  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.
