon surface and macrocyclic ligand effects were optimized with 16(Cl)FePc attached to py-SWCNT, which is more active than both FePc on SWCNT and FePc on py-SWCNT. Here we show that both the axial ligand and the electron withdrawing groups (-Cl) have a combined collaborative effect in increasing the catalytic activity for ORR of Fe-phthalocyanines confined on the external walls of single-wall carbon nanotubes.

Unraveling electrochemical oxygen reduction mechanism on single‐atom catalysts by a computational investigation

The extension of low-expense and stable electrocatalysts for oxygen reduction reaction (ORR) is of importance to improve the performance of metal-air batteries and fuel cells. In this work, we unravel the ORR electrocatalytical mechanisms on a series of transition metal atom-doped on the defect graphene (TM@sv-graphene) by carrying out spin-polarized first-principles computations. The formation energy of the TM@sv-graphene, which is related to its stability, along with the binding energy of O2, OOH, 2OH, OH, and O species are evaluated. The calculations of Gibbs free energy show that two different pathways, O* mechanism and 2OH* mechanism, of ORR compete with each other based on the structures of intermediates (OOH, 2OH, OH and O). It is found that Co, Rh, Ir, Pt, and Mn@sv-graphene favor the O* mechanism while Ag, Au, Cd, Cu, Zn, Fe, Ni, Pd, Sc, Cr, Ti, Zr, and V@sv-graphene strongly promote the 2OH* mechanism. The overpotential (η) of the ORR is predicted and can be a valid descriptor that manifests the catalytic activity of different TM@sv-graphene. Among these catalysts, the Pd@sv-graphene (η = 1.20 V) exhibits the best activity for the ORR. The results provide new insight into electrochemical mechanism of ORR for novel single-atom electrocatalyst.

Oxygen Reduction Reaction at Co and Fe MN5 Catalysts. Calculated and Experimental O2-Fe and O2-Co Binding Energy, Activity Indexes, Volcano Correlations

The oxygen reduction reaction (ORR) is a fundamental chemical reaction in industrial processes as well as in living systems, being O2, the final electron (e-) acceptor of many reactions. Since then its importance in the fuel cell technology where energy would be stored in the form of H2 to be oxidized in conjunction with the reduction of the cheap and abundant O2. However, the ORR is a complicated reaction which involves the transfer of 4 electrons and 4 protons and for its nature, it proceeds through the consequent formation of more than one intermediate accounting for the so-called “scaling correlations” [1]. The complexity of the reaction determines the slow kinetics and the difficulties into finding an adequate catalyst for it to proceed without energy losses. The “industrial standard” catalysts for this reaction are based on the very expensive and rare Pt metal. An uncountable number of non-precious metal catalysts (NPMC) have been studied with the purpose to replace Pt. In our research group, we are adopting various strategies to increase the activity and the stability of metal phthalocyanines like the substitution of planar neutral residues with more electron-negative ones, and the addition of axial back ligands [2-5]. In this research work we studied the electrocatalytic activity towards the ORR of a new compound i.e. the iron 1,2,3,4,8,9,10,11,15,16,17,18,22,23,24,25-hexadeca(fluoro) phthalocyanine (16(F)FePc) in the absence and in the presence of a fifth pyridine axial ligand (FeN5). Interesting the 16(F)FePc appears to be the most active among all the FeN4 studied to the moment. The very high redox potential of the active Fe(III)/Fe(II) redox couple (-0.075 V and 0.44 V vs. SCE at pH 13 and at pH 1 respectively) confirms the correlation between the activity of the catalyst vs. redox potential of the active redox couple of the metal in the catalyst. 16(F)FePc was so active towards the ORR that the production of H2O2 measured at rotating ring electrodes was nil at pH 13 and very low at pH 1. In the presence of pyridine axial ligand, the redox potential increased of almost 60 mV and catalytic currents and stability of the catalyst also drastically increased. The catalysts were characterized with electrochemical techniques and by EPR and XPS spectroscopy in the presence and in the absence of O2. We could therefore experimentally evaluate the binding energy of O2 to the Fe metal centre. Ab initio calculations, confirm the experimental data and the importance of the pyridine axial ligand to lower the binding energy of O2 to the Fe metal centre because of decoupling of the Fe from the carbon support and changes in the geometrical and electronic structure.[1] Reactivity Descriptors for the Activity of Molecular MN4 Catalysts for the Oxygen Reduction Reaction. Angew. Chem. Int. Ed., 55 (2016) 14510-14521. J.H. Zagal, M.T.M. Koper.[2] Adsorption of 4,4 ́-dithiodipyridine axially coordinated to Iron(II) phthalocyanine on Au(111) as a new strategy for oxygen reduction electrocatalysis. Chemphyschem, (2018), 19(13), 1599-1604.S. Herrera, F. J. Williams, E. J. Calvo, F. Tasca.[3] Biomimicking vitamin B12. A Co phthalocyanine pyridine axial ligand coordinated catalyst for the oxygen reduction reaction. Electrochimica Acta. (2018), 265, 547-555. J. Riquelme, K. Neira, W. Orellana, P. Hermosilla, J. F. Marco, J. H. Zagal, F. Tasca.[4] Comparison of the Catalytic Activity for the Reduction of O2 of Fe and Co MN4 Complexes Adsorbed on Edge Plane Graphite Electrodes and on Carbon Nanotubes. Physical Chemistry Chemical Physics. (2017), 19(31), 20441-20450. R. Venegas, F. J. Recio, J. Riquelme, K. Neira, J. F. Marco, I. Ponce, J. H. Zagal, F. Tasca.[5] Biomimetic reduction of O2 in acid medium on iron phthalocyanines axially coordinated to pyridine anchored on carbon nanotubes”. Journal of Material Chemistry A. (2017), 5(24), 12054-12059. R. Venegas, F. J. Recio, J. Riquelme, K. Neira, J. F. Marco, I. Ponce, J. H. Zagal, F. Tasca.

