Mg-doped Ta3N5 nanorods coated with a conformal CoOOH layer for water oxidation: bulk and surface dual modification of photoanodes

Abstract

Charge separation/transfer and photocorrosion are two major factors limiting the photoelectrochemical (PEC) applications of the Ta₃N₅ photocatalyst. Herein, we have fabricated Ta₃N₅ single-crystal nanorods with Mg doping by flux-assisted crystal growth, aiming to shorten the charge transport distance and increase the electrical conductivity. The optimized Mg-doped Ta₃N₅ photoanodes exhibit an unprecedented PEC water splitting activity with an AM 1.5G photocurrent of 1.5 mA cm⁻² at 1.23 V_RHE. The high performance is attributed to the fact that the bulk modification, Mg doping, can induce oxygen-impurity surface states as effective electron trap centers, thus increasing the electrical conductivity of Ta₃N₅ and charge separation efficiency. After a conformal surface modification with CoOOH by a simple electrodeposition method as a water oxidation electrocatalyst to improve the hole extraction and reaction kinetics, the Mg-doped Ta₃N₅ photoanodes afford an over 4-fold increase in photocurrent (ca. 6.5 mA cm⁻² at 1.23 V_RHE) and about 70% retention of the initial photocurrent after 70 min irradiation at 1.0 V_RHE. Our results testify that the bulk and surface co-modification is an effective route to develop high-performance PEC water splitting devices.