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    garciae@stanford.edu
    University - Staff Department: SLAC National Accelerator Laboratory Position: Project Scientist
    • 2575 Sand Hill Rd
    • Mailstop 0069
    • Menlo Park,  California  94025 

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  • Mail Code: 69

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All Publications

  • Catalytic consequences of ultrafine Pt clusters supported on SrTiO3 for photocatalytic overall water splitting JOURNAL OF CATALYSIS Qureshi, M., Garcia-Esparza, A. T., Jeantelot, G., Ould-Chikh, S., Aguilar-Tapia, A., Hazemann, J., Basset, J., Loffreda, D., Le Bahers, T., Takanabe, K. 2019; 376: 180–90

    View details for DOI 10.1016/j.jcat.2019.06.045

    View details for Web of Science ID 000488417200019

  • Full in silico DFT characterization of lanthanum and yttrium based oxynitride semiconductors for solar fuels JOURNAL OF MATERIALS CHEMISTRY C Garcia-Esparza, A. T., Tyminska, N., Al Orabi, R., Le Bahers, T. 2019; 7 (6): 1612–21

    View details for DOI 10.1039/c8tc05749d

    View details for Web of Science ID 000459572600017

  • Exposed Equatorial Positions of Metal Centers via Sequential Ligand Elimination and Installation in MOFs JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Yuan, S., Zhang, P., Zhang, L., Garcia-Esparza, A. T., Sokaras, D., Qin, J., Feng, L., Day, G. S., Chen, W., Drake, H. F., Elumalai, P., Madrahimov, S. T., Sun, D., Zhou, H. 2018; 140 (34): 10814–19

    Abstract

    Metal-organic frameworks (MOFs) provide highly designable platforms to construct complex coordination architectures for targeted applications. Herein, we demonstrate that trans-coordinated metal centers with exposed equatorial positions can be placed in a MOF matrix. A Zr-based MOF, namely, PCN-160, was initially synthesized as a scaffold structure. Postsynthetic linker labilization was subsequently implemented to partially remove the original dicarboxylate linkers and incorporate pyridinecarboxylates. A pair of neighboring pyridyl groups was arranged at proper proximity within the framework to form trans-binding sites that accommodate different metal cations including Mn2+, Fe2+, Co2+, Ni2+, Cu2+, and Pd2+. Furthermore, the trans-coordinated Ni2+ sites in porous frameworks can be readily accessed by substrates along the equatorial plane, facilitating the catalysis as manifested by the superior activity in ethylene dimerization over that observed for a cis-chelated catalyst.

    View details for PubMedID 30089362

  • An Oxygen-Insensitive Hydrogen Evolution Catalyst Coated by a Molybdenum-Based Layer for Overall Water Splitting ANGEWANDTE CHEMIE-INTERNATIONAL EDITION Garcia-Esparza, A. T., Shinagawa, T., Ould-Chikh, S., Qureshi, M., Peng, X., Wei, N., Anjum, D. H., Clo, A., Weng, T., Nordlund, D., Sokaras, D., Kubota, J., Domen, K., Takanabe, K. 2017; 56 (21): 5780-5784

    Abstract

    For overall water-splitting systems, it is essential to establish O2-insensitive cathodes that allow cogeneration of H2and O2. An acid-tolerant electrocatalyst is described, which employs a Mo-coating on a metal surface to achieve selective H2evolution in the presence of O2. In operando X-ray absorption spectroscopy identified reduced Pt covered with an amorphous molybdenum oxyhydroxide hydrate with a local structural order composed of polyanionic trimeric units of molybdenum(IV). The Mo layer likely hinders O2gas permeation, impeding contact with active Pt. Photocatalytic overall water splitting proceeded using MoOx/Pt/SrTiO3with inhibited water formation from H2and O2, which is the prevailing back reaction on the bare Pt/SrTiO3photocatalyst. The Mo coating was stable in acidic media for multiple hours of overall water splitting by membraneless electrolysis and photocatalysis.

