掺杂石墨烯锚定过渡金属氧化物催化剂的构筑以及电还原二氧化碳制备乙醇研究

Electrochemical reduction of CO2 to ethanol, a clean and renewable liquid fuel with high heating value, is an attractive strategy for global warming mitigation and resource utilization. So far, a large number of metals, metal oxides, metal sulfides, and carbon-based materials have been developed for the electrochemical reduction of CO2，and considerable progress has been made in the electrochemical conversion of CO2 into C1 chemicals and their catalytic reaction mechanism. However, the detailed mechanistic insights into CO2 reduction reaction, especially reaction pathways towards C2 products, are still limited partly because of the insufficient knowledge regarding to reaction intermediates. Moreover, challenges remain in CO2 electrochemical conversion, such as poor C2 selectivity, low energy conversion efficiency, and difficulty in mass production of catalysts. Therefore, the project presented here intends to design and construct transition metal oxide anchored on doped graphene composites as electrocatalysts for CO2 electrochemical reduction by using a liquid-phase exfoliated graphene PVA aqueous dispersion on larger scale as a raw material. The primary missions were focused on to adjust the coordination between PVA on the graphene surface and metal ions for controlling the structures and properties of the composites, to illuminate the structure-activity relationship between the structure of the composite catalysts and the performance of electroreduction CO2 to ethanol; to find the adsorption/desorption state of CO2 and product on the catalyst surface and reaction intermediates, to reveal the synergistic mechanism of metal oxides and the doped graphene for the electrochemical reduction CO2 into ethanol. The purpose of this project is to understand the formation mechanism of CO2 electroreduction to C2, and then develop highly active electrocatalysts to increase selectivity of production of ethanol via electroreduction of CO2.

CO2电还原制备燃料和高附加值的化学品，是缓解气候变暖和资源利用的有效策略之一。目前，大量的金属、金属氧化物和硫化物、碳基材料等已开发用于CO2电化学还原，在转化CO2为C1化学品及其催化机理的研究取得了较大进展。但是，对CO2电还原为C2化学品缺乏系统的理解，且存在C2选择性差、能源转化效率低、催化剂难以规模化制备等难点问题。因此，本申请课题拟以宏量制备的液相剥离石墨烯PVA水性分散液为原料，调节石墨烯表面PVA与金属离子的配位作用，构筑高活性的掺杂石墨烯锚定的过渡金属氧化物复合催化剂；阐明复合催化剂的结构与CO2还电原转化为乙醇性能之间的构效关系；探究CO2和产物在催化剂表面的吸脱附状态和反应中间体，揭示过渡金属氧化物与掺杂石墨烯协同电催化还原CO2为乙醇的反应机制。本申请项目的目的在于了解CO2还原为C2化学品的反应机制，开发高活性的电催化剂以提高CO2电还原制备乙醇的选择性。

利用可再生电能将CO2转化为高附加值的化学品，对实现“双碳”目标、降低传统化石资源依赖是至关重要。然而，对于高活性、稳定性和选择性的CO2还原催化剂的合理设计仍然面临着巨大挑战。.针对CO2电还原中难以在高电流获得高选择性的难点，我们创新性的提出了将具有高析氢过电位的Hg元素引入连接金属卟啉（Hg-MTPP）作为催化剂的策略。借助DFT计算，优化了Hg-MTPP催化剂，解决了高电流密度下析氢的问题，实现了安培级电流密度及高CO法拉第效率，揭示了其电还原催化机制。针对单原子催化剂大规模制备的难题，我们开发了一种通用的多米诺反应策略，实现了规模化制备的单原子负载的氮掺杂碳材料（M-SA/NC），系统研究了该方法的普适性以及催化剂的电还原CO2的性能和机制。.金属Cu是唯一可将CO2高选择性电还原为多碳产物的催化材料，但由于Cu催化剂的Cuδ+活性位在CO2反应过程中极不稳定，在高电流密度下面临着选择性低和耐久性差的巨大挑战。因此，我们通过表面配位策略制备了超稳定Cu基纳米催化剂，解决了铜催化剂在大电流密度下的高C2+产物（主要为C2H5OH）的选择性和稳定性问题。另外，目前由CO2电还原高效合成C3产物还鲜有报道，我们将铜催化剂与实验自制的石墨烯纳米片复合，利用石墨烯的限域作用，促使Cu表面产生高覆盖度的*CO中间体，促进C-C耦合的产生，实现了丙醇的高效合成。此外，CO2电还原反应通常发生在碱性/中性流动池中，这不可避免地产生碳酸盐沉淀和低CO2利用效率而阻碍该技术的商业化发展。因此，我们利用氧化硅在酸性条件的稳定性，制备了超薄SiO2层包覆的Cu催化剂，实现了Cu催化剂在酸性条件下稳定地将CO2电还原为C2+产物。同时，我们通过原位光谱技术和第一性原理计算阐明了催化剂的组成、结构等对反应中间体和活性位的影响，揭示了其电还原反应机制。这些研究成果将为设计和开发该高效CO2电还原催化剂提供实验和理论依据。