A simple general descriptor for rational design of graphyne-based bifunctional electrocatalysts toward hydrogen evolution and oxygen reduction reactions

The high cost and relative scarcity of platinum (Pt) restrict large-scale commercialization of fuel cells, which has spurred researchers to develop low-cost alternatives integrating with high hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR) catalytic activity. Herein, we performed density functional theory (DFT) calculations to explore the electrocatalytic activity of graphyne nanotubes (GyNTs). Several GyNTs were found to be potential metal-free electrocatalysts, with both HER and ORR activity superior to Pt. Moreover, we revealed a linear relationship between the Gibbs free energy change of O2 adsorption (ΔGOOH) and binding energy of H adsorption (ΔEH), which could be attributed to the fact that both the CO bond of OOH adsorption and the CH bond of H adsorption are single bonds. Therefore, ΔEH is proposed as a general descriptor for the rational design of bifunctional graphyne materials toward HERs and ORRs. Our findings provide a simple strategy for the rational design of bifunctional materials.

Superatomic Signature and Reactivity of Silver Clusters with Oxygen: Double Magic Ag 17 – with Geometric and Electronic Shell Closure

Understanding the stability and reactivity of silver clusters toward oxygen provides insights to design new materials of coinage metals with atomic precision. Herein, we report a systematic study o...

Density Functional Theory Study of Oxygen Reduction on Graphene and Platinum Surfaces of Pt–Graphene Hybrids

Based on recent studies, an epitaxial monolayer of Pt on graphene yielded an enhanced catalytic activity with unprecedented stability resulting in an improved catalyst lifetime. We showed that the origin of this stability is due to strong Pt–C covalency and unique Pt and graphene surface morphologies compared to precedent physically binding metal–graphene surfaces or impurity-doped graphene catalysts. In this study, the oxygen reduction reaction (ORR) mechanisms on both surfaces are investigated using density functional theory for the first time. This two-dimensional catalyst possesses two reactive surfaces for ORR: one is the Pt surface and the other is the graphene surface. The graphene surface is found to have an undulated morphology from the sp2–sp3 alternating hybridization of carbon atoms in graphene, which are generated due to the covalent bond formation with Pt atoms. The sp2 region of graphene provides active reaction sites for the ORR, and all active sites on the Pt surface are characterized from the Pt–C(sp3) bonds. It is revealed that O2 adsorption takes place via a dissociative chemisorption mechanism on both catalytic surfaces. Compared to the Pt surface, ORR on the graphene surface would be more facile due to a weaker O2 binding energy and a lower overpotential. This study shows that a Pt–graphene hybrid system without defects or impurities on graphene is capable of exhibiting an electrochemical catalytic activity.

