【作者】 张琪；

【导师】 王春刚；

【作者基本信息】 东北师范大学 ， 物理化学， 2021， 博士

【摘要】 全球环境和能源危机已经引起了人们的广泛关注,并激励我们不断寻找可满足现代社会能源需求的可持续能源存储和转换系统。由可再生能源衍生的电力驱动的电催化水分解已被确定为未来能源生产的潜在和实用策略,但受限于其反应动力学缓慢和催化剂成本过高。低成本和高性能的非贵金属基催化剂的构建已成为解决这些巨大挑战的最有效方法之一。近些年来,人们通过各种方法来合成了许多非贵金属基催化剂。一方面可以降低催化过程中需要的过电势从而减少电能的消耗,另一方面是增强催化剂的稳定性。然而,大多数已报道的电催化性能还无法与贵金属催化剂媲美。基于此问题,本文构建了几种过渡金属基电催化剂,通过纳米结构的设计,异质界面的构建,巧妙地调整催化剂的电子状态,能带结构和电子结构,从而增强了基于过渡金属基催化剂的电化学分解水的性能。主要研究内容和结果如下:（1）我们通过一种新颖的方法成功制备了氮掺杂碳包覆的钴/氮化钒（Co/VN@N-C）纳米球,利用钒酸钴/聚多巴胺纳米球（Co₂VO₄/PDA）的脱氧来原位生成Co纳米颗粒,同时PDA提供了氮源用来原位形成VN纳米晶体。从而在纳米球中形成Co/VN的异质结构,异质结构的协同作用促进了催化性能的提升。此外,PDA碳化可以生成微介孔共存的氮掺杂碳层,可以提升Co/VN@N-C纳米球催化剂的稳定性。所得到的Co/VN@N-C纳米球催化剂获得了优秀的析氢反应（HER）和析氧反应（OER）催化性能。（2）在这项工作中,我们通过简便的方法合成了由超小硫化镍/硫化钼双面神（Ni S₂/Mo S₂ Janus）亚基堆积而成的蛋黄蛋壳纳米球。超小Ni S₂/Mo S₂ Janus亚基上是由二维的Mo S₂纳米片和一维Ni S₂颗粒组成,且他们的粒径大大的减小,使蛋黄蛋壳纳米球具有两种金属硫化物的许多“亲密”的界面,从而极大地促进了水分子的解离。鉴于小尺寸的Ni S₂/Mo S₂ Janus亚基,以及其丰富的边缘位点和高界面密度,所制备的Ni S₂/Mo S₂蛋黄壳型纳米球表现出高的电催化活性,达到10 m A cm^-2时,HER和OER的过电势分别为135和293 m V。（3）本文在泡沫镍（NF）基底上构建了垂直生长的单层粒子排列的薄纱状纳米片,该纳米片是由超小的镍（Ni）和三氧化二钒（V₂O₃）纳米粒子组成的莫特-肖特基（Mott-Schottky）异质结交替排列而成。Ni和V₂O₃在Mott-Schottky异质结上的粒径大大减小,提高了单位面积上材料的Mott-Schottky异质结的数量。此外,将异质结重复排布到单层纳米片中使得异质结能够充分暴露于电解质中。肖特基异质结就像嵌入薄纱状单层纳米片中的无数电荷转移“工作站”一样,促使纳米片上面绝大部分的材料都能参与电子转移并成为催化活性位点。另外,由于强的毛细作用力,薄纱状的单层纳米片结构有助于将液相电解质泵送到催化剂的表面。所制备的V₂O₃/Ni/NF Mott-Schottky催化剂具有优异的HER性能,10m A cm^-2时的过电势仅为54 m V,仅需-107 m V即可获得-100 m A cm^-2的电流密度。此外,V₂O₃/Ni/NF Mott-Schottky电催化剂表现出出色的尿素氧化反应（UOR）活性:相对于可逆氢电极（RHE）电压需要1.40、1.51和1.61 V,可达到100、500和1000 m A cm^-2的电流密度。（4）本文利用相分离的方法,将钒酸镍（Ni₃V₂O₈）前躯体作为“种子”,三聚氰胺作为“土壤”提供碳源和氮源,在碳布纤维上“垂直生长”氮掺杂的碳纳米管阵列,同时纳米管中复合了超小的氮化钒/镍（VN/Ni）的异质结,得到了类似试管刷形貌的VN/Ni异质结复合的氮掺杂碳纳米管阵列（Ni/VN/N-CNTA@CC）。将小尺寸的VN/Ni异质结镶嵌在氮掺杂的碳纳米管上犹如修筑了一条持续电子转移的“高速公路”,加速了异质结构与碳布间的电子快速转移,从而实现优异的催化性能。形貌调控方面,垂直生长的碳纳米管阵列犹如针头,不利于气体产物的附着,加速了生成产物的脱附,从而提升了电催化的性能。得益于以上优点,所制备的Ni/VN/N-CNTA@CC催化剂具备优异的HER性能并表现出出色的UOR反应活性。更多还原

