The p-type Cu2O/n-type TaON heterojunction nanorod array passivated with ultrathin carbon sheath as a surface protection layer is excellent in photoelectrochemical water splitting.

Ta 3 N 5 nanorod arrays were fabricated by nitridation of fluorine-containing tantalum oxide (F-Ta 2 O 5 ) nanorod arrays grown in situ on Ta substrates by a one-pot vapour-phase hydrothermal induced selfassembly technique. In this protocol, the in situ generation and the morphology of arrays elaborately adjusted by reaction time, play a vital role in the formation of the F-Ta 2 O 5 nanorod arrays and a highly conductive interlayer between the nanorods and the substrate. Due to the shape anisotropy, ordered hierarchical structure and high surface area, a high photoelectrochemical activity was achieved by the optimum Ta 3 N 5 nanorod photoelectrode with a photocurrent density of 1.22 mA cm À2 under AM 1.5G irradiation at 1.23 V vs. RHE (reversible hydrogen electrode). Furthermore, a higher and more stable photocurrent was demonstrated by combining the highly active Ta 3 N 5 nanorods with stable Co 3 O 4 / Co(OH) 2 (Co 3 O 4 /Co(II)) bilayer catalysts when compared with that demonstrated for Co(II)/Ta 3 N 5 and Co 3 O 4 /Ta 3 N 5 photoelectrodes, exhibiting that not only is the onset potential negatively shifted but also the photocurrent and the stability are significantly improved, which is correlated to an order of magnitude reduction in the resistance to charge transfer at the Ta 3 N 5 /H 2 O interface. Specifically, about 92% of the initial stable photocurrent remains after long-term irradiation at 1.23 V vs. RHE. At 1.23 V vs. RHE, the photocurrent density of Co 3 O 4 /Co(II)/Ta 3 N 5 arrays reached 3.64 mA cm À2 under AM 1.5G simulated sunlight at 100 mW cm À2 , and a maximum IPCE of 39.5% was achieved at 440 nm. This combination of catalytic activity, stability, and conformal decoration makes this a promising approach to improve the photoelectrochemical performance of photoanodes in the general field of energy conversion. Broader contextPhotoelectrochemical (PEC) water splitting based on semiconductor materials is a promising approach to harvest and store solar energy and may have the potential to supply the world's energy demand with a clean and sustainable chemical fuel. Tantalum nitride (Ta 3 N 5 ) is an attractive photoanode material due to its high theoretical solar-to-hydrogen efficiency (15.9% under AM 1.5G illumination), suitable valence band positions for water oxidation, excellent stability, and low material cost. However, it is a challenge to design stable structures that can be used as anodes in the photoelectrochemical cells. In this work, we create the rst Co 3 O 4 /Co(II)/Ta 3 N 5 nanorod array photoanode with a better photoelectrochemical performance to perform water oxidation and generate photocurrent. This strategy as a promising avenue provides new insights into the design and tailoring of tantalum nitride to enhance the photoelectrochemical performance of photoanodes in the general eld of energy conversion.

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