All Publications

  • Understanding trends in C-H bond activation in heterogeneous catalysis. Nature materials Latimer, A. A., Kulkarni, A. R., Aljama, H., Montoya, J. H., Yoo, J. S., Tsai, C., Abild-Pedersen, F., Studt, F., Nørskov, J. K. 2016


    While the search for catalysts capable of directly converting methane to higher value commodity chemicals and liquid fuels has been active for over a century, a viable industrial process for selective methane activation has yet to be developed. Electronic structure calculations are playing an increasingly relevant role in this search, but large-scale materials screening efforts are hindered by computationally expensive transition state barrier calculations. The purpose of the present letter is twofold. First, we show that, for the wide range of catalysts that proceed via a radical intermediate, a unifying framework for predicting C-H activation barriers using a single universal descriptor can be established. Second, we combine this scaling approach with a thermodynamic analysis of active site formation to provide a map of methane activation rates. Our model successfully rationalizes the available empirical data and lays the foundation for future catalyst design strategies that transcend different catalyst classes.

    View details for DOI 10.1038/nmat4760

    View details for PubMedID 27723737

  • Automated Discovery and Construction of Surface Phase Diagrams Using Machine Learning JOURNAL OF PHYSICAL CHEMISTRY LETTERS Ulissi, Z. W., Singh, A. R., Tsai, C., Norskov, J. K. 2016; 7 (19): 3931-3935


    Surface phase diagrams are necessary for understanding surface chemistry in electrochemical catalysis, where a range of adsorbates and coverages exist at varying applied potentials. These diagrams are typically constructed using intuition, which risks missing complex coverages and configurations at potentials of interest. More accurate cluster expansion methods are often difficult to implement quickly for new surfaces. We adopt a machine learning approach to rectify both issues. Using a Gaussian process regression model, the free energy of all possible adsorbate coverages for surfaces is predicted for a finite number of adsorption sites. Our result demonstrates a rational, simple, and systematic approach for generating accurate free-energy diagrams with reduced computational resources. The Pourbaix diagram for the IrO2(110) surface (with nine coverages from fully hydrogenated to fully oxygenated surfaces) is reconstructed using just 20 electronic structure relaxations, compared to approximately 90 using typical search methods. Similar efficiency is demonstrated for the MoS2 surface.

    View details for DOI 10.1021/acs.jpclett.6b01254

    View details for Web of Science ID 000384966500036

    View details for PubMedID 27558978

  • Two-Dimensional Materials as Catalysts for Energy Conversion CATALYSIS LETTERS Siahrostami, S., Tsai, C., Karamad, M., Koitz, R., Garcia-Melchor, M., Bajdich, M., Vojvodic, A., Abild-Pedersen, F., Norskov, J. K., Studt, F. 2016; 146 (10): 1917-1921
  • How Doped MoS2 Breaks Transition-Metal Scaling Relations for CO2 Electrochemical Reduction ACS CATALYSIS Hong, X., Chan, K., Tsai, C., Norskov, J. K. 2016; 6 (7): 4428-4437
  • Direct Water Decomposition on Transition Metal Surfaces: Structural Dependence and Catalytic Screening CATALYSIS LETTERS Tsai, C., Lee, K., Yoo, J. S., Liu, X., Aljama, H., Chen, L. D., Dickens, C. F., Geisler, T. S., Guido, C. J., Joseph, T. M., Kirk, C. S., Latimer, A. A., Loong, B., McCarty, R. J., Montoya, J. H., Power, L., Singh, A. R., Willis, J. J., Winterkorn, M. M., Yuan, M., Zhao, Z., Wilcox, J., Norskov, J. K. 2016; 146 (4): 718-724
  • Scaling Relationships for Binding Energies of Transition Metal Complexes CATALYSIS LETTERS Wang, Y., Montoya, J. H., Tsai, C., Ahlquist, M. S., Norskov, J. K., Studt, F. 2016; 146 (2): 304-308
  • Chemical and Phase Evolution of Amorphous Molybdenum Sulfide Catalysts for Electrochemical Hydrogen Production. ACS nano Lee, S. C., Benck, J. D., Tsai, C., Park, J., Koh, A. L., Abild-Pedersen, F., Jaramillo, T. F., Sinclair, R. 2016; 10 (1): 624-632