【Abstract】 The global environmental and energy crisis have attracted wide attention and led to continuous efforts to find sustainable energy storage and conversion systems that can meet the energy needs of modern society.Electrocatalytic water splitting derived from renewable energy sources has been identified as a potential and practical strategy for future energy production.However,this promising approach is limited by its slow reaction kinetics and high cost.The construction of low-cost and high-performance non-precious metal-based catalysts has become one of the most effective ways to solve these big challenges.In recent years,many non-precious metal based catalysts have been synthesized by various methods.The purpose,on the one hand,is to reduce the potential in the catalytic process so as to reduce the consumption of electric energy,and on the other hand,is to enhance the stability of the catalyst.However,the most reported electrocatalytic performance is not comparable to that of precious metal catalysts.Based on this problem,several transition metal-based electrocatalysts were constructed in this paper through the design of nanostructure.The construction of heterogeneous interface could enhance the catalytic performance so as to improve the performance of water splitting based on transition metal-based catalysts.The main research contents and results are as follows:（1）We have successfully prepared nitrogen-doped carbon-coated cobalt/vanadium nitride（Co/VN@N-C）nanospheres by means of a novel method.The reduction of Co2VO4/polydopamine（Co2VO4/PDA）was used to generate Co nanoparticles in situ,and the formation of VN nanocrystals was also provided with a nitrogen source of PDA.In addition,PDA carbonization led to the formation of N-C coating.The Co/VN@N-C nanosphere catalyst obtained excellent catalytic performance.（2）In this work,the ultrafine NiS₂/MoS₂ Janus subunits organized on the yolk-shell nanospheres were synthesized by a novel and facile approach.The greatly reduced particle size of both two dimensional MoS₂ and one dimensional NiS₂ on the ultrafine NiS₂/MoS₂ Janus subunits endowed the yolk-shell nanospheres with numerous intimate interfaces of the bimetal sulfide hybrids greatly promoting intimate electronic interaction and dissociation of water molecules.Benefiting from the ultrafine NiS₂/MoS₂ Janus subunits,abundant edge sites and the high density of interfaces,the as-prepared NiS₂/MoS₂ yolk-shell nanospheres exhibited high electrocatalytic activity with a low?10 of 135 and 293 m V for hydrogen evolution reaction（HER）and oxygen evolution reaction（OER）,respectively.Meanwhile,a low cell voltage（1.58 V）was achieved by using NiS₂/MoS₂ yolk-shell nanospheres as both anode and cathode.This study has significant indications in exploring the ultrafine nanoparticles for water splitting reaction,fuel cells and organic synthesis.（3）The Mott-Schottky heterojunction formed at the interface of ultrafine metallic Ni and semiconducting V2O3 nanoparticles was constructed,and the heterojunctions were“knitted”into the tulle-like monolayer nanosheets on nickel foam（NF）.The greatly reduced particle sizes of both Ni and V2O3 on the Mott-Schottky heterojunction highly enhanced the number of Schottky heterojunctions per unit area of the materials.Moreover,arranging the heterojunctions into the monolayer nanosheets made the heterojunctions repeat and expose to the electrolyte sufficiently.The Schottky heterojunctions were like countless self-powered charge transfer workstations embedded in the tulle-like monolayer nanosheets,promoting maximum of the materials to participate into the electron transfer and become catalytic active sites.In addition,the tulle-like monolayer nanosheet structure can assist in pumping liquid phase electrolyte to the surface of catalysts,owing to the strong capillary force.The as-prepared V2O3/Ni/NF Mott-Schottky catalyst exhibited excellent HER performance with a low?10 of 54 m V and only needs-107 m V to get the current density of-100 m A cm^-2.Furthermore,V2O3/Ni/NF Schottky electrocatalyst exhibited excellent UOR activity:1.40,1.51 and 1.61 V versus reversible hydrogen electrode（RHE）voltage were required to reach a current density of 100,500 and 1000 m A cm^-2,respectively.（4）In this paper,the Ni₃V₂O₈ precursor was like a“seed”,and melamine was like“soil”providing the source of carbon and nitrogen,to“grow”vertical nitrogen doped carbon nanotube arrays on the carbon cloth fiber,using the method of phase separation.The VN/Ni heterojunction composite with nitrogen doped carbon nanotubes arrays（Ni/VN/N-CNTA@CC）were prepared,which was similar to the tube brush.The ultrasmall size VN/Ni heterojunction embedded on the nitrogen-doped carbon nanotubes was like building a“highway”for the continuous electron transfer,which accelerated the rapid electron transfer between the heterostructure and the carbon cloth to achieve excellent catalytic performance.In terms of morphology regulation,the vertically grown carbon nanotube array was like a needle,which was not conducive to the adhesion of bubbles,and accelerated the desorption of generated products,thus improving the performance of electrocatalysis.Thanks to the above advantages,the obtained Ni/VN/N-CNTA@CC catalyst has excellent HER and UOR performance.更多还原