Browsing by Author "Wang, Zhiming"

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    A TiO2/FeMnP Core/Shell Nanorod Array Photoanode for Efficient Photoelectrochemical Oxygen Evolution
    (American Chemical Society, 2017) Schipper, Desmond E.; Zhao, Zhenhuan; Leitner, Andrew P.; Xie, Lixin; Qin, Fan; Alam, Md Kamrul; Chen, Shuo; Wang, Dezhi; Ren, Zhifeng; Wang, Zhiming; Bao, Jiming; Whitmire, Kenton H.
    A variety of catalysts have recently been developed for electrocatalytic oxygen evolution, but very few of them can be readily integrated with semiconducting light absorbers for photoelectrochemical or photocatalytic water splitting. Here, we demonstrate an efficient core/shell photoanode with a highly active oxygen evolution electrocatalyst shell (FeMnP) and semiconductor core (rutile TiO2) for photoelectrochemical oxygen evolution reaction. Metal–organic chemical vapor deposition from a single-source precursor was used to ensure good contact between the FeMnP and the TiO2. The TiO2/FeMnP core/shell photoanode reaches the theoretical photocurrent density for rutile TiO2 of 1.8 mA cm–2 at 1.23 V vs reversible hydrogen electrode under simulated 100 mW cm–2 (1 sun) irradiation. The dramatic enhancement is a result of the synergistic effects of the high oxygen evolution reaction activity of FeMnP (delivering an overpotential of 300 mV with a Tafel slope of 65 mV dec–1 in 1 M KOH) and the conductive interlayer between the surface active sites and semiconductor core which boosts the interfacial charge transfer and photocarrier collection. The facile fabrication of the TiO2/FeMnP core/shell nanorod array photoanode offers a compelling strategy for preparing highly efficient photoelectrochemical solar energy conversion devices.
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    Bifunctional metal phosphide FeMnP films from single source metal organic chemical vapor deposition for efficient overall water splitting
    (Elsevier, 2017) Zhao, Zhenhuan; Schipper, Desmond E.; Leitner, Andrew P.; Thirumalai, Hari; Chen, Jing-Han; Xie, Lixin; Qin, Fan; Alam, Md Kamrul; Grabow, Lars C.; Chen, Shuo; Wang, Dezhi; Ren, Zhifeng; Wang, Zhiming; Whitmire, Kenton H.; Bao, Jiming
    Developing stable and efficient bifunctional catalysts for overall water splitting into hydrogen and oxygen is a critical step in the realization of several clean-energy technologies. Here we report a robust and highly active electrocatalyst that is constructed by deposition of the ternary metal phosphide FeMnP onto graphene-protected nickel foam by metal-organic chemical vapor deposition from a single source precursor. FeMnP exhibits high electrocatalytic activity toward both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). Utilizing FeMnP/GNF as both the anode and the cathode for overall water splitting, a current density of 10 mA cm−2 is achieved at a cell voltage of as low as 1.55 V with excellent stability. Complementary density functional theory (DFT) calculations suggest that facets exposing both Fe and Mn sites are necessary to achieve high HER activity. The present work provides a facile strategy for fabricating highly efficient electrocatalysts from earth-abundant materials for overall water splitting.
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    Effects of Catalyst Phase on the Hydrogen Evolution Reaction of Water Splitting: Preparation of Phase-Pure Films of FeP, Fe2P, and Fe3P and Their Relative Catalytic Activities
    (American Chemical Society, 2018) Schipper, Desmond E.; Zhao, Zhenhuan; Thirumalai, Hari; Leitner, Andrew P.; Donaldson, Samantha L.; Kumar, Arvind; Qin, Fan; Wang, Zhiming; Grabow, Lars C.; Bao, Jiming; Whitmire, Kenton H.
