Refining Defect States in W18O49 by Mo Doping: A Strategy for Tuning N2 Activation towards Solar-Driven Nitrogen Fixation,Journal of the American Chemical Society

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Refining Defect States in W18O49 by Mo Doping: A Strategy for Tuning N2 Activation towards Solar-Driven Nitrogen Fixation
Journal of the American Chemical Society ( IF 14.4 ) Pub Date : 2018-07-05 , DOI: 10.1021/jacs.8b02076
Ning Zhang ₁ , Abdul Jalil ₁ , Daoxiong Wu ₁ , Shuangming Chen ₁ , Yifei Liu ₁ , Chao Gao ₁ , Wei Ye ₁ , Zeming Qi ₁ , Huanxin Ju ₁ , Chengming Wang ₁ , Xiaojun Wu ₁ , Li Song ₁ , Junfa Zhu ₁ , Yujie Xiong ₁

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Photocatalysis may provide an intriguing approach to nitrogen fixation, which relies on the transfer of photoexcited electrons to the ultrastable N≡N bond. Upon N2 chemisorption at active sites (e.g., surface defects), the N2 molecules have yet to receive energetic electrons toward efficient activation and dissociation, often forming a bottleneck. Herein, we report that the bottleneck can be well tackled by refining the defect states in photocatalysts via doping. As a proof of concept, W18O49 ultrathin nanowires are employed as a model material for subtle Mo doping, in which the coordinatively unsaturated (CUS) metal atoms with oxygen defects serve as the sites for N2 chemisorption and electron transfer. The doped low-valence Mo species play multiple roles in facilitating N2 activation and dissociation by refining the defect states of W18O49: (1) polarizing the chemisorbed N2 molecules and facilitating the electron transfer from CUS sites to N2 adsorbates, which enables the N≡N bond to be more feasible for dissociation through proton coupling; (2) elevating defect-band center toward the Fermi level, which preserves the energy of photoexcited electrons for N2 reduction. As a result, the 1 mol % Mo-doped W18O49 sample achieves an ammonia production rate of 195.5 μmol gcat-1 h-1, 7-fold higher than that of pristine W18O49. In pure water, the catalyst demonstrates an apparent quantum efficiency of 0.33% at 400 nm and a solar-to-ammonia efficiency of 0.028% under simulated AM 1.5 G light irradiation. This work provides fresh insights into the design of photocatalyst lattice for N2 fixation and reaffirms the versatility of subtle electronic structure modulation in tuning catalytic activity.

中文翻译：

通过 Mo 掺杂精炼 W18O49 中的缺陷状态：调整 N2 活化以实现太阳能驱动固氮的策略

光催化可能为固氮提供了一种有趣的方法，它依赖于光激发电子转移到超稳定的 N≡N 键。在活性位点（例如，表面缺陷）处发生 N2 化学吸附后，N2 分子尚未接收高能电子以实现有效的激活和解离，这通常会形成瓶颈。在这里，我们报告说，通过掺杂改进光催化剂中的缺陷态可以很好地解决瓶颈问题。作为概念证明，W18O49 超薄纳米线被用作精细 Mo 掺杂的模型材料，其中具有氧缺陷的配位不饱和 (CUS) 金属原子作为 N2 化学吸附和电子转移的位点。掺杂的低价钼物质通过细化 W18O49 的缺陷态在促进 N2 活化和解离方面发挥多种作用：(1) 使化学吸附的 N2 分子极化，促进电子从 CUS 位点转移到 N2 吸附物，使 N≡N 键更容易通过质子耦合解离；(2) 将缺陷带中心提升到费米能级，这保留了用于 N2 还原的光激发电子的能量。结果，1 mol % Mo 掺杂的 W18O49 样品实现了 195.5 μmol gcat-1 h-1 的氨产率，是原始 W18O49 的 7 倍。在纯水中，该催化剂在模拟 AM 1.5 G 光照射下在 400 nm 处表现出 0.33% 的表观量子效率和 0.028% 的太阳能转化氨效率。这项工作为 N2 固定光催化剂晶格的设计提供了新的见解，并重申了微妙的电子结构调节在调节催化活性方面的多功能性。

更新日期：2018-07-05

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