Ralph L. House
University of North Carolina at Chapel Hill
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Publication
Featured researches published by Ralph L. House.
Journal of the American Chemical Society | 2014
Sheng Zhang; Peng Kang; Stephen M. Ubnoske; M. Kyle Brennaman; Na Song; Ralph L. House; Jeffrey T. Glass; Thomas J. Meyer
Nitrogen-doped carbon nanotubes are selective and robust electrocatalysts for CO2 reduction to formate in aqueous media without the use of a metal catalyst. Polyethylenimine (PEI) functions as a co-catalyst by significantly reducing catalytic overpotential and increasing current density and efficiency. The co-catalysis appears to help in stabilizing the singly reduced intermediate CO2(•-) and concentrating CO2 in the PEI overlayer.
Proceedings of the National Academy of Sciences of the United States of America | 2012
Javier J. Concepcion; Ralph L. House; John M. Papanikolas; Thomas J. Meyer
In the early 1970s, the works by Fujishima and Honda (1) and Honda et al. (2) reported on the results of a now famous experiment. They showed that band gap excitation of anatase TiO2 in a photoelectrochemical cell with a Pt counter electrode and an applied bias resulted in water splitting into hydrogen and oxygen. The timing of the result was impeccable. In 1973, the Organization of the Petroleum Exporting Countries (OPEC) declared an embargo on oil imports to the West, resulting in gasoline shortages and long lines at gas pumps. Suddenly, there was a pressing need for energy independence and new ways of providing for the energy-hungry economies of Western Europe, Japan, and the United States. The international research community responded. There was a short lived explosion of interest in converting sunlight into high-energy molecules by what we now call artificial photosynthesis to make solar fuels. Target reactions were water splitting into hydrogen and oxygen (1) and light-driven reduction of CO2 by water to give CO, other oxygenates, or hydrocarbons. Methane is shown as the product in equation 2, but the ultimate target is liquid hydrocarbons to power our existing energy infrastructure (1 and 2):
Journal of the American Chemical Society | 2016
M. Kyle Brennaman; Robert J. Dillon; Leila Alibabaei; Melissa K. Gish; Christopher J. Dares; Dennis L. Ashford; Ralph L. House; Gerald J. Meyer; John M. Papanikolas; Thomas J. Meyer
The dye-sensitized photoelectrosynthesis cell (DSPEC) integrates high bandgap, nanoparticle oxide semiconductors with the light-absorbing and catalytic properties of designed chromophore-catalyst assemblies. The goals are photoelectrochemical water splitting into hydrogen and oxygen and reduction of CO2 by water to give oxygen and carbon-based fuels. Solar-driven water oxidation occurs at a photoanode and water or CO2 reduction at a cathode or photocathode initiated by molecular-level light absorption. Light absorption is followed by electron or hole injection, catalyst activation, and catalytic water oxidation or water/CO2 reduction. The DSPEC is of recent origin but significant progress has been made. It has the potential to play an important role in our energy future.
Journal of Physical Chemistry A | 2010
Brian P. Mehl; Ralph L. House; Abhineet Uppal; Amanda Reams; Chuan Zhang; Justin R. Kirschbrown; John M. Papanikolas
Images of second harmonic generation (SHG) in needle-shaped ZnO rods obtained from individual structures show areas of enhanced second harmonic intensity along the longitudinal axis of the rod that are periodically distributed and symmetrically situated relative to the rod midpoint. The spatial modulation is a direct consequence of the fundamental optical field coupling into standing wave resonator modes of the ZnO structure, leading to an enhanced backscattered second harmonic condition that cannot be achieved in bulk ZnO. A more complicated second harmonic image is observed when excitation is below the band gap, which is attributed to whispering gallery modes. This physical phenomenon, which extends beyond just ZnO to many other optical materials, could pave the way to new applications that exploit the nonlinear optical properties of individual structures.
Journal of Physical Chemistry B | 2013
Brian P. Mehl; Justin R. Kirschbrown; Michelle M. Gabriel; Ralph L. House; John M. Papanikolas
Femtosecond pump-probe microscopy is used to investigate the charge recombination dynamics at different points within a single needle-shaped ZnO rod. Recombination in the tips of the rod occurs through an excitonic or electron-hole plasma state, taking place on a picosecond time scale. Photoexcitation in the larger diameter sections of the interior exhibit dramatically slower recombination that occurs primarily through defects sites, i.e., trap mediated recombination. Transient absorption imaging shows that the spatial variation in the dynamics is also influenced by the cavity resonances supported within the hexagonal cross section of the rod. Finite element simulations suggest that these optical resonator modes produce qualitatively different intensity patterns in the two different locations. Near the end of the rod, the intensity pattern has significant standing-wave character, which leads to the creation of photoexcited carriers in the core of the structure. The larger diameter regions, on the other hand, exhibit intensity distributions in which the whispering gallery (WG) mode character dominates. At these locations, the photoexcited carriers are produced in subsurface depletion zone, where the internal fields separate the electrons and holes and lead to a greater degree of trap recombination on longer time scales.
Proceedings of SPIE | 2009
Ralph L. House; Brian P. Mehl; Chuan Zhang; Justin R. Kirschbrown; Scott C. Barnes; John M. Papanikolas
The demand for novel optoelectronic and photonic technologies has fueled an intense research effort to synthesize and characterize nanostructured semiconductor materials with unique properties that lend themselves to technological innovation. Zinc Oxide has emerged as an attractive candidate for a variety of applications, due in part to a large second order nonlinear susceptibility, its wide band-gap and large exciton binding energy. We have used time-resolved nonlinear two-photon emission and second harmonic generation microscopy to characterize the optical properties and excited state dynamics of individual rods. Ultrafast emission microscopy is used to follow the trapping dynamics of photoexcited charge carriers. Our results show a time-dependent red-shift in the trap emission band that is interpreted as arising from carrier percolation through trap states. In a second series of experiments, second harmonic generation (SHG) microscopy illustrates the connection between the optical mode structure of the object and its nonlinear mixing efficiency. Images show a periodic modulation in the SHG efficiency that is symmetrically situated relative to the rod midpoint. This phenomenon arises when the fundamental optical field couples into standing wave resonator modes of the structure and is a direct manifestation of the tapered shape of the rod.
Journal of Materials Chemistry | 2013
Leila Alibabaei; Hanlin Luo; Ralph L. House; Paul G. Hoertz; Rene Lopez; Thomas J. Meyer
Journal of Photochemistry and Photobiology C-photochemistry Reviews | 2015
Ralph L. House; Neyde Yukie Murakami Iha; Rodolfo L. Coppo; Leila Alibabaei; Benjamin D. Sherman; Peng Kang; M. Kyle Brennaman; Paul G. Hoertz; Thomas J. Meyer
Journal of Physical Chemistry C | 2008
David J. Styers-Barnett; Stephen P. Ellison; Brian P. Mehl; Brittany C. Westlake; Ralph L. House; Cheol Park; Kristopher E. Wise; John M. Papanikolas
Journal of Physical Chemistry Letters | 2011
Brian P. Mehl; Justin R. Kirschbrown; Ralph L. House; John M. Papanikolas