Academic Appointments

  • Physical Science Research Scientist, Mechanical Engineering

All Publications

  • Intercalation of Hydrogen in Perovskite Oxide for Pseudocapacitive Energy Storage CHEMISTRY OF MATERIALS Lin, M., Lu, M., Chou, H., Wan, G., Chen, C. 2023; 35 (24): 10487-10494
  • Low-temperature carbon dioxide conversion via reverse water-gas shift thermochemical looping with supported iron oxide CELL REPORTS PHYSICAL SCIENCE Sun, E., Wan, G., Haribal, V., Gigantino, M., Marin-Quiros, S., Oh, J., Vailionis, A., Tong, A., Randall, R., Rojas, J., Gupta, R., Majumdar, A. 2023; 4 (9)
  • Dynamic and reversible transformations of subnanometre-sized palladium on ceria for efficient methane removal NATURE CATALYSIS Jiang, D., Wan, G., Halldin Stenlid, J., Garcia-Vargas, C. E., Zhang, J., Sun, C., Li, J., Abild-Pedersen, F., Tassone, C. J., Wang, Y. 2023
  • Transport Mediating Core-Shell Photocatalyst Architecture for Selective Alkane Oxidation. Nano letters Xie, C., Sun, E., Wan, G., Zheng, J., Gupta, R., Majumdar, A. 2023


    The high activation barrier of the C-H bond in methane, combined with the high propensity of methanol and other liquid oxygenates toward overoxidation to CO2, have historically posed significant scientific and industrial challenges to the selective and direct conversion of methane to energy-dense fuels and chemical feedstocks. Here, we report a unique core-shell nanostructured photocatalyst, silica encapsulated TiO2 decorated with AuPd nanoparticles (TiO2@SiO2-AuPd), that prevents methanol overoxidation on its surface and possesses high selectivity and yield of oxygenates even at high UV intensity. This room-temperature approach achieves high selectivity for oxygenates (94.5%) with a total oxygenate yield of 15.4 mmol/gcat·h at 9.65 bar total pressure of CH4 and O2. The working principles of this core-shell photocatalyst were also systematically investigated. This design concept was further demonstrated to be generalizable for the selective oxidation of other alkanes.

    View details for DOI 10.1021/acs.nanolett.2c04567

    View details for PubMedID 36689625

  • Phase Transition Dynamics in a Complex Oxide Heterostructure PHYSICAL REVIEW LETTERS Zhang, Q., Hu, G., Starchenko, V., Wan, G., Dufresne, E. M., Dong, Y., Liu, H., Zhou, H., Jeen, H., Saritas, K., Krogel, J. T., Reboredo, F. A., Lee, H., Sandy, A. R., Almazan, I., Ganesh, P., Fong, D. D. 2022; 129 (23): 235701


    Understanding the behavior of defects in the complex oxides is key to controlling myriad ionic and electronic properties in these multifunctional materials. The observation of defect dynamics, however, requires a unique probe-one sensitive to the configuration of defects as well as its time evolution. Here, we present measurements of oxygen vacancy ordering in epitaxial thin films of SrCoO_{x} and the brownmillerite-perovskite phase transition employing x-ray photon correlation spectroscopy. These and associated synchrotron measurements and theory calculations reveal the close interaction between the kinetics and the dynamics of the phase transition, showing how spatial and temporal fluctuations of heterointerface evolve during the transformation process. The energetics of the transition are correlated with the behavior of oxygen vacancies, and the dimensionality of the transformation is shown to depend strongly on whether the phase is undergoing oxidation or reduction. The experimental and theoretical methods described here are broadly applicable to in situ measurements of dynamic phase behavior and demonstrate how coherence may be employed for novel studies of the complex oxides as enabled by the arrival of fourth-generation hard x-ray coherent light sources.

