Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Open top anodic Ta3N5 nanotubes for higher solar water splitting
  efficiency   In the present work we grow self-organized Ta2O5 nanotube layers in a
H2SO4/NH4F electrolyte at various elevated temperatures. Under optimized
conditions we obtain 4 {\mu}m long nanotubes that are well adherent to the
substrate and can be grown very homogenous over large surface areas. Moreover,
the key advantage of this approach is that an open top morphology (initiation
layer free) is obtained. After a suitable conversion treatment in NH3
atmosphere Ta3N5 nanotubes are obtained, that after (Co-Pi+Co(OH)x)
modification provide, under AM 1.5G illumination conditions, a
photoelectrochemical current response of 4.7 mA cm-2 at 1.23 V vs RHE.

6
The categories of this paper are: astro-ph
25
The categories of this paper are: patt-sol
23
The categories of this paper are: solv-int
35
The categories of this paper are: mtrl-th
3
The categories of this paper are: physics
9
The categories of this paper are: nlin
15
The categories of this paper are: nucl-ex
28
The categories of this paper are: alg-geom
29
The categories of this paper are: funct-an
18
The categories of this paper are: econ
36
The categories of this paper are: cmp-lg
20
The categories of this paper are: acc-phys
14
The categories of this paper are: math-ph
27
The categories of this paper are: comp-gas
12
The categories of this paper are: nucl-th
30
The categories of this paper are: q-alg