Zhang Ning, Jalil Abdul, Wu Daoxiong, Chen Shuangming, Liu Yifei, Gao Chao, Ye Wei, Qi Zeming, Ju Huanxin, Wang Chengming, Wu Xiaojun, Song Li, Zhu Junfa, Xiong Yujie
Hefei National Laboratory for Physical Sciences at the Microscale, iChEM (Collaborative Innovation Center of Chemistry for Energy Materials), School of Chemistry and Materials Science, and National Synchrotron Radiation Laboratory , University of Science and Technology of China , Hefei , Anhui 230026 , P. R. China.
J Am Chem Soc. 2018 Aug 1;140(30):9434-9443. doi: 10.1021/jacs.8b02076. Epub 2018 Jul 17.
Photocatalysis may provide an intriguing approach to nitrogen fixation, which relies on the transfer of photoexcited electrons to the ultrastable N≡N bond. Upon N chemisorption at active sites (e.g., surface defects), the N 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, WO 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 N chemisorption and electron transfer. The doped low-valence Mo species play multiple roles in facilitating N activation and dissociation by refining the defect states of WO: (1) polarizing the chemisorbed N molecules and facilitating the electron transfer from CUS sites to N 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 N reduction. As a result, the 1 mol % Mo-doped WO sample achieves an ammonia production rate of 195.5 μmol g h, 7-fold higher than that of pristine WO. 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 N fixation and reaffirms the versatility of subtle electronic structure modulation in tuning catalytic activity.
光催化可能为固氮提供一种引人入胜的方法，该方法依赖于光激发电子向超稳定的N≡N键的转移。在活性位点（如表面缺陷）发生氮化学吸附时，氮分子尚未获得高能电子以实现有效活化和解离，这常常形成一个瓶颈。在此，我们报道通过掺杂来优化光催化剂中的缺陷态可以很好地解决这一瓶颈问题。作为概念验证，采用WO超薄纳米线作为精细钼掺杂的模型材料，其中具有氧缺陷的配位不饱和（CUS）金属原子作为氮化学吸附和电子转移的位点。掺杂的低价钼物种通过优化WO的缺陷态在促进氮活化和解离方面发挥多种作用：（1）使化学吸附的氮分子极化，并促进电子从CUS位点转移到氮吸附物上，这使得N≡N键通过质子耦合更易于解离；（2）将缺陷带中心提升至费米能级，从而保留光激发电子用于氮还原的能量。结果，1 mol%钼掺杂的WO样品实现了195.5 μmol g⁻¹ h⁻¹的氨生成速率，比原始WO高7倍。在纯水中，该催化剂在400 nm处表现出0.33%的表观量子效率，在模拟AM 1.5 G光照下太阳能到氨的效率为0.028%。这项工作为用于固氮的光催化剂晶格设计提供了新的见解，并再次证实了精细电子结构调制在调节催化活性方面的多功能性。
