【作者】 李喆；

【导师】 杜希文；

【作者基本信息】 天津大学 ， 材料学， 2020， 博士

【摘要】 电催化剂的催化活性由其电子结构所决定。晶体缺陷可以有效地调控催化剂的电子结构并使其催化活性相较于完美晶体发生巨大变化。如何在不同的材料中引入特定的晶体缺陷从而对催化活性进行有效调控,同时对催化机理进行全面的阐释是目前电催化领域的一个难题。本论文利用激光液相烧蚀法在多种材料中创造出不同的晶体缺陷使其催化活性得到显著提升,并从实验与理论两个方面对催化机理进行了阐释,取得了如下研究发现:1.堆垛层错可以将对HER非活性的Ag催化剂改性为高活性催化剂。通过激光液相烧蚀的非平衡强烈作用在Ag纳米颗粒中创造出大量的堆垛层错。堆垛层错使Ag纳米颗粒晶格内含有大量的拉伸应变,同时降低其表面原子配位数。拉伸应变与低配位数的共同作用显著提升了Ag的氢吸附能力,使Ag纳米颗粒催化剂的HER催化活性得到巨大提升。2.激光的强烈的非平衡作用可以制备出具有超小粒径以及含有大量氧空位的Co₃O₄纳米颗粒。超小粒径使催化剂暴露出更多的催化位点,同时氧空位提升了Co₃O₄纳米颗粒的ORR/OER本征催化活性以及材料的导电性,诸多因素的共同作用使其具有优异的ORR/OER双功能催化活性。3.氧空位可以作为媒介实现对Co₃O₄中Co离子价态的连续可调,同时Co离子价态与Co₃O₄的OER催化活性之间存在着火山图关系。通过激光液相烧蚀制备出含有大量氧空位且表面带有正电的Co₃O₄纳米颗粒以及表面带有负电的Ag纳米颗粒,利用静电引力二者可以组装成核壳结构。由于Ag与Co₃O₄间的电子转移可以诱导Co离子价态的变化,通过控制二者的比例可以连续调控Co离子价态。OER电催化测试以及理论计算表明Co₃O₄的OER催化活性与其Co离子价态存在着火山图关系。4.拉伸应变可以显著提升Ag催化剂的ORR本征催化活性,与Cu₂O结合可以实现超越商用Pt/C的ORR催化性能。通过激光液相烧蚀Ag Cu合金制备出Cu₂O掺杂的表面具有坑洞的Ag纳米颗粒。理论计算与实验证明,Cu₂O的存在一方面使Ag晶格中具有拉伸应变,拉伸应变可以提升Ag催化剂的ORR本征催化活性;另一方面Cu₂O具有很强的氧气吸附能力,与纳米颗粒表面坑洞的限域效应相结合使Ag催化位点周围含有很高的氧气分子浓度。这些因素共同作用使Ag纳米颗粒表现出超越商用Pt/C的ORR催化活性。5.压缩应变可以优化贵金属氧化物的碱性HER催化活性,同时提高其相转变势垒,实现贵金属氧化物高效稳定地催化碱性HER反应。通过激光液相烧蚀制备出Rh O₂镶嵌在Rh基体的草莓状结构纳米颗粒,由于二者的晶格失配使RhO₂中含有压缩应变。一系列理论计算和实验结果证明,压缩应变可以优化其HER催化活性并有效地提高Rh O₂的相转变势垒使之稳定地催化HER反应,其最大稳定工作电压可达-0.3 V vs.RHE。更多还原

【Abstract】 The catalytic activity of electrocatalyst is determined by its electronic structure.Crystal defects can effectively regulate the electronic structure of catalyst,and make its catalytic activity change dramatically when compared to perfect crystal.But how to create specific crystal defects in different materials to achieve effective adjustment of catalytic activity,and explain the catalytic mechanisms comprehensively is still a great challenge in electrocatalysis.In this paper,different kinds of crystal defects have been created in various materials by laser ablation in liquid,of which the catalytic activities have been improved greatly.And the catalytic mechanisms have also been explained through experimental and theoretical researches.The following research findings have been obtained.1.Stacking faults could modify Ag from an inactive HER catalyst to a high active catalyst.A large number of stacking faults have been created in Ag nanoparticles by the intense non-equilibrium effect of laser ablation in liquid.Stacking faults could bring a high tensile strain in Ag nanoparticles and reduce the surface atomic coordination number at the same time.The combination of tensile strain and low coordination number could significantly improve the hydrogen adsorption capacity and the HER catalytic activity of Ag nanoparticle.2.The intense non-equilibrium effect of the laser could produce Co₃O₄nanoparticles with ultrasmall particle size and a large number of oxygen vacancies.The ultrasmall particle size could make the catalyst expose more catalytic sites.In the meanwhile,oxygen vacancies enhance the ORR/OER intrinsic catalytic activity and the conductivity of Co₃O₄ nanoparticles.The combination of these factors makes Co₃O₄show excellent ORR/OER bifunctional catalytic activity.3.Oxygen vacancy can be used as a medium to adjust the valence state of Co ions in Co₃O₄ continuously,and there is a volcano plot relationship between the valence state of Co ions and the OER catalytic activity of Co₃O₄.Positive-charged Co₃O₄nanoparticles which contains a large amount of oxygen vacancies and negative-charged Ag nanoparticles were prepared by laser ablation in liquid,which can be assembled into a core-shell structure as a result of the electrostatic attraction.The electron transfer between Ag and Co₃O₄ could change the valence state of Co ions,and the valence state of Co ions can be continuously adjusted by controlling the ratio of Ag and Co₃O₄.OER electrocatalysis test and theoretical calculations show that there is a volcano plot relationship between OER catalytic activity and the Co ion valence of Co₃O₄.4.Tensile strain can significantly improve the intrinsic ORR catalytic activity of Ag catalysts,when combines with Cu₂O,the composite catalyst achieve an excellent ORR catalytic activity which could exceed commercial Pt/C.Cu₂O-doped Ag nanoparticles with pits on the surface were prepared by laser ablation of Ag Cu alloy target in liquid.Theoretical calculations and experiments proved that the existing of Cu₂O makes Ag contain lattice tensile strain,which can improve the intrinsic ORR catalytic activity of Ag.At the same time,Cu₂O possesses a strong adsorption capacity of oxygen,which generates a high concentration of oxygen molecules around Ag catalytic sites combining with the confinement effect of pits on surface of nanoparticles.All of these factors work together to make the Ag nanoparticles show an excellent ORR catalytic activity which could exceed commercial Pt/C.5.Compressive strain can optimize the alkaline HER catalytic activity and improve the phase transition barrier of noble metal oxides,which makes noble metal oxide could catalyze alkaline HER reaction efficiently and stably.A strawberry-like nanoparticle with Rh O₂ embedded in Rh substrate was prepared by laser ablation in liquid.Compressive strain exists in Rh O₂ because of the lattice mismatch between Rh and Rh O₂.A series of theoretical calculations and experiments prove that compressive strain could optimize the HER catalytic activity and improve the phase transition barrier of Rh O₂ effectively.The Rh O₂ catalyst with compressive strain can catalyze the HER reaction stably,and its maximum stable working potential could reach-0.3 V vs.RHE.更多还原