Intrinsic Activity of Metal Centers in Metal-Nitrogen-Carbon Single-Atom Catalysts for Hydrogen Peroxide Synthesis.

Metal-nitrogen-carbon (M-N-C) single-atom catalysts (SACs) show high catalytic activity for many important chemical reactions. However, an understanding of their intrinsic catalytic activity remains ambiguous because of the lack of well-defined atomic structure control in current M-N-C SACs. Here, we use covalent organic framework SACs with an identical metal coordination environment as model catalysts to elucidate the intrinsic catalytic activity of various metal centers in M-N-C SACs. A pH-universal activity trend is discovered among six 3d transition metals for hydrogen peroxide (H2O2) synthesis, with Co having the highest catalytic activity. Using density functional calculations to access a total of 18 metal species, we demonstrate that the difference in the binding energy of O2* and HOOH* intermediates (EO2* - EHOOH*) on single metal centers is a reliable thermodynamic descriptor to predict the catalytic activity of the metal centers. The predicted high activity of Ir centers from the descriptor is further validated experimentally. This work suggests a class of structurally defined model catalysts and clear mechanistic principles for metal centers of M-N-C SACs in H2O2 synthesis, which may be further extendable to other reactions.

Influence of Cyano Substituents on the Electron Density and Catalytic Activity Towards the Oxygen Reduction Reaction for Iron Phthalocyanine

Iron(II) 2,3,9,10,16,17,23,24-octa(cyano)phthalocyanine (OCNFePc), was tested as a catalyst for the oxygen reduction reaction (ORR) adsorbed on carbon nanotubes. The composite was analyzed spectroscopically and electrochemically characterized at pH 13 and pH 1. The composite showed close to 4 electron processes at pH 13. Computational analysis indicates that the O2 molecule binds end-on to the metal center and that the dioxygen molecule is dissociated on both the Fe metal center and the corral ring. An Analysis of the molecular electrostatic potential confirms the behavior of cyano residues as electron-withdrawing moieties in OCNFePc. As a result of its catalytic behavior and theoretical analysis of its O2 binding energy, OCNFePc was placed in a high position on a volcano correlation of similar phthalocyanine composites.

Enhancing water splitting via weakening H2 and O2 adsorption on NiCo-LDH@CdS due to interstitial nitrogen doping: A close look at the mechanism of electron transfer

This paper is a report on the development of a convenient approach to fabricating a very efficient hybrid photoelectrocatalyst for water splitting. This photoelectrocatalyst consists of nickel–cobalt layered double hydroxide as the core, cadmium sulfide as the shell, and nitrogen, hence [email protected] For the electrocatalytic activity to be improved, the H2 and O2 binding energy needs to be weakened. The interstitial nitrogen doping on [email protected] can increase electrocatalytic activity to a great extent. [email protected] nanoparticles are obtained by subjecting to nitriding the [email protected] electrode coated with polyvinylpyrrolidone nanosheets. This electrode has a large specific surface area, allows fast transfer of electrons, and exhibits long-term stability. The experimental results presented in this paper reveal that interstitial nitrogen doping largely reduces H2 and O2 binding energy and lowers the activation barrier for the formation and splitting of water.

Influence of cyano substituents on the electron density and catalytic activity towards the oxygen reduction reaction for iron phthalocyanine. The case for Fe(II) 2,3,9,10,16,17,23,24-octa(cyano)phthalocyanine

Iron(II) 2,3,9,10,16,17,23,24-octa(cyano)phthalocyanine (OCNFePc), was tested as a catalyst for the oxygen reduction reaction (ORR) adsorbed on carbon nanotubes. The composite was analyzed spectroscopically and electrochemically characterized at pH 13 and pH 1. The composite showed close to 4 electron processes at pH 13. Computational analysis indicates that the O2 molecule binds end-on to the metal center and that the dioxygen molecule is dissociated on both the Fe metal center and the corral ring. An Analysis of the molecular electrostatic potential confirms the behavior of cyano residues as electron-withdrawing moieties in OCNFePc. As a result of its catalytic behavior and theoretical analysis of its O2 binding energy, OCNFePc was placed in a high position on a volcano correlation of similar phthalocyanine composites.

