Nowadays, there is a great interest in the economic success of direct-ethanol fuel cells; however, our atomistic understanding of the designing of stable and low-cost catalysts for the steam reforming of ethanol is still far from satisfactory, in particular due to the large number of undesirable intermediates. In this study, we will report a first-principles investigation of the adsorption properties of ethanol and water at low coverage on close-packed transition-metal (TM) surfaces, namely, Fe(110), Co(0001), Ni(111), Cu(111), Ru(0001), Rh(111), Pd(111), Ag(111), Os(0001), Ir(111), Pt(111), and Au(111), employing density functional theory (DFT) calculations. We employed the generalized gradient approximation with the formulation proposed by Perdew, Burke, and Erzenholf (PBE) to the exchange-correlation functional and the empirical correction proposed by S. Grimme (DFT+D3) for the van der Waals correction. We found that both adsorbates binds preferentially near or on the on-top sites of the TM surfaces through the O atoms. The PBE adsorption energies of ethanol and water decreases almost linearly with the increased occupation of the 4d and 5dd-band, while there is a deviation for the 3d systems. The van der Waals correction affects the linear behavior and increases the adsorption energy for both adsorbates, which is expected as the van der Waals energy due to the correlation effects is strongly underestimated by DFT-PBE for weak interacting systems. The geometric parameters for water/TM are not affected by the van der Waals correction, i.e., both DFT and DFT+D3 yield an almost parallel orientation for water on the TM surfaces; however, DFT+D3 changes drastically the ethanol orientation. For example, DFT yields an almost perpendicular orientation of the C–C bond to the TM surface, while the C–C bond is almost parallel to the surface using DFT+D3 for all systems, except for ethanol/Fe(110). Thus, the van der Waals correction decreases the distance of the C atoms to the TM surfaces, which might contribute to break the C–C bond. The work function decreases upon the adsorption of ethanol and water, and both follow the same trends, however, with different magnitude (larger for ethanol/TM) due to the weak binding of water to the surface. The electron density increases mainly in the region between the topmost layer and the adsorbates, which explains the reduction of the substrate work function.

An atom-level ab initio understanding of the structural, energetic, and electronic properties of nanoclusters with diameter size from 1 to 2 nm figures as a prerequisite to foster their potential technological applications. However, because of several challenges such as the identification of ground-state structures by experimental and theoretical techniques, our understanding is still far from satisfactory, and further studies are required. We report a systematic ab initio investigation of the 55-atom metal nanoclusters, (M 55 ), including alkaline, transitional, and post-transitional metals, that is, a total of 42 systems. Our calculations are based on all-electron density functional theory within the Perdew−Burke−Ernzerhof (PBE) functional combined with van der Waals (vdW) correction, spin−orbit coupling (SOC) for the valence states. Furthermore, we also investigated the role of the localization of the d states by using the PBE+U functional. We found a strong preference for the putative PBE global-minimum configurations for the compact Mackay icosahedron structure, namely, 16 systems (Na, Mg, K, Sc, Ti, Co, Ni, Cu, Rb, Y, Ag, Cs, Lu, Hf, Re, Hg), while several systems adopt alternative compact structures such as 6 polytetrahedron (Ca, Mn, Fe, Sr, Ba, Tl) and 10 structures derived from crystalline face-centered cubic and hexagonal close-packed (HCP) fragments (Cr, Nb, Mo, Tc, Ru, Rh, Pd, Ta, W, Os). However, the 10 remaining systems adopt less compact structures based on the distorted reduced-core structure (V, Zn, Zr, Cd, In, Pt, Au), tetrahedral-like (Al, Ga), and one HCP wheel-type (Ir) structure. The binding energy shows a quasi-parabolic behavior as a function of the atomic number, and hence the occupation of the bonding and antibonding states defines the main trends (binding energy, equilibrium bond lengths, etc.). On average, the binding energy of the M 55 systems represents 79% of the cohesive energy of the respective bulk systems. The addition of the vdW correction changes the putative global-minimum configurations (pGMCs) for selected cases, in particular, for post-transitional metal systems. As expected, the PBE+U functional increases the total magnetic moment, which can be explained by the increased localization of the d states, which also contributed to increase the number of atoms in the core region (increase coordination) of the pGMCs. In contrast with the effects induced by the vdW correction and localization of the d states, the addition of the SOC coupling cannot change the lowest energy configurations, but it affects the electronic properties, as expected from previous calculations for 13-atom clusters.