    View details for DOI 10.1002/anie.201701861

    View details for Web of Science ID 000400755800021

    View details for PubMedID 28407339

  • Photophysical Properties of SrTaO2N Thin Films and Influence of Anion Ordering: A Joint Theoretical and Experimental Investigation CHEMISTRY OF MATERIALS Ziani, A., Le Paven, C., Le Gendre, L., Marlec, F., Benzerga, R., Tessier, F., Chevire, F., Hedhili, M. N., Garcia-Esparza, A. T., Melissen, S., Sautet, P., Le Bahers, T., Takanabe, K. 2017; 29 (9): 3989–98

    View details for DOI 10.1021/acs.chemmater.7b00414

    View details for Web of Science ID 000401221700020

  • Cu-Sn Bimetallic Catalyst for Selective Aqueous Electroreduction of CO2 to CO ACS CATALYSIS Sarfraz, S., Garcia-Esparza, A. T., Jedidi, A., Cavallo, L., Takanabe, K. 2016; 6 (5): 2842–51

    View details for DOI 10.1021/acscatal.6b00269

    View details for Web of Science ID 000375894500015

  • A simplified theoretical guideline for overall water splitting using photocatalyst particles JOURNAL OF MATERIALS CHEMISTRY A Garcia-Esparza, A. T., Takanabe, K. 2016; 4 (8): 2894–2908

    View details for DOI 10.1039/c5ta06983a

    View details for Web of Science ID 000371077300015

  • Insight on Tafel slopes from a microkinetic analysis of aqueous electrocatalysis for energy conversion SCIENTIFIC REPORTS Shinagawa, T., Garcia-Esparza, A. T., Takanabe, K. 2015; 5: 13801

    Abstract

    Microkinetic analyses of aqueous electrochemistry involving gaseous H2 or O2, i.e., hydrogen evolution reaction (HER), hydrogen oxidation reaction (HOR), oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), are revisited. The Tafel slopes used to evaluate the rate determining steps generally assume extreme coverage of the adsorbed species (θ≈0 or ≈1), although, in practice, the slopes are coverage-dependent. We conducted detailed kinetic analyses describing the coverage-dependent Tafel slopes for the aforementioned reactions. Our careful analyses provide a general benchmark for experimentally observed Tafel slopes that can be assigned to specific rate determining steps. The Tafel analysis is a powerful tool for discussing the rate determining steps involved in electrocatalysis, but our study also demonstrated that overly simplified assumptions led to an inaccurate description of the surface electrocatalysis. Additionally, in many studies, Tafel analyses have been performed in conjunction with the Butler-Volmer equation, where its applicability regarding only electron transfer kinetics is often overlooked. Based on the derived kinetic description of the HER/HOR as an example, the limitation of Butler-Volmer expression in electrocatalysis is also discussed in this report.

    View details for DOI 10.1038/srep13801

    View details for Web of Science ID 000360796400002

    View details for PubMedID 26348156

    View details for PubMedCentralID PMC4642571

  • Tungsten Carbide Nanoparticles as Efficient Cocatalysts for Photocatalytic Overall Water Splitting CHEMSUSCHEM Garcia-Esparza, A. T., Cha, D., Ou, Y., Kubota, J., Domen, K., Takanabe, K. 2013; 6 (1): 168–81

    Abstract

    Tungsten carbide exhibits platinum-like behavior, which makes it an interesting potential substitute for noble metals in catalytic applications. Tungsten carbide nanocrystals (≈5 nm) are directly synthesized through the reaction of tungsten precursors with mesoporous graphitic C(3)N(4) (mpg-C(3)N(4)) as the reactive template in a flow of inert gas at high temperatures. Systematic experiments that vary the precursor compositions and temperatures used in the synthesis selectively generate different compositions and structures for the final nanocarbide (W(2)C or WC) products. Electrochemical measurements demonstrate that the WC phase with a high surface area exhibits both high activity and stability in hydrogen evolution over a wide pH range. The WC sample also shows excellent hydrogen oxidation activity, whereas its activity in oxygen reduction is poor. These tungsten carbides are successful cocatalysts for overall water splitting and give H(2) and O(2) in a stoichiometric ratio from H(2)O decomposition when supported on a Na-doped SrTiO(3) photocatalyst. Herein, we present tungsten carbide (on a small scale) as a promising and durable catalyst substitute for platinum and other scarce noble-metal catalysts in catalytic reaction systems used for renewable energy generation.