    View details for DOI 10.1103/PhysRevLett.129.235701

    View details for Web of Science ID 000921040200015

    View details for PubMedID 36563221

  • Iron-Poor Ferrites for Low-Temperature CO2 Conversion via Reverse Water-Gas Shift Thermochemical Looping ACS SUSTAINABLE CHEMISTRY & ENGINEERING Rojas, J., Sun, E., Wan, G., Oh, J., Randall, R., Haribal, V., Jung, I., Gupta, R., Majumdar, A. 2022
  • Reaction-Mediated Transformation of Working Catalysts ACS CATALYSIS Wan, G., Zhang, G., Chen, J., Toney, M. F., Miller, J. T., Tassone, C. J. 2022
  • More powerful twistron carbon nanotube yarn mechanical energy harvesters. Advanced materials (Deerfield Beach, Fla.) Wang, Z., Mun, T. J., Machado, F. M., Moon, J. H., Fang, S., Aliev, A. E., Zhang, M., Cai, W., Mu, J., Hyeon, J. S., Park, J. W., Conlin, P., Cho, K., Gao, E., Wan, G., Huynh, C., Zakhidov, A. A., Kim, S. J., Baughman, R. H. 2022: e2201826


    Stretching a coiled carbon nanotube (CNT) yarn can provide large, reversible electrochemical capacitance changes, which convert mechanical energy to electricity. Here we show that the performance of these "twistron" harvesters can be increased by optimizing the alignment of precursor CNT forests, plastically stretching the precursor twisted yarn, applying much higher tensile loads during pre-coiling twist than for coiling, using electrothermal pulse annealing under tension, and incorporating reduced graphene oxide nanoplates. The peak output power for a 1Hz and a 30Hz sinusoidal deformation were 0.73 and 3.19kW kg-1 , which are 24 and 13-fold that of previous twistron harvesters at these respective frequencies. This performance at 30Hz was over 12-fold that of other prior-art mechanical energy harvesters for frequencies between 0.1Hz and 600Hz. The maximum energy conversion efficiency was 7.2-fold that for previous twistrons. Twistron anode and cathode yarn arrays were stretched 180° out-of-phase by locating them in the negative and positive compressibility directions of hinged wine-rack frames, thereby doubling the output voltage and reducing the input mechanical energy. This article is protected by copyright. All rights reserved.

    View details for DOI 10.1002/adma.202201826

    View details for PubMedID 35475584

  • A reconfigurable crosslinking system via an asymmetric metal-ligand coordination strategy POLYMER CHEMISTRY An, X., Li, Y., Xu, M., Xu, Z., Ma, W., Du, R., Wan, G., Yan, H., Cao, Y., Ma, D., Zhang, Q., Jia, X. 2022

    View details for DOI 10.1039/d2py00132b

    View details for Web of Science ID 000782249200001

  • Water or Anion? Uncovering the Zn2+ Solvation Environment in Mixed Zn(TFSI)(2) and LiTFSI Water-in-Salt Electrolytes ACS ENERGY LETTERS Zhang, Y., Wan, G., Lewis, N. C., Mars, J., Bone, S. E., Steinrueck, H., Lukatskaya, M. R., Weadock, N. J., Bajdich, M., Borodin, O., Tokmakoff, A., Toney, M. F., Maginn, E. J. 2021; 6 (10): 3458-3463
  • Direct methane activation by atomically thin platinum nanolayers on two-dimensional metal carbides NATURE CATALYSIS Li, Z., Xiao, Y., Chowdhury, P., Wu, Z., Ma, T., Chen, J., Wan, G., Kim, T., Jing, D., He, P., Potdar, P. J., Zhou, L., Zeng, Z., Ruan, X., Miller, J. T., Greeley, J. P., Wu, Y., Varma, A. 2021; 4 (10): 882-891
  • Tailoring the Local Environment of Platinumin Single-Atom Pt1/CeO2 Catalysts for Robust Low-Temperature CO Oxidation. Angewandte Chemie (International ed. in English) Jiang, D., Yao, Y., Li, T., Wan, G., Pereira-Hernandez, X. I., Lu, Y., Tian, J., Khivantsev, K., Engelhard, M. H., Sun, C., Garcia-Vargas, C. E., Hoffman, A. S., Bare, S. R., Datye, A. K., Hu, L., Wang, Y. 2021


    Single-atom Pt 1 /CeO 2 catalyst by atom trapping (AT, 800 o C in air) shows excellent thermal stability, however, it is inactive for CO oxidation at low temperatures due to over-stabilization of Pt 2+ in a highly symmetric square-planar Pt 1 O 4 coordination. Reductive activation forming Pt nanoparticles (NPs) results in enhanced activity, however, NPs are easily oxidized leading to drastic activity loss. Here we show that tailoring the local environment of isolated Pt 2+ via thermal-shock (TS) synthesis leads to a highly active and thermally stable Pt 1 /CeO 2 catalyst. Ultrafast shockwaves (> 1200 o C) in an inert atmosphere induce surface reconstruction of CeO 2 , generating Pt single atoms in an asymmetric Pt 1 O 4 configuration. Originating from this unique coordination, Pt 1 delta+ in a partially reduced state dynamically evolved during CO oxidation, resulting in an exceptional low-temperature performance. The CO oxidation reactivity on the Pt 1 /CeO 2 _TS catalyst is retained under oxidizing conditions.