In general, because of the high computational demand, most theoretical studies addressing cationic and anionic clusters assume structural relaxation from the ground state neutral geometries. Such approach has its limits as some clusters could undergo a drastic structural deformation upon gaining or losing one electron. By engaging symmetry-unrestricted density functional calculations with an extensive search among various structures for each size and state of charge, we addressed the investigation of the technologically relevant Cu(n) and Pt(n) clusters for n = 2-14 atoms in the cationic, neutral, and anionic states to analyze the behavior of the structural, electronic, and energetic properties as a function of size and charge state. Moreover, we considered potentially high-energy isomers allowing foresight comparison with experimental results. Considering fixed cluster sizes, we found that distinct charge states lead to different structural geometries, revealing a clear tendency of decreasing average coordination as the electron density is increased. This behavior prompts significant changes in all considered properties, namely, energy gaps between occupied and unoccupied states, magnetic moment, detachment energy, ionization potential, center of gravity and "bandwidth" of occupied d-states, stability function, binding energy, electric dipole moment and sd hybridization. Furthermore, we identified a strong correlation between magic Pt clusters with peaks in sd hybridization index, allowing us to conclude that sd hybridization is one of the mechanisms for stabilization for Pt(n) clusters. Our results form a well-established basis upon which a deeper understanding of the stability and reactivity of metal clusters can be built, as well as the possibility to tune and exploit cluster properties as a function of size and charge.

Glycerol (GlOH) accumulation and its very low price constitute a real problem for the biodiesel industry. To overcome these problems, it is imperative to find new GlOH applications. In this context, electrochemistry arises as an important alternative to the production of energy or fine chemicals using GlOH as a reactant. To make these opportunities a reality, it is fundamentally necessary to understand how the glycerol electro-oxidation reaction (GEOR) occurs on catalysts used in real systems. Thus, research using model surfaces generates the first insight into the electrochemistry of extremely complex real catalysts. Accordingly, in this work, we generate Pt(100) disturbed surfaces in a reproducible manner, carefully controlling the surface defect density. Then, GEOR is studied on well-ordered Pt(100) and on the disturbed Pt(100) surfaces in 0.5 M H 2 SO 4 using cyclic voltammetry (CV) and in-situ Fourier transform infrared spectroscopy (FTIR). The CV profile of GEOR consists of a single peak in the positive scan. The onset reaction displays the influence of defects present on the surface. On a surface with a high degree of disorder, the main GlOH oxidation process begins at 0.8 V vs. RHE, whereas for well-ordered Pt(100), it starts 0.1 V earlier. FTIR experiments show the presence of carbon monoxide and carbonyl absorption bands. The electrochemical and spectroelectrochemical results are supported by computational calculations (DFT) showing that both CO and GlOH bind more strongly on disturbed than well-ordered surfaces. Thus, our experiments show that Pt-CO (or other GlOH residue) bond breaking may be the GEOR rate determining step.

Glycerol has been suggested as an additional energy source for hydrogen production for fuel cell applications, and several experimental studies have been reported on glycerol conversion on transition-metal surfaces; however, our atomistic understanding of glycerol−metal interactions is still far from satisfactory. In this work, we will report a theoretical investigation of the adsorption properties of glycerol on the Pt(110), Pt(100), and Pt(111) surfaces based on density functional theory (DFT) calculations with van der Waals (vdW) corrections to the DFT total energy. In the lowest energy configurations, which differ by millielectron volts, glycerol is almost parallel to the Pt surfaces and interacts with the Pt surfaces via one of the hydroxyl groups near the on-top Pt sites, which strongly affects the orientation of glycerol relative to the surface. Our results and analyses indicate that the adsorbate structure is among the high energy configurations of glycerol in gas phase. The vdW correction enhances the adsorption energy and hence decreases the equilibrium glycerol−metal distance; in particular, it affects mainly the adsorbate structure for glycerol on Pt(110), leading to the binding of two edge glycerol hydroxyl groups to the Pt(110) surface. Moreover, the vdW correction enhances the magnitude of the glycerol adsorption energy more on Pt(111) and less on Pt(110) surfaces; however, without changing the relative order of the adsorption energies, that is, glycerol binds more strongly on Pt(110) and more weakly on Pt(111) surface. We found large work function changes (0.7−1.0 eV) upon glycerol adsorption and negligible changes in the Bader charges of the H, C, O, and Pt atoms, and hence, polarization effects play a crucial role in the interaction mechanism.

