Alain R. Puente Santiago

Bio: Alain R. Puente Santiago is an academic researcher from University of Texas at El Paso. The author has contributed to research in topics: Catalysis & Electrocatalyst. The author has an hindex of 13, co-authored 25 publications receiving 416 citations. Previous affiliations of Alain R. Puente Santiago include University of Córdoba (Spain).

Tuning of Trifunctional NiCu Bimetallic Nanoparticles Confined in a Porous Carbon Network with Surface Composition and Local Structural Distortions for the Electrocatalytic Oxygen Reduction, Oxygen and Hydrogen Evolution Reactions.

Abstract: The rational design of multifunctional catalysts that use non-noble metals to facilitate the interconversion between H2, O2, and H2O is an intense area of investigation. Bimetallic nanosystems with highly tunable electronic, structural, and catalytic properties that depend on their composition, structure, and size have attracted considerable attention. Herein, we report the synthesis of bimetallic nickel-copper (NiCu) alloy nanoparticles confined in a sp2 carbon framework that exhibits trifunctional catalytic properties toward hydrogen evolution (HER), oxygen reduction (ORR), and oxygen evolution (OER) reactions. The electrocatalytic functions of the NiCu nanoalloys were experimentally and theoretically correlated with the composition-dependent local structural distortion of the bimetallic lattice at the nanoparticle surfaces. Our study demonstrated a downshift of the d-band of the catalysts that adjusts the binding energies of the intermediate catalytic species. XPS analysis revealed that the binding energy for Ni 2p3/2 band of the Ni0.25Cu0.75/C nanoparticles was shifted ∼3 times compared to other bimetallic systems, and this was correlated to the high electrocatalytic activity observed. Interestingly, the bimetallic Ni0.25Cu0.75/C catalyst surpassed the OER performance of RuO2 benchmark catalyst exhibiting a small onset potential of 1.44 V vs RHE and an overpotential of 400 mV at 10 mA·cm-2 as well as the electrochemical long-term stability of commercial RuO2 and Pt catalysts and kept at least 90% of the initial current applied after 20 000 s for the OER/ORR/HER reactions. This study reveals significant insight about the structure-function relationship for non-noble bimetallic nanostructures with multifunctional electrocatalytic properties.

Co-Cu Bimetallic Metal Organic Framework Catalyst Outperforms the Pt/C Benchmark for Oxygen Reduction.

Abstract: Platinum (Pt)-based-nanomaterials are currently the most successful catalysts for the oxygen reduction reaction (ORR) in electrochemical energy conversion devices such as fuel cells and metal-air batteries. Nonetheless, Pt catalysts have serious drawbacks, including low abundance in nature, sluggish kinetics, and very high costs, which limit their practical applications. Herein, we report the first rationally designed nonprecious Co-Cu bimetallic metal-organic framework (MOF) using a low-temperature hydrothermal method that outperforms the electrocatalytic activity of Pt/C for ORR in alkaline environments. The MOF catalyst surpassed the ORR performance of Pt/C, exhibiting an onset potential of 1.06 V vs RHE, a half-wave potential of 0.95 V vs RHE, and a higher electrochemical stability (ΔE1/2 = 30 mV) after 1000 ORR cycles in 0.1 M NaOH. Additionally, it outperformed Pt/C in terms of power density and cyclability in zinc-air batteries. This outstanding behavior was attributed to the unique electronic synergy of the Co-Cu bimetallic centers in the MOF network, which was revealed by XPS and PDOS.

Tailoring the Interfacial Interactions of van der Waals 1T-MoS2/C60 Heterostructures for High-Performance Hydrogen Evolution Reaction Electrocatalysis.

Abstract: Fullerene-based low-dimensional (LD) heterostructures have emerged as excellent energy conversion materials. We constructed van der Waals 1T-MoS2/C60 0D-2D heterostructures via a one-pot synthetic approach for catalytic hydrogen generation. The interfacial 1T-MoS2-C60 and C60-C60 interactions as well as their electrocatalytic properties were finely controlled by varying the weight percentages of the fullerenes. 1T-MoS2 platforms provided a novel template for the formation of C60 nanosheets (NSs) within a very narrow fullerene concentration range. The heterostructure domains of 1T-MoS2 and C60 NSs exhibited excellent hydrogen evolution reaction (HER) performances, with one of the lowest onset potentials and ΔGH* values for LD non-precious nanomaterials reported to date.

Tuning the Intermolecular Electron Transfer of Low-Dimensional and Metal-Free BCN/C60 Electrocatalysts via Interfacial Defects for Efficient Hydrogen and Oxygen Electrochemistry.

