Preparation And Solar Water Splitting Properties Of Efficient Ta₃N₅ Microsphere Photoanode

p-n tandem photoelectrochemical cell is a very promising technology for solar water splitting. Ta3N5 is one of ideal photoanodes because of its high theoretical efficiency and reasonable band positions. Microsphere structure can enhance light absorption by increasing free path of light. Nevertheless, currently reported preparation methods for Ta3N5 microsphere particles are relatively cumbersome and often in the assistance of additional agents. Hence, it is desirable to look for a simple method to prepare microsphere Ta3N5 film.In this context, Ta3N5 microsphere photoanode was prepared by a new in-situ hydrolysis deposition method from tantalum ethoixde (Ta(OEt)5) methanol solution without any additional agents. And the effects of aging time on the physical and chemical properties of Ta3N5 microsphere photoanode are systematically investigated.The main contents are concluded as below:(1) Hydrolysis deposition process of Ta3N5 microsphere particles. During the preparation process, it was found that only after methanol was aged, will white film be deposited on the substrate. SEM shows that precipitate precursor is microsphere, which proves that microsphere particles have already been formed during the deposition process. Cross-sectional SEM image of cracked Ta3N5 microsphere shows many nanoparticles inside the sphere. It is a strong evidence that microsphere is directly from the agglomeration of nanoparticles. TGA reveals lots of organic groups exist in precipitate and FT-IR shows the existence of-OH group, which was still existed even after calcination at 250℃. It illustrates that -OH group is not only from absorbed water, but also from the hydrolysis of Ta(OEt)s. From above analysises, it can be confirmed that Ta3N5 microsphere particles come from the hydrolysis of Ta(OEt)5 and subsequent agglomeration of nanoparticles.(2) Effects of methanol aging time on the morphology and transportation resistance of Ta3N5 microsphere film. When the aging time is beyond 10 h, the transportation resistance of Ta3N5 microsphere film will increase sharply, resulting in a dramatic decrease of photocurrent. The reason is that a very thick film is deposited on the substrate very quickly due to the rapid hydrolysis of Ta(OEt)s, but the film will cracks after it drys, bringing out thick but sparsely distributed fragmentations, as well as weaker adhension to the substrate.(3) Photoelectrochemical performance of Ta3N5 microsphere film. Because microsphere structure can increase free path of photon, light absorption can be increased greatly. The light absorption efficiency of Ta3N5 microsphere film keeps around 80% in the intrinsic absorption of Ta3N5. After loaded with Co-Pi, under the illumination of AM 1.5 G, Ta3N5 microsphere film shows a 2.8 mA/cm2 at 1.23 V vs. RHE and 7.3 mA/cm2 at 1.6 V vs. RHE.In conclusion, in-situ hydrolysis deposition is a new and simple method for preparation of efficient Ta3N5 microsphere film. It is suitable for different substrates, including transparent substrate. Furthermore, the photocurrent of Ta3N5 microsphere film can be further improved by optimizing preparation conditions for achieving efficient solar water splitting.