Wet ammonia Synthesis of Semiconducting N:Ta₂O₅, Ta₃N₅ and ¦Â-TaON Films for Photoanode Applications

详细信息    查看全文

• 作者：Ali Dabirian ; Hans van¡¯t Spijker ; Roel van de Krol
• 关键词：tantalum oxynitride ; photoanodes ; water splitting ; optical monitoring ; tantalum nitride ; ammonolysis
• 刊名：Energy Procedia
• 出版年：2012
• 出版时间：2012
• 年：2012
• 卷：22
• 期：Complete
• 页码：15-22
• 全文大小：1255 K

文摘

Tantalum oxynitride (¦Â-TaON) is a promising photoanode material for photoelectrochemical water splitting. However, the synthesis of phase-pure ¦Â-TaON films is a challenging task. This paper describes a novel approach to achieve this by the controlled nitridation of Ta₂O₅ films under a flow of ammonia gas (ammonolysis), which was obtained by bubbling argon through an aqueous ammonium hydroxide solution followed by a 5 ? molecular sieve to remove the water. Depending on the nitridation conditions, either nitrogen-doped Ta₂O₅ or Ta₃N₅ was obtained as a thermodynamically stable phase. The evolution of the nitridation process was monitored in-situ using optical transmission spectroscopy, which revealed that the transformation of Ta₂O₅ to Ta₃N₅ occurred within minutes, through a series of intermediate oxynitride phases. This suggested the possibility of synthesizing the desired ¦Â-TaON phase by quenching the sample at the right time during the nitridation process. By choosing the right ammonolysis conditions (750 ¡ãC, flow rate 50 ml/min.), we were able to slow down the nitridation process and terminate it before the oxide was fully converted to Ta₃N₅. A post-nitridation heat treatment at 800 ¡ãC indeed resulted in the formation of the desired ¦Â-TaON phase.