    Amorphous MoSx is a highly active, earth-abundant catalyst for the electrochemical hydrogen evolution reaction. Previous studies have revealed that this material initially has a composition of MoS3, but after electrochemical activation, the surface is reduced to form an active phase resembling MoS2 in composition and chemical state. However, structural changes in the MoSx catalyst and the mechanism of the activation process remain poorly understood. In this study, we employ transmission electron microscopy (TEM) to image amorphous MoSx catalysts activated under two hydrogen-rich conditions: ex situ in an electrochemical cell and in situ in an environmental TEM. For the first time, we directly observe the formation of crystalline domains in the MoSx catalyst after both activation procedures as well as spatially localized changes in the chemical state detected via electron energy loss spectroscopy. Using density functional theory calculations, we investigate the mechanisms for this phase transformation and find that the presence of hydrogen is critical for enabling the restructuring process. Our results suggest that the surface of the amorphous MoSx catalyst is dynamic: while the initial catalyst activation forms the primary active surface of amorphous MoS2, continued transformation to the crystalline phase during electrochemical operation could contribute to catalyst deactivation. These results have important implications for the application of this highly active electrocatalyst for sustainable H2 generation.

    View details for DOI 10.1021/acsnano.5b05652

    View details for PubMedID 26624225

  • Activating and optimizing MoS2 basal planes for hydrogen evolution through the formation of strained sulphur vacancies NATURE MATERIALS Li, H., Tsai, C., Koh, A. L., Cai, L., Contryman, A. W., Fragapane, A. H., Zhao, J., Han, H. S., Manoharan, H. C., Abild-Pedersen, F., Norskov, J. K., Zheng, X. 2016; 15 (1): 48-?

    View details for DOI 10.1038/NMAT4465

    View details for Web of Science ID 000366690600019

  • Theoretical insights into the hydrogen evolution activity of layered transition metal dichalcogenides SURFACE SCIENCE Tsai, C., Chan, K., Norskov, J. K., Abild-Pedersen, F. 2015; 640: 133-140
  • Predicting Promoter-Induced Bond Activation on Solid Catalysts Using Elementary Bond Orders JOURNAL OF PHYSICAL CHEMISTRY LETTERS Tsai, C., Latimer, A. A., Yoo, J. S., Studt, F., Abild-Pedersen, F. 2015; 6 (18): 3670-3674
  • The Challenge of Electrochemical Ammonia Synthesis: A New Perspective on the Role of Nitrogen Scaling Relations CHEMSUSCHEM Montoya, J. H., Tsai, C., Vojvodic, A., Norskov, J. K. 2015; 8 (13): 2180-2186


    The electrochemical production of NH3 under ambient conditions represents an attractive prospect for sustainable agriculture, but electrocatalysts that selectively reduce N2 to NH3 remain elusive. In this work, we present insights from DFT calculations that describe limitations on the low-temperature electrocatalytic production of NH3 from N2 . In particular, we highlight the linear scaling relations of the adsorption energies of intermediates that can be used to model the overpotential requirements in this process. By using a two-variable description of the theoretical overpotential, we identify fundamental limitations on N2 reduction analogous to those present in processes such as oxygen evolution. Using these trends, we propose new strategies for catalyst design that may help guide the search for an electrocatalyst that can achieve selective N2 reduction.

    View details for DOI 10.1002/cssc.201500322

    View details for Web of Science ID 000357619000003

  • Transition-metal doped edge sites in vertically aligned MoS2 catalysts for enhanced hydrogen evolution NANO RESEARCH Wang, H., Tsai, C., Kong, D., Chan, K., Abild-Pedersen, F., Norskov, J. K., Cui, Y. 2015; 8 (2): 566-575
  • Rational design of MoS2 catalysts: tuning the structure and activity via transition metal doping CATALYSIS SCIENCE & TECHNOLOGY Tsai, C., Chan, K., Norskov, J. K., Abild-Pedersen, F. 2015; 5 (1): 246-253

    View details for DOI 10.1039/c4cy01162g

    View details for Web of Science ID 000348358200027

  • Designing an improved transition metal phosphide catalyst for hydrogen evolution using experimental and theoretical trends ENERGY & ENVIRONMENTAL SCIENCE Kibsgaard, J., Tsai, C., Chan, K., Benck, J. D., Norskov, J. K., Abild-Pedersen, F., Jaramillo, T. F. 2015; 8 (10): 3022-3029

    View details for DOI 10.1039/c5ee02179k

    View details for Web of Science ID 000362351700024

  • Activating and optimizing MoS2 basal planes for hydrogen evolution through the formation of strained sulphur vacancies Nature Materials Li, H., Tsai, C., Koh, A., Cai, L., Contryman, A. W., Fragapane, A. H., Zhao, J., Han, H., Manoharan, H. C., Abild-Pedersen, F., Nørskov, J. K., Zheng, X. 2015

