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All Publications


  • Enhancing Mo:BiVO4 Solar Water Splitting with Patterned Au Nanospheres by Plasmon-Induced Energy Transfer ADVANCED ENERGY MATERIALS Kim, J., Shi, X., Jeong, M., Park, J., Han, H., Kim, S., Guo, Y., Heinz, T. F., Fan, S., Lee, C., Park, J., Zheng, X. 2018; 8 (5)
  • Understanding activity trends in electrochemical water oxidation to form hydrogen peroxide NATURE COMMUNICATIONS Shi, X., Siahrostami, S., Li, G., Zhang, Y., Chakthranont, P., Studt, F., Jaramillo, T. F., Zheng, X., Norskov, J. K. 2017; 8: 701

    Abstract

    Electrochemical production of hydrogen peroxide (H2O2) from water oxidation could provide a very attractive route to locally produce a chemically valuable product from an abundant resource. Herein using density functional theory calculations, we predict trends in activity for water oxidation towards H2O2 evolution on four different metal oxides, i.e., WO3, SnO2, TiO2 and BiVO4. The density functional theory predicted trend for H2O2 evolution is further confirmed by our experimental measurements. Moreover, we identify that BiVO4 has the best H2O2 generation amount of those oxides and can achieve a Faraday efficiency of about 98% for H2O2 production.Producing hydrogen peroxide via electrochemical oxidation of water is an attractive route to this valuable product. Here the authors theoretically and experimentally investigate hydrogen peroxide production activity trends for a range of metal oxides and identify the optimal bias ranges for high Faraday efficiencies.

    View details for PubMedID 28951571

  • Unassisted photoelectrochemical water splitting exceeding 7% solar-to-hydrogen conversion efficiency using photon recycling NATURE COMMUNICATIONS Shi, X., Jeong, H., Oh, S. J., Ma, M., Zhang, K., Kwon, J., Choi, I. T., Choi, I. Y., Kim, H. K., Kim, J. K., Park, J. H. 2016; 7

    Abstract

    Various tandem cell configurations have been reported for highly efficient and spontaneous hydrogen production from photoelectrochemical solar water splitting. However, there is a contradiction between two main requirements of a front photoelectrode in a tandem cell configuration, namely, high transparency and high photocurrent density. Here we demonstrate a simple yet highly effective method to overcome this contradiction by incorporating a hybrid conductive distributed Bragg reflector on the back side of the transparent conducting substrate for the front photoelectrochemical electrode, which functions as both an optical filter and a conductive counter-electrode of the rear dye-sensitized solar cell. The hybrid conductive distributed Bragg reflectors were designed to be transparent to the long-wavelength part of the incident solar spectrum (λ>500 nm) for the rear solar cell, while reflecting the short-wavelength photons (λ<500 nm) which can then be absorbed by the front photoelectrochemical electrode for enhanced photocurrent generation.

    View details for DOI 10.1038/ncomms11943

    View details for PubMedID 27324578

  • Understanding the synergistic effect of WO3-BiVO4 heterostructures by impedance spectroscopy PHYSICAL CHEMISTRY CHEMICAL PHYSICS Shi, X., Herraiz-Cardona, I., Bertoluzzi, L., Lopez-Varo, P., Bisquert, J., Park, J. H., Gimenez, S. 2016; 18 (13): 9255-9261

    Abstract

    WO3-BiVO4 n-n heterostructures have demonstrated remarkable performance in photoelectrochemical water splitting due to the synergistic effect between the individual components. Although the enhanced functional capabilities of this system have been widely reported, in-depth mechanistic studies explaining the carrier dynamics of this heterostructure are limited. The main goal is to provide rational design strategies for further optimization as well as to extend these strategies to different candidate systems for solar fuel production. In the present study, we perform systematic optoelectronic and photoelectrochemical characterization to understand the carrier dynamics of the system and develop a simple physical model to highlight the importance of the selective contacts to minimize bulk recombination in this heterostructure. Our results collectively indicate that while BiVO4 is responsible for the enhanced optical properties, WO3 controls the transport properties of the heterostructured WO3-BiVO4 system, leading to reduced bulk recombination.