Abstract: The development of low-dimensional (LD) supramolecular materials with multifunctional electrocatalytic properties has sparked the attention of the catalysis community. Herein, we report the synthesis of a new class of 0D-2D heterostructures composed of boron carbon nitride nanosheets (BCN NSs) and fullerene molecules (C60/F) that exhibit multifunctional electrocatalytic properties for the hydrogen evolution/oxidation reactions (HER/HOR) and the oxygen evolution/reduction reactions (OER/ORR). The electrocatalytic properties were studied with varying F:BCN weight ratios to optimize the intermolecular electron transfer (ET) from the BCN NSs to the electron-accepting C60 molecules. The nanohybrid supramolecular material with 10 wt % F in BCN NSs (10% F/BCN) exhibited the largest Raman and C 1s binding energy shifts, which were associated with greater cooperativity interactions and enhanced ET processes at the F/BCN interface. This synergistic interfacial phenomenon resulted in highly active catalytic sites that markedly boosted electrocatalytic activity of the material. The 10% F/BCN showed the highest tetrafunctional catalytic performance, outperforming the OER catalytic activity of commercial RuO2 catalysts with a η10 of 390 mV and very competitive onset potential values of -0.042 and 0.92 V vs RHE for HER and ORR, respectively, and a current density value of 1.47 mA cm-2 at 0.1 V vs RHE with an ultralow ΔGH* value of -0.03 eV toward the HOR process. Additionally, the 10% F/BCN catalyst was also used as both cathode and anode in a water splitting device, delivering a cell potential of 1.61 V to reach a current density of 10 mA cm-2.

Essentials Of Computational Chemistry Theories And Models

Abstract: The fact that a new text book introducing the essentials of computational chemistry contains more than 500 pages shows impressively the grown and still growing size and importance of this field of chemistry. The author’s objectives of the book, using his own words, are “to provide a survey of computational chemistry its underpinnings, its jargon, its strengths and weaknesses that will be accessible to both the experimental and theoretical communities”. This design as a general introduction into computational chemistry makes it an alternative to Andrew R. Leach’s well-established “Molecular Modeling” (Prentice Hall) and Frank Jensen’s “Introduction to Computational Chemistry” (Wiley), although the latter focuses on the theory of electronic structure methods. Cramer’s “Essentials” covers force field and molecular orbital theory, Monte Carlo and Molecular Dynamics simulations, thermodynamic and electronic (spectroscopic) property calculation, condensed phase treatment and a few more topics. Moreover, the book contains thirteen selected case studies sexamples taken from the literature sto illustrate the application of the just presented theoretical and computational models. This especially makes the text book well suited for both classroom discussion and self-study. Each chapter of “Essentials” covers a main topic of computational chemistry and will be briefly described here; all chapters are ended by a bibliography and suggested additional readings as well as the literature references cited in the text. In chapter 1 the author defines basic terms such as “theory”, “model”, and “computation”, introduces the concept of the potential energy surface and provides some general considerations about hardware and software. Interestingly, the first equation occurring in the text is not Schro ̈dinger’s equation, as is the case for most computational chemistry introductions, but the famous Einstein relation. The second chapter deals with molecular mechanics. It explains the different potential energy contributions, introduces the field of structure optimization, and provides an overview of the variety of modern force fields. Chapter 3 covers the simulation of molecular ensembles. It defines phase space and trajectories and shows the formalism of, and problems and difference between, Monte Carlo and molecular dynamics. In chapter 4 the author introduces the foundations of molecular orbital theory. Basic concepts such as Hamilton operator, LCAO basis set approach, many-electron wave functions, etc. are explained. To illuminate the LCAO variational process, the Hu ̈ckel theory is presented with an example. Chapter 5 deals with semiempirical molecular orbital (MO) theory. Besides the classical approaches (extended Hu ̈ckel, CNDO, INDO, NDDO) and methods (e.g., MNDO, AM1, PM3) and their performance, examples are provided from the ongoing development in that still fascinating area. Ab initio MO theory is presented in chapter 6; the basis set concept is discussed in detail, and, after some considerations from an user’s point of view, the general performance of ab initio methods is explicated. The next chapter covers the problem of electron correlation and gives the most prominent solutions for its treatment: configuration interaction, theory of the multiconfiguration self-consistent field, perturbation, and coupled cluster. Practical issues are also discussed. Chapter 8’s topic is density functional theory (DFT). Its theoretical foundation, methodology, and some functionals as well as its pros and cons compared to MO theory are presented together with a general performance overview. The next two chapters deal with charge distribution, derived and spectroscopic properties (e.g., atomic charges, polarizability, rotational, vibrational, and NMR spectra), and thermodynamic properties (e.g., zero-point vibrational energy, free energy of formation, and reaction). The modeling of condensed phases is addressed in chapters 11 (implicit models) and 12 (explicit models), which closes with a comparison between the two approaches. Chapter 13 familiarizes the reader with hybrid quantum mechanical/molecular mechanical (QM/MM) models. Polarization as well as the problematic implications of unsaturated QM and MM components are discussed, and empirical valence bond methods are also presented. The treatment of excited states is the topic of chapter 14; besides CI and MCSCF as computational methods, transition probabilities and solvatochromism are discussed. The last chapter deals with reaction dynamics, mostly adiabaticskinetics, rate constants, reaction paths, and transition state theory are section topics here sbut also nonadiabatic, introducing curve crossing and Marcus theory in brief. The appendix is divided into four parts: an acronym glossary (which is very helpful), an overview of symmetry and group theory, an introduction to spin algebra, and finally a section about orbital localization. A rather detailed index ends the book. The “Essentials” writing style fits the fascinating topic: one reads on and on andssurprise! sanother chapter has been absorbed. The text is complemented by a large number of black and white figures and clear tables, mostly self-explanatory with descriptive captions. The use of equations and mathematical formulas in general is well-balanced, and the level of math should be understandable for every natural scientist with some basic knowledge of physics. There are only a few minor shortcomings: for example, a literature reference cited in the text (“Beck et al.”, p 142) is missing in the bibliography; “Kronecker” is mistyped with o ̈; and the author completely forgot to reference Leach’s text book when referring to other computational chemistry introductions. However, the author has established a specific errata web page (http://pollux.chem.umn.edu/ ∼cramer/Errors.html) with all known errors. These will be corrected in the next printing or next revised edition, respectively. With its emphasis, on one hand, on the basic concepts and applications rather than pure theory and mathematics, and on the other hand, coverage of quantum mechanical and classical mechanical models including examples from inorganic, organic, and biological chemistry, “Essentials” is a useful tool not only for teaching and learning but also as a quick reference, and thus will most probably become one of the standard text books for computational chemistry.

