Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Photoanodes Based on TiO$_2$ and $\alpha$-Fe$_2$O$_3$ for Solar Water
  Splitting Superior Role of 1D Nanoarchitectures and of Combined
  Heterostructures   Solar driven photoelectrochemical water splitting (PEC-WS) using
semiconductor photoelectrodes represents a promising approach for a sustainable
and environmentally friendly production of renewable energy vectors and fuel
sources, such as dihydrogen (H2). In this context, titanium dioxide (TiO$_2$)
and iron oxide (hematite, $\alpha$-Fe$_2$O$_3$) are among the most investigated
candidates as photoanode materials, mainly owing to their resistance to
photocorrosion, non-toxicity, natural abundance, and low production cost. Major
drawbacks are, however, an inherently low electrical conductivity and a limited
hole diffusion length that significantly affect the performance of TiO$_2$ and
$\alpha$-Fe$_2$O$_3$ in PEC devices. To this regard, one-dimensional (1D)
nanostructuring is typically applied as it provides several superior features
such as a significant enlargement of the material surface area, extended
contact between the semiconductor and the electrolyte and, most remarkably,
preferential electrical transport that overall suppress charge carrier
recombination and improve TiO$_2$ and $\alpha$-Fe$_2$O$_3$
photo-electrocatalytic properties. The present review describes various
synthetic methods, properties and PEC applications of 1D-photoanodes
(nanotubes, nanorods, nanofibers, nanowires) based on titania, hematite, and on
$\alpha$-Fe$_2$O$_3$/TiO$_2$ heterostructures. Various routes towards
modification and enhancement of PEC activity of 1D photoanodes are also
discussed including doping, decoration with co-catalysts and heterojunction
engineering. Finally, the challenges related to the optimization of charge
transfer kinetics in both oxides are highlighted.

31
The categories of this paper are: ao-sci
17
The categories of this paper are: q-fin
22
The categories of this paper are: chao-dyn
6
The categories of this paper are: astro-ph
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The categories of this paper are: hep-ex
2
The categories of this paper are: math
14
The categories of this paper are: math-ph
23
The categories of this paper are: solv-int
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The categories of this paper are: alg-geom
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The categories of this paper are: supr-con
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The categories of this paper are: cmp-lg
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The categories of this paper are: chem-ph
0
The categories of this paper are: hep-ph
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The categories of this paper are: nucl-th
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The categories of this paper are: eess
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The categories of this paper are: gr-qc