Photoelectrochemical
(PEC) water splitting is an important and
rapidly developing technology that produces H2 as a renewable
resource, but local surface investigations remain a major challenge.
Using scanning electrochemical cell microscopy (SECCM), the PEC catalytic
effects of anatase TiO2-nanotube arrays grown on Ti felt
are explored. The SECCM imaging is performed both perpendicular and
parallel to the nanotube growth direction. In contrast to bulk cyclic
voltammetry measurements, SECCM measures only the upper region of
the nanotubes that remain in contact with the electrolyte, which provides
a better understanding of the phenomena connected to the longitudinal
charge transport. Despite the presence of regions with higher and
lower photocurrent, the PEC reactivities of the nanotube tops and
walls are roughly comparable with each other. The data support the
model of orthogonal electron–hole separation. This model facilitates
the photogenerated hole diffusion over the short distance to the electrolyte
interface due to the sufficient transport of photoexcited electrons
along the long axial direction of TiO2 nanotubes and is
often applied to one-dimensional systems. Observed results were additionally
supported by the nanotube decoration with photoelectrochemically deposited
PbO2 particles.
The Naradani Formation is located to the south of the Torinosu Group in the Sakawa district of Kochi, southwest Japan, and consists of a linear, narrowly distributed series of marine clastic deposits that contain allochthonous limestone blocks. This formation was previously correlated to the Bajocian-Bathonian Middle Jurassic using brachiopods extracted from the limestone blocks, with later radiolarian correlations suggesting an Oxfordian-Kimmeridgian Upper Jurassic age. The formation has also been interpreted to underlie the Upper Jurassic-Lower Cretaceous Torinosu Group. However, the discovery of two stage-diagnostic aspidoceratid ammonoids, Aspidoceras sp. and Hybonoticeras sp., from muddy sandstones in the stratotype area of the Naradani Formation casts doubt on these previous interpretations. Aspidoceras was widespread during the latest Jurassic, and the presence of Hybonoticeras limits this short stratigraphic interval to the Kimmeridgian-Tithonian boundary in various Tethyan sections. This clearly suggests a latest Jurassic age for the Naradani Formation and generally supports the radiolarian biostratigraphy age-assignment. However, the ranges of ammonoids from the Naradani Formation overlap those from the Torinosu Group, meaning that it is not possible to determine an age-difference between these two lithostratigraphic units. Further research is needed to test other hypotheses, for example to determine whether heterotopic facies relationships exist between the Naradani Formation and the Torinosu Group.
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