Exploring facile strategies for high-oxidation-state metal nitride synthesis: carbonate-assisted one-step synthesis of Ta3N5 films for solar water splitting

One-step nitridation process of Ta foils with and without the assistance of CO2 under ammonia flow. [Display omitted] Metal nitrides are widely studied due to their outstanding physical properties, including high hardness, high thermal and chemical stability, low electrical resistivity etc. Generally, metal nitrides can be obtained from the direct reaction of metal and ammonia/nitrogen. However, some of the metal nitrides, such as Ta3N5, cannot be synthesized by direct nitridation of metals. To achieve Ta3N5, high-oxidation-state Ta precursors like Ta2O5, NaTaO3, TaS3, K6Ta10.8O30, Ta(N(CH3)2)5 and TaCl5 have to be employed, which is a time-consuming and laborious process with the possibility of introducing undesirable impurities. Here taking Ta3N5 as an example, a facile carbonate-assisted one-step nitridation method is proposed, which enables the direct synthesis of high-oxidation-state metal nitride films from metal precursors under ammonia flow. The mechanism of the nitridation process has been studied, which carbon dioxide released from carbonates decomposition reacts with metallic Ta and assists the one-step conversion of metallic Ta to Ta3N5. The as-prepared Ta3N5 film, after modified with NiFe layered double hydroxide, exhibits promising water splitting performance and stability. This method avoids the preoxidation process of metal precursors in high-oxidation-state metal nitride synthesis, and may facilitate the direct fabrication of other important metal nitrides besides Ta3N5.