用电催化氧气析出过程中氧气泡行为及对催化剂性能影响

时间：2021-06-10 10:11:16 来源：蒲公英阅读网 本文已影响人

相关热词搜索：氧气 析出 催化剂

　 摘

　要 为了解决全球能源需求和化石燃料储备的消耗问题、降低污染排放，人们不断地寻找替代能源。电解水将水分解成氢和氧的方法已经有几个世纪的历史了，它可以作为一种能量储存手段，且能获得能量密度高、清洁的氢能源。然而析氧反应（OER）的缓慢动力学、其导致增加的能耗、以及电解槽高昂的成本限制了电解水的高效利用。因此掌握氧气析出原理、找到降低阳极反应过电位的方法对于提高能量效率及经济效益至关重要。本文从气泡析出原理出发，研究改变材料的成分、形貌对氧气泡行为的影响，进而引起的 OER 催化性能的变化。

　(1)

　氧气泡析出原理 氧气泡析出的行为，包括成核、生长、脱离三个步骤。成核需要满足溶解气体在电解质中过饱和的条件，可以用经典成核理论来解释，即临界半径决定其成核；生长包括气泡沿着气液界面的扩散和合并；脱离是由表面张力、气体压力以及浮力共同决定的，研究气泡脱离半径是加快脱离的关键。

　(2)

　催化剂材料的设计 目前电催化活性及稳定性最好的为 Ir、Ru 等贵金属，但贵金属含量稀缺、价格昂贵，将 Ni、Co、Fe 等过渡金属掺杂到贵金属氧化物晶格中即可降低成本。本文在分析文献后，得出 Ni 作为掺杂相，IrO 2 为主晶相可获得比其他掺杂氧化物具备更为优良的活性和稳定性的结论。

　(3)

　催化剂材料-氧气泡行为-性能间关系 向催化剂表面引入微/介孔和裂纹皆可增大材料的活性比表面积。孔洞提供的活性成核位点将溶解气体从溶液中去除，并使气泡附近的浓度接近饱和浓度，达到析出所需的条件。由于这种过饱和程度非常高，可以在孔隙中建立非常高的浓度梯度，通过扩散快速去除产生的气体。裂纹腔则可以容纳电解液，从而为电化学反应提供更有效的反应内表面积，提高析氧反应的速率。因此，当气泡的形成和去除被加速，表面的活性区域将被不断暴露出来，从而使氧气析出速率变快，进一步使催化活性得到提高。

　本文拟设计用溶胶凝胶-热分解法制备 IrO 2 纳米颗粒、氨络合法制备 IrO 2纳米微/介孔颗粒（IrO 2 -p）、热分解-酸洗法制备 IrNiO x 纳米微/介孔颗粒（IrNiO x -p）；基于 X 射线衍射谱和 X 射线光电子能谱的表征及分析可以证

　明成功将Ni掺杂到IrO 2 晶格中，且经过酸洗分相的IrNiO x 获得微/介孔结构，扫描电子显微镜、透射电子显微镜的表征可进一步证实了这一点。电化学性能测试可显示微/介孔结构、Ni 掺杂均能不同程度地提高活性表面积、OER 活性，降低 Tafel 斜率且符合文献值（60mV/dec）的范围。

　设计通过溶胶凝胶-热处理法，原料和溶剂配比分别 1:1 和 1:30 制备裂纹表面和无裂纹表面的 IrNiO x 涂层。通过扫描电子显微镜观察到高浓度下裂纹表面的形成，并经过电化学性能测试的对比和文献分析得出裂纹对活性比表面积、OER 活性及 Tafel 斜率的改善作用。

　不同催化剂上氧气泡析出的行为可通过 CCD 相机观察。通过分析预测结果，希望得出孔洞、裂缝的存在可加快气泡析出速率、减小气泡脱离尺寸。

　 关键词：

　析氧反应，电解催化剂，氧气泡行为，溶胶凝胶法，Ni 掺杂 IrO 2

　(论文) - III - The Behavior of Oxygen Bubbles in the Oxygen Evolution Reaction and the Influence on the Performance of Catalysts Abstract In order to solve the problem of global energy demand and reduce pollution emissions, people are constantly looking for alternative energy sources. Electrolysis of water, which splits water into hydrogen and oxygen, has been used for centuries as a means of storing energy and obtaining clean sources of hydrogen with high energy density. However, the slow kinetics of oxygen evolution reaction (OER), the increased energy consumption, and the high cost of electrolysis cell limit the highly efficient utilization of electrolysis of water. Thus, it is essential to understand the mechanism of oxygen evolution and find ways to reduce the overpotential of OER aiming at improving the energy efficiency for economic benefits. Based on the principle of bubble evolution, this paper studies the effect of changing the composition and morphology of materials on the behavior of oxygen bubbles, and what changes they bring about in OER catalytic performance. (1)

