2 research outputs found
Dynamic Nuclear Polarization NMR of Low‑γ Nuclei: Structural Insights into Hydrated Yttrium-Doped BaZrO<sub>3</sub>
We demonstrate that solid-state NMR
spectra of challenging nuclei
with a low gyromagnetic ratio such as yttrium-89 can be acquired quickly
with indirect dynamic nuclear polarization (DNP) methods. Proton to <sup>89</sup>Y cross polarization (CP) magic angle spinning (MAS) spectra
of Y<sup>3+</sup> in a frozen aqueous solution were acquired in minutes
using the AMUPol biradical as a polarizing agent. Subsequently, the
detection of the <sup>89</sup>Y and <sup>1</sup>H NMR signals from
technologically important hydrated yttrium-doped zirconate ceramics,
in combination with DFT calculations, allows the local yttrium and
proton environments present in these protonic conductors to be detected
and assigned to different hydrogen-bonded environments
Homogeneous Electron Doping into Nonstoichiometric Strontium Titanate Improves Its Photocatalytic Activity for Hydrogen and Oxygen Evolution
Water
splitting using a semiconductor photocatalyst has been extensively
studied as a means of solar-to-hydrogen energy conversion. Powder-based
semiconductor photocatalysts, in particular, have tremendous potential
in cost mitigation due to system simplicity and scalability. The control
and implementation of powder-based photocatalysts are, in reality,
quite complex. The identification of the semiconductor–photocatalytic
activity relationship and its limiting factor has not been fully solved
in any powder-based semiconductor photocatalyst. In this work, we
present systematic and quantitative evaluation of photocatalytic hydrogen
and oxygen evolution using a model strontium titanate powder/aqueous
solution interface in a half reaction. The electron density was controlled
from 10<sup>16</sup> to 10<sup>20</sup> cm<sup>–3</sup> throughout
the strontium titanate powder by charge compensation with oxygen nonstoichiometry
(the amount of oxygen vacancy) while maintaining its crystallinity,
chemical composition, powder morphology, and the crystal and electronic
structure of the surface. The photocatalytic activity of hydrogen
evolution from aqueous methanol solution was stable and enhanced by
40-fold by the electron doping. The enhancement was correlated well
with increased Δabsorbance, an indication of prolonged lifetime
of photoexcited electrons, observed by transient absorption spectroscopy.
Photocatalytic activity of oxygen evolution from aqueous silver nitrate
solution was also enhanced by 3-fold by the electron doping. Linear
correlation was found between the photocatalytic activity and the
degree of surface band bending, ΔΦ, above 1.38 V. The
band bending, potential downhill for electronic holes, enlarges the
total flux of photoexcited holes toward the surface, which drives
the oxygen evolution reaction