    View details for DOI 10.1039/c5cp07905e

    View details for Web of Science ID 000373000100052

  • Understanding the synergistic effect of WO3-BiVO4 heterostructures by impedance spectroscopy. Physical chemistry chemical physics Shi, X., Herraiz-Cardona, I., Bertoluzzi, L., Lopez-Varo, P., Bisquert, J., Park, J. H., Gimenez, S. 2016; 18 (13): 9255-9261

    Abstract

    WO3-BiVO4 n-n heterostructures have demonstrated remarkable performance in photoelectrochemical water splitting due to the synergistic effect between the individual components. Although the enhanced functional capabilities of this system have been widely reported, in-depth mechanistic studies explaining the carrier dynamics of this heterostructure are limited. The main goal is to provide rational design strategies for further optimization as well as to extend these strategies to different candidate systems for solar fuel production. In the present study, we perform systematic optoelectronic and photoelectrochemical characterization to understand the carrier dynamics of the system and develop a simple physical model to highlight the importance of the selective contacts to minimize bulk recombination in this heterostructure. Our results collectively indicate that while BiVO4 is responsible for the enhanced optical properties, WO3 controls the transport properties of the heterostructured WO3-BiVO4 system, leading to reduced bulk recombination.

    View details for DOI 10.1039/c5cp07905e

    View details for PubMedID 26975634

  • A 3D triple-deck photoanode with a strengthened structure integrality: enhanced photoelectrochemical water oxidation NANOSCALE Ma, M., Shi, X., Zhang, K., Kwon, S., Li, P., Kim, J. K., Thanh Tran Phu, T. T., Yi, G., Park, J. H. 2016; 8 (6): 3474-3481

    Abstract

    WO3/BiVO4 is one of the attractive Type II heterojunctions for photoelectrochemical (PEC) water splitting due to its well-matched band edge positions and visible light harvesting abilities. However, two light absorption components generally suffer from poor charge collection and cannot be efficiently utilized because of non-ideal interfaces. Herein, a triple-deck three-dimensional (3D) architecture was designed through a one-step shaping process with an additional stress relaxation WO3 underlayer. The final photoanodes showed a promising photocurrent density of 5.1 mA cm(-2) at 1.23 V vs. RHE under AM 1.5G illumination. Using the uniformly distributed oxygen evolution co-catalyst (OEC) layer as the outer most shell of the WO3/BiVO4/OEC triple-deck 3D structure with a dense WO3 underlayer, the water splitting efficiency was improved dramatically by facilitating the charge transfer process at the electrode/electrolyte interface.

    View details for DOI 10.1039/c5nr08604c

    View details for Web of Science ID 000369908900037

    View details for PubMedID 26797394

  • General Characterization Methods for Photoelectrochemical Cells for Solar Water Splitting CHEMSUSCHEM Shi, X., Cai, L., Ma, M., Zheng, X., Park, J. H. 2015; 8 (19): 3192-3203

    Abstract

    Photoelectrochemical (PEC) water splitting is a very promising technology that converts water into clean hydrogen fuel and oxygen by using solar light. However, the characterization methods for PEC cells are diverse and a systematic introduction to characterization methods for PEC cells has rarely been attempted. Unlike most other review articles that focus mainly on the material used for the working electrodes of PEC cells, this review introduces general characterization methods for PEC cells, including their basic configurations and methods for characterizing their performance under various conditions, regardless of the materials used. Detailed experimental operation procedures with theoretical information are provided for each characterization method. The PEC research area is rapidly expanding and more researchers are beginning to devote themselves to related work. Therefore, the content of this Minireview can provide entry-level knowledge to beginners in the area of PEC, which might accelerate progress in this area.

    View details for DOI 10.1002/cssc.201500075

    View details for Web of Science ID 000362729800001

    View details for PubMedID 26365789