面向二氧化碳电化学还原的纳米多孔银基催化剂研究

The fast increase in fossil energy consumption has resulted in a sturdy growth of CO2 concentration in the atmosphere; it is urgent to develop cost-effective processes to reduce CO2. Electrochemical reduction of CO2 is one of the most interesting research topics, and the electrode catalyst is the key to realize the industrialization of the electroreduction process. Among all those catalysts investigated for CO2 electro-reduction, Au has been recognized to be the most efficient catalyst with high selectivity to CO production, but the scarcity of Au restricts its practical application. Compared to Au, Ag is much cheaper and exhibits comparable CO selectivity, however, despite the recent improvements, the highest overall mass catalytic activity of Ag reported to date was only 4% of that of Au, which largely offset the cost advantage of Ag. In this project, we propose a simple electrolysis of solid silver halides to prepare nanoporous Ag with the size of primary silver particles adjustable. By electrochemical reduction of AgCl, we have prepared Ag catalyst that shows a catalytic active comparable to Au. On this basis, we will further investigate the reduction process of silver halides, aiming to control the formation and growth of the primary silver particles; we will try to get deep understanding of the structure-activity relationship of the nanoporous silver catalyst towards the electro-reduction of CO2; we will try to prepare nanoporous silver alloys as well, aiming to develop novel alloy catalysts for CO2 electro-reduction; We will also study the synergistic catalysis of ionic liquids and nanoporous silver (or silver alloys). The achievements from this Project will be both of fundamental and application significance. We hope to push forward the implementation of the industrialization of the CO2 electrolysis.

大气环境中的CO2浓度随着人类对化石能源需求的不断增加而逐年稳步增长。目前迫切需要发展高效率、低成本的CO2回收技术。CO2电化学还原是其中重要的研究方向之一，而电极催化剂是其产业化实现的关键。在所研究的催化剂中，Au的高活性，高CO产物选择性已得到认可，但稀缺性制约了其实际应用。与Au相比，Ag很便宜，且同样CO选择性高，但文献报道银的最高活性仅约为Au的4%，这极大抵消了Ag的价格优势。本项目提出通过电解卤化银制备银原生粒子可调的纳米多孔银，目前已获得催化活性可与Au相比拟的Ag催化剂。在此基础上，本项目将深入研究卤化银还原过程中银原生粒子的形成和生长及其控制机制；深入理解纳米多孔银催化剂的构效关系；探索新型纳米多孔银合金催化剂及其制备技术；深入理解离子液体在纳米多孔银基电极上对CO2还原的协同催化作用。项目研究所获成果将兼具基础及应用价值，希望能推动CO2电解还原的产业化实现。

电化学还原是实现我国碳中和目标最有前景的研究方向之一，其中催化剂体系是发展电化学CO2还原技术的关键。在众多金属材料中，Ag对CO2的电催化有一定的特异性，且CO选择性高，但离应用仍有一段距离。有鉴于此，本项目研究致力于发展高活性及高选择性纳米多孔银及银合金电极催化剂，并围绕其发展CO2还原催化活性的电解液体系，主要研究内容及成果包括：（1）通过电解固态金属卤化物制备了催化剂原始粒子尺寸及孔隙率可调、催化层厚度在微米级范围内可控的纳米多孔银，可将银颗粒的尺寸降低至50纳米以下，显著提高了银电极的催化活性和CO选择性。（2）首次报道了羟基功能化离子液体对CO2还原的特异性催化作用。研究表明，相较于普通离子液体，羟基离子液体可以降低CO2还原的起波电势，进一步提高其还原电流及CO选择性；通过第一性原理计算结合实验研究揭示了羟基提供质子跃迁通道从而催化CO2还原的机理。（3）提出并实验验证了醇与咪唑类离子液体对于CO2还原的协同催化作用；通过醇结构及其与离子液体比例优化获得了CO2还原活性及CO选择性。（4）通过固态化合物电解法制备了纳米多孔Ag-Sn催化剂，通过前躯体设计和比例调控提升了该纳米多孔双金属催化剂对CO2电还原的催化活性及甲酸选择性。（5）受项目固态化合物电解制备纳米多孔材料这一思路启发，提出了金属硅化物电解制备超细纳米硅及无定型碳电化学石墨化制备纳米多孔石墨的新技术，有望突破相关材料的批量化制备瓶颈。项目研究可为发展高活性CO2电还原催化剂及电解液催化体系提高理论及实践指导，所提出的固态化合物电解制备纳米多孔材料具有可推广性和良好的应用前景。