零价金属原子插层的垂直阵列MoS2纳米片电催化还原CO2性能及机理研究

For electrocatalytic reduction of CO2 with MoS2 in aqueous solution, lower efficiency and poor selectivity are two key scientific questions that need to be addressed. Metal catalysts with atomic thickness have unique activity and selectivity. However, they usually suffer from some problems including instability and easy aggregation. MoS2 possesses layered structure and its interlamellar separation can be used as confinement spacing for chemical intercalation of metal atoms. The metal atoms/MoS2 vertical nanosheets arrays can be fabricated through controllable chemical intercalation of metal atoms into interlamellar spacing of MoS2. Based on the synergistic effect between the intercalated metal atoms and MoS2 nanosheets, several metal/MoS2 composite electrocatalysts with high efficiency and good selectivity were screened out through systematically surveying the influence of the intercalated metal atoms on electrocatalytic performance of MoS2. The electrocatalytic reduction mechanism of CO2 was discussed on the basis of the ideal model provided by ultrathin metal atoms/MoS2 nanosheets and experimental results. The relationships between the metal atoms/MoS2 nanosheets structure and the electrocatalytic performance of CO2 reduction was elucidated through the comprehensive analyses on adsorption ability of the material on CO2, electrochemically active surface area, a series of contrastive experiment, theoretical calculations, and many more. We hope to provide new idea and method for designing and preparing new types of highly efficient electrocatalysts with good selectivity. The related studies involve material, energy and green catalytic chemistry and have important academic significance and potential applications.

本项目针对水溶液体系中MoS2电催化还原CO2所面临的效率低与选择性差两个关键科学问题，依据原子厚度金属催化剂所具有的独特活性与选择性，考虑原子厚度金属存在难稳定、易聚集等缺点，提出以MoS2晶体层间作为限域空间，采用可控的金属原子化学插层到MoS2层间，构筑插层金属原子/MoS2纳米片垂直阵列，通过系统考察不同金属原子插层MoS2对其催化性能的影响，发挥插层金属原子与MoS2之间的协同效应，筛选出高效兼具选择性的金属原子/MoS2复合电催化剂用于CO2电还原。以超薄插层金属原子/MoS2纳米片为理想研究模型，基于实验结果，理解其电催化还原CO2机制。综合材料对CO2的吸附能力、电化学活性面积、对比试验以及理论计算等各方面分析结果，阐明插层金属原子/MoS2纳米片的结构与电催化性能之间的构效关系，为制备成本低、活性高、选择性好的可用于电催化还原CO2的新型电催化材料提供新思路和新方法。

目前报道的大部分电催化剂，在水溶中电化学催化还原CO2面临效率低与选择性差两个关键科学问题。本项目以MoS2为主要研究模型，以金属Mo丝网为基底，合成了具有丰富暴露边的MoS2纳米片阵列。利用1T型MoS2纳米片自身的还原性、歧化反应、羰基金属化物的可控分解反应等，制备出了不同金属负载的MoS2纳米片复合电催化剂，系统研究了几种零价金属对MoS2的性能调控作用。实验结果表明，零价金属能够增强MoS2的电催化活性。负载超小金纳米颗粒可以电催化还原CO2形成可观的CO气体，精细的调节金的负载量和反应条件，可以调控产物中CO与H2的比例。尽管不同零价金属修饰的MoS2能够电催化还原CO2获得不同产物，但由于MoS2纳米片暴露的活性边造成析氢反应严重，产物选择性较差。针对该问题，我们通过原子层技术，构筑了超薄TiO2 (2 nm)/MoS2复合电催化剂。实验与理论计算结果表明，同构的TiO2超薄层抑制了析氢反应，减少了界面电荷传递阻力，形成的Ti与Mo双活性位点，促进了OC-CO的偶联反应以及随后的质子耦合电子传递过程。结果，该复合电催化剂能够电催化还原CO2形成乙醇与少量的乙酸。在−0.60 V （相对可逆氢电极），CO2饱和的0.5M NaHCO3溶液中，乙醇的法拉第效率能够达到50%。基于理论计算，一种新的CO偶联反应调节机制被建议。受此工作启发，我们进一步合成了三元金属硫化物ZnIn2S4，我们的研究结果表明该三元金属硫化物可以有效还原CO2生成CO，在−0.60 V （相对可逆氢电极），法拉第效率为80%。我们的研究表明，理性设计含有双金属的三元金属硫化物能够获得高效的CO2还原电催化剂。此外，我们发展了晶界工程策略和双金属化效应，有效提升了铋在水溶液体系电催化还原CO2合成甲酸的活性与选择性。研究工作已发表SCI论文13篇，授权发明专利10项，培养毕业硕士生8名。