化石燃料的使用推动了人类工业时代的进步，随之带来了全球变暖以及环境污染等问题，开发先进、低成本及环境友好型高能量密度的储能装置迫在眉睫。可充电锂氧气电池具有较高的理论比能量密度（约11680 Wh·kg-1），能够满足高续航里程电动汽车以及先进能量储存转换设备的需求，成为候选化学电源之一。锂氧气电池放电产物Li2O2绝缘难溶，导致电极反应动力学缓慢，电池能量效率低、倍率性能差、循环寿命有限。开发具有优异氧还原反应（ORR）/氧析出反应（OER）性能的双功能电催化剂有望解决这一关键问题。二维MXene材料（钛碳化物）比表面积大、导电性高，可作为优良的导电基底，在电化学领域显示出广阔应用前景。本论文以二维Ti3C2Tx材料为基底，负载非贵金属材料，结合杂原子掺杂和构建异质界面策略，围绕锂氧气电池正极催化剂的微结构设计和表界面性能优化开展了以下研究：

（1）表面功能化N-TiO2/Ti3C2Tx异质结构的构筑及锂氧气电池性能研究。密度泛函理论（DFT）计算显示，N-TiO2/Ti3C2Tx异质结催化剂在费米能级处具有较高的DOS，说明其具有较高的电导率和高电催化活性位点，表面功能化的异质结构具有更多活性电子，可以优化催化剂对LiO2和Li2O2的吸附，计算结果显示N-TiO2/Ti3C2Tx和TiO2/Ti3C2Tx在（001）面上的吸附能分别为-2.88和-5.33 eV，强于-0.44 eV的Ti3C2Tx和-0.1 eV的碳材料，较低的吸附能有利于降低电池反应过电位，促进电化学反应的进行。通过实验制备了氮掺杂TiO2/Ti3C2Tx异质结构，材料结构表征和测试显示：氮元素掺杂进TiO2/Ti3C2Tx异质结构中，并且形成了Ti-O-N或Ti-N-O键，制备出的N-TiO2/Ti3C2Tx异质结构比表面积大，有利于电池性能的提升。电池测试结果表明，N-TiO2/Ti3C2Tx异质结构用作锂氧气电池正极材料，在限流100 mA g-1时，其放电比容量可达15298 mAh g-1；当限流为500 mA g-1，容量为500 mAh g-1时，过电位低至0.47 V，且可稳定循环200圈以上。原位微分电化学质谱（DEMS）和扫描电子显微镜（SEM）和拉曼光谱（Raman）等对反应机理进行了详细阐述，结果显示，在充电过程中，N-TiO2/Ti3C2Tx电催化剂中CO2释放量比TiO2/Ti3C2Tx电催化剂中CO2的释放量低41.82%，说明N-TiO2/Ti3C2Tx异质结构可以更好的调节Li2O2/LiO2可逆的生成和分解，降低因各种副反应造成的极化现象，有利于提升锂氧气电池性能。

（2）Co2N/Co3O4-Ti3C2Tx（NCT）异质结的制备及锂氧气电池性能研究。构建异质界面是提升电化学反应动力学的一项重要策略，通过水热-煅烧方法，将Ti3C2Tx基底上的Co3O4纳米粒子部分氮化形成Co2N/Co3O4异质结，构建异质结反应界面加速界面电子转移，提高锂氧气电池电化学性能。将其用作锂氧气电池正极材料时，在电流密度100 mA g-1时，NCT异质结的放电比容量为14271 mAh g-1，高于Co3O4-Ti3C2Tx正极（11173 mAh g-1）和Ti3C2Tx正极（9822 mAh g-1）。在电流500 mA g-1，容量500 mAh g-1条件下，首次循环过电位降低至0.65 V，并且能够稳定循环300圈以上，是目前MXene基锂氧气电池性能的最优值。采用原位DEMS、SEM和拉曼光谱等对反应机理进行详细研究，由于NCT电催化剂对放电产物Li2O2/LiO2的吸附能较低，全容量放电后电极表面出现纳米片组成的花状放电产物，在充电过程中更容易被分解。在充电过程中，NCT电催化剂的DEMS测试曲线中CO2的含量低至1.08 %，表明NCT异质结复合材料具有优异的电催化活性，有效减弱因不良反应导致的极化现象，提升锂氧气电池电化学反应可逆性，为正极电催化剂的设计与研究提供思路。

（3）CoP/Ti3C2Tx复合材料的制备及锂氧气电池性能研究。通过理论计算CoP/Ti3C2Tx复合材料的活性电子吸附能，采用水热-煅烧策略，在Ti3C2Tx表面和层间原位生长CoP纳米粒子，用作锂氧气电池正极材料。CoP纳米粒子在Ti3C2Tx 表面的附着降低了CoP纳米粒子的团聚特性，有效抑制了Ti3C2Tx纳米片的堆叠，增大了比表面积。CoP/Ti3C2Tx复合材料具有CoP纳米粒子出色的电催化活性和Ti3C2Tx优异的导电性，用作锂氧气电池正极时，显示出良好的电池性能。电池测试结果表明，CoP/Ti3C2Tx复合材料用于锂氧气电池正极催化剂时，在100 mA g-1的电流密度下，放电比容量可达17413 mAh g-1。在电流为500 mA g-1，容量为500 mAh g-1时，表现出较低的过电位1.25 V，能够稳定循环40圈。优于纯CoP纳米粒子和纯Ti3C2Tx MXene材料。