The glycerol electrooxidation reaction (GEOR) has attracted huge interest in the last decade due to the very low price and availability of this polyol. In this work, we studied the GEOR on Pt(111) electrodes by introducing different densities of random defects. Our results showed that the generation of defects on Pt(111) slightly modified the GEOR onset potential, however it generates changes in the voltammetric oxidation charges and also in the relative production of CO to carbonyl containing compounds, C[double bond, length as m-dash]O. The voltammetric profiles in the forward scan show two oxidation peaks. FTIR data show that the first one is connected with the GlOH dissociative adsorption to form CO (and others intermediates) while the second one, at higher potentials, matches the onsets of the CO oxidation to CO and the C[double bond, length as m-dash]O production. FTIR also confirms that the lower activity of defected electrodes at lower potentials is connected to a higher CO poisoning. DFT calculations show that the presence of CO molecules on a Pt defected surface keeps water and GlOH molecules far from the surface and linked by H bonds. This paper is the last of a series of three works where we explore the GEOR on an important number of different Pt surfaces. These works show that it is difficult to oxidize GlOH at potentials lower than 0.6 V (under our experimental conditions) without suffering an important electrode poisoning (mainly by CO). Since the structure of nanoparticles might be mimicked by defected single crystals, these sets of reports provide a considerable amount of information concerning the influence of such surfaces towards GlOH reaction in acidic media. Therefore, if the well-known "nano"-effect does not produce substantial changes in the activity of Pt materials, they are not useful to be applied in a Direct Glycerol Fuel Cell (DGFC). On the other hand, it is very interesting that the density of electrode defects permits us to tune the relative production of CO to C[double bond, length as m-dash]O.

We have performed a systematic investigation of 4-atom transition-metal (TM) clusters (TM = Cu, Ru, Rh, Pd, Ag, Os, Ir, Pt, and Au) supported on the unreduced CeO 2 (111) surface using density functional theory calculations within the Perdew−Burke−Ernzerhof functional and on-site Coulomb interactions for the Ce f-states. We found two structure TM 4 patterns on CeO 2 (111), namely, twodimensional (2D) arrays with zigzag orientation for Ru, Rh, Os, and Ir and tetrahedral three-dimensional (3D) configurations for Cu, Pd, Ag, Pt, and Au. Our analyses indicate that the occupation of the antibonding d-states and the hybridization of the TM d-states with O p-states play a crucial role in the magnitude of the TM−TM and TM−O interactions and determine the formation of the 2D and 3D configurations on CeO 2 (111). The interaction of TM 4 with the CeO 2 ( 111) surface changes the nature of the occupied Ce f-states from itinerant (Ce IV in the clean surface) to localized (Ce III ) states; hence, it increases the atomic size of Ce III compared with Ce IV by 4.4%, which plays a crucial role in building in a lateral tensile strain in the topmost Ce layer in the surface. Furthermore, we found an enhancement of the electron localization of the TM d-states upon the adsorption of TM 4 on CeO 2 (111). We found that the number of Ce atoms in the Ce III oxidation state depends on the TM element and structure. For Ru, Rh, Os, and Ir on CeO 2 (111), all the Ce atoms in the topmost Ce layer change the oxidation state from IV to III (i.e., 100%), while for (Pd, Pt) and (Cu, Ag, Au) on CeO 2 (111), only 25% and 50% of Ce atoms, respectively, convert the oxidation state from IV to III.

Steam reforming of ethanol–water mixture is a promising renewable route to obtain hydrogen; however, our atomistic understanding of the interaction of ethanol–water mixture with transition-metal surfaces is far from satisfactory. In this work, we report a density functional theory investigation of the adsorption properties of the ethanol–water mixture on the Pt(111) surface employing semilocal exchange-correlation functional within nonlocal van der Waals corrections. From our calculations and analysis, we found that water molecules are located near the surface instead of ethanol, which is in contrast with our initial expectation based on the large magnitude of the adsorption energy of ethanol on Pt(111) compared with water/Pt(111). We found that the formation of hydrogen bonds among ethanol–ethanol, water–water, and ethanol–water molecules plays an important role in the adsorbate structure of the ethanol–water mixture on Pt(111), in particular, due to the enhancement of the binding energy of the hydrogen bonds induced by the interaction with the Pt(111) surface. We found that the van der Waals correction does not strongly affect the adsorbate structures of the ethanol–water mixture; however, as expected, it enhances the adsorption energy, which is coverage-dependent. Furthermore, we also report results and analysis for the adsorption of ethanol and water molecules on the Pt(111).