High-Throughput Screening of Synergistic Transition Metal Dual-Atom Catalysts for Efficient Nitrogen Fixation.

Abstract: Great enthusiasm in single-atom catalysts (SACs) for the nitrogen reduction reaction (NRR) has been aroused by the discovery of metal-Nx as a promising catalytic center. However, the poor activity and low selectivity of available SACs are far away from the industrial requirement. Through the first-principles high-throughput screening, we find that Fe-Fe distributed on graphite carbon nitride (Fe2/g-CN) can manipulate the binding strength of the target reaction species (compromises the ability to adsorb N2H and NH2), therefore achieving the best NRR performance among 23 transition metal (TM) centers. Our results show that Fe2/g-CN achieves a high theoretical Faradaic efficiency of 100% and, impressively, the lowest limiting potential of -0.13 V. Particularly, multiple-level descriptors shed light on the origin of NRR activity, achieving a fast prescreening among various candidates. Our predictions not only accelerate discovery of catalysts for ammonia synthesis but also contribute to further elucidate the structure-performance correlations.

Environmental Transformations of Silver Nanoparticles: Impact on Stability and Toxicity

Abstract: Silver nanoparticles (Ag-NPs) readily transform in the environment, which modifies their properties and alters their transport, fate, and toxicity. It is essential to consider such transformations when assessing the potential environmental impact of Ag-NPs. This review discusses the major transformation processes of Ag-NPs in various aqueous environments, particularly transformations of the metallic Ag cores caused by reactions with (in)organic ligands, and the effects of such transformations on physical and chemical stability and toxicity. Thermodynamic arguments are used to predict what forms of oxidized silver will predominate in various environmental scenarios. Silver binds strongly to sulfur (both organic and inorganic) in natural systems (fresh and sea waters) as well as in wastewater treatment plants, where most Ag-NPs are expected to be concentrated and then released. Sulfidation of Ag-NPs results in a significant decrease in their toxicity due to the lower solubility of silver sulfide, potentiall...

The Critical Impacts of Ligands on Heterogeneous Nanocatalysis: A Review

Abstract: Ligand utilization is a necessary and powerful technique for the colloidal synthesis of nanoparticles (NPs) with controllable sizes and regulated morphologies. For catalysis applications, it is com...