Porous TaON Photoanodes Loaded with Cobalt-Based Cocatalysts for Efficient and Stable Water Oxidation Under Visible Light

Porous photoanodes for visible-light-induced water oxidation were prepared via simple electrophoretic deposition of TaON particles, preliminarily modified with CoO _x nanoparticles, on a Ti substrate. Post-necking process involving methanolic TaCl₅ solution and subsequent heating in NH₃ stream formed bridges between TaON particles, which facilitated electron transport within the porous electrode and thereby increased the photocurrent significantly. The temperature of the NH₃ treatment in the post-necking process significantly influenced both the charge transport through the bridges and the activity of the CoO _x cocatalyst for water oxidation, thus producing maximum photocurrent after heating at 723 K. The highly dispersed CoO _x nanoparticles considerably improved the stability of the photocurrent due to efficient capture of photogenerated holes and consequent reduction of the probability of self-oxidative deactivation of the TaON surface. The combination of phosphate buffer solutions with a highly dispersed CoO _x cocatalyst on the TaON surface significantly increased the photocurrent due to the in situ photoelectrochemical production of an amorphous cobalt/phosphate (Co–Pi) phase, which covers the TaON surface almost entirely, and consequently improved the its stability in long-term photoirradiation.