基于水氧化反应的光催化固氮材料和催化机理研究

Ammonia as an important chemical plays a crucial role in the national economy. However, current nitrogen fixation routes consumed large amount of energy which accounts for ~2% of the annual electricity consumption. How to realize artificial nitrogen fixation and conversion to ammonia with low energy consumption is a key scientific problem to be solved, and has become a hot research topic. The rapidly developing photocatalysis provides a new route for nitrogen fixation. In this proposal, metal oxides/nitrides are selected as the research objects. The adsorption, activation, hydrogenation, and desorption processes of nitrogen, water oxidization to produce protons, and protons coupled electrons transfer under illumination will be systematically studied to investigate the relationships between the surface structures, proton-electron coupling transfer, and the photocatalytic ammonia production performances. The mechanism and key steps to promote photocatalytic ammonia production efficiency will be revealed. This project aims at obtaining high efficient photocatalysts for nitrogen fixation. The detailed contents include: (1) Theoretical calculation and analysis of the band structure and the associated adsorption model of nitrogen on different photocatalysts. (2) Controllable synthesis of different photocatalysts. (3) Investigating the photocatalytic nitrogen fixation performances of different photocatalysts via theoretical analysis and experimental observations. (4) Exploring the properties of possible intermediates in the photocatalytic nitrogen fixation processes and disclosing the specific way of the photocatalytic nitrogen fixation and conversion to ammonia. The successful implementation of this project will provide new routes for the design and synthesis of highly efficient nitrogen fixation photocatalysts, and new mechanisms for the photocatalytic ammonia production.

氨作为重要的化工产品在国民经济中举足轻重，但人工合成氨的能耗和碳排放巨大，温和条件下人工固氮合成氨是一个亟待解决的科技难题和研究热点。太阳能光催化技术近期的研究进展为人工固氮提供了新的视角。本项目拟以基于水氧化反应的光催化材料为研究对象，在室温常压下通过光催化分解H2O提供质子，同时光生电子还原活化N2，并与质子结合实现NH3的合成，探索光催化材料的表面缺陷酸碱活性位、质子-电子耦合传导与光催化合成氨之间的关联规律，研制出高效的光催化固氮材料，具体内容包括：理论分析光催化材料的电子结构，构建N2和H2O在其表面的解离吸附模型，指导光催化材料的表面态优化，制备出所设计的光催化材料并实现光能利用率的提升；以H2O和N2为原料的光催化合成氨作为模型反应来研究光催化材料的固氮性能；探究中间物种的性质，确立由N2向NH3转化的具体途径。本项目的实施，对实现常温常压下高效固氮研究具有重大的科学意义。

人工固氮合成氨，传统的合成方法需要高温高压的苛刻条件。在温和条件下合成氨是近百年来科学家们奋斗的目标。利用光催化的方法在常温常压下实现氮气的还原合成氨是本项目的研究目标。经过4年的努力，我们发现了几类光催化材料体系具备固氮的性能，包括BiO, MoS2, LaFeO3, Bi24O31Br10(OH)δ等，并且探索了光催化固氮合成氨效率的提升机制和途径：发现疏水性的表面有助于氮气的吸附，表面碱性位有助于固氮能力的提升；进一步的，通过表面缺陷的调控和表面修饰，实现氮气的吸附活化；构建复合材料体系，利用不同的半导体的特性，通过优势互补，实现固氮合成氨性能的提升；发现杂多酸的多电子多质子的储存能力对氮气还原合成氨的多电子多质子过程具有优秀的提升能力，从而发展出一类新颖的光催化固氮合成氨复合材料体系，在固氮领域具有深远的发展潜力。这些研究结果为固氮领域的研究工作做出了有益的积累，为促进合成氨领域的发展做出了积极的努力。