有机体系锂空气电池氧还原反应四电子途径催化剂的设计与构筑

Nonaqueous Li-air batteries have attracted extensive attention owing to their ultrahigh theoretical energy density. However, the current cathode catalysts can only promote the oxygen reduction reaction to proceed via a two-electron transfer mechanism, so that the actual energy density of Li-air batteries is severely restricted. This project proposes a novel concept called “step-by-step electrocatalysis” ―balance the active sites of the two-step, two-electron reactions (O2/Li2O2 and Li2O2/Li2O) to construct a composite catalytic system, and explore an efficient approach for realizing the oxygen reduction reaction to proceed via a four-electron transfer pathway. First, we will research the catalysts for these two-step transfer reactions, respectively; and investigate the effects of the structure and composition of catalysts on the two-step reactions, and the formation rules and structural features of lithium oxides; then, thoroughly study the influence of the interface structure of the catalysts/lithium oxides on the reactions. On this basis, we will design and construct the composite catalysts; and combine the in-situ electrochemical techniques with the quantum calculations to reveal the synergistic mechanism of the components of composite catalysts; and then clarify the principles and theoretical basis for the catalyst design, and construct and optimize the catalysts, accordingly, so that the resultant catalysts can catalyze the oxygen reduction reaction to proceed through the four-electron transfer pathway. This study will focus on exploring on the realization conditions and reaction mechanism of the four-electron oxygen reduction process in Li-air batteries, so that the current cathode electrocatalytic theory could be perfected and enriched, which would have great significance in promoting the development of Li-air batteries.

有机体系锂空气电池鉴于其超高的理论比能量而广受关注，但目前的阴极电催化剂仅能促进氧还原反应按两电子机理进行，严重制约了其能量密度的进一步提升。本项目提出“分步电催化”理念，通过兼顾O2/Li2O2与Li2O2/Li2O两分步两电子转换反应的活性位构筑复合催化体系，探索实现氧还原四电子反应的途径。项目首先分别研究两分步转换反应适合的催化剂，考察催化剂的结构组成对两步反应的影响机制及锂氧化物的生成规律与结构特征，重点探讨催化剂/锂氧化物的界面结构对反应的影响规律；在此基础上进行复合催化剂设计构筑，通过电化学原位分析及量子化学计算揭示复合催化剂各组分的协同作用机理，进而明晰氧还原四电子反应催化剂的设计原则及理论依据，并据此构筑和优化该催化剂。本研究将致力于探索锂空气电池氧还原四电子反应的实现条件及反应机理，完善和丰富锂空气电池阴极电催化理论，对促进锂空气电池的发展具有重要意义。

锂空气电池具有超高的理论比能量，是极具应用潜力的二次储能装置。但目前锂空气电池仍面临着充放电过电位高、电极及电解液稳定性差等诸多问题。其中阴极催化剂的问题尤为明显，主要体现在阴极催化剂的催化活性、稳定性、催化剂毒化保护和利用率等。本项目主要针对上述问题，分别研究了碳基催化剂、非碳基催化剂以及可溶性氧化还原介体分子催化剂在锂空气电池中的应用，力求改善锂氧电池空气电极动力学缓慢、循环性能差等问题。重点研究了高活性氧还原/氧析出催化剂的设计及其作用机理。探索了掺杂碳催化剂、贵金属、钙钛矿、液相分子氧化还原介体等不同种类催化剂的电化学性能。研究表明掺杂碳等催化剂的引入能够有效降低空气电极充放电过电位，进而提升锂空气电池体系的循环稳定性。相对于固相催化剂，液相氧化还原介体类分子催化剂有效避免了固体催化剂的钝化问题，同时保证了催化剂与放电产物之间足够的接触面积，进而表现出更加优异的催化活性。详细研究了各催化剂结构组成对放电产物的结构及生长方式、空气电极性能的影响规律，结合理论计算，为催化剂的理性设计提供了有益指导。