Ultrathin Cobalt Oxide Interlayer Facilitated Hole Storage for Sustained Water Oxidation over Composited Tantalum Nitride Photoanodes

The hole-storage layer (HSL) strategy has been demonstrated as an efficient interfacial modification method to overcome the instability of tantalum nitride (Ta3N5) photoanodes and further boost high performance in photoelectrochemical (PEC) water oxidation reaction. Herein, we report that the CoO x /Ni­(OH) x bilayer as a typical HSL could effectively extract and store photogenerated holes from Ta3N5, resulting in a decent photocurrent enhancement and stable water oxidation for at least 30 h. Most strikingly, the reversible formation of Co­(IV) species inside the ultrathin CoO x layer during PEC water oxidation is found to regulate the hole-storage process, leading to facilitated photogenerated hole extraction capacity and suppressed charge recombination. Furthermore, upon the insertion of the CoO x /Ni­(OH) x bilayer for the Ta3N5/CoPi photoanode, the photocurrent could be evidently increased, emphasizing the general applicability of the HSL strategy in promoting water oxidation reaction.