    View details for DOI 10.1002/cssc.201200780

    View details for Web of Science ID 000313702200022

    View details for PubMedID 23255471

  • Contribution of electrolyte in nanoscale electrolysis of pure and buffered water by particulate photocatalysis SUSTAINABLE ENERGY & FUELS Qureshi, M., Garcia-Esparza, A. T., Shinagawa, T., Sautet, P., Le Bahers, T., Takanabe, K. 2018; 2 (9): 2044–52

    View details for DOI 10.1039/c8se00272j

    View details for Web of Science ID 000443282700012

  • Efficient electrochemical water oxidation in neutral and near-neutral systems with a nanoscale silver-oxide catalyst NANOSCALE Joya, K. S., Ahmad, Z., Joya, Y. F., Garcia-Esparza, A. T., de Groot, H. M. 2016; 8 (32): 15033–40

    Abstract

    In electrocatalytic water splitting systems pursuing for renewable energy using sunlight, developing robust, stable and easily accessible materials operating under mild chemical conditions is pivotal. We present here a unique nanoparticulate type silver-oxide (AgOx-NP) based robust and highly stable electrocatalyst for efficient water oxidation. The AgOx-NP is generated in situ in a HCO3(-)/CO2 system under benign conditions. Micrographs show that they exhibit a nanoscale box type squared nano-bipyramidal configuration. The oxygen generation is initiated at low overpotential, and a sustained O2 evolution current density of >1.1 mA cm(-2) is achieved during prolonged-period water electrolysis. The AgOx-NP electrocatalyst performs exceptionally well in metal-ion free neutral or near-neutral carbonate, phosphate and borate buffers relative to recently reported Co-oxide and Ni-oxide based heterogeneous electrocatalysts, which are unstable in metal-ion free electrolytes and tend to deactivate with time and lose catalytic performance during long-term experimental tests.

    View details for DOI 10.1039/c6nr03147a

    View details for Web of Science ID 000381415200016

    View details for PubMedID 27472834

  • Mechanistic Switching by Hydronium Ion Activity for Hydrogen Evolution and Oxidation over Polycrystalline Platinum Disk and Platinum/Carbon Electrodes CHEMELECTROCHEM Shinagawa, T., Garcia-Esparza, A. T., Takanabe, K. 2014; 1 (9): 1497–1507

    View details for DOI 10.1002/celc.201402085

    View details for Web of Science ID 000342817800009

  • Tethering Metal Ions to Photocatalyst Particulate Surfaces by Bifunctional Molecular Linkers for Efficient Hydrogen Evolution CHEMSUSCHEM Yu, W., Isimjan, T., Del Gobbo, S., Anjum, D. H., Abdel-Azeim, S., Cavallo, L., Garcia-Esparza, A. T., Domen, K., Xu, W., Takanabe, K. 2014; 7 (9): 2575–83

    Abstract

    A simple and versatile method for the preparation of photocatalyst particulates modified with effective cocatalysts is presented; the method involves the sequential soaking of photocatalyst particulates in solutions containing bifunctional organic linkers and metal ions. The modification of the particulate surfaces is a universal and reproducible method because the molecular linkers utilize strong covalent bonds, which in turn result in modified monolayer with a small but controlled quantity of metals. The photocatalysis results indicated that the CdS with likely photochemically reduced Pd and Ni, which were initially immobilized via ethanedithiol (EDT) as a linker, were highly efficient for photocatalytic hydrogen evolution from Na2S-Na2SO3-containing aqueous solutions. The method developed in this study opens a new synthesis route for the preparation of effective photocatalysts with various combinations of bifunctional linkers, metals, and photocatalyst particulate materials.

    View details for DOI 10.1002/cssc.201402297

    View details for Web of Science ID 000342813300029

    View details for PubMedID 25138439

  • Photoelectrochemical and electrocatalytic properties of thermally oxidized copper oxide for efficient solar fuel production JOURNAL OF MATERIALS CHEMISTRY A Garcia-Esparza, A. T., Limkrailassiri, K., Leroy, F., Rasul, S., Yu, W., Lin, L., Takanabe, K. 2014; 2 (20): 7389–7401

    View details for DOI 10.1039/c4ta00442f

    View details for Web of Science ID 000334998400036

  • Synthesis of tantalum carbide and nitride nanoparticles using a reactive mesoporous template for electrochemical hydrogen evolution JOURNAL OF MATERIALS CHEMISTRY A Alhajri, N. S., Yoshida, H., Anjum, D. H., Garcia-Esparza, A. T., Kubota, J., Domen, K., Takanabe, K. 2013; 1 (40): 12606–16

    View details for DOI 10.1039/c3ta12984e

    View details for Web of Science ID 000325414000031