双金属位点单原子催化剂的制备及其电化学合成氨性能研究

Electrochemical synthesis of NH3 is an attractive technology and has numerous advantages such as ambient and atmospheric operation, simple apparatus and easy to be coupled with renewable energy conversion technologies. However, due to the difficulty in the activation of nitrogen molecules and the fierce hydrogen evolution reaction, the activity and selectivity of the existing catalysts are still far below the industrial demand. Single-atom catalysts with dual-metal sites are expected to combine the advantages of single-atom catalysts and alloy catalysts and to exhibit superior performance over both. Therefore, this project intends to tune the electronic structure and coordination environment of the active sites, and achieve the design of the catalysts at the atomic level by preparing a series of single atom catalysts with dual metal sits, in order to promote the adsorption and activation of nitrogen molecules and inhibit the hydrogen evolution reaction. Firstly, preparation methods and parameters of single atom catalysts with dual-metal sites will be explored in detail to obtain the optimal preparation technology. Then, the influence of the atomic composition and the structure of the catalysts on the performance of electrochemical synthesis of ammonia will be studied. Finally, based on the experimental results, theoretical calculations will be performed to study the catalytic mechanism of the catalysts, which is expected to provide guidance for the preparation of high-performance catalysts and promote the development of electrochemical synthesis of ammonia. The preliminary research results have proved the feasibility of the project.

电化学合成氨可在常温常压下进行、装置简单且易于和可再生能源转换技术相结合，因此具有广阔的研究和应用前景。然而由于氮气分子活化困难及析氢竞争反应剧烈, 现有电化学合成氨催化剂的活性和选择性仍远达不到工业的需求。而双金属位点的单原子催化剂有望结合单原子和合金催化剂的优点，表现出优于两者的性能。因此，本项目拟通过制备一系列双金属位点单原子催化剂调控活性位点的电子结构和配位环境，实现催化剂原子层面上的优化和设计，以促进氮气分子的吸附活化并抑制析氢反应的发生。首先，探索制备方法和参数，获取最优的双金属位点单原子催化剂制备工艺；随后，研究双金属位点单原子催化剂的原子组成和结构对其电化学合成氨性能的影响规律；最后，根据实验结果进行理论计算研究双金属位点单原子催化剂在电化学合成氨反应中的作用机理，以指导高性能催化剂的合成，促进电化学合成氨的发展和应用。初步的研究结果证明了该项目的可行性。

合成氨工业奠定了高压化工和现代农业的基础，对国民经济和社会发展具有重要意义。电催化氮还原合成氨可在常温常压下利用氮气和水合成氨，是近年来电催化领域的研究热点。另一方面，人工固氮行为产生了多种形式的氮污染，通过电催化过程将含氮污染物回收为氨引起了研究者们的关注。本课题基于电催化合成氨的研究现状，致力于电化学合成氨催化剂的研发，实现了双金属位点单原子催化剂的可控制备，但遗憾的是所制备催化剂的电催化氮还原合成氨性能并不理想；此外开发了高效的电催化硝酸根还原合成氨催化剂，所制备的铜基催化剂由Cu2O和少量Cu0组成，结晶度较低，表面存在大量无定型结构，因其独特的结构，该催化剂在-0.6 V vs. RHE时产氨速率和法拉第效率分别可达32.2 mg h-1 cm-2和86.8%，该项工作为高性能电化学硝酸根还原合成氨催化剂的制备提供了新的思路。