Harb Moussab, Sautet Philippe, Nurlaela Ela, Raybaud Pascal, Cavallo Luigi, Domen Kazunari, Basset Jean-Marie, Takanabe Kazuhiro
Division of Physical Sciences and Engineering, KAUST Catalysis Center (KCC), King Abdullah University of Science and Technology (KAUST), 4700 KAUST, Thuwal 23955-6900, Kingdom of Saudi Arabia.
Phys Chem Chem Phys. 2014 Oct 14;16(38):20548-60. doi: 10.1039/c4cp03594a. Epub 2014 Aug 22.
Finding an ideal photocatalyst for achieving efficient overall water splitting still remains a great challenge. By applying accurate first-principles quantum calculations based on DFT with the screened non-local hybrid HSE06 functional, we bring rational insights at the atomic level into the influence of non-stoichiometric compositions on essential properties of tantalum (oxy)nitride compounds as visible-light-responsive photocatalysts for water splitting. Indeed, recent experiments show that such non-stoichiometry is inherent to the nitridation methods of tantalum oxide with unavoidable oxygen impurities. We considered here O-enriched Ta3N5 and N-enriched TaON materials. Although their structural parameters are found to be very similar to those of pure compounds and in good agreement with available experimental studies, their photocatalytic features for visible-light-driven overall water splitting reactions show different behaviors. Further partial nitration of TaON leads to a narrowed band gap, but partially oxidizing Ta3N5 causes only subtle changes in the gap. The main influence, however, is on the band edge positions relative to water redox potentials. The pure Ta3N5 is predicted to be a good candidate only for H(+) reduction and H2 evolution, while the pure TaON is predicted to be a good candidate for water oxidation and O2 evolution. Non-stoichiometry has here a positive influence, since partially oxidized tantalum nitride, Ta(3-x)N(5-5x)O5x (for x≥ 0.16) i.e. with a composition in between TaON and Ta3N5, reveals suitable band edge positions that correctly bracket the water redox potentials for visible-light-driven overall water splitting reactions. Among the various explored Ta(3-x)N(5-5x)O5x structures, a strong stabilization is obtained for the configuration displaying a strong interaction between the O-impurities and the created Ta-vacancies. In the lowest-energy structure, each created Ta-vacancy is surrounded by five O-impurity species substituting the five N sites characterizing one octahedral environment.
寻找一种理想的光催化剂以实现高效的全水分解仍然是一个巨大的挑战。通过基于密度泛函理论（DFT）并采用筛选非局域杂化HSE06泛函进行精确的第一性原理量子计算，我们从原子层面深入了解了非化学计量组成对氮化钽（氧）化物作为用于水分解的可见光响应光催化剂的基本性质的影响。事实上，最近的实验表明，这种非化学计量是氧化钽氮化方法中不可避免地存在氧杂质所固有的。我们在此考虑了富氧的Ta3N5和富氮的TaON材料。尽管发现它们的结构参数与纯化合物的结构参数非常相似，并且与现有实验研究结果吻合良好，但它们在可见光驱动的全水分解反应中的光催化特性表现出不同的行为。TaON的进一步部分硝化导致带隙变窄，但Ta3N5的部分氧化仅使带隙发生细微变化。然而，主要影响在于相对于水氧化还原电位的能带边缘位置。预测纯Ta3N5仅对H(+)还原和H2析出是良好的候选材料，而纯TaON则被预测为水氧化和O2析出的良好候选材料。非化学计量在此具有积极影响，因为部分氧化的氮化钽Ta(3 - x)N(5 - 5x)O5x（对于x≥0.16），即组成介于TaON和Ta3N5之间的材料，显示出合适的能带边缘位置，能够正确地界定用于可见光驱动的全水分解反应的水氧化还原电位。在各种探索的Ta(3 - x)N(5 - 5x)O5x结构中，对于显示出O杂质与产生的Ta空位之间强相互作用的构型，获得了很强的稳定性。在能量最低的结构中，每个产生的Ta空位被五个O杂质物种包围，这些O杂质取代了表征一个八面体环境的五个N位点。