    View details for DOI 10.1038/nmat4465

  • Predicting Promoter-Induced Bond Activation on Solid Catalysts Using Elementary Bond Orders JOURNAL OF PHYSICAL CHEMISTRY LETTERS Tsai, C., Latimer, A. A., Yoo, J., Studt, F., Abild-Pedersen, F. 2015; 6 (18): 3670–3674
  • Operando Characterization of an Amorphous Molybdenum Sulfide Nanoparticle Catalyst during the Hydrogen Evolution Reaction JOURNAL OF PHYSICAL CHEMISTRY C Casalongue, H. G., Benck, J. D., Tsai, C., Karlsson, R. K., Kaya, S., Ng, M. L., Pettersson, L. G., Abild-Pedersen, F., Norskov, J. K., Ogasawara, H., Jaramillo, T. F., Nilsson, A. 2014; 118 (50): 29252-29259

    View details for DOI 10.1021/jp505394e

    View details for Web of Science ID 000346759300037

  • Understanding the Reactivity of Layered Transition-Metal Sulfides: A Single Electronic Descriptor for Structure and Adsorption JOURNAL OF PHYSICAL CHEMISTRY LETTERS Tsai, C., Chan, K., Norskov, J. K., Abild-Pedersen, F. 2014; 5 (21): 3884-3889

    View details for DOI 10.1021/jz5020532

    View details for Web of Science ID 000344579500041

  • Molybdenum Sulfides and Selenides as Possible Electrocatalysts for CO2 Reduction CHEMCATCHEM Chan, K., Tsai, C., Hansen, H. A., Norskov, J. K. 2014; 6 (7): 1899-1905
  • Tuning the MoS2 Edge-Site Activity for Hydrogen Evolution via Support Interactions NANO LETTERS Tsai, C., Abild-Pedersen, F., Norskov, J. K. 2014; 14 (3): 1381-1387


    The hydrogen evolution reaction (HER) on supported MoS2 catalysts is investigated using periodic density functional theory, employing the new BEEF-vdW functional that explicitly takes long-range van der Waals (vdW) forces into account. We find that the support interactions involving vdW forces leads to significant changes in the hydrogen binding energy, resulting in several orders of magnitude difference in HER activity. It is generally seen for the Mo-edge that strong adhesion of the catalyst onto the support leads to weakening in the hydrogen binding. This presents a way to optimally tune the hydrogen binding on MoS2 and explains the lower than expected exchange current densities of supported MoS2 in electrochemical H2 evolution studies.

    View details for DOI 10.1021/nl404444k

    View details for Web of Science ID 000335720300044

    View details for PubMedID 24499163

  • Active edge sites in MoSe2 and WSe2 catalysts for the hydrogen evolution reaction: a density functional study PHYSICAL CHEMISTRY CHEMICAL PHYSICS Tsai, C., Chan, K., Abild-Pedersen, F., Norskov, J. K. 2014; 16 (26): 13156-13164


    MoSe2 and WSe2 nanofilms and nanosheets have recently been shown to be active for electrochemical H2 evolution (HER). In this work, we used periodic density functional theory to investigate the origin of the catalytic activity on these materials. We determined the relevant structures of the Mo/W-edges and the Se-edges under HER conditions and their differential hydrogen adsorption free energies. The Mo-edge on MoSe2 and the Se-edge on both MoSe2 and WSe2 are found to be the predominantly active facets for these catalysts, with activity predicted to be comparable to or better than MoS2. On the other hand, the (0001) basal planes are found to be inert. We further explain the enhanced activity at the edges in terms of localized edge states, which provide insight into the trends in HER activity seen between the two catalysts. Our results thus suggest that an optimal catalyst design should maximize the exposure of edge sites. Comparisons are also made between the transition metal selenide catalysts and their sulfide counterparts in order to understand the consequences of having either Mo/W or Se/S atoms. It is found that linear scaling relations describe the S/Se binding onto the edge and the H binding onto the S/Se.

    View details for DOI 10.1039/c4cp01237b

    View details for Web of Science ID 000337785400019

    View details for PubMedID 24866567

  • Synthesis of high-energy anatase nanorods via an intermediate nanotube morphology CHEMICAL PHYSICS LETTERS Finkelstein-Shapiro, D., Tsai, C. Y., Li, S., Gray, K. A. 2012; 546: 106-108