Tungsten doping of Ta3N5-Nanotubes for Band Gap Narrowing and Enhanced   Photoelectrochemical Water Splitting Efficiency
  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. 
Sabina Grigorescu, Benedikt Baerhausen, Lei Wang, Anca Mazare, Jeong   Eun Yoo, Robert Hahn, Patrik Schmuki
cond-mat.mtrl-sci