    View details for DOI 10.1002/anie.202108585

    View details for PubMedID 34346155

  • Water-in-Salt LiTFSI Aqueous Electrolytes. 1. Liquid Structure from Combined Molecular Dynamics Simulation and Experimental Studies. The journal of physical chemistry. B Zhang, Y., Lewis, N. H., Mars, J., Wan, G., Weadock, N. J., Takacs, C. J., Lukatskaya, M. R., Steinruck, H., Toney, M. F., Tokmakoff, A., Maginn, E. J. 2021


    The concept of water-in-salt electrolytes was introduced recently, and these systems have been successfully applied to yield extended operation voltage and hence significantly improved energy density in aqueous Li-ion batteries. In the present work, results of X-ray scattering and Fourier-transform infrared spectra measurements over a wide range of temperatures and salt concentrations are reported for the LiTFSI (lithium bis(trifluoromethane sulfonyl)imide)-based water-in-salt electrolyte. Classical molecular dynamics simulations are validated against the experiments and used to gain additional information about the electrolyte structure. Based on our analyses, a new model for the liquid structure is proposed. Specifically, we demonstrate that at the highest LiTFSI concentration of 20 m the water network is disrupted, and the majority of water molecules exist in the form of isolated monomers, clusters, or small aggregates with chain-like configurations. On the other hand, TFSI- anions are connected to each other and form a network. This description is fundamentally different from those proposed in earlier studies of this system.

    View details for DOI 10.1021/acs.jpcb.1c02189

    View details for PubMedID 33904299

  • Elucidation of the Active Sites in Single-Atom Pd-1/CeO2 Catalysts for Low-Temperature CO Oxidation ACS CATALYSIS Jiang, D., Wan, G., Garcia-Vargas, C. E., Li, L., Pereira-Hernandez, X., Wang, C., Wang, Y. 2020; 10 (19): 11356–64
  • Interfacial Speciation Determines Interfacial Chemistry: X-ray-Induced Lithium Fluoride Formation from Water-in-salt Electrolytes on Solid Surfaces. Angewandte Chemie (International ed. in English) Steinrueck, H., Cao, C., Lukatskaya, M., Takacs, C., Wan, G., Mackanic, D., Tsao, Y., Zhao, J., Helms, B., Xu, K., Borodin, O., Wishart, J. F., Toney, M. 2020


    Super-concentrated "water-in-salt" electrolytes recently spurred resurgent interest for high energy density aqueous lithium-ion batteries. Thermodynamic stabilization at high concentrations and kinetic barriers towards interfacial water electrolysis significantly expand the electrochemical stability window, facilitating high voltage aqueous cells. Here we investigated LiTFSI/H 2 O electrolyte interfacial decomposition pathways in the "water-in-salt" and "salt-in-water" regimes using synchrotron X-rays, which produce electrons at the solid-electrolyte interface to mimic reductive environments, and simultaneously probe the structure of surface films using X-ray diffraction. We observed the surface-reduction of TFSI - at super-concentration, leading to lithium fluoride interphase formation, while precipitation of the lithium hydroxide was not observed. The mechanism behind this photoelectron-induced reduction was revealed to be concentration-dependent interfacial chemistry that only occurs among closely contact ion-pairs, which constitutes the rationale behind the "water-in-salt" concept.

    View details for DOI 10.1002/anie.202007745

    View details for PubMedID 32881197

  • NASICON Na3V2(PO4)(3) Enables Quasi-Two-Stage Na+ and Zn2+ Intercalation for Multivalent Zinc Batteries CHEMISTRY OF MATERIALS Ko, J. S., Paul, P. P., Wan, G., Seitzman, N., DeBlock, R., Dunn, B. S., Toney, M. F., Weker, J. 2020; 32 (7): 3028–35