Plasma-enhanced chemical vapor deposition Ta3N5 synthesis leading to high current density during PEC oxygen evolution

Abstract

A new route for the preparation of tantalum nitride (Ta₃N₅) thin films for photoelectrochemical (PEC) applications was demonstrated, based on plasma-enhanced chemical vapor deposition (PCVD). Ta₃N₅ was produced on a Ta foil substrate using PCVD with a Ta precursor, followed by NH₃ nitridation at high temperatures. Various characterization techniques were used to assess the properties of the resulting films, including X-ray diffraction, scanning electron microscopy-energy dispersive X-ray spectroscopy, cross-sectional scanning transmission electron microscopy with elemental mapping, cross-sectional high resolution transmission electron spectroscopy, and X-ray photoelectron spectroscopy. This PCVD technique formed an amorphous phase that was converted into a multilayer structure having the composition TaO_x/Ta₃N₅/Ta₃N₅ + Ta₂N/Ta during nitridation. Photoelectrochemical (PEC) trials assessing the progress of the oxygen evolution reaction showed a high photocurrent density of 8.1 mA cm⁻² at 1.23 V vs. RHE under simulated solar radiation. This represents one of the highest values ever reported for Ta₃N₅ without further modification or the addition of a surface layer. The incident photon-to-current efficiency of this specimen reached a maximum of 67% at 500 nm and the device was stable for up to 60 min. The superior PEC performance obtained in this work is attributed to the formation of a highly crystalline, compact and uniform Ta₃N₅ + Ta₂N layer.