　Oxygen bubble evolution principle. The behavior of oxygen bubble evolution usually involves three steps: nucleation, growth and detachment. Nucleation can be explained by classical nucleation theory, that is, the critical radius determines nucleation. Growth includes the diffusion and coalescence of bubbles along the gas-liquid interface. The detachment is determined by surface tension, gas pressure and buoyancy. The study of bubble separation radius is the key to accelerate the detachment. (2)

　The design of catalyst materials At present, precious metals such as Ir and Ru are still the best electrocatalysts towards OER. In view of their limited reserve, it is considered as one of effective ways to reduce the utilization and the cost of precious metals by doping transition metals such as Ni, Co and Fe into the lattice of these noble metal oxides. In this design, after analyzing the literatures, it is expected that the Ni doped IrO 2

　will have better activity and stability than other doped oxides. (3)

　Relationships among materials, the behavior of oxygen bubbles and performance of catalysts. The active specific surface area can be increased by introducing micro/mesoporous or cracks into the catalysts surface. The active nucleation sites provided by pores remove the dissolved gas from the solution and make the concentration near the bubble in the vicinity of the saturation concentration, which

　(论文) - IV - achieve the conditions required for evolution. Because of high supersaturation, very high concentration gradients can be established in the pores to rapidly remove the bubbles by diffusion. The cracks can accommodate the electrolyte, thus providing a more effective internal surface area for the electrochemical reaction and increasing the rate of oxygen evolution reaction. Therefore, when the formation and removal of bubbles are accelerated, the active areas on the surface will be exposed continuously, so that the oxygen evolution rate becomes faster and further improve the catalytic activity. This paper intends to design IrO 2

　nanoparticles prepared by sol-gel-thermal deposition. Ammonia complex-based method was applied to IrO 2 micro/mesoporous nanoparticles(IrO 2 -p), and IrNiO x

　micro/mesoporous nanoparticles (IrNiO x -p) can be prepared by thermal decomposition-pickling. XRD and XPS results show that the success will be Ni doped into the IrO 2 lattice. and split-phase NiO x

　is removed to form a micro/mesoporous structure after pickling. SEM, TEM observation further confirm these results. Electrochemical performance tests show that micro/mesoporous structure and Ni doping could increase the active surface area, OER activity, and reduce the slope of Tafel to meet the range of the literature value (60mV/dec). Then, Crack and crack-free IrNiO x

　coatings are intended to be prepared by sol-gel - heat treatment with material and solvent ratios of 1:1 and 1:30, respectively. The formation of the crack surface under high concentration is detected by SEM. The improvement effect of the crack on the active specific surface area, OER activity and the slope of Tafel are obtained through comparison of electrochemical performance tests and analysis of literature. Finally, this paper observed the behavior of bubble evolution with CCD camera. Then it analyzes and predicts the observation results. The existence of holes and cracks accelerated the bubble evolution rate and reduce the detachment radius of a bubble.

　 Key Words ：

　oxygen evolution reaction ， electrocatalyst ， behavior of bubbles ，sol-gel method ，Ni-doped IrO 2

　(论文) - V - 目 目

　 录

　 摘

　要 ...................................................................................................................... I

　Abstract .................................................................................................................. III

　1 引

　言 .................................................................................................................. 7

　2 文献综述 .............................................................................................................. 8

　2.1 析氧反应 .................................................................................................... 8

　2.2 氧气泡行为研究进展 ................................................................................ 9

　2.2.1 气泡成核 ........................................................................................ 10

　2.2.2 气泡生长 ........................................................................................ 11

　2.2.3 气泡脱离 ........................................................................................ 12

　2.2.4 气泡行为参数 ................................................................................ 14

　2.2.5 气泡的电化学影响 ........................................................................ 16

　2.3 电解催化剂研究进展 .............................................................................. 19

　2.3.1 贵金属催化剂 ................................................................................ 19

　2.3.2 过渡金属催化剂 ............................................................................ 21

　2.4 催化剂性能参数 ...................................................................................... 21

　3 研究工作方案 .................................................................................................... 24

　3.1 论文研究总体方案 .................................................................................. 24

　3.1.1 材料选择 ........................................................................................ 24

　3.1.2 结构设计 ........................................................................................ 24

　3.1.3 设计方案 ........................................................................................ 26

　3.2 实验材料 .................................................................................................. 27

　3.3 样品制备 .................................................................................................. 28

　3.3.1 IrO 2 纳米颗粒的制备 ...................................................................... 28

　3.3.2 IrO 2 纳米微/介孔颗粒的制备 ......................................................... 28

　3.3.3 IrNiO x 纳米微/介孔颗粒的制备 ..................................................... 29

　3.3.4 IrNiO x 表面膜的制备 ...................................................................... 29

　3.4 性能测试 .................................................................................................. 30

　3.4.1 X 射线衍射分析（XRD）

　............................................................. 30

　3.4.2 X 射线光电子能谱分析（XPS）

　.................................................. 30

　3.4.3 X 射线荧光光谱分析（XRF）

　...........