The use of fossil fuels promotes the progress of human industrial age, which brings global warming and environmental pollution and other problems. It is extremely urgent to develop advanced, low-cost and environmentally friendly energy storage devices. Rechargeable lithium oxygen battery has attracted much attention because of its high theoretical energy density (~11680 Wh·kg-1), which can meet the needs of electric vehicles with long range and advanced energy storage and conversion equipment. It has become one of the candidate chemical power sources. However, the discharge product Li2O2 is insoluble, which leads to slow electrode reaction kinetics, low energy efficiency, poor rate performance and limited cycle life. The development of dual-function electrocatalysts with excellent oxygen reduction reaction (ORR) / oxygen evolution reaction (OER) performance is expected to solve this key problem. Two-dimensional MXene material has large specific surface area and high electrical conductivity, which can be used as an excellent conductive substrate and shows a broad application prospect in the field of energy storage and conversion. In this paper, two-dimensional Ti3C2Tx material was used as the substrate, non-noble metal materials were loaded, and heteroatomic doping and heterogeneous interface construction strategy were combined to carry out the following studies on the microstructure design and surface interface performance optimization of lithium oxygen battery cathode catalyst:

(1) Construction of surface-functionalized N-TiO2/Ti3C2Tx heterostructures and study on the performance of lithium oxygen batteries. Density Functional theory (DFT) study showed N-TiO2/Ti3C2Tx heterostructure catalyst had outstanding conductivity and abundant electrocatalytic active site. The surface functionalized heterostructure had more active electrons, which could optimize the adsorption of LiO2 and Li2O2 on the catalyst, reduce the overpotential of the battery, and facilitate the electrochemical reaction. The heterostructure of nitrogen-doped TiO2/Ti3C2Tx was prepared through experiments. The characterization and testing of the material structure showed that the Nitrogen was doped into TiO2/Ti3C2Tx heterostructure, and Ti-O-N or Ti-N-O bond was formed. The N-TiO2/Ti3C2Tx heterostructure prepared had large specific surface area, which was conducive to the improvement of battery performance. The results showed that when N-TiO2/Ti3C2Tx heterostructure was used as anode material of lithium oxygen battery, the specific discharge capacity could reach 15298 mAh g-1, when the current density was limited at 100 mA g-1. When the current density was limited at 500 mA g-1 and the limiting capacity was limited at 500 mAh g-1, the overpotential was as low as 0.47 V, and the cycle could be stable for more than 200 cycles. In situ DEMS, and in situ SEM and Raman spectroscopy were used to elucidated the reaction mechanism in detail. The amount of CO2 released in N-TiO2/Ti3C2Tx electrocatalyst was 41.82 % lower than that in TiO2/Ti3C2Tx electrocatalyst, indicating that N-TiO2/Ti3C2Tx heterojunctions can better regulate the reversible generation and decomposition of Li2O2/LiO2 and reduce the polarization caused by various side reactions. It was helpful to promote the performance of Li-O2 battery.

(2) Preparation of Co2N/Co3O4-Ti3C2Tx (NCT) heterojunction and performance of lithium oxygen battery. The construction of heterogeneous interface was an important strategy to promote the reaction kinetics. By hydrothermal and calcination methods, Co3O4 nanoparticles on Ti3C2Tx were partially nitrided to form Co2N/Co3O4 heterojunction, and the heterogeneous junction reaction interface was constructed to accelerate the electron transfer on the interface, thus improving the electrochemical performance of lithium oxygen battery. The discharge capacity of NCT heterojunction was 14271 mAh g-1 when the current density was 100 mA g-1, which was higher than that of Co3O4-Ti3C2Tx cathode (11173 mAh g-1) and Ti3C2Tx cathode (9822 mAh g-1). Under the condition of current density of 500 mA g-1 and limited capacity of 500 mAh g-1, the first cycle overpotential was reduced to 0.65 V and could be stable for more than 300 cycles, which was the optimal performance value of MXene based lithium oxygen battery at present. The reaction mechanism was described in detail by in situ DEMS, SEM and Raman spectroscopy. Due to the low adsorption energy of NCT electrocatalyst for the discharge product Li2O2/LiO2, flower-like discharge products composed of nanosheets appeared on the electrode surface after full capacity discharge. It's more likely to break down during charging. During the charging process, The CO2 content of NCT electrocatalyst was as low as 1.08 % in DEMS test curve, indicating that the NCT heterojunction composite material had excellent electrocatalytic activity, effectively reduced the polarization phenomenon caused by adverse reactions, and improved the reaction reversibility of lithium oxygen battery. It was beneficial for design and research of cathode electrocatalyst for lithium oxygen battery.

(3) Preparation of CoP/Ti3C2Tx composite and performance of lithium oxygen battery. The active electron adsorption energy of CoP/Ti3C2Tx composite was calculated theoretically, and the CoP nanoparticles were grown on the surface and between layers of Ti3C2Tx by hydrothermal and calcination strategies. The CoP nanoparticles were applied to the positive catalyst of lithium oxygen battery. The adhesion of CoP nanoparticles on the surface of Ti3C2Tx reduced the agglomeration characteristics of CoP nanoparticles, effectively inhibited the stacking of Ti3C2Tx nanosheets. CoP/Ti3C2Tx composite had excellent electrocatalytic activity of CoP nanoparticles and excellent electrical conductivity of Ti3C2Tx. As a cathode material of lithium oxygen battery, it showed good electrochemical performance. The results showed that the discharge capacity of CoP/Ti3C2Tx composite could reach 17413 mAh g-1 at the current density of 100 mA g-1 when used as cathode catalyst for lithium oxygen battery. When the current density was 500 mA g-1 and the limited capacity was 500 mAh g-1, it showed a low over-potential of 1.25 V and could be stable for 40 cycles. Superior to pure CoP nanoparticles and pure Ti3C2Tx MXene materials.