    The comparative catalytic activities of iron phosphides, FexP (xﾠ= 1ﾖ3), have been established with phase-pure material grown by chemical vapor deposition (CVD) from single-source organometallic precursors. This is the first report of the preparation of phase-pure thin films of FeP and Fe2P, and their identity was established with scanning-electron microscopy, X-ray photoelectron spectroscopy, and powder X-ray diffraction. All materials were deposited on fluorine-doped tin oxide (FTO) for evaluation of their activities toward the hydrogen evolution reaction (HER) of water splitting in 0.5 M H2SO4. HER activity follows the trend Fe3P > Fe2P > FeP, with Fe3P having the lowest overpotential of 49 mV at a current density of 10 mA cmﾖ2. Density functional theory (DFT) calculations are congruent with the observed activity trend with hydrogen binding favoring the iron-rich terminating surfaces of Fe3P and Fe2P over the iron-poor terminating surfaces of FeP. The results present a clear trend of activity with iron-rich phosphide phases outperforming phosphorus rich phases for hydrogen evolution. The films of Fe2P were grown using Fe(CO)4PH3ﾠ(1), while the films of FeP were prepared using either Fe(CO)4PtBuH2ﾠ(2) or the new molecule {Fe(CO)4P(H)tBu}2ﾠ(3) on quartz and FTO. Compoundﾠ3ﾠwas prepared from the reaction of PCl2tBu with a mixture of Na[HFe(CO)4] and Na2[Fe(CO)4] and characterized by single-crystal X-ray diffraction, ESI-MS, elemental analysis, andﾠ31P/1H NMR spectroscopies. Films of Fe3P were prepared as previously described from H2Fe3(CO)9PtBu (4).
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    Excitonic Resonant Emission–Absorption of Surface Plasmons in Transition Metal Dichalcogenides for Chip-Level Electronic–Photonic Integrated Circuits
    (American Chemical Society, 2016) Zhu, Zhuan; Yuan, Jiangtan; Zhou, Haiqing; Hu, Jonathan; Zhang, Jing; Wei, Chengli; Yu, Fang; Chen, Shuo; Lan, Yucheng; Yang, Yao; Wang, Yanan; Niu, Chao; Ren, Zhifeng; Lou, Jun; Wang, Zhiming; Bao, Jiming
    The monolithic integration of electronics and photonics has attracted enormous attention due to its potential applications. A major challenge to this integration is the identification of suitable materials that can emit and absorb light at the same wavelength. In this paper we utilize unique excitonic transitions in WS2 monolayers and show that WS2 exhibits a perfect overlap between its absorption and photoluminescence spectra. By coupling WS2 to Ag nanowires, we then show that WS2 monolayers are able to excite and absorb surface plasmons of Ag nanowires at the same wavelength of exciton photoluminescence. This resonant absorption by WS2 is distinguished from that of the ohmic propagation loss of silver nanowires, resulting in a short propagation length of surface plasmons. Our demonstration of resonant optical generation and detection of surface plasmons enables nanoscale optical communication and paves the way for on-chip electronic–photonic integrated circuits.
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    Vacancy-mediated anomalous phononic and electronic transport in defective half-Heusler ZrNiBi
    (Springer Nature, 2023) Ren, Wuyang; Xue, Wenhua; Guo, Shuping; He, Ran; Deng, Liangzi; Song, Shaowei; Sotnikov, Andrei; Nielsch, Kornelius; van den Brink, Jeroen; Gao, Guanhui; Chen, Shuo; Han, Yimo; Wu, Jiang; Chu, Ching-Wu; Wang, Zhiming; Wang, Yumei; Ren, Zhifeng
    Studies of vacancy-mediated anomalous transport properties have flourished in diverse fields since these properties endow solid materials with fascinating photoelectric, ferroelectric, and spin-electric behaviors. Although phononic and electronic transport underpin the physical origin of thermoelectrics, vacancy has only played a stereotyped role as a scattering center. Here we reveal the multifunctionality of vacancy in tailoring the transport properties of an emerging thermoelectric material, defective n-type ZrNiBi. The phonon kinetic process is mediated in both propagating velocity and relaxation time: vacancy-induced local soft bonds lower the phonon velocity while acoustic-optical phonon coupling, anisotropic vibrations, and point-defect scattering induced by vacancy shorten the relaxation time. Consequently, defective ZrNiBi exhibits the lowest lattice thermal conductivity among the half-Heusler family. In addition, a vacancy-induced flat band features prominently in its electronic band structure, which is not only desirable for electron-sufficient thermoelectric materials but also interesting for driving other novel physical phenomena. Finally, better thermoelectric performance is established in a ZrNiBi-based compound. Our findings not only demonstrate a promising thermoelectric material but also promote the fascinating vacancy-mediated anomalous transport properties for multidisciplinary explorations.