Coupled Cluster Study of the Interactions of AnO2, AnO2+, and AnO22+ (An = U, Np) with N2 and CO.

Thermochemical and spectroscopic properties for actinyl complexes involving UO22+/1+/0 and NpO22+/1+/0 with N2 and CO, together with the UO2-O2, UO2+-O2, and UO2+-NO complexes, have been studied for the first time using an accurate composite coupled cluster approach. Two general bonding motifs were investigated, end-on (η1) and side-on (η2) relative to the metal center of the actinyls. For end-on CO complexes, both C-coordinated (An-C) and O-coordinated (An-O) structures were examined, with the former always being lower in energy. All of the η1 complexes were calculated to be stable, with dissociation energies ranging from 2 to 36 kcal/mol, except for that of UO2+-O2 (the η1 orientation for UO2+-NO was not amenable to single reference coupled cluster). In agreement with a previous study, the η2 structure for UO2+-O2 was calculated to be relatively strongly bound, by 22.3 kcal/mol in this work. The closely related NO complex, however, had a calculated dissociation energy of just 4.0 kcal/mol. The binding energy of O2 to neutral UO2 in a η2 orientation was calculated to be very strong, 75.4 kcal/mol, and strongly resembled a UO2+(O2-) complex at equilibrium. The N-N and C-O bonds were found to be somewhat activated for all the side-on (η2) neutral An(IV) complexes, with stretching frequencies of N2 or CO being red-shifted by as much as 480 cm-1 with a 0.06 Å bond length elongation. Dissociation energies for the η1 complexes are strongly correlated with the extent of electron transfer from ligand to actinyl. The nature of bonding in the actinyl complexes is examined using natural resonance theory (NRT). The correlation between bonding motif and small molecule activation is in agreement with experiments in condensed phases.

Experimental reactivity descriptors of M-N-C catalysts for the oxygen reduction reaction

Pyrolyzed non-precious metal catalysts (NPMCs) are promising materials to replace platinum-based catalysts in the cathode of the fuel cells. These catalysts present high catalytic activity both in alkaline and acid media for the oxygen reduction reaction (ORR). These catalysts are essentially heterogeneous as they can present different types of active sites. MNx structures have been proposed as the most active for the ORR, similar to those of the MN4 structures of metal porphyrins and phthalocyanines. Several parameters have been proposed as reactivity descriptors to correlate the structure of these materials with their catalytic activity, such as the amount of MNx and of pyridinic nitrogens in the graphitic structure. In this study, we have explored the metal center redox potential of the catalyst as an overall reactivity descriptor. We have investigated this descriptor for pyrolyzed and intact catalysts for the ORR in acid and basic media. We have found that for all catalysts tested, there is a linear correlation between the redox potential of the catalyst and the catalytic activity expressed as (log i)E). The activity increases as the redox potential becomes more positive. The correlation gives a straight line of slope close to +0.12 V/decade which agrees with the theoretical slope proposed in a previous publication assuming the adsorbed M − O2 follows a Langmuir isotherm and that the redox potential is directly linked to the M − O2 binding energy. The Tafel plots present two slopes, at low and high overpotentials. Based on these results, we proposed two different mechanisms. The low Tafel slopes of −60 mV appear at potentials where the surface concentration of M(II) active sites is potential dependent (close to the onset potential). At higher overpotentials the surface coverage of M(II) becomes constant and the slope changes to −0.120 V/decade.

