Tungsten doping of Ta3N5-nanotubes for band gap narrowing and enhanced photoelectrochemical water splitting efficiency

•This work shows a successful band-gap reduction in Ta3N5 nanotubes by W doping.•The doping process occurs in-situ during the anodic growth from a TaW substrate.•W doped Ta3N5 nanotubes provide enhanced PEC performance under AM 1.5 conditions.

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 Co(OH)x as co-catalyst show ~ 33% higher photocurrents in photoelectrochemical (PEC) water splitting than pure Ta3N5.