  Ordered W-doped Ta2O5 nanotube arrays were grown by self-organizing
electrochemical anodization of TaW alloys with different tungsten
concentrations and by a suitable high temperature ammonia treatment, fully
converted to W:Ta3N5 tubular structures. A main effect found is that W doping
can decrease the band gap from 2 eV (bare Ta3N5) down to 1.75 eV. Ta3N5
nanotubes grown on 0.5 at% W alloy and modified with (CoOH)x as co-catalyst
show ~33% higher photocurrents in photoelectrochemical (PEC) water splitting
than pure Ta3N5.