Molecular conductance versus inductive effects of axial ligands on the electrocatalytic activity of self-assembled iron phthalocyanines: The oxygen reduction reaction

The construction of self-assembled iron phthalocyanine (FePc) systems on gold electrodes modified by self-assembled monolayers (SAMs) is becoming an interesting strategy for obtaining electrocatalytic molecular building blocks for the oxygen reduction reaction (ORR). In this work, we have measured the conductance of pyridiniums axial ligands at the single molecule level using the scanning tunneling microscope-based break-junction method (STM-Break Junction) to study the role of the axial ligand on the activity of the self-assembled FePc systems on a gold electrode surface. The electron-pulling effect of pyridinium axial ligands is known to increase the electrocatalytic activity of FePc for the oxygen reduction reaction (ORR). We have used these systems as a platform for carrying out a comparative study for understanding the real influence of the proximal axial ligands. Further, these ligands act as molecular wires between the gold electrode surface and the FePc molecule. The pyridinium molecules were synthesized following a series of structural variations using a basic molecular backbone. From conductance measurements obtained for each pyridinium molecule, it was possible to establish that electron transport through each pyridinium does not influence the activity of FePc for ORR in alkaline media. In addition, the DFT calculations shows that the axial ligand in FePc modifies its catalytic activity by decreasing the binding energy of O2 to the Fe site.

Developing Platinum Group Metal Free Catalysts with Multiple Metal Centers for the Oxygen Reduction Reaction in Acid

Remarkable advancement of Platinum group metal-free (PGM-free) catalysts for the oxygen reduction reaction (ORR) in acidic media makes it potentially feasible as an alternate to Pt-based catalysts in polymer electrolyte fuel cells (PEMFCs). The current leading PGM-free catalysts are composed of single transition metal atoms embedded in microporous nitrogen-doped carbon matrix (M-N-C). The commercialization of M-N-C catalysts in PEMFCs has been impeded by the insufficient activity and particularly durability. The limited ORR performance is likely owing to the single metal center configuration that causes low active site density, undesired O2 binding configuration and energy toward the metal center, etc. These inherent limitations of M-N-C catalysts motivate us to move toward Mx-N-C with multiple metal center (MMC) sites. On account of this, herein a multidentate ligand platform is utilized to prepare a series of bimetallic coordination complexes. These complexes were then used as the metal precursors to produce Mx-N-C with MMC sites by incorporating them into microporous nitrogen-doped carbon matrix via both pyrolysis and surface deposition approaches without breaking the pre-existing multiple nuclear structure. The formation of MMC sites is supported by multiple characterizations. The high ORR activity achieved is tentatively related to MMC sites that promotes the desorption of oxygen adsorbates and suppress the site-blocking effect at elevated potentials. Further improvement, however, is limited by the low concentration of MMC sites. densification of MMC sites is undergoing. Acknowledgement This work was supported by the US Department of Energy under award number DE-EE0008416. The authors declare no competing financial interests. MRCAT operations are supported by the Department of Energy and the MRCAT member institution. This research used resources of the Advanced Photon Source, a DOE Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357.

Molecular and Dissociative Adsorption of Oxygen on Au-Pd Bimetallic Clusters: Role of Composition and Spin State of the Cluster.

Utilization of molecular oxygen as an oxidizing agent in industrially important reactions is the ultimate goal to design environmentally benign processes under ambient conditions. However, the high thermal stability and a large O–O dissociation barrier in O2 molecule pose a great challenge toward its successful application in the oxidative chemistry. To achieve this goal, different catalysts based on monometallic and bimetallic clusters have been developed over the years to promote binding and dissociation of molecular oxygen. The successful design of efficient metal cluster catalysis needs an in-depth knowledge of synergistic effects between different metal atoms and intrinsic catalytic mechanisms for O2 adsorption and dissociation. Here, we present a systematic theoretical investigation of reaction pathways for O2 adsorption and dissociation on Au8, Pd8, and Au8–nPdn (n = 1–7) nanoclusters in different spin states. The density functional calculations point out that the O2 dissociation barriers can be significantly reduced with the help of certain bimetallic clusters along specific spin channels. Our results particularly indicate that Au5Pd3 and Au1Pd7 show very large O2 binding energies of 1.76 and 1.69 eV, respectively. The enhanced O2 binding subsequently leads to low activation barriers of 0.98 and 1.19 eV along the doublet and quartet spin channels, respectively, without the involvement of any spin flip-over for O2 dissociation. Furthermore, the computed O2 dissociation barriers are significantly low as compared to the already reported barriers (1.95–3.65 eV) on monometallic and bimetallic Au–Ag clusters. The results provide key mechanistic insights into the interaction and dissociation of molecular oxygen with Au–Pd clusters, which can prove informative for the design of efficient catalysts for oxidative chemistry involving molecular oxygen as a reactant.