Fine synthesis of photocatalitic thin films based on oxynitrides for water splitting with high efficiency

利用光催化剂从阳光和水中制取氢气是从根本上解决能源问题的一种潜在途径。本项目的目的是研制基于d^0和d^10族(氧)氮化物的光催化薄膜，用于可见光照射下的无偏压分解水。首先，我们开展了GaN/ZnO固溶体光电极的研制工作。将(Ga_&lt；1x&gt；Zn_x)(N_&lt；1x&gt；O_x)粉末粘贴到导电玻璃上制备了光电极。我们深入研究了表面改性的效果。结果发现，负载IrO2作为助催化剂后，光电流得到极大的提高。此外，从光电极析出的气体是O_2，而从对电极析出的气体是H_2。析出气体的量与光电流一致。下一步，我们在硫氧化物中扩展目标材料。硫化物被认为是一种光功能材料。然而，它们在水中通常不稳定，被认为不适合在水中用作光催化剂。我们探索了硫氧化合物在水中作为光催化剂的潜在可能性。我们发现La_5Ti_2AgS_5O_7在水中制氢方面具有很好的潜力。通过在导电衬底上粘贴粉末和/或射频磁控溅射的方法制备了光电极。通过光电化学测试，发现La5Ti2AgS5O7为p型半导体。P型光电极有望在不自降解的情况下放出氢气。这些光电极具有从水和阳光中产生H_2和O_2的实用潜力，还需要更广泛的研究。

The hydrogen production by a photocatalyst from sunlight and water is a potential approach to solve the energy problems essentially. The purpose of this projict is the development of photocatalitic films based on d^0 and/of d^10 group (oxy)nitrides for water splitting under visible light illumination without bias voltage. First, we carried out the development of photoelectrode based on a solid solution of GaN and ZnO. The photoelectrodes were prepared by pasting (Ga_<1x>Zn_x)(N_<1x>O_x) powder onto conducting glass. We intensively surveyed the effects of surface modification. As a result, we found that photocurrent is extremely enhanced by the loading of IrO_2 as a cocatalyst. Moreover, the gas evolved from the photoelectrode was found to be O_2, while the gas evolved from the counter electrode was found to be H_2. The amount of evolved gases is consistent with the photocurrent. Next, we expanded target materials in oxysulfide. Sulfides are known as a photofunctional material. They are, however, generally unstable in water and believed to be unsuitable for a photocatalyst in water. We explore the potential possibilities of oxysulfides as a photocatalyst in water. We found that La_5Ti_2AgS_5O_7 have promising potential for H_2 production from water. Photoelectrodes were prepared by pasting powder and/or by RF magnetron sputtering on conducting substrates. By photoelectrochemical measurements, La_5Ti_2AgS_5O_7 was found to p-type semiconductor. P-type photoelectrodes are expected to evolve H_2 without self-degradation. These photoelectrodes have practical potential to produce H_2 and O_2 from water and sunlight